WO2017152298A1 - Multi-wall carbon nanotubes for the adsorption of hydrogen, production method and purification method - Google Patents
Multi-wall carbon nanotubes for the adsorption of hydrogen, production method and purification method Download PDFInfo
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- WO2017152298A1 WO2017152298A1 PCT/CL2017/050013 CL2017050013W WO2017152298A1 WO 2017152298 A1 WO2017152298 A1 WO 2017152298A1 CL 2017050013 W CL2017050013 W CL 2017050013W WO 2017152298 A1 WO2017152298 A1 WO 2017152298A1
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- Prior art keywords
- nanotubes
- hydrogen
- carbon nanotubes
- magnetite
- carbon
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Classifications
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- B01J20/02—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof comprising inorganic material
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- C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
- C23C16/00—Chemical coating by decomposition of gaseous compounds, without leaving reaction products of surface material in the coating, i.e. chemical vapour deposition [CVD] processes
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Definitions
- MWCNT MULTIPLE WALL CARBON NANOTUBES
- the present invention relates to multi-wall carbon nanotubes (MWCNT), for molecular hydrogen adsorption, method of obtaining nanotubes by chemical vapor deposition technique by aerosol assisted vapor (AACVD, of its acronym in English, Aerosol Assisted Chemical Vapor Deposition) using as magnetite mineral catalyst with a purity> 85%, and method of purification of said nanotubes obtained to increase its hydrogen adsorption capacity.
- MWCNT multi-wall carbon nanotubes
- AACVD aerosol assisted vapor
- magnetite mineral catalyst with a purity> 85%
- carbon nanostructures such as fullerenes, graphite, carbon nanofibers, carbon nanotubes with multiple or single walls, among others, according to A.C. Dillon, K.M. Jones, T.A. Bekkedahl, C.H. Kiang, D.S. Bethune, M.J. Heben Storage of hydrogen in single-walled carbon nanotubes. Nature 386 (1997) 377-379, Alan Chambers, Col ⁇ n Park, R. Terry K. Baker, Nelly M. Rodr ⁇ guez. Hydrogen Storage in Graphite Nanofibers. J. Phys. Chem. B 102 (1998) 4253-4256, E. Poirier, R.
- Applied Physics Letters 74 (1999) teaches to purify the single-wall carbon nanotubes obtained by evaporation with an ultrasound scattering and dispersion technique showed a percentage of stored gravimetric hydrogen of greater than 8% by weight at -193.1 ⁇ (80K ) and a pressure of 16 KPa (158 atm).
- the surface area BET of the nanotubes was 285 m 2 / g.
- Lithium-doped nanotubes showed a percentage of stored gravimetric hydrogen of 20% by weight at 200-400 ⁇ C (473-673 ⁇ ) and a pressure of 1 atm, meanwhile, the doped with potassium (K-MWCNT) showed a percentage of stored gravimetric hydrogen of 14% by weight at ⁇ 39.8 ⁇ ( ⁇ 313 ⁇ ) and a pressure of 1 atm.
- K-MWCNT doped with potassium
- Ralph T. Yang Hydrogen storage by alkali-doped carbon nanotubes-revisited. Carbon 38 (2000) 623-626 was based on previous work to produce the same nanotubes and use them to adsorb hydrogen.
- Li-MWCNT Lithium-doped nanotubes
- nanotubes were subjected to another treatment in 100 ml 5M of HN0 3 assisted with ultrasound between 1-24 hours at a power of 50W / cm 2 , to be subsequently cooled to I CC.
- the nanotubes resulted in a maximum stored percentage of gravimetric hydrogen of 1.5% by weight at 24.8 ⁇ (298 ⁇ ) and a pressure of 0.08 MPa.
- the nanotubes grew in an aligned fashion on quartz substrates and had an internal diameter of 1 1 nm and an external diameter of 34 nm, a BET surface area of 131 m 2 / g, and a pore size distribution of 1 -300 nm.
- the nanotubes resulted in a percentage of stored gravimetric hydrogen of 3.4% by weight at a temperature of 16.8 ⁇ (290K) and a pressure of 3-10 MPa.
- Mater. Chem. Phys. 78 (2002) 144-148 obtained multiple-walled nanotubes (MWCNT) by catalytic decomposition of acetylene on cobalt nanoparticles contained in mesoporous silica at a temperature of 750 ⁇ for 30 min, using nitrogen as a entrainment gas.
- MWCNT multiple-walled nanotubes
- the MWCNT with a diameter between 20-30 nm, were doped with N 2 in a quartz reactor at a temperature of 500 ⁇ for 2 hours and then washed with KN0 3 to dop them with potassium ions.
- the nanotubes resulted in a percentage of stored gravimetric hydrogen of 3.2% by weight at a temperature of 100 ⁇ (373.2 ⁇ ) and at a pressure of 12 MPa.
- the annealed nanotubes resulted in a percentage of stored gravimetric hydrogen of 3.98% by weight at a temperature of 24.8 ⁇ (298K) and a pressure of 10 MPa.
- Carbon 41 (2003) 2471-2476 obtained multiple wall nanotubes (MWCNT) by catalytic decomposition of benzene using the floating catalyst method with a horizontal reaction chamber, resulting in nanotubes with diameters smaller than 30 nm.
- the pore size of The MWCNT was 2-5 nm with a BET surface area of 25-178 m 2 / g.
- the nanotubes resulted in a percentage of stored gravimetric hydrogen of 0.8-4.6% by weight at a temperature of 19.8 ⁇ (293K) and a pressure of 13 MPa.
- JP2003238101 developed a milling-based method to transform carbon nanotubes with inter-layer spacings of 0.34 nm, diameter between 1 -100 nm and length between 20-100 nm in compartments to incorporate hydrogen in these in situ at room temperature and a pressure between OMPa-1 MPa.
- the nanotubes resulted in a percentage of stored gravimetric hydrogen less than 6.7% by weight.
- US 200501 18091 A1 used single-wall nanotubes in the form of skeins with a diameter between 0.4-1 nm and an average length of 1000 nm to store hydrogen, reporting an adsorption between 4 kcal / mole H 2 -8 kcal / mole H 2 . It describes the method and the device comprising said nanotubes for the storage and release of hydrogen.
- US 20090272935 A1 obtained nanotubes (SWCNT, MWCNT or mixtures thereof) by chemical vapor deposition method (CVD) assisted with metal catalyst with densities of 0.2-1.5 g / cm 3 , purities greater than 98%, surface area from 600 to 2600 m 2 / g, and mesopore diameter of 1.0 to 5.0 nm. These nanotubes resulted in a percentage of stored gravimetric hydrogen of 0.4% by weight at a temperature of 24.8 ⁇ (298 ⁇ K) and a pressure of 10 MPa.
- CVD chemical vapor deposition method
- the MWCNT used three different purification methods that involve the following sequences: a) oxidation in air at a temperature of 900 ⁇ and washed with HCI, b) the nanotubes obtained in a) were mixed with KOH powder and treated thermally at a temperature 850 ⁇ c) MWCNTs obtained by CVD HAD and were heat - treated at a temperature of 850 ⁇ under an atmosphere of C0 2 and then washed with HCI. The average diameters were 1, 8 nm for the SWCNT and 30 nm for the MWCNT.
- the nanotubes resulted in a percentage of stored gravimetric hydrogen of maximum 1.7% by weight at a temperature of 24.8 ⁇ (298 ⁇ ) and a pressure of 12 MPa.
- the preparation was carried out by the vapor phase thermo-chemical deposition method (TCVD) using as a catalyst a Fe / Ni / MgO mixture.
- TCVD vapor phase thermo-chemical deposition method
- they purified the MWCNT using a calcination sequence at a temperature of 450 ⁇ in an environment of 0 2 , cooling to room temperature, immersion in hydrofluoric acid (HF) at room temperature, immersion in sulfuric acid (H 2 S0 4 ) at its boiling temperature, immersion in nitric acid (HN0 3 ) at its boiling temperature, washed with deionized water until it reaches a neutral pH and, dried at a temperature of 150 ⁇ , for a purification efficiency of 93.5%.
- HF hydrofluoric acid
- H 2 S0 4 sulfuric acid
- HN0 3 nitric acid
- nitrate solutions of Ca, Co, Fe, Ni, and Pd were used in distilled water under stirring, subsequently filter and heat the sample to a temperature of 200 ⁇ .
- the average diameter of the CNT was 60 nm, with an I G / ID from Raman 2, 1.
- Purified and functionalized nanotubes resulted in a percentage of stored gravimetric hydrogen between 0.3-7% by weight.
- MWCNT multiple wall nanotubes
- the MWCNT was obtained by the solvothermal method with solvent-catalytic assembly using an autoclave. To purify the MWCNT, a sequence of washing and filtering with ethanol, dilute acid, and doubly deionized water, ultrasound, drying in air at room temperature and vacuum drying between 69, 8-79, 5 utilizó was used. In the meantime, the surface modification was carried out with solutions of H 2 S0 4 / HN0 3 at a temperature of ' ⁇ ' ⁇ 9.8 q C.
- JP2001 146408 (A) documents KR20010091479 (A), JP2004292310 (A), JP2004313906 (A), JP2004059409 (A), US 8454922 B2, US 20090123789 A1, JP201 1255314, US 8076034 B1, KR20120002043 (A), and CN103883872 (A).
- the present invention provides carbon nanotubes for hydrogen adsorption applications, and a two-stage method for obtaining said carbon nanotubes economically, these being: 1) obtaining nanotubes by chemical vapor deposition technique (AACVD) ) using as a magnetite mineral catalyst and a camphor / alcohol solution as a carbon source, and 2) purification of the nanotubes obtained by heat treatment and acid treatment.
- AACVD chemical vapor deposition technique
- one aspect of the invention corresponds to multi-wall carbon nanotubes (MWCNT) resulting from the method of obtaining by the chemical vapor deposition technique. by aerosol as well as those modified physically and chemically as a result of the purification method.
- MWCNT multi-wall carbon nanotubes
- Multi-wall carbon nanotubes Obtained by AACVD Technique
- MWCNT Multiple-Wall Carbon Nanotubes Obtained by AACVD Technique
- IG / ID symmetry / disorder
- they have a percentage of stored gravimetric hydrogen between 0.2-1.7% by weight at a temperature of ⁇ ⁇ 9 ⁇ (2,
- Figure 1 shows the scanning electron microscopy (SEM) images where the nanotubes and their morphology are observed
- Figure 2 shows the transmission electron microscopy (TEM) images where the multipared diameters and thicknesses are observed of the nanotube, in addition to the nanoparticles adhered to the walls of these
- Figure 3 shows the phases present in the nanotube by X-ray diffraction technique.
- Figure 4 and Table 1 show the Raman spectra of the nanotubes, where the different vibrational energies for the carbon nanotubes phase and the degree of crystallinity or defects of these, respectively, are appreciated.
- Figures 1A-1 D Scanning electron microscopy images of the powders obtained with the AACVD technique for samples M1 (a and b) and M3 (c and d).
- Figures 2A-2F Transmission and high resolution electron microscopy images for CNT powders obtained by AACVD technique of samples M3 (a-c) and M2 (d-f).
- Figure 3 X-ray diffraction pattern of the powders obtained with the AACVD technique.
- Figure 4. Raman spectroscopy of the powders obtained with the AACVD technique.
- Figure 5A-5D Scanning electron microscopy images and dispersive energy spectra of samples M1 and M2 after the purification process.
- Figures 6A-6F Transmission electron microscopy images of the M1 and M2 samples after the purification process.
- FIGS 7A-7B Results DRX of samples M1 and M2 after the purification process, the nomenclature used is as follows: S / T (without purification), TT (Heat treatment), HF (treatment with hydrofluoric acid and ultrasound) and HCI (acid treatment hydrochloric).
- Figure 9 Method for obtaining carbon nanotubes by AACVD technique.
- Figure 10 Schematic representation of the arrangement used for the AACVD process.
- the present invention provides carbon nanotubes for hydrogen adsorption applications, and a two-stage method for obtaining said carbon nanotubes economically, these being: 1) obtaining nanotubes by chemical vapor deposition technique (AACVD), using as a magnetite mineral catalyst and a solution of camphor / alcohol as a carbon source, and 2) purification of the nanotubes obtained by heat treatment and acid treatment.
- AACVD chemical vapor deposition technique
- the present invention provides multiple-walled carbon nanotubes (MWCNT) resulting from the method of obtaining by the technique of chemical deposition in the vapor-assisted vapor phase as well as those modified in physico-chemical form as a result of the method of purification.
- the multiple-wall carbon nanotubes (MWCNT) obtained by AACVD technique have an agglomerated type morphology similar to a wool ball, with small nanotube threads with lengths greater than 1 ⁇ , average diameter between 20-40 nm, multipared thicknesses Between 4.3-9.0 nm and each nanotube is composed of 13 to 27 concentric nanotubes.
- Nanoparticles of iron oxides with sizes smaller than 50 nm are attached to the outer walls, and have a mixture of phases (amorphous carbon, multi-walled carbon nanotubes, iron oxides and zeolite). They have a symmetry / disorder ratio (I G / ID) from Raman between 0.95-1, 49. Finally, they have a percentage of stored gravimetric hydrogen between 0.2-1.7% by weight at a temperature of ⁇ ⁇ 9 ⁇ (2,393K) and a pressure of 44 Torr (5,8 KPa).
- the multiple wall carbon nanotubes obtained are presented in the form of agglomerations similar to a ball of wool, with small nanotube threads with lengths greater than 1 ⁇ .
- multi-wall carbon nanotubes have nanoparticles with sizes smaller than 50 nm attached to the outer walls.
- the multipared thicknesses are between 4.3-9 nm that consist of 13 to 27 concentric nanotubes.
- the nanotubes obtained have an average diameter between 20-40 nm.
- the change in the crystalline structure of the magnetite is a product of the reduction of the iron present when it has contact with the carbonaceous material, giving rise to the iron carbide (Fe 3 C) and ferrous oxide (FeO) phases.
- the G band is related to the symmetry of the graphite E 2 g in the inter-wall mode, which reflects the intensity sp 2 of the hybridized carbon atoms.
- the other band D indicates the disorder of carbon atoms.
- the slight change in intensity values is due to the increase in walls present in the nanotube that is reflected in the decrease in inter-wall distance (DK Singh, PK lyer, PK Giri. Diameter dependence of interwall separation and strain in multiwalled carbon nanotubes probed by X-ray diffraction and Raman scattering studies. Diamond & Related Materials 43 (2014) 66-71, AC Ferrari, J. Robertson.
- the multiple-walled carbon nanotubes (MWCNT) obtained after the purification method have as a constituent element carbon, global spiral morphology and a corrugated surface that extends from the outer layers to the inner ones, as well as the disappearance of the nanoparticles adhered to the walls of these. They have a high crystallinity resulting from the elimination of amorphous carbon, with a symmetry disorder (I G / ID) from Raman between 0.63-1, 22, and an area BET surface between 53.5-729.4 m 2 / g determined by adsorption of N 2 at a temperature of -196 ⁇ (77.1 K) following the lodges method described in US 5,653,951. Finally, they have a percentage of stored gravimetric hydrogen between 0.1 -3.5% by weight at a temperature of 19 ⁇ (293 ⁇ K) and a pressure of 44 Torr (5.8 KPa).
- Figures 5-8 The effectiveness of the purification method for multi-walled carbon nanotubes in regard to the removal of impurities, modification of morphology, and increase in surface defects is set forth in Figures 5-8, and Table 2.
- the Figures 5A-5D shows scanning electron microscopy images and dispersive energy spectra, where the elementary chemical composition of carbon nanotubes can be seen
- Figures 6A-6F shows transmission electron microscopy images of nanotubes where Observe the change in the morphology of the nanotubes and the elimination of the nanoparticles that were attached to the walls of these
- Figures 7A-7B shows the evolution of the disappearance of the contaminating phases in the nanotube during the method of purification by X-ray diffraction technique.
- Figure 8 and Table 2 show the Raman spectra after the puri process fication, where the different vibrational energies for the carbon nanotube phase are appreciated, and the degree of crystallinity or defects induced in the nanotubes, respectively.
- Stage 1 Obtaining Multiple Wall Carbon Nanotubes (MWCNT) by AACVD
- Another aspect of the invention corresponds to the method and the selection of variables together with their values to synthesize the multi-walled carbon nanotubes (MWCNT) by the AACVD technique.
- the present method for obtaining carbon nanotubes is composed of three steps (see Figure 9), these being: 1) preparation of the carbon source, 2) preparation of the catalyst / support mixture and 3) obtaining of nanotubes by AACVD technique. Each step is described below, indicating its relationship with the State of the Art.
- the reagents and the way to prepare the carbon source to be used in the AACVD method to obtain CNT was taken from E. Mosquera, DE Diaz-Droguett, N. Carvajal, M. Roble, M. Morel, R. Espinoza. Characterization and Hydrogen Storage in Multi-Walled Carbon Nanotubes Grown by Aerosol- Assisted CVD Method. Diamond & Related Materials 43 (2014) 66-71, which describe that approximately 2.0 g of Camphor (Ci 0 H 16 O) with 95% purity, are mixed with 10 ml of isopropyl alcohol (2% w / w) in a magnetic stirrer
- the ratio w / v camphor to isopropyl alcohol can vary in the range of 1: 5 to 3: 7
- Step 2 Preparation of catalyst / support mixture
- the material used as a catalyst is mineral magnetite concentrate with the following description:
- Magnetite ore 325 mesh (less than 45 ⁇ ) with 80% magnetite phase and 20% silicates and other iron oxides.
- Magnetite ore 325 mesh (less than 45 ⁇ ) with 98% magnetite phase and 2% silicates and hematite.
- the material used as a support is a zeolite (molecular sieve: alkali metal metal silicate / calcium, chromatograph grade, linde / Coast engineering laboratory / Redondo Beach CA-USA).
- the preparation of the catalyst / support mixture is carried out in a solid state by dry mechanical grinding using an agate mortar for 10 minutes.
- the mixing ratios of the catalyst and support used are shown in Table 3.
- the catalyst to support ratio in w / w may vary in the range of 100: 0 to 50:50.
- Step 3 Obtaining carbon nanotubes by AACVD method
- an aerosol-assisted vapor phase chemical deposition system (AACVD) is used, which is shown in Figure 10, where in E. Mosquera, DE Diaz-Droguett, N. Carvajal, M. Roble, M. Morel, R. Espinoza. Characterization and Hydrogen Storage in Multi-Walled Carbon Nanotubes Grown by Aerosol- Assisted CVD Method. Diamond & Related Materials 43 (2014) 66-71, the principle of operation is described.
- the method uses the AACVD technique according to the following steps and values of its variables: i)
- the solution (2) is placed in the ultrasonic nebulizer (1) at a frequency between 1, 7-2.5 MHz.
- the reactor (4) which is defined by a quartz tube (5) inserted in the furnace by means of an argon or nitrogen transport gas (3) at a flow of between 0 , 5-2 L / min; iii) the mist reacts with the catalyst or catalyst / support mixture (8), which is spread a length (7) between 4-6 cm within the reactor heating zone (6) with a length between 12 -15 cm whose temperature at that time is between 600-900 ⁇ ; iv) After 20-40 min of process, the reactor is allowed to cool to room temperature using the oven's own thermal inertia; and v) After cooling, the quartz tube (5) is dismantled from the oven and the resulting powder that can be nanotubes or a mixture of nanotubes with residues (9) is extracted.
- Other equipment components include a waste scrubber bottle (10) and a gas outlet
- Table 4 summarizes the yield and use of the carbonaceous raw material achieved with the method under the conditions described for obtaining multiple wall carbon nanotubes (MWCNT).
- Stage 2 Purification of Multiple Wall Carbon Nanotubes (MWCNT) Obtained by AACVD
- MWCNT Multiple Wall Carbon Nanotubes
- Another aspect of the invention corresponds to the purification method, and the selection of variables together with their values to purify the multi-walled carbon nanotubes (MWCNT) obtained by the AACVD technique.
- Step 1 Heat treatment. They are placed between 400-558 mg of the nanotubes obtained in a tubular furnace (Nabetrtherm RHTH brand 12-600 / 16 with heating rate ⁇ ⁇ ) at a temperature of between 400-550 ⁇ for 1-3 hours. Subsequently, it is allowed to cool to room temperature between 6-12 hours.
- the objective with this step is to achieve the elimination of amorphous carbon A. Reyhani, S. Z. Mortazavi, S. Mirershadi, A. Z. Moshfegh, P. Parvin, A. Nozad. Hydrogen storage in decorated multiwalled carbon nanotubes by Ca, Co, Fe, Ni, and Pd nanoparticles under ambient conditions. J. Phys. Chem. C. 1 15 (201 1) 6994-7001.
- Step 2 Treatment with hydrofluoric acid (HF) solution in ultrasonic bath.
- the samples from step 1 are placed in hydrofluoric acid solution (with a concentration between 20-60% and in a HF: CNT ratio between 1: 3 to 3: 5 depending on volume) under ultrasonic bath (ELMASONIC brand E 30 H) at a frequency between 25-40 kHz for 1 -3 hours.
- ELMASONIC brand E 30 H ultrasonic bath
- the resulting solution is allowed to stand for 10-30 minutes in an extraction hood, after which time, the supernatant liquid is removed with disposable micro pipettes.
- This step is performed at a pressure of 101.3 KPa (1 atmosphere) and room temperature (25 ⁇ ). The objective with this step is to achieve the removal of alumino-silicates from zeolite A.
- Step 3 Wash and spin.
- the samples from step 2 are subjected to a wash-spin cycle until they reach a neutral pH.
- a washing agent deionized water is used and each centrifuge is carried out for 4 minutes at 3500 rpm in an ELCEMCC60CLA # IV anti-centrifuge equipment for eppendorf tubes of 1.5 m Prism (Labnet USA). Once the neutral pH is reached, a final wash with ethanol is performed.
- Step 4 drying.
- the samples from step 3 are dried in the environment for 30-50 hours in a container (beaker).
- Step 5 Treatment with hydrochloric acid (HCI) solution.
- HAI hydrochloric acid
- the samples from step 4 are placed in hydrochloric acid solution (with a concentration between 30-45% and in an HCLCNT ratio between 1: 3 to 3: 5 depending on volume) for 20-30 hours at steady state .
- the supernatant liquid is removed with disposable micro pipettes.
- the objective with this step is to achieve the elimination of iron present in nanotubes Mauricio Morel (2013). Synthesis of Magnetic Nanocomposites with Conjugated Polymers: Study of their Magnetic and Optical Properties. PhD thesis in Materials Science, Faculty of Physical and Mathematical Sciences (University of Chile).
- Step 6 Wash and spin.
- the samples from step 5 are subjected to a wash-spin cycle until they reach a neutral pH.
- a washing agent deionized water is used and each centrifuge is performed for 4 minutes at 3500 rpm in ELCEMCC60CLA # Microcentrifuge for eppendorf tubes of 1, 5 mi Prism (Labnet USA). Once the neutral pH is reached, a final wash with ethanol is performed.
- Step 7 The solid resulting from step 6 is dried in an oven with a vacuum system (-0.1 MPa) Leybold brand (Mod: D1, 6B) at a temperature of 80 ⁇ for 1 hour.
- Table 5 summarizes the efficiency of the purification process of multiple-wall carbon nanotubes obtained from the AACVD technique. Table 5. Performance and efficiency of the purification process of multiple wall carbon nanotubes.
- H 2 (99.995%, 0 2 ⁇ 5 ppm, H 2 0 ⁇ 8 ppm, C0 2 + CO ⁇ 4 ppm, N 2 ⁇ 20 ppm and THC ⁇ 5 ppm
- H 2 99.995%, 0 2 ⁇ 5 ppm, H 2 0 ⁇ 8 ppm, C0 2 + CO ⁇ 4 ppm, N 2 ⁇ 20 ppm and THC ⁇ 5 ppm
- H 2 99.995%, 0 2 ⁇ 5 ppm, H 2 0 ⁇ 8 ppm, C0 2 + CO ⁇ 4 ppm, N 2 ⁇ 20 ppm
- Figure 13 shows the results against the hydrogen adsorption behavior (H 2 ) as a function of the pressure for the carbon nanotubes without the purification process
- Figure 14 shows the results against the hydrogen adsorption behavior ( H 2 ) depending on the pressure for carbon nanotubes with the purification process.
- Sample M1 demonstrates an increasing adsorption process as the pressure increases, this is due to the combination of synthesis method-starting material and purification process.
- the M3 sample was carried out under a different purification where only concentrated hydrochloric acid was used and then passed to the hydrogen adsorption part, although the adsorption improved by a couple of points with respect to the unpurified carbon nanotube , this is well below the samples M1 and M2. This effect is mainly due to an incomplete purification process, which by leaving present impurities of the zeolite type decreases the adsorption property.
- Camphor (Ci 0 H 16 O) with 95% purity are taken, mixed with 10 ml of isopropyl alcohol (10 ml at 2% w / w) on a magnetic stirrer for 5 minutes.
- Step 2 Preparation of catalyst / support mixture
- a dry mechanical grinding is performed in agate mortar for 10 minutes of magnetite ore with 98% magnetite phase 325 mesh (less than 45 ⁇ ) with a Zeolite (molecular sieve: alkali-metal alumina silicate / calcium, chromatograph grade, edge / Coast engineering I abo ry time / Redondo Beach CA-USA) in a proportion of 66% to 34%, respectively.
- Zeolite molecular sieve: alkali-metal alumina silicate / calcium, chromatograph grade, edge / Coast engineering I abo ry time / Redondo Beach CA-USA
- Step 3 Obtaining nanotubes by AACVD technique
- the multiple-wall carbon nanotubes (MWCNT) obtained have an agglomerate morphology, with an average length of 1.5 microns, average diameter 30 nm, multipared thicknesses between 4.5-7.0 nm and each nanotube is composed of 15-20 concentric nanotubes.
- Nanoparticles of iron oxides with sizes 20-30 nm are attached to the outer walls, and they present a mixture of phases (amorphous carbon, multi-walled carbon nanotubes, iron oxides and zeolite). They have a symmetry / disorder (IG / ID) ratio from Raman of 1, 02.
- Step 4 Heat treatment.
- a tubular oven with heating rate 15 velocidad ⁇ at a temperature of between 450 ⁇ for 1 hour is placed between 500 mg of the nanotubes obtained in step 3. Subsequently, it is allowed to cool to room temperature for 11 hours.
- Step 5 Treatment with hydrofluoric acid (HF) solution in ultrasonic bath.
- HF hydrofluoric acid
- the samples from step 4 are placed in hydrofluoric acid solution (with a concentration between 40% and in an HF: CNT ratio between 1: 3 depending on volume) under ultrasonic bath (ELMASONIC E 30 H mark) at a frequency between 37 kHz for 1 hour. Subsequently, the resulting solution is allowed to stand for 20 minutes in an extraction hood, after which time, the supernatant liquid is removed with disposable micro pipettes. This step is performed at a pressure of 1 atmosphere and room temperature (25 ⁇ ).
- Step 6 Wash and spin.
- the samples from step 5 are subjected to a wash-spin cycle until they reach a neutral pH.
- a washing agent deionized water is used and each centrifuge is performed for 4 minutes at 3500 rpm in an ELCEMCC60CLA # Microcentrifuge for eppendorf tubes of 1 .5 mi Prism (Labnet USA). Once the neutral pH is reached, a final wash with ethanol is performed.
- Step 7 drying.
- the samples from step 6 are dried in the environment for 48 hours in a container (for example a beaker).
- Step 8 Treatment with hydrochloric acid (HCI) solution.
- step 7 The samples from step 7 are placed in hydrochloric acid solution (with a concentration between 37% and in an HCI: CNT ratio of 1: 3 as a function of volume) for 24 hours at steady state. Subsequently, the supernatant liquid is removed with disposable micro pipettes.
- Step 9 Wash and spin.
- the samples from step 8 are subjected to a wash-spin cycle until they reach a neutral pH.
- a washing agent deionized water is used and each centrifuge is performed for 4 minutes at 3500 rpm in ELCEMCC60CLA # Microcentrifuge for eppendorf tubes of 1, 5 mi Prism (Labnet USA). Once the neutral pH is reached, a final wash with ethanol is performed.
- the solid resulting from step 9 is dried in an oven with a vacuum system (-0.1 MPa) Leybold brand (Mod: D1, 6B) at a temperature of 80 ⁇ for 1 hour.
- the multiple-walled carbon nanotubes (MWCNT) after purification have as a constituent element carbon, global spiral morphology and a corrugated surface that extends from the outer layers to the innermost, as well as the disappearance of the nanoparticles adhered to the walls of these.
- Step 1 The multi-walled carbon nanotubes (MWCNT) obtained after the purification treatment are deposited on the surface of a quartz crystal microbalance (QC) at 25 ⁇ , where said suspension is obtained by dispersing the MWCNT in alcohol Sonopropyl isopropyl using an ultrasonic bath for 7 minutes.
- MWCNT multi-walled carbon nanotubes
- Step 2 After the deposit, the QC is located on the head of a quartz crystal microbalance system (model SQM-310) and placed inside a vacuum chamber.
- the chamber is pumped up to 101, 3 (7x10 "6 Torr) using turbo and rotary pumps that operate in series.
- a gate valve placed between the chamber and the turbo pump isolates the vacuum chamber, allowing pressurization with H 2 ( Indura, 99.995%, 0 2 ⁇ 5 ppm, H 2 0 ⁇ 8 ppm, C0 2 + CO ⁇ 4 ppm, N 2 ⁇ 20 ppm and THC ⁇ 5 ppm) by injecting it through a needle valve.
- H 2 Indura, 99.995%, 0 2 ⁇ 5 ppm, H 2 0 ⁇ 8 ppm, C0 2 + CO ⁇ 4 ppm, N 2 ⁇ 20 ppm and THC ⁇ 5 ppm
- Step 3 The change in mass on hydrogen adsorption is determined by monitoring in situ changes in the resonance frequency of the QC as a function of time while the sample is exposed to hydrogen for 8 minutes.
- Step 4 After exposure to H 2 , the chamber is pumped back to 101.3 KPa (7x10 "6 Torr), and the process is repeated by injecting hydrogen until the highest pressure is reached. Pressures between 399.6 Pa a 732.6 Pa (3 and 55 Torr) are monitored with a capacitive meter (Baratron from MKS Instruments) for the different hydrogenation cycles.
- Step 5 The Sauerbrey ' s equation (ec. 1) is used to calculate the mass of adsorbed hydrogen in the carbon nanotube.
- the adsorption value by weight of hydrogen determined by the described method was 3.5 for the purified multi-wall carbon nanotubes, while the value obtained for the same sample of unpurified MWCNT was 0.5.
Abstract
The invention relates to multi-wall carbon nanotubes (MWCNT) for the adsorption of molecular hydrogen, a method for producing the nanotubes via aerosol-assisted chemical vapour deposition (AACVD), using magnetite with a purity of >85% as a mineral catalyst, and a method for purifying said nanotubes in order to increase their capacity for hydrogen adsorption.
Description
NANOTUBOS DE CARBONO DE PARED MULTIPLE (MWCNT) PARA ADSORCION DE HIDROGENO, METODO DE OBTENCION Y METODO DE PURIFICACION Campo de la invención MULTIPLE WALL CARBON NANOTUBES (MWCNT) FOR HYDROGEN ADSORTION, METHOD OF OBTAINING AND PURIFICATION METHOD Field of the invention
La presente invención se refiere a nanotubos de carbono de pared múltiple (MWCNT de sus siglas en inglés, Multi-Wall Carbón Nanotubes) para adsorción de hidrógeno molecular, método de obtención de los nanotubos por técnica de deposición química en fase vapor asistida por aerosol (AACVD, de sus siglas en inglés, Aerosol Assisted Chemical Vapor Deposition) utilizando como catalizador mineral magnetita con una pureza >85%, y método de purificación de dichos nanotubos obtenidos para incrementar su capacidad de adsorción de hidrógeno. The present invention relates to multi-wall carbon nanotubes (MWCNT), for molecular hydrogen adsorption, method of obtaining nanotubes by chemical vapor deposition technique by aerosol assisted vapor ( AACVD, of its acronym in English, Aerosol Assisted Chemical Vapor Deposition) using as magnetite mineral catalyst with a purity> 85%, and method of purification of said nanotubes obtained to increase its hydrogen adsorption capacity.
Antecedentes y Técnica Relevante Background and Relevant Technique
El hidrógeno molecular (H2), se propuso como una posible fuente alternativa de combustible desde hace más de dos décadas. Desafortunadamente, el hidrógeno molecular presenta numerosos inconvenientes que han impedido su uso a gran escala como combustible. Una de las desventajas es que se encuentra en estado gaseoso, lo que hace que el hidrógeno sea difícil de almacenar y transportar en grandes cantidades de forma segura. Molecular hydrogen (H 2) was proposed as a possible alternative fuel source for more than two decades. Unfortunately, molecular hydrogen has numerous drawbacks that have prevented its large-scale use as a fuel. One of the disadvantages is that it is in a gaseous state, which makes hydrogen difficult to store and transport in large quantities safely.
Para hacer frente a este problema, se han desarrollado diferentes técnicas, entre ellas, el almacenamiento de hidrógeno en tanques de alta presión (30,4 MPa), y licuefacción del hidrógeno a temperaturas menores a 20eK con un sistema de refrigeración a base de helio. Sin embargo, ambas técnicas consumen una gran cantidad de energía bien sea, para la generación de la alta presión o para licuar el hidrógeno. Otras técnicas incluyen la adsorción de hidrógeno en materiales sólidos, entre los cuales se han estudiado hidruros de metales, microesferas de vidrio, súper carbono activado, entre otros, sin algún
resultado relevante debido a su baja capacidad de almacenamiento (ver USNo.6.672.077 B1 ). To cope with this problem, different techniques have been developed, including the storage of hydrogen in high-pressure tanks (30.4 MPa), and liquefaction of hydrogen at temperatures below 20 e K with a cooling system based helium However, both techniques consume a large amount of energy either for high pressure generation or to liquefy hydrogen. Other techniques include the adsorption of hydrogen in solid materials, among which metal hydrides, glass microspheres, activated super carbon, among others, have been studied without any relevant result due to its low storage capacity (see US 6,672,077 B1).
En lo que respecta a las nanoestructuras, se ha podido constatar que el hidrógeno puede ser almacenado en nanoestructuras de carbono, tales como, fullerenos, grafito, nanofibras de carbono, nanotubos de carbono de pared múltiple o simple, entre otros, de acuerdo con A.C. Dillon, K.M. Jones, T.A. Bekkedahl, C.H. Kiang, D.S. Bethune, M.J. Heben. Storage of hydrogen in single-walled carbón nanotubes. Nature 386 (1997) 377-379, Alan Chambers, Colín Park, R. Terry K. Baker, Nelly M. Rodríguez. Hydrogen Storage in Graphite Nanofibers. J. Phys. Chem. B 102 (1998) 4253-4256, E. Poirier, R. Chahine, T.K. Bose. Hydrogen adsorption in carbón nanostructures. International Journal of Hydrogen Energy 26 (2001 ) 831 -835, H-M. Cheng, Q-H. Yang, C. Liu. Hydrogen storage in carbón nanotubes. Carbón 39 (2001 ) 1447- 1454, y en el documento USNo.5.653.951 . Dentro de esta aproximación, los nanotubos de carbono debido a su estructura tubular única (pared múltiple o pared simple), gran área superficial específica, y buena estabilidad química y térmica, han sido propuestos para su aplicación en el almacenamiento de hidrógeno. Como resultados de estos esfuerzos tenemos los siguientes antecedentes: With regard to nanostructures, it has been found that hydrogen can be stored in carbon nanostructures, such as fullerenes, graphite, carbon nanofibers, carbon nanotubes with multiple or single walls, among others, according to A.C. Dillon, K.M. Jones, T.A. Bekkedahl, C.H. Kiang, D.S. Bethune, M.J. Heben Storage of hydrogen in single-walled carbon nanotubes. Nature 386 (1997) 377-379, Alan Chambers, Colín Park, R. Terry K. Baker, Nelly M. Rodríguez. Hydrogen Storage in Graphite Nanofibers. J. Phys. Chem. B 102 (1998) 4253-4256, E. Poirier, R. Chahine, T.K. Bose Hydrogen adsorption in carbon nanostructures. International Journal of Hydrogen Energy 26 (2001) 831-835, H-M. Cheng, Q-H. Yang, C. Liu. Hydrogen storage in carbon nanotubes. Coal 39 (2001) 1447-1454, and in US 5,653,951. Within this approach, carbon nanotubes due to their unique tubular structure (multiple wall or single wall), large specific surface area, and good chemical and thermal stability, have been proposed for application in hydrogen storage. As a result of these efforts we have the following background:
A.C. Dillon, K.M. Jones, T.A. Bekkedahl, C.H. Kiang, D.S. Bethune, M.J. Heben. Storage of hydrogen in single-walled carbón nanotubes. Nature 386 (1997) 377-379, obtuvieron nanotubos de carbono de pared simple (SWCNT) en forma de fibras y con baja pureza por co-evaporación de cobalto y grafito en un arco eléctrico, dichas fibras contenían entre 7-14 ramilletes cada uno con un diámetro de 12 Á, mostrando un porcentaje de hidrógeno gravimétrico almacenado de 5-10% en peso a -0,15Ό (273Ή) y u na presión de 0,040 MPa. Este mismo autor en otro trabajoA.C. Dillon, K.M. Jones, T.A. Bekkedahl, C.H. Kiang, D.S. Bethune, M.J. Heben Storage of hydrogen in single-walled carbon nanotubes. Nature 386 (1997) 377-379, obtained single-walled carbon nanotubes (SWCNT) in the form of fibers and with low purity by co-evaporation of cobalt and graphite in an electric arc, these fibers contained between 7-14 corsages each with a diameter of 12 Á, showing a percentage of stored gravimetric hydrogen of 5-10% by weight at -0.15Ό (273Ή) and a pressure of 0.040 MPa. This same author in another work
(http://www1 .eere.energy.gov/hydrogenandfuelcells/pdfs/30535am.pdf) obtuvo
nanotubos de carbono de pared simple por técnica de láser pulsado y luego los purificó en HN03. Los nanotubos mostraron un porcentaje de hidrógeno gravimétrico almacenado de 7% en peso a 24,8Ό y un a presión de 0,040 MPa. Y. Ye, C. C. Ahn, C. Witham, B. Fultz, J. Liu, A. G. Rinzler, D. Colbert, K. A. Smith, R. E. Smalley. Hydrogen adsorption and cohesive energy of single- walled carbón nanotubes. Applied Physics Letters 74 (1999) enseña purificar los nanotubos de carbono de pared simple obtenidos por evaporación con una técnica de corte y dispersión con ultrasonido mostraron un porcentaje de hidrógeno gravimétrico almacenado de mayor a 8% en peso a -193,1 Ό (80K) y una presión de 16 KPa (158 atm). El área s uperficial BET de los nanotubos fue de 285 m2/g. (http: // www1 .eere.energy.gov / hydrogenandfuelcells / pdfs / 30535am.pdf) obtained single wall carbon nanotubes by pulsed laser technique and then purified them in HN0 3 . The nanotubes showed a percentage of stored gravimetric hydrogen of 7% by weight at 24.8Ό and a pressure of 0.040 MPa. Y. Ye, CC Ahn, C. Witham, B. Fultz, J. Liu, AG Rinzler, D. Colbert, KA Smith, RE Smalley. Hydrogen adsorption and cohesive energy of single-walled carbon nanotubes. Applied Physics Letters 74 (1999) teaches to purify the single-wall carbon nanotubes obtained by evaporation with an ultrasound scattering and dispersion technique showed a percentage of stored gravimetric hydrogen of greater than 8% by weight at -193.1 Ό (80K ) and a pressure of 16 KPa (158 atm). The surface area BET of the nanotubes was 285 m 2 / g.
C. Liu, Y. Y. Fan, M. Liu, H. T. Cong, H. M. Cheng, M. S. Dresselhaus. Hydrogen Storage in Single-Walled Carbón Nanotubes at Room Temperature. Science 286, 1 127 (1999) obtuvieron nanotubos de carbono de pared simple (SWCNT) a partir de la técnica descarga de arco de hidrógeno semi-continua y luego los purificaron con HN03 con una eficiencia de purificación del 75%, dichos nanotubos con un diámetro promedio de 1 ,85 nm mostraron un porcentaje de hidrógeno gravimétrico almacenado de 3,5-4,5% en peso a 24,8<C y una presión de 0,040 MPa. C. Liu, YY Fan, M. Liu, HT Cong, HM Cheng, MS Dresselhaus. Hydrogen Storage in Single-Walled Carbon Nanotubes at Room Temperature. Science 286, 1 127 (1999) obtained single-wall carbon nanotubes (SWCNT) from the semi-continuous hydrogen arc discharge technique and then purified them with HN0 3 with a purification efficiency of 75%, said nanotubes with an average diameter of 1.85 nm showed a percentage of stored gravimetric hydrogen of 3.5-4.5% by weight at 24.8 < C and a pressure of 0.040 MPa.
Chen P, Wu X, Lin J, Tan KL. High H2 uptake by alkali-doped carbón nanotubes under ambient pressure and modérate temperatures. Science 285 (1999) 91 -93 obtuvieron nanotubos de carbono de pared múltiple (MWCNT) dopados con litio y potasio por descomposición catalítica de CH4 en catalizador de Ni-MgO o Ni- CaO y luego purificados en HN03 con una eficiencia de purificación del 95%. La longitud de los nanotubos fue en promedio de 100 nm con una distancia interplanar entre tubos de 0,347 nm. Los nanotubos dopados con litio (Li- MWCNT) mostraron un porcentaje de hidrógeno gravimétrico almacenado de 20% en peso a 200-400<C (473-673Ή) y una presión d e 1 atm, entre tanto, los
dopados con potasio (K-MWCNT) mostraron un porcentaje de hidrógeno gravimétrico almacenado de 14% en peso a <39,8Ό (< 313Ή) y una presión de 1 atm. Por su parte, Ralph T. Yang. Hydrogen storage by alkali-doped carbón nanotubes-revisited. Carbón 38 (2000) 623-626 se basó en el anterior trabajo para producir los mismo nanotubos y los utilizo para adsorber hidrógeno. Los nanotubos dopados con litio (Li-MWCNT) mostraron un porcentaje de hidrógeno gravimétrico almacenado de 2,5% en peso a 200-400Ό (473-673Ή) y una presión de 101 ,3 KPa (1 atm), entre tanto, los dopados con potasio (K- MWCNT) mostraron un porcentaje de hidrógeno gravimétrico almacenado de 1 ,8% en peso a <39,8<C (<313<K) y una presión de 0, 1 MPa. Chen P, Wu X, Lin J, Tan KL. High H 2 uptake by alkali-doped carbon nanotubes under ambient pressure and modérate temperatures. Science 285 (1999) 91-93 obtained multiple-walled carbon nanotubes (MWCNT) doped with lithium and potassium by catalytic decomposition of CH 4 in Ni-MgO or Ni-CaO catalyst and then purified in HN0 3 with purification efficiency 95% The length of the nanotubes was on average 100 nm with an interplanar distance between tubes of 0.347 nm. Lithium-doped nanotubes (Li-MWCNT) showed a percentage of stored gravimetric hydrogen of 20% by weight at 200-400 < C (473-673Ή) and a pressure of 1 atm, meanwhile, the doped with potassium (K-MWCNT) showed a percentage of stored gravimetric hydrogen of 14% by weight at <39.8Ό (<313Ή) and a pressure of 1 atm. On the other hand, Ralph T. Yang. Hydrogen storage by alkali-doped carbon nanotubes-revisited. Carbon 38 (2000) 623-626 was based on previous work to produce the same nanotubes and use them to adsorb hydrogen. Lithium-doped nanotubes (Li-MWCNT) showed a percentage of stored gravimetric hydrogen of 2.5% by weight at 200-400Ό (473-673Ή) and a pressure of 101.3 KPa (1 atm), meanwhile, the doped with potassium (K-MWCNT) showed a percentage of stored gravimetric hydrogen of 1.8% by weight at <39.8 < C (<313 < K) and a pressure of 0.1 MPa.
Zhu HW, Ci Li, Chen A, Mao ZQ, Xu CL, Xiao X, Wei BQ, Liang J, Wu DH. Hydrogen uptake in multi-walled carbón nanotubes at room temperature. Hydrogen Energy Progress XIII, proceedings of the 13th World hydrogen energy conference, Beijing (China): International Association for Hydrogen Energy, 2000, p. 560-4 obtuvieron nanotubos de pared múltiple (MWCNT) que mostraron un porcentaje de hidrógeno gravimétrico almacenado de 5% en peso a una temperatura menor a 26,8Ό (<300tK) y una pre sión de 10 MPa. Zhu HW, Ci Li, Chen A, Mao ZQ, Xu CL, Xiao X, Wei BQ, Liang J, Wu DH. Hydrogen uptake in multi-walled carbon nanotubes at room temperature. Hydrogen Energy Progress XIII, proceedings of the 13th World hydrogen energy conference, Beijing (China): International Association for Hydrogen Energy, 2000, p. 560-4 obtained multiple wall nanotubes (MWCNT) that showed a percentage of stored gravimetric hydrogen of 5% by weight at a temperature lower than 26.8Ό (<300 t K) and a pressure of 10 MPa.
Hirscher M, Becher M, Quintel A, Skakalova V, Choi YM, Roth S, Stepanek I, Bernier P, Leonhardt A, Fink J. Hydrogen desorption measurements on carbón nanotubes and graphite. In: Extended abstracts, Eurocarbon 2000. Berlín (Germán): Germán Carbón Group (DKG), 2000, páginas 91-92 obtuvieron nanotubos de pared simple (SWCNT) que mostraron un porcentaje de hidrógeno gravimétrico almacenado de 0,1 % en peso a una temperatura entre <26,8-246,8<C (<300-520cK) y una presión de 0,1 MPa . Hirscher M, Becher M, Quintel A, Skakalova V, Choi YM, Roth S, Stepanek I, Bernier P, Leonhardt A, Fink J. Hydrogen desorption measurements on carbon nanotubes and graphite. In: Extended abstracts, Eurocarbon 2000. Berlin (Germán): Germán Carbón Group (DKG), 2000, pages 91-92 obtained single wall nanotubes (SWCNT) that showed a percentage of stored gravimetric hydrogen of 0.1% by weight at a temperature between <26.8-246.8 < C (<300-520 c K) and a pressure of 0.1 MPa.
Beguin F, Frackpwiak E. Storage of energy in carbón nanotubes. In: Extended abstracts, Eurocarbon 2000. Berlín (Germán): Germán Carbón Group (DKG), 2000, páginas 9-10 obtuvieron nanotubos de carbono de pared múltiple
(MWCNT) por método de electro deposición con un porcentaje de hidrógeno gravimétrico almacenado de 0,1 % en peso. Beguin F, Frackpwiak E. Storage of energy in carbon nanotubes. In: Extended abstracts, Eurocarbon 2000. Berlin (German): German Coal Group (DKG), 2000, pages 9-10 obtained multiple-wall carbon nanotubes (MWCNT) by electrodeposition method with a percentage of stored gravimetric hydrogen of 0.1% by weight.
Nützenadel C, Zuttel A, Chartouni D, Schlapbach L. Electrochemical storage of hydrogen in nanotube materials. Electrochem Solid-State Lett 2 (1999) 30-35 y Nützenadel C, Zuttel A, Emmenegger C, Sudan P, Schlapbach L. Electrochemical storage of hydrogen in carbón single wall nanotubes. In: Tomanek D, Enbody RJ, editors, Science and application of nanotubes, New York: Kluwer Academic Publishing/Plenum Press, 2000, páginas 205-13, utilizaron nanotubos pared múltiple (MWCNT) y simple (SWCNT) comerciales de la empresa MER Corporation con diámetros de 2-15 nm y pureza de 10- 40% (MWCNT) de fase CNT y, 0,7-1 ,2 nm y pureza de 50-70% (SWCNT) de fase CNT para pruebas de adsorción de hidrógeno por métodos electroquímicos a 24,8Ό (298Ή), dando como result ado un porcentaje de hidrógeno gravimétrico almacenado de 2% en peso. Nützenadel C, Zuttel A, Chartouni D, Schlapbach L. Electrochemical storage of hydrogen in nanotube materials. Electrochem Solid-State Lett 2 (1999) 30-35 and Nützenadel C, Zuttel A, Emmenegger C, Sudan P, Schlapbach L. Electrochemical storage of hydrogen in carbon single wall nanotubes. In: Tomanek D, Enbody RJ, editors, Science and application of nanotubes, New York: Kluwer Academic Publishing / Plenum Press, 2000, pages 205-13, used commercial multi-wall (MWCNT) and simple (SWCNT) nanotubes from MER Corporation with diameters of 2-15 nm and purity of 10-40% (MWCNT) of CNT phase and 0.7-1.2 nm and purity of 50-70% (SWCNT) of CNT phase for hydrogen adsorption tests by electrochemical methods at 24.8Ό (298Ή), resulting in a percentage of stored gravimetric hydrogen of 2% by weight.
A Züttel, Ch Nützenadel, P Sudan, Ph Mauron, Ch Emmenegger, S Rentsch, L Schlapbach, A Weidenkaff, T Kiyobayashi. Hydrogen sorption by carbón nanotubes and other carbón nanostructures. Journal of Alloys and Compounds 330-332 (2002) 676-682 obtuvieron nanotubos (SWCNT y MWCNT) por pirólisis de acetileno (12% acetileno en nitrógeno). Algunas muestras fueron purificadas con HN03 y otras más fueron muestras comerciales de MER Corporation, Dynamic Enterprises Ltd. reportando valores de adsorción de hidrógeno de 0,1 -2% en masa de hidrógeno. El área superficial BET de los nanotubos evaluados fue menor a 377 m2/g. To Züttel, Ch Nützenadel, P Sudan, Ph Mauron, Ch Emmenegger, S Rentsch, L Schlapbach, A Weidenkaff, T Kiyobayashi. Hydrogen surprise by carbon nanotubes and other carbon nanostructures. Journal of Alloys and Compounds 330-332 (2002) 676-682 obtained nanotubes (SWCNT and MWCNT) by pyrolysis of acetylene (12% acetylene in nitrogen). Some samples were purified with HN0 3 and others were commercial samples from MER Corporation, Dynamic Enterprises Ltd. reporting hydrogen adsorption values of 0.1-2% by mass of hydrogen. The BET surface area of the nanotubes evaluated was less than 377 m 2 / g.
M. Hirscher, M. Becher, M. Haluska, U. Dettlaff-Weglikowska, A. Quintel, G.S. Duesberg, Y.-M. Choi, P. Downes, M. Hulmán, S. Roth, I. Stepanek, P. Bernier. Hydrogen storage in sonicated carbón materials. Applied Physics A 72 (2001 ) 129-132 utilizaron nanotubos (SWCNT) comerciales y de universidades obtenidos por proceso de ablación láser que luego fueron purificados por
método cromatográfico de 3 etapas, estas incluyen: tratamiento con ácido nítrico, centrifugado, decantación, lavado con agua destilada, ultrasonido, vacío, elusión en una columna llena de poliacrilato de potasio con agua destilada para una eficiencia de purificación del 40%. Estos nanotubos, fueron sometidos a otro tratamiento en 100 mi 5M de HN03 asistido con ultrasonido entre 1 -24 horas a una potencia de 50W/cm2, para ser posteriormente enfriados a I CC. Los nanotubos dieron como resulta do un porcentaje de hidrógeno gravimétrico almacenado máximo de 1 ,5% en peso a 24,8Ό (298Ή) y una presión de 0,08 MPa. M. Hirscher, M. Becher, M. Haluska, U. Dettlaff-Weglikowska, A. Quintel, GS Duesberg, Y.-M. Choi, P. Downes, M. Hulmán, S. Roth, I. Stepanek, P. Bernier. Hydrogen storage in sonicated carbon materials. Applied Physics A 72 (2001) 129-132 used commercial and university nanotubes (SWCNT) obtained by laser ablation process that were then purified by 3-stage chromatographic method, these include: treatment with nitric acid, centrifugation, decantation, washing with distilled water, ultrasound, vacuum, elution on a column filled with potassium polyacrylate with distilled water for a purification efficiency of 40%. These nanotubes were subjected to another treatment in 100 ml 5M of HN0 3 assisted with ultrasound between 1-24 hours at a power of 50W / cm 2 , to be subsequently cooled to I CC. The nanotubes resulted in a maximum stored percentage of gravimetric hydrogen of 1.5% by weight at 24.8Ό (298Ή) and a pressure of 0.08 MPa.
H. Zhu, A. Cao, X. Li, C. Xu, Z. Mao, D. Rúan, J. Liang, D.Wu. Hydrogen adsorption in bundles of well-aligned carbón nanotubes at room temperature. Appl. Surf. Sci. 178 (2001 ) 50-55 obtuvieron madejos de nanotubos (MWCNT) por el método de pirólisis de silano mezclado con un catalizador de ferroceno a una temperatura de 800Ό en un tiempo de 30 min. Lo s nanotubos crecieron de forma alineada sobre sustratos de cuarzo y presentaron un diámetro interno de 1 1 nm y un diámetro externo de 34 nm, un área superficial BET de 131 m2/g, y una distribución de tamaño de poro de 1 -300 nm. Los nanotubos dieron como resultado un porcentaje de hidrógeno gravimétrico almacenado de 3,4% en peso a una temperatura de 16,8Ό (290K) y a una pr esión de 3-10 MPa. H. Zhu, A. Cao, X. Li, C. Xu, Z. Mao, D. Ruan, J. Liang, D.Wu. Hydrogen adsorption in bundles of well-aligned carbon nanotubes at room temperature. Appl. Surf. Sci. 178 (2001) 50-55 obtained hanks of nanotubes (MWCNT) by the silane pyrolysis method mixed with a ferrocene catalyst at a temperature of 800Ό in a time of 30 min. The nanotubes grew in an aligned fashion on quartz substrates and had an internal diameter of 1 1 nm and an external diameter of 34 nm, a BET surface area of 131 m 2 / g, and a pore size distribution of 1 -300 nm. The nanotubes resulted in a percentage of stored gravimetric hydrogen of 3.4% by weight at a temperature of 16.8Ό (290K) and a pressure of 3-10 MPa.
W.Z. Huang, X.B. Zhang, J.P. Tu, F.Z. Kong, J.X. Ma, F. Liu, H.M. Lu, CP. Chen. The effect of pretreatments on hydrogen adsorption of multi-walled carbón nanotubes. Mater. Chem. Phys. 78 (2002) 144-148 obtuvieron nanotubos de pared múltiple (MWCNT) por descomposición catalítica de acetileno sobre nanopartículas de cobalto contenidas en sílice mesoporosa a una temperatura de 750Ό por 30 min, utilizando com o gas de arrastre el nitrógeno. Para purificarlos se colocaron en HN03 por 48 horas y luego una solución de HF (38%) por 24 horas, finalmente se lavaron con agua destilada y se secaron a una temperatura de ~\ 20Ό en aire, para una eficiencia de
purificación del 95%. Los MWCNT con un diámetro entre 20-30 nm, se doparon con N2 en un reactor de cuarzo a uan temperatura de 500Ό por 2 horas y luego se lavaron con KN03 para doparlos con iones de potasio. Los nanotubos dieron como resultado un porcentaje de hidrógeno gravimétrico almacenado de 3,2% en peso a una temperatura de 100Ό (373, 2Ή) y a una presión de 12 MPa. WZ Huang, XB Zhang, JP Tu, FZ Kong, JX Ma, F. Liu, HM Lu, CP. Chen. The effect of pretreatments on hydrogen adsorption of multi-walled carbon nanotubes. Mater. Chem. Phys. 78 (2002) 144-148 obtained multiple-walled nanotubes (MWCNT) by catalytic decomposition of acetylene on cobalt nanoparticles contained in mesoporous silica at a temperature of 750Ό for 30 min, using nitrogen as a entrainment gas. To purify them, they were placed in HN0 3 for 48 hours and then a solution of HF (38%) for 24 hours, finally washed with distilled water and dried at a temperature of ~ \ 20Ό in air, for an efficiency of 95% purification. The MWCNT with a diameter between 20-30 nm, were doped with N 2 in a quartz reactor at a temperature of 500Ό for 2 hours and then washed with KN0 3 to dop them with potassium ions. The nanotubes resulted in a percentage of stored gravimetric hydrogen of 3.2% by weight at a temperature of 100Ό (373.2Ή) and at a pressure of 12 MPa.
L. Ci, H. Zhu, B. Wei, C. Xu, D. Xu. Annealing amorphous carbón nanotubes for their application in hydrogen storage. Appl. Surf. Sci. 205 (2003) 39-43 obtuvieron nanotubos de carbono por método de catalizador flotante, donde una mezcla de benceno, ferroceno y tiofeno se introducen en un reactor a una temperatura de 1 100-1200Ό en presencia de gas hidr ógeno, dando nanotubos con diámetros entre 10-60 nm. Para eliminar el carbono amorfo de los nanotubos, estos se someten a un recocido isotérmico a una temperatura entre 1700-2200Ό por 120 min en atmósfera de argón. Los nanotubos recocidos dieron como resultado un porcentaje de hidrógeno gravimétrico almacenado de 3,98% en peso a una temperatura de 24,8Ό (298K) y una presión de 10 MPa. P.-X. Hou, S.-T. Xu, Z. Ying, Q.-H. Yang, C. Liu, H.-M. Cheng. Hydrogen adsorption/desorption behavior of multiwalled carbón nanotubes with different diameters. Carbón 41 (2003) 2471 -2476 obtuvieron nanotubos de pared múltiple (MWCNT) por descomposición catalítica de benceno usando el método de catalizador flotante con una cámara de reacción horizontal, dando como resultado nanotubos con diámetros menores a 30 nm. Posterior a la síntesis, purificaron los MWCNT utilizando una secuencia de sometimiento a agua hervida, secado, oxidación en aire a 464,8Ό (738K ) para remover el carbón amorfo, tratamiento con ácido clorhídrico para remover las trazas metálicas del catalizador, lavado con agua desionizada, secado. Posteriormente, para remover posible gas adsorbido y oxígeno, se realizó un pre-tratamiento de calentamiento a una temperatura de 799,8Ό (1073Ή) . El tamaño de poro de
los MWCNT fue de 2-5 nm con un área superficial BET de 25-178 m2/g. Los nanotubos dieron como resultado un porcentaje de hidrógeno gravimétrico almacenado de 0,8-4,6% en peso a una temperatura de 19,8Ό (293K) y una presión de 13 MPa. L. Ci, H. Zhu, B. Wei, C. Xu, D. Xu. Annealing amorphous carbon nanotubes for their application in hydrogen storage. Appl. Surf. Sci. 205 (2003) 39-43 obtained carbon nanotubes by floating catalyst method, where a mixture of benzene, ferrocene and thiophene is introduced into a reactor at a temperature of 1 100-1200Ό in the presence of hydrogen gas, giving nanotubes with diameters between 10-60 nm. To remove the amorphous carbon from the nanotubes, these are subjected to an isothermal annealing at a temperature between 1700-2200Ό for 120 min under an argon atmosphere. The annealed nanotubes resulted in a percentage of stored gravimetric hydrogen of 3.98% by weight at a temperature of 24.8Ό (298K) and a pressure of 10 MPa. P.-X. Hou, S.-T. Xu, Z. Ying, Q.-H. Yang, C. Liu, H.-M. Cheng Hydrogen adsorption / desorption behavior of multiwalled carbon nanotubes with different diameters. Carbon 41 (2003) 2471-2476 obtained multiple wall nanotubes (MWCNT) by catalytic decomposition of benzene using the floating catalyst method with a horizontal reaction chamber, resulting in nanotubes with diameters smaller than 30 nm. After the synthesis, they purified the MWCNT using a sequence of submission to boiled water, drying, oxidation in air at 464.8Ό (738K) to remove the amorphous carbon, treatment with hydrochloric acid to remove the metal traces of the catalyst, washing with water deionized, dried. Subsequently, to remove possible adsorbed gas and oxygen, a pre-treatment of heating was carried out at a temperature of 799.8Ό (1073Ή). The pore size of The MWCNT was 2-5 nm with a BET surface area of 25-178 m 2 / g. The nanotubes resulted in a percentage of stored gravimetric hydrogen of 0.8-4.6% by weight at a temperature of 19.8Ό (293K) and a pressure of 13 MPa.
JP2003238101 desarrollaron un método basado en molienda para transformar nanotubos de carbono con espaciamientos de inter-capa de 0,34 nm, diámetro entre 1 -100 nm y longitud entre 20-100 nm en compartimientos para incorporar hidrógeno en estos in situ a temperatura ambiente y una presión entre OMPa- 1 MPa. Los nanotubos dieron como resultado un porcentaje de hidrógeno gravimétrico almacenado menor a 6,7% en peso. JP2003238101 developed a milling-based method to transform carbon nanotubes with inter-layer spacings of 0.34 nm, diameter between 1 -100 nm and length between 20-100 nm in compartments to incorporate hydrogen in these in situ at room temperature and a pressure between OMPa-1 MPa. The nanotubes resulted in a percentage of stored gravimetric hydrogen less than 6.7% by weight.
K. Shen, H. Xu, Y. Jiang, T. Pietra. The role of carbón nanotube structure in purification and hydrogen adsorption. Carbón 42 (2004) 2315-2322 utilizaron nanotubos (SWCNT y MWCNT) comerciales de M.E.R Corporation, Nanolab, CarboLex Inc., Nano Carb Inc., los cuales fueron obtenidos por descarga de arco de carbono (CAD), deposición química en fase vapor asistida por catalizador flotante (CVD), y el proceso HiPco. Antes de la prueba de adsorción de hidrógeno las muestras fueron sometidas a un tratamiento de purificación oxidativa que implica una secuencia de reflujo en HNO3, filtrado, lavado con agua deionizada, secado y oxidación en aire a una temperatura de 559, 8Ό (833Ή). Los nanotubos dieron como resultado un por centaje de hidrógeno gravimétrico almacenado de 1 % en peso a una temperatura de -269, 1 Ό (4Ή) y una presión de 136 kPa. K. Shen, H. Xu, Y. Jiang, T. Pietra. The role of carbon nanotube structure in purification and hydrogen adsorption. Carbon 42 (2004) 2315-2322 used commercial nanotubes (SWCNT and MWCNT) from MER Corporation, Nanolab, CarboLex Inc., Nano Carb Inc., which were obtained by carbon arc discharge (CAD), chemical vapor deposition assisted by floating catalyst (CVD), and the HiPco process. Before the hydrogen adsorption test, the samples were subjected to an oxidative purification treatment that involves a reflux sequence in HNO 3 , filtering, washing with deionized water, drying and oxidation in air at a temperature of 559.8Ό (833Ή) . The nanotubes resulted in a percentage of stored gravimetric hydrogen of 1% by weight at a temperature of -269, 1 Ό (4Ή) and a pressure of 136 kPa.
US 20140319044 A1 recubrieron nanotubos de carbono utilizando como base benceno, luego de un tratamiento de purificación para mejorar la adsorción y mejorar la retención de hidrógeno adsorbido para evitar su escape. US 20140319044 A1 coated carbon nanotubes using benzene as a base, after a purification treatment to improve adsorption and improve retention of adsorbed hydrogen to prevent its escape.
US 200501 18091 A1 utilizaron nanotubos de pared simple en forma de madejos con diámetro entre 0,4-1 nm y una longitud promedio de 1000 nm para almacenar hidrógeno, reportando una adsorción entre 4 kcal/mole H2-8
kcal/mole H2. Describe el método y el dispositivo que comprende dichos nanotubos para el almacenamiento y liberación del hidrógeno. US 200501 18091 A1 used single-wall nanotubes in the form of skeins with a diameter between 0.4-1 nm and an average length of 1000 nm to store hydrogen, reporting an adsorption between 4 kcal / mole H 2 -8 kcal / mole H 2 . It describes the method and the device comprising said nanotubes for the storage and release of hydrogen.
US 20090272935 A1 obtuvieron nanotubos (SWCNT, MWCNT o sus mezclas) por método deposición química en fase vapor (CVD) asistido con catalizador metálico con densidades de 0,2-1 ,5 g/cm3, purezas mayores al 98%, área superficiales de 600 a 2600 m2/g, y diámetro de mesoporo de 1 ,0 a 5,0 nm. Estos nanotubos dieron como resultado un porcentaje de hidrógeno gravimétrico almacenado de 0,4% en peso a una temperatura de 24,8Ό (298<K) y una presión de 10 MPa. US 20090272935 A1 obtained nanotubes (SWCNT, MWCNT or mixtures thereof) by chemical vapor deposition method (CVD) assisted with metal catalyst with densities of 0.2-1.5 g / cm 3 , purities greater than 98%, surface area from 600 to 2600 m 2 / g, and mesopore diameter of 1.0 to 5.0 nm. These nanotubes resulted in a percentage of stored gravimetric hydrogen of 0.4% by weight at a temperature of 24.8Ό (298 < K) and a pressure of 10 MPa.
C. Liu, Y. Chen, C-Z. Wu, S-T. Xu, H-M. Cheng. Hydrogen storage in carbón nanotubes revisited. Carbón 48 (2010) 452-455 obtuvieron nanotubos (SWCNT y MWCNT) por método de descarga de arco de hidrógeno (HAD) y método de deposición química en fase vapor asistida por catalizador flotante (CVD). Posterior a esto, los SWCNT fueron purificados haciendo uso de una secuencia de molienda mecánica, tratamiento con HN03, reflujo con H202, sonicación en solución de NaOH, lavado con agua desionizada. Para el caso de los MWCNT utilizaron tres diferentes métodos de purificación que implican las siguientes secuencias: a) oxidación en aire a una temperatura de 900Ό y lavado con HCI, b) los nanotubos obtenidos en a) se mezclaron con polvo de KOH y fueron tratados térmicamente a una temperatura de 850Ό, y c) los MWCNT obtenidos por HAD y CVD fueron tratados térmicamente a una temperatura de 850Ό bajo una atmósfera de C02 y luego lavados con HCI. Los diámetros promedios fueron de 1 ,8 nm para los SWCNT y de 30 nm para los MWCNT. Los nanotubos dieron como resultado un porcentaje de hidrógeno gravimétrico almacenado de máximo 1 ,7% en peso a una temperatura de 24,8Ό (298Ή) y una presión de 12 MPa. C. Liu, Y. Chen, CZ. Wu, ST. Xu, HM. Cheng Hydrogen storage in carbon nanotubes revisited. Carbon 48 (2010) 452-455 obtained nanotubes (SWCNT and MWCNT) by hydrogen arc discharge method (HAD) and chemical vapor deposition method assisted by floating catalyst (CVD). After this, the SWCNT were purified using a mechanical grinding sequence, treatment with HN0 3 , refluxing with H 2 0 2 , sonication in NaOH solution, washing with deionized water. In the case of the MWCNT they used three different purification methods that involve the following sequences: a) oxidation in air at a temperature of 900Ό and washed with HCI, b) the nanotubes obtained in a) were mixed with KOH powder and treated thermally at a temperature 850Ό c) MWCNTs obtained by CVD HAD and were heat - treated at a temperature of 850Ό under an atmosphere of C0 2 and then washed with HCI. The average diameters were 1, 8 nm for the SWCNT and 30 nm for the MWCNT. The nanotubes resulted in a percentage of stored gravimetric hydrogen of maximum 1.7% by weight at a temperature of 24.8Ό (298Ή) and a pressure of 12 MPa.
E. Mosquera, D.E. Diaz-Droguett, N. Carvajal, M. Roble, M. Morel, R. Espinoza. Characterization and Hydrogen Storage in Multi-Walled Carbón Nanotubes
Grown by Aerosol-Assisted CVD Method. Diamond & Related Materials 43 (2014) 66-71 obtuvieron nanotubos de pared múltiple (MWCNT) por deposición química en fase vapor asistida por aerosol a partir de una mezcla de alcanfor/alcohol y como catalizador el níquel soportado en una zeolita. Los diámetros promedios fueron de 20-200 nm, con una pureza mayor a 96% (sin tratamiento de purificación) y una relación lG/lD a partir de Raman entre 0,63- 1 ,2. Los nanotubos dieron como resultado un porcentaje de hidrógeno gravimétrico almacenado entre 1 ,5-2,1 % en peso a una temperatura de 19Ό (293<K) y una presión de 40 Torr (5,3KPa). E. Mosquera, DE Diaz-Droguett, N. Carvajal, M. Roble, M. Morel, R. Espinoza. Characterization and Hydrogen Storage in Multi-Walled Carbon Nanotubes Grown by Aerosol-Assisted CVD Method. Diamond & Related Materials 43 (2014) 66-71 obtained multiple wall nanotubes (MWCNT) by chemical vapor deposition assisted by aerosol from a camphor / alcohol mixture and as a catalyst the nickel supported on a zeolite. The average diameters were 20-200 nm, with a purity greater than 96% (without purification treatment) and a ratio l G / l D from Raman between 0.63-1.2. The nanotubes resulted in a percentage of gravimetric hydrogen stored between 1.5-2.1% by weight at a temperature of 19Ό (293 < K) and a pressure of 40 Torr (5.3KPa).
Otras aproximaciones para aumentar la capacidad de adsorción de los nanotubos de carbono se basan en la modificación superficial o funcionalización de estos nanotubos con materiales afines con el hidrógeno. Por ejemplo, A. Reyhani y colaboradores (A. Reyhani, S. Z. Mortazavi, S. Mirershadi, A. Z. Moshfegh, P. Parvin, A. Nozad. Hydrogen storage in decorated multiwalled carbón nanotubes by Ca, Co, Fe, Ni, and Pd nanoparticles under ambient conditions. J. Phys. Chem. C. 1 15 (201 1 ) 6994- 7001 ) obtuvieron nanotubos de pared múltiple (MWCNT) funcionalizados con Ca, Co, Fe, Ni, y Pd. La obtención se llevó a cabo por el método de deposición termo-química en fase vapor (TCVD) utilizando como catalizador una mezcla de Fe/Ni/MgO. Posterior a la síntesis, purificaron los MWCNT utilizando una secuencia de calcinación a una temperatura de 450Ό en ambiente de 02, enfriamiento a temperatura ambiente, inmersión en ácido fluorhídrico (HF) a temperatura ambiente, inmersión en ácido sulfúrico (H2S04) a su temperatura de ebullición, inmersión en ácido nítrico (HN03) a su temperatura de ebullición, lavado con agua desionizada hasta alcanzar un pH neutro y, secado a una temperatura de 150Ό, para una eficiencia de purifi cación del 93,5%. Para la funcionalización de los MWCNT purificados se utilizaron soluciones de nitrato de Ca, Co, Fe, Ni, y Pd en agua destilada bajo agitación, posteriormente se
filtra y se calienta la muestra a una temperatura de 200Ό. El diámetro promedio de los CNT fue de 60 nm, con una relación IG/ID a partir de Raman de 2, 1 . Los nanotubos purificados y funcionalizados dieron como resultado un porcentaje de hidrógeno gravimétrico almacenado entre 0,3-7% en peso. K-S. Lin y colaboradores K-S. Lin, Y-J. Mai, S-R. Li, C-W. Shu, C-H. Wang. Characterization and hydrogen storage of surface-modified multiwalled carbón nanotubes for fuel cell application. Journal of Nanomaterials 201 2 (2012) 1 -12 obtuvieron nanotubos de pared múltiple (MWCNT) funcionalizados con COOH, OH, o N02 o dopadas con Ti-NaAIH4 o nanopartículas de Pd. La obtención de los MWCNT fue por el método solvotermal con ensamble-catalítico solvente utilizando una autoclave. Para purificar los MWCNT se utilizó una secuencia de lavado y filtrado con etanol, acido diluido, y agua doblemente desionizada, ultrasonido, secado en aire a temperatura ambiente y secado al vacío entre 69, 8-79, 5Ό. Entre tanto, la modificación superfici al se llevó a cabo con soluciones de H2S04/HN03 a una temperatura de '\ '\ 9,8qC. El dopaje con Ti- NaAIH4 o nanopartículas de Pd de algunas muestras de MWCNT se llevó a cabo por molienda mecánica. El volumen de poro total de los MWCNT fue de 0, 18-0,38 cm3/g con un área superficial BET de 79,4-128,6 m2/g. Los nanotubos dieron como resultado un porcentaje de hidrógeno gravimétrico almacenado de máximo 3,8% en peso. Dentro de esta misma línea, el documento US20091 94736 (A1 ), describe un método para dopar nanotubos de carbono con níquel para aplicación en adsorción de hidrógeno. Other approaches to increase the adsorption capacity of carbon nanotubes are based on the surface modification or functionalization of these nanotubes with materials related to hydrogen. For example, A. Reyhani et al. (A. Reyhani, SZ Mortazavi, S. Mirershadi, AZ Moshfegh, P. Parvin, A. Nozad. Hydrogen storage in decorated multiwalled carbon nanotubes by Ca, Co, Fe, Ni, and Pd nanoparticles under ambient conditions J. Phys. Chem. C. 1 15 (201 1) 6994-7001) obtained multiple wall nanotubes (MWCNT) functionalized with Ca, Co, Fe, Ni, and Pd. The preparation was carried out by the vapor phase thermo-chemical deposition method (TCVD) using as a catalyst a Fe / Ni / MgO mixture. After synthesis, they purified the MWCNT using a calcination sequence at a temperature of 450Ό in an environment of 0 2 , cooling to room temperature, immersion in hydrofluoric acid (HF) at room temperature, immersion in sulfuric acid (H 2 S0 4 ) at its boiling temperature, immersion in nitric acid (HN0 3 ) at its boiling temperature, washed with deionized water until it reaches a neutral pH and, dried at a temperature of 150Ό, for a purification efficiency of 93.5%. For the functionalization of purified MWCNT, nitrate solutions of Ca, Co, Fe, Ni, and Pd were used in distilled water under stirring, subsequently filter and heat the sample to a temperature of 200Ό. The average diameter of the CNT was 60 nm, with an I G / ID from Raman 2, 1. Purified and functionalized nanotubes resulted in a percentage of stored gravimetric hydrogen between 0.3-7% by weight. KS Lin et al. KS. Lin, YJ. Mai, SR. Li, CW. Shu, CH. Wang. Characterization and hydrogen storage of surface-modified multiwalled carbon nanotubes for fuel cell application. Journal of Nanomaterials 201 2 (2012) 1-12 obtained multiple wall nanotubes (MWCNT) functionalized with COOH, OH, or N0 2 or doped with Ti-NaAIH 4 or Pd nanoparticles. The MWCNT was obtained by the solvothermal method with solvent-catalytic assembly using an autoclave. To purify the MWCNT, a sequence of washing and filtering with ethanol, dilute acid, and doubly deionized water, ultrasound, drying in air at room temperature and vacuum drying between 69, 8-79, 5 utilizó was used. In the meantime, the surface modification was carried out with solutions of H 2 S0 4 / HN0 3 at a temperature of ' \ ' \ 9.8 q C. Doping with Ti-NaAIH 4 or Pd nanoparticles of some samples of MWCNT was carried out by mechanical grinding. The total pore volume of the MWCNT was 0.18-0.38 cm 3 / g with a BET surface area of 79.4-128.6 m 2 / g. The nanotubes resulted in a percentage of stored gravimetric hydrogen of maximum 3.8% by weight. Within this same line, US20091 94736 (A1), describes a method for doping carbon nanotubes with nickel for application in hydrogen adsorption.
Otros antecedentes relacionados con la selección de características morfológicas (diámetro, área superficial, longitud, forma, uso de recubrimiento, uso de dopaje etc.) para la adsorción de hidrógeno en nanotubos de carbono (SWCNT y MWCNT), en conjunto con el empaquetamiento de estos en dispositivos para almacenamiento, transporte y posterior liberación de hidrógeno, pueden ser encontrados en documentos JP2001 146408 (A),
KR20010091479 (A), JP2004292310 (A), JP2004313906 (A), JP2004059409 (A), US 8454922 B2, US 20090123789 A1 , JP201 1255314, US 8076034 B1 , KR20120002043 (A), y CN103883872 (A). Other background related to the selection of morphological characteristics (diameter, surface area, length, shape, use of coating, use of doping etc.) for the adsorption of hydrogen in carbon nanotubes (SWCNT and MWCNT), together with the packing of these in devices for storage, transport and subsequent release of hydrogen, can be found in JP2001 146408 (A) documents, KR20010091479 (A), JP2004292310 (A), JP2004313906 (A), JP2004059409 (A), US 8454922 B2, US 20090123789 A1, JP201 1255314, US 8076034 B1, KR20120002043 (A), and CN103883872 (A).
En consecuencia, es claro que todavía existe una gran necesidad en el estado del arte para obtener un material base nanotubos de carbono (de pared múltiple o simple) que almacene hidrógeno y que cumpla con las condiciones de ser relativamente económico, seguro, fácil de usar, y reutilizable sin necesidad de regeneración. Consequently, it is clear that there is still a great need in the state of the art to obtain a carbon nanotube base material (multiple or single wall) that stores hydrogen and meets the conditions of being relatively economical, safe, easy to use , and reusable without regeneration.
Descripción de la Invención Description of the Invention
La presente invención provee nanotubos de carbono para aplicaciones en adsorción de hidrógeno, y método de dos etapas para obtener dichos nanotubos de carbono de forma económica, siendo estas: 1 ) obtención de nanotubos por técnica de deposición química en fase vapor asistida por aerosol (AACVD) utilizando como catalizador mineral de magnetita y una solución de alcanfor/alcohol como fuente de carbono, y 2) purificación de los nanotubos obtenidos por tratamiento térmico y tratamiento con ácidos. The present invention provides carbon nanotubes for hydrogen adsorption applications, and a two-stage method for obtaining said carbon nanotubes economically, these being: 1) obtaining nanotubes by chemical vapor deposition technique (AACVD) ) using as a magnetite mineral catalyst and a camphor / alcohol solution as a carbon source, and 2) purification of the nanotubes obtained by heat treatment and acid treatment.
Nanotubos de Carbono de Pared Múltiple para Adsorción de Hidrógeno De acuerdo con los elementos anteriores, un aspecto de la invención corresponde a los nanotubos de carbono de pared múltiple (MWCNT) resultantes del método de obtención por la técnica de deposición química en fase de vapor asistida por aerosol así como también los modificados de forma físico-química como resultado del método de purificación. Multiple Wall Carbon Nanotubes for Hydrogen Adsorption In accordance with the above elements, one aspect of the invention corresponds to multi-wall carbon nanotubes (MWCNT) resulting from the method of obtaining by the chemical vapor deposition technique. by aerosol as well as those modified physically and chemically as a result of the purification method.
Nanotubos de Carbono de Pared Múltiple Obtenidos por Técnica AACVD Los nanotubos de carbono de pared múltiple (MWCNT) obtenidos por técnica AACVD presentan una morfología de tipo aglomerado similar a una bola de lana, con pequeños hilos de nanotubos con longitudes menores a 1 μηι, diámetro promedio entre 20-40 nm, espesores de multipared entre 4,3-9,0 nm y cada nanotubo se compone de 13 a 27 nanotubos concéntricos. Tienen
adheridos en las paredes externas nanopartículas de óxidos de hierro con tamaños menores a 50 nm, y presentan una mezcla de fases (carbón amorfo, nanotubos de carbono de pared múltiple, óxidos de hierro y zeolita). Tienen una relación simetría/desorden (IG/ID) a partir de Raman entre 0,95-1 ,49. Finalmente, presentan un porcentaje de hidrógeno gravimétrico almacenado entre 0,2-1 ,7% en peso a una temperatura de ~\ 9Ό (2 93K) y una presión de 44 Torr (5,8 KPa). Multiple-Wall Carbon Nanotubes Obtained by AACVD Technique Multi-wall carbon nanotubes (MWCNT) obtained by AACVD technique have a morphology of a ball-like chip type, with small nanotube threads with lengths less than 1 μηι, diameter average between 20-40 nm, multipared thicknesses between 4.3-9.0 nm and each nanotube is composed of 13 to 27 concentric nanotubes. Have adhered to the external walls nanoparticles of iron oxides with sizes smaller than 50 nm, and present a mixture of phases (amorphous carbon, multi-walled carbon nanotubes, iron oxides and zeolite). They have a symmetry / disorder (IG / ID) ratio from Raman between 0.95-1, 49. Finally, they have a percentage of stored gravimetric hydrogen between 0.2-1.7% by weight at a temperature of ~ \ 9Ό (2,393K) and a pressure of 44 Torr (5,8 KPa).
La evidencia de formación de los nanotubos de carbono de pared múltiple y los valores de sus características antes mencionadas, se expone en las Figuras 1 - 4, y Tabla 1 . La Figura 1 muestra las imágenes de microscopía electrónica de barrido (SEM) donde se observan los nanotubos y su morfología, entre tanto, la Figura 2 muestra las imágenes de microscopía electrónica de transmisión (TEM) donde se observan los diámetros y los espesores de multipared del nanotubo, además de las nanopartículas adheridas en las paredes de estos, la Figura 3 por su parte, muestra las fases presentes en el nanotubo por técnica de difracción de rayos X. Finalmente, la Figura 4 y la Tabla 1 muestran los espectros Raman de los nanotubos, donde se aprecian las diferentes energías vibracionales para la fase nanotubos de carbono y el grado de cristalinidad o defectos de estos, respectivamente. The evidence of the formation of the multiple-wall carbon nanotubes and the values of their characteristics mentioned above, is shown in Figures 1-4, and Table 1. Figure 1 shows the scanning electron microscopy (SEM) images where the nanotubes and their morphology are observed, meanwhile, Figure 2 shows the transmission electron microscopy (TEM) images where the multipared diameters and thicknesses are observed of the nanotube, in addition to the nanoparticles adhered to the walls of these, Figure 3 on the other hand, shows the phases present in the nanotube by X-ray diffraction technique. Finally, Figure 4 and Table 1 show the Raman spectra of the nanotubes, where the different vibrational energies for the carbon nanotubes phase and the degree of crystallinity or defects of these, respectively, are appreciated.
Breve Descripción de las Figuras Brief Description of the Figures
Figuras 1A-1 D. Imágenes de microscopía electrónica de barrido de los polvos obtenidos con la técnica AACVD para las muestras M1 (a y b) y M3 (c y d). Figuras 2A-2F. Imágenes de microscopía electrónica de transmisión y alta resolución para los CNT polvos obtenidos por técnica AACVD de las muestras M3 (a-c) y M2 (d-f). Figures 1A-1 D. Scanning electron microscopy images of the powders obtained with the AACVD technique for samples M1 (a and b) and M3 (c and d). Figures 2A-2F. Transmission and high resolution electron microscopy images for CNT powders obtained by AACVD technique of samples M3 (a-c) and M2 (d-f).
Figura 3. Patrón de difracción rayos X de los polvos obtenidos con la técnica AACVD.
Figura 4. Espectroscopia Raman de los polvos obtenidos con la técnica AACVD. Figure 3. X-ray diffraction pattern of the powders obtained with the AACVD technique. Figure 4. Raman spectroscopy of the powders obtained with the AACVD technique.
Figura 5A-5D. Imágenes de microscopía electrónica de barrido y espectros de energía dispersiva de las muestras M1 y M2 luego del proceso de purificación. Figuras 6A-6F. Imágenes de microscopía electrónica de trasmisión de las muestras M1 y M2 luego del proceso de purificación. Figure 5A-5D. Scanning electron microscopy images and dispersive energy spectra of samples M1 and M2 after the purification process. Figures 6A-6F. Transmission electron microscopy images of the M1 and M2 samples after the purification process.
Figuras 7A-7B. Resultados DRX de las muestras M1 y M2 luego del proceso de purificación, la nomenclatura utilizada es la siguiente: S/T (sin purificación), TT (Tratamiento térmico), HF (tratamiento con ácido fluorhídrico y ultrasonido) y HCI (tratamiento con ácido clorhídrico). Figures 7A-7B. Results DRX of samples M1 and M2 after the purification process, the nomenclature used is as follows: S / T (without purification), TT (Heat treatment), HF (treatment with hydrofluoric acid and ultrasound) and HCI (acid treatment hydrochloric).
Figura 8. Espectroscopia Raman de las muestras M1 y M2 luego del proceso de purificación. Figure 8. Raman spectroscopy of samples M1 and M2 after the purification process.
Figura 9. Método para la obtención de nanotubos de carbono por técnica AACVD. Figure 9. Method for obtaining carbon nanotubes by AACVD technique.
Figura 10. Representación esquemática del arreglo utilizado para el proceso AACVD. Figure 10. Schematic representation of the arrangement used for the AACVD process.
Figura 11. Imagen de los polvos (mezcla de nanotubos y residuos del proceso) obtenidos con la técnica AACVD. Figure 11. Image of the powders (mixture of nanotubes and process residues) obtained with the AACVD technique.
Figura 12. Método para la remoción de impurezas y acondicionamiento de los nanotubos de carbono obtenidos en la Etapa 1 . Figure 12. Method for removal of impurities and conditioning of carbon nanotubes obtained in Stage 1.
Figura 13. Comportamiento de adsorción de hidrógeno (H2) en función de la presión para los nanotubos de carbono sin el proceso de purificación. Figure 13. Behavior of hydrogen adsorption (H 2 ) as a function of pressure for carbon nanotubes without the purification process.
Figura 14. Comportamiento de adsorción de hidrógeno (H2) en función de la presión para los nanotubos de carbono purificados. Figure 14. Adsorption behavior of hydrogen (H 2 ) as a function of pressure for purified carbon nanotubes.
Descripción Detallada de la Invención Detailed description of the invention
La presente invención provee nanotubos de carbono para aplicaciones en adsorción de hidrógeno, y método de dos etapas para obtener dichos nanotubos de carbono de forma económica, siendo estas: 1 ) obtención de
nanotubos por técnica de deposición química en fase vapor asistida por aerosol (AACVD), utilizando como catalizador mineral de magnetita y una solución de alcanfor/alcohol como fuente de carbono, y 2) purificación de los nanotubos obtenidos por tratamiento térmico y tratamiento con ácidos. The present invention provides carbon nanotubes for hydrogen adsorption applications, and a two-stage method for obtaining said carbon nanotubes economically, these being: 1) obtaining nanotubes by chemical vapor deposition technique (AACVD), using as a magnetite mineral catalyst and a solution of camphor / alcohol as a carbon source, and 2) purification of the nanotubes obtained by heat treatment and acid treatment.
De esta forma, la presente invención provee nanotubos de carbono de pared múltiple (MWCNT) resultantes del método de obtención por la técnica de deposición química en fase de vapor asistida por aerosol así como también los modificados de forma físico-química como resultado del método de purificación. Los nanotubos de carbono de pared múltiple (MWCNT) obtenidos por técnica AACVD presentan una morfología de tipo aglomerado similar a una bola de lana, con pequeños hilos de nanotubos con longitudes mayores a 1 μηι, diámetro promedio entre 20-40 nm, espesores de multipared entre 4,3-9,0 nm y cada nanotubo se compone de 13 a 27 nanotubos concéntricos. Tienen adheridos en las paredes externas nanopartículas de óxidos de hierro con tamaños menores a 50 nm, y presentan una mezcla de fases (carbón amorfo, nanotubos de carbono de pared múltiple, óxidos de hierro y zeolita). Tienen una relación simetría/desorden (IG/ID) a partir de Raman entre 0,95-1 ,49. Finalmente, presentan un porcentaje de hidrógeno gravimétrico almacenado entre 0,2-1 ,7% en peso a una temperatura de ~\ 9Ό (2 93K) y una presión de 44 Torr (5,8 KPa). Thus, the present invention provides multiple-walled carbon nanotubes (MWCNT) resulting from the method of obtaining by the technique of chemical deposition in the vapor-assisted vapor phase as well as those modified in physico-chemical form as a result of the method of purification. The multiple-wall carbon nanotubes (MWCNT) obtained by AACVD technique have an agglomerated type morphology similar to a wool ball, with small nanotube threads with lengths greater than 1 μηι, average diameter between 20-40 nm, multipared thicknesses Between 4.3-9.0 nm and each nanotube is composed of 13 to 27 concentric nanotubes. Nanoparticles of iron oxides with sizes smaller than 50 nm are attached to the outer walls, and have a mixture of phases (amorphous carbon, multi-walled carbon nanotubes, iron oxides and zeolite). They have a symmetry / disorder ratio (I G / ID) from Raman between 0.95-1, 49. Finally, they have a percentage of stored gravimetric hydrogen between 0.2-1.7% by weight at a temperature of ~ \ 9Ό (2,393K) and a pressure of 44 Torr (5,8 KPa).
La evidencia de formación de los nanotubos de carbono de pared múltiple y los valores de sus características antes mencionadas se expone en las Figuras 1 - 4, y Tabla 1 . The evidence of the formation of multiple wall carbon nanotubes and the values of their characteristics mentioned above are set forth in Figures 1-4, and Table 1.
De las Figuras 1 A-1 D se puede observar que los nanotubos de carbono de pared múltiple obtenidos se presentan en forma de aglomeraciones similar a una bola de lana, con pequeños hilos de nanotubos con longitudes mayores a1 μηι.
De la Figuras 2A-2F se puede observar que los nanotubos de carbono de pared múltiple tienen adheridos en las paredes externas nanopartículas con tamaños menores a 50 nm. Los espesores de multipared están entre 4,3-9 nm que se componen de 13 a 27 nanotubos concéntricos. Los nanotubos obtenidos presentan un diámetro promedio entre 20-40 nm. From Figures 1 A-1 D it can be seen that the multiple wall carbon nanotubes obtained are presented in the form of agglomerations similar to a ball of wool, with small nanotube threads with lengths greater than 1 μηι. From Figures 2A-2F it can be seen that multi-wall carbon nanotubes have nanoparticles with sizes smaller than 50 nm attached to the outer walls. The multipared thicknesses are between 4.3-9 nm that consist of 13 to 27 concentric nanotubes. The nanotubes obtained have an average diameter between 20-40 nm.
De la Figura 3, se puede observar la fase asociada a los nanotubos de carbono de pared múltiple (29=26,34°) (A. Kubota, H. Miyaoka, M. Tsubota, K. Shi moda, T. Ichikawa, Y. Kojima. Synthesis and characterization of magnesium-carbon compounds for hydrogen storage. Carbón 56 (2013) 50-55 y Z. Q. Li, C. J. Lu, Z. P. Xia, Y. Zhou, Z. Luo. X-ray diffraction patterns of graphite and turbostratic carbón. Carbón 45 (2007) 1686-1695), así como también fases de óxidos de hierro y zeolita, residuos del catalizador y soporte utilizados en el proceso. El cambio en la estructura cristalina de la magnetita es producto de la reducción del hierro presente al tener contacto con el material carbonoso, dando origen a las fases carburo de hierro (Fe3C) y oxido ferroso (FeO). From Figure 3, the phase associated with multiple-walled carbon nanotubes (29 = 26.34 °) can be observed (A. Kubota, H. Miyaoka, M. Tsubota, K. Shi moda, T. Ichikawa, Y Kojima Synthesis and characterization of magnesium-carbon compounds for hydrogen storage Carbon 56 (2013) 50-55 and ZQ Li, CJ Lu, ZP Xia, Y. Zhou, Z. Luo X-ray diffraction patterns of graphite and turbostratic coal Carbon 45 (2007) 1686-1695), as well as phases of iron and zeolite oxides, catalyst residues and support used in the process. The change in the crystalline structure of the magnetite is a product of the reduction of the iron present when it has contact with the carbonaceous material, giving rise to the iron carbide (Fe 3 C) and ferrous oxide (FeO) phases.
De la Figura 4 se puede observar las dos bandas características de las estructuras grafiticas, siendo estas la banda G y la banda D. La banda G está relacionada con la simetría del grafito E2g del modo ínter pared, el cual refleja la intensidad sp2 de los átomos de carbón hibridizado. La otra banda D indica el desorden de los átomos de carbono. El leve cambio en los valores de intensidad se debe al aumento de paredes presente en el nanotubo que se refleja en la disminución de distancia ínter pared (D. K. Singh, P.K. lyer, P.K. Giri. Diameter dependence of interwall separation and strain in multiwalled carbón nanotubes probed by X-ray diffraction and Raman scattering studies. Diamond & Related Materials 43 (2014) 66-71 , A. C. Ferrari, J. Robertson. Resonante Raman spectroscopy of disordered, amorphous and diamond like- carbon. Phys. Rev. B. 64 (2001 ) 075414). Los nanotubos de pared múltiple obtenidos presentan una mezcla de carbón amorfo y formas grafiticas
cristalinas (S. D. M. Brown, A. Jorio, M. S. Dressel aus, G. Dressel aus. Observations of the D-band feature in the Raman spectra of carbón nanotubes. Phys. Rev. B. 64 (2001 ) 073403, T. Belin, F. Epron. Characterization methods of carbón nanotubes: A review. Mater. Sci. Eng. B. 1 1 9 (2005) 1 05-1 1 8). From Figure 4 you can see the two characteristic bands of the graffiti structures, these being the G band and the D band. The G band is related to the symmetry of the graphite E 2 g in the inter-wall mode, which reflects the intensity sp 2 of the hybridized carbon atoms. The other band D indicates the disorder of carbon atoms. The slight change in intensity values is due to the increase in walls present in the nanotube that is reflected in the decrease in inter-wall distance (DK Singh, PK lyer, PK Giri. Diameter dependence of interwall separation and strain in multiwalled carbon nanotubes probed by X-ray diffraction and Raman scattering studies. Diamond & Related Materials 43 (2014) 66-71, AC Ferrari, J. Robertson. Resonant Raman spectroscopy of disordered, amorphous and diamond like-carbon. Phys. Rev. B. 64 ( 2001) 075414). The multiple wall nanotubes obtained have a mixture of amorphous carbon and graffiti forms Crystalline (SDM Brown, A. Jorio, MS Dressel aus, G. Dressel aus. Observations of the D-band feature in the Raman spectra of carbon nanotubes. Phys. Rev. B. 64 (2001) 073403, T. Belin, F Epron. Characterization methods of carbon nanotubes: A review. Mater. Sci. Eng. B. 1 1 9 (2005) 1 05-1 1 8).
Tabla 1. Relación (lD/lG) grado de defectos presentes en los nanotubos obtenidos. Table 1. Relation (l D / l G ) degree of defects present in the nanotubes obtained.
Teniendo en cuenta el criterio que valores de ID/IG cercanos a uno indican que hay más defectos en las paredes de grafeno y un menor grado de cristalinidad en el material carbonoso (T. Belin, F. Epron. Characterization methods of carbón nanotubes: A review. Mater. Sci. Eng. B. 1 19 (2005) 105-1 1 8), de la Tabla 1 se puede concluir que los nanotubos obtenidos presentan un alto grado de defectos, además de desorden y carbón amorfo (W. Cho, M. Schulz, V. Shanov (2013). Kinetics of Growing Centimeter Long Carbón Nanotube Arrays, Syntheses and Applications of Carbón Nanotubes and Their Composites. Dr. Satoru Suzuki (Ed.), ISBN: 978-953-51 -1 125-2, InTech, DOI : 10.5772/50837). Nanotubos de Carbono de Pared Múltiple Después del Método de Taking into account the criteria that I D / IG values close to one indicate that there are more defects in graphene walls and a lower degree of crystallinity in the carbonaceous material (T. Belin, F. Epron. Characterization methods of carbon nanotubes: On review, Mater. Sci. Eng. B. 1 19 (2005) 105-1 1 8), from Table 1 it can be concluded that the nanotubes obtained have a high degree of defects, in addition to disorder and amorphous carbon (W. Cho, M. Schulz, V. Shanov (2013) Kinetics of Growing Centimeter Long Carbon Nanotube Arrays, Syntheses and Applications of Carbon Nanotubes and Their Composites Dr. Satoru Suzuki (Ed.), ISBN: 978-953-51 -1 125-2, InTech, DOI: 10.5772 / 50837). Multiple Wall Carbon Nanotubes After the Method of
Purificación Purification
Los nanotubos de carbono de pared múltiple (MWCNT) obtenidos luego del método de purificación presentan como elemento constituyente al carbono, morfología global tipo espiral y una superficie corrugada que se extiende desde las capas externas a las más internas, así como la desaparición de las nanopartículas adheridas en las paredes de estos. Presentan una elevada cristalinidad producto de la eliminación del carbón amorfo, con una relación simetría desorden (IG/ID) a partir de Raman entre 0,63-1 ,22, y un área
superficial BET entre 53,5-729,4 m2/g determinada por adsorción de N2 a una temperatura de -196Ό (77,1 K) siguiendo las método logias descritas en USNo.5.653.951 . Finalmente, presentan un porcentaje de hidrógeno gravimétrico almacenado entre 0,1 -3,5% en peso a una temperatura de 19Ό (293<K) y una presión de 44 Torr (5,8 KPa). The multiple-walled carbon nanotubes (MWCNT) obtained after the purification method have as a constituent element carbon, global spiral morphology and a corrugated surface that extends from the outer layers to the inner ones, as well as the disappearance of the nanoparticles adhered to the walls of these. They have a high crystallinity resulting from the elimination of amorphous carbon, with a symmetry disorder (I G / ID) from Raman between 0.63-1, 22, and an area BET surface between 53.5-729.4 m 2 / g determined by adsorption of N 2 at a temperature of -196Ό (77.1 K) following the lodges method described in US 5,653,951. Finally, they have a percentage of stored gravimetric hydrogen between 0.1 -3.5% by weight at a temperature of 19Ό (293 < K) and a pressure of 44 Torr (5.8 KPa).
La efectividad del método de purificación para los nanotubos de carbono de pared múltiple en lo que respecta a la eliminación de impurezas, modificación de la morfología, e incremento en los defectos superficiales se expone en las Figuras 5-8, y Tabla 2. Las Figuras 5A-5D muestra imágenes de microscopía electrónica de barrido y espectros de energía dispersiva, de donde se aprecia la composición química elemental de los nanotubos de carbono, entre tanto, las Figuras 6A-6F muestra imágenes de microscopía electrónica de transmisión de los nanotubos donde se observa el cambio en la morfología de los nanotubos y la eliminación de las nanopartículas que estaban adheridas a las paredes de estos, las Figuras 7A-7B por su parte, muestra la evolución de la desaparición de las fases contaminantes en el nanotubo durante el método de purificación por técnica de difracción de rayos X. Finalmente, la Figura 8 y la Tabla 2 muestran los espectros Raman luego del proceso de purificación, donde se aprecian las diferentes energías vibracionales para la fase nanotubos de carbono, y el grado de cristalinidad o defectos inducidos en los nanotubos, respectivamente. The effectiveness of the purification method for multi-walled carbon nanotubes in regard to the removal of impurities, modification of morphology, and increase in surface defects is set forth in Figures 5-8, and Table 2. The Figures 5A-5D shows scanning electron microscopy images and dispersive energy spectra, where the elementary chemical composition of carbon nanotubes can be seen, meanwhile, Figures 6A-6F shows transmission electron microscopy images of nanotubes where Observe the change in the morphology of the nanotubes and the elimination of the nanoparticles that were attached to the walls of these, Figures 7A-7B on the other hand, shows the evolution of the disappearance of the contaminating phases in the nanotube during the method of purification by X-ray diffraction technique. Finally, Figure 8 and Table 2 show the Raman spectra after the puri process fication, where the different vibrational energies for the carbon nanotube phase are appreciated, and the degree of crystallinity or defects induced in the nanotubes, respectively.
Del análisis composicional de las Figuras 5A-5D, es posible indicar que se encontró carbono en las tres muestras, lo que indica que se eliminaron la totalidad de elementos contaminantes de los nanotubos luego del proceso de purificación. From the compositional analysis of Figures 5A-5D, it is possible to indicate that carbon was found in the three samples, indicating that all the nanotube contaminants were removed after the purification process.
En las imágenes M1 y M2 (Figura 6) se observa una modificación en la morfología de los nanotubos de carbono, constatándose que las capas externas del nanotubo presentan un tipo de "corrugado" el cual se traspasa
hacia las capas interiores, lo cual queda demostrado como una serie de líneas perpendiculares a la dirección preferencial del nanotubo. También se observa que los nanotubos tienen zonas que adquieren un comportamiento tipo espiral, lo cual a su vez permite el entrecruzamiento con otros nanotubos más cortos (M1 ). In the images M1 and M2 (Figure 6) there is a modification in the morphology of the carbon nanotubes, confirming that the outer layers of the nanotube have a type of "corrugated" which is transferred towards the inner layers, which is demonstrated as a series of lines perpendicular to the preferential direction of the nanotube. It is also observed that nanotubes have zones that acquire a spiral-like behavior, which in turn allows cross-linking with other shorter nanotubes (M1).
De las Figuras 7A-7B, se observa que en la muestra M2 hay una oxidación parcial de Fe3C en Fei ,53(01-1)0,502,5 producto de la exposición del polvo al oxigeno durante el tratamiento térmico. Luego del tratamiento con ácido fluorhídrico se aprecia la desaparición de los óxidos de hierro y del carburo de hierro, pero se forma FeF3 debido a la reacción de transferencia atómica, donde el átomo de flúor reemplaza al de carbono. Posteriormente, con el tratamiento de HCI, desaparecen los picos de FeF3, dejando como fase mayoritaria la de los nanotubos de carbono, mostrando de esta manera la efectividad del método de purificación propuesto para eliminar las nanopartículas contaminantes. Entre tanto, para la muestra M1 , se observa que en la muestra sin purificación se aprecian los picos de la zeolita y magnetita (Fe304), entre tanto, después del tratamiento térmico se muestra la oxidación del hierro a la fases hematita (Fe2Ü3) y se mantienen la fase magnetita. Luego del tratamiento con ácido fluorhídrico se observa la eliminación de los picos de zeolita y hematita, pero se presenta la formación de FeF3. Finalmente, con el tratamiento con ácido clorhídrico se observa el incremento en la intensidad del pico de MWCNTs, y se elimina la fase FeF3 así como gran parte de la fase magnetita, mostrando de esta manera la efectividad del método de purificación propuesto incluso cuando se usa como soporte la zeolita. From Figures 7A-7B, it is observed that in the sample M2 there is a partial oxidation of Fe 3 C in Fei, 53 (01-1) 0.502.5 due to the exposure of the powder to oxygen during the heat treatment. After treatment with hydrofluoric acid, the disappearance of iron oxides and iron carbide can be seen, but FeF 3 is formed due to the atomic transfer reaction, where the fluorine atom replaces the carbon atom. Subsequently, with the treatment of HCI, the FeF 3 peaks disappear, leaving the carbon nanotubes as the majority phase, thus showing the effectiveness of the purification method proposed to eliminate the contaminating nanoparticles. Meanwhile, for the sample M1, it is observed that in the sample without purification the peaks of the zeolite and magnetite (Fe 3 0 4 ) are appreciated, meanwhile, after the heat treatment the oxidation of the iron to the hematite phases is shown ( Fe2Ü 3 ) and the magnetite phase is maintained. After treatment with hydrofluoric acid, the elimination of the peaks of zeolite and hematite is observed, but the formation of FeF 3 is presented. Finally, with the hydrochloric acid treatment the increase in the intensity of the MWCNT peak is observed, and the FeF 3 phase is eliminated as well as a large part of the magnetite phase, thus showing the effectiveness of the proposed purification method even when use zeolite as support.
De la Figura 8, se puede observar las dos bandas características de las estructuras grafiticas, siendo estas la banda G (alrededor de 1600 cm"1) y la banda D (1350 cm"1), lo que indica que luego del tratamiento térmico no hay destrucción de la estructura de los nanotubos de carbono.
Tabla 2. Relación (I D/IG) grado de defectos presentes en los nanotubos luego del proceso de purificación. From Figure 8, you can see the two characteristic bands of the graffiti structures, these being the G band (around 1600 cm "1 ) and the D band (1350 cm " 1 ), which indicates that after the heat treatment no there is destruction of the structure of carbon nanotubes. Table 2. Relationship (ID / IG) degree of defects present in the nanotubes after the purification process.
Método de Obtención de Nanotubos de Carbono de Pared Múltiple para Adsorción de Hidrógeno Method of Obtaining Multiple Wall Carbon Nanotubes for Hydrogen Adsorption
Etapa 1 : Obtención de Nanotubos de Carbono de Pared Múltiple (MWCNT) por AACVD Stage 1: Obtaining Multiple Wall Carbon Nanotubes (MWCNT) by AACVD
Otro aspecto de la invención corresponde al método y la selección de variables junto con sus valores para sintetizar los nanotubos de carbono de pared múltiple (MWCNT) por la técnica AACVD.
El presente método para la obtención de nanotubos de carbono se compone de tres pasos (ver Figura 9), siendo estos: 1 ) la preparación de la fuente de carbono, 2) preparación de la mezcla catalizador/soporte y 3) obtención de nanotubos por técnica AACVD. A continuación se describe cada paso, indicando su relación con el Estado del Arte. Another aspect of the invention corresponds to the method and the selection of variables together with their values to synthesize the multi-walled carbon nanotubes (MWCNT) by the AACVD technique. The present method for obtaining carbon nanotubes is composed of three steps (see Figure 9), these being: 1) preparation of the carbon source, 2) preparation of the catalyst / support mixture and 3) obtaining of nanotubes by AACVD technique. Each step is described below, indicating its relationship with the State of the Art.
Paso 1 : Preparación de la fuente de carbono (solución A) Step 1: Preparation of the carbon source (solution A)
Los reactivos y la forma de preparar la fuente de carbono para ser utilizada en el método AACVD para obtener CNT fue tomada de E. Mosquera, D.E. Diaz- Droguett, N. Carvajal, M. Roble, M. Morel, R. Espinoza. Characterization and Hydrogen Storage in Multi-Walled Carbón Nanotubes Grown by Aerosol- Assisted CVD Method. Diamond & Related Materials 43 (2014) 66-71 , los cuales describen que aproximadamente 2,0 gr de Alcanfor (Ci0H16O) con 95% pureza, se mezclan con 10ml de alcohol isopropilico (2% p/p) en un agitador magnético. The reagents and the way to prepare the carbon source to be used in the AACVD method to obtain CNT was taken from E. Mosquera, DE Diaz-Droguett, N. Carvajal, M. Roble, M. Morel, R. Espinoza. Characterization and Hydrogen Storage in Multi-Walled Carbon Nanotubes Grown by Aerosol- Assisted CVD Method. Diamond & Related Materials 43 (2014) 66-71, which describe that approximately 2.0 g of Camphor (Ci 0 H 16 O) with 95% purity, are mixed with 10 ml of isopropyl alcohol (2% w / w) in a magnetic stirrer
La razón p/v alcanfor a alcohol isopropilico puede variar en el rango de 1 :5 a 3:7 The ratio w / v camphor to isopropyl alcohol can vary in the range of 1: 5 to 3: 7
Paso 2: Preparación de mezcla catalizador/soporte Step 2: Preparation of catalyst / support mixture
El material utilizado como catalizador es concentrado de magnetita mineral con la siguiente descripción: The material used as a catalyst is mineral magnetite concentrate with the following description:
Mineral de magnetita malla 325 (menor a 45 μηι) con 80% fase magnetita y 20% silicatos y otros óxidos de hierro. Magnetite ore 325 mesh (less than 45 μηι) with 80% magnetite phase and 20% silicates and other iron oxides.
Mineral de magnetita malla 325 (menor a 45 μηι) con 98% fase magnetita y 2% silicatos y hematita. Magnetite ore 325 mesh (less than 45 μηι) with 98% magnetite phase and 2% silicates and hematite.
El material utilizado como soporte es una zeolita (tamiz molecular: álcali-metal alumino silicato/calcio, grado cromatografo, linde/Coast engineering laboratory/Redondo Beach CA-USA).
La preparación de la mezcla catalizador/soporte se lleva a cabo en estado sólido por molienda mecánica en seco haciendo uso de un mortero de ágata por 10 minutos. Para la presente invención las proporciones de mezcla del catalizador y soporte utilizadas se muestran en la Tabla 3. The material used as a support is a zeolite (molecular sieve: alkali metal metal silicate / calcium, chromatograph grade, linde / Coast engineering laboratory / Redondo Beach CA-USA). The preparation of the catalyst / support mixture is carried out in a solid state by dry mechanical grinding using an agate mortar for 10 minutes. For the present invention the mixing ratios of the catalyst and support used are shown in Table 3.
Tabla 3. Proporciones en porcentaje de catalizador (mineral de magnetita) y soporte (zeolita) en la mezcla. Table 3. Proportions in percentage of catalyst (magnetite mineral) and support (zeolite) in the mixture.
La relación catalizador a soporte en p/p puede variar en el rango de 100:0 a 50:50. The catalyst to support ratio in w / w may vary in the range of 100: 0 to 50:50.
Paso 3: Obtención de nanotubos de carbono por método AACVD Step 3: Obtaining carbon nanotubes by AACVD method
Para la reacción de producción de nanotubos de carbono se utiliza un sistema de deposición química en fase vapor asistida por aerosol (AACVD, siglas en inglés), el cual se muestra en la Figura 10, donde en E. Mosquera, D.E. Diaz- Droguett, N. Carvajal, M. Roble, M. Morel, R. Espinoza. Characterization and Hydrogen Storage in Multi-Walled Carbón Nanotubes Grown by Aerosol- Assisted CVD Method. Diamond & Related Materials 43 (2014) 66-71 , se describe el principio de funcionamiento.
Para la presente invención, el método utiliza la técnica AACVD de acuerdo con los siguientes pasos y valores de sus variables: i) Se coloca en el nebulizador ultrasónico (1 ) a una frecuencia entre 1 ,7-2,5 MHz la solución (2) de alcanfor y etanol (solución A) con el propósito de generar una niebla; ii) una vez generada la niebla, esta se transporta al reactor (4) que es definido por un tubo de cuarzo (5) insertado en el horno por medio de un gas transportador de argón o nitrógeno (3) a un flujo de entre 0,5-2 L/min; iii) la neblina reacciona con el catalizador o la mezcla catalizador/soporte (8), el cual se encuentra esparcido una longitud (7) de entre 4-6 cm dentro de la zona de calentamiento del reactor (6) con longitud de entre 12-15 cm cuya temperatura en ese momento es de entre 600-900Ό; iv) Luego de 20-40 min de proceso, se deja enfriar el reactor a temperatura ambiente utilizando la propia inercia térmica del horno; y v) Posterior al enfriamiento, se desarticula el tubo de cuarzo (5) del horno y se extrae el polvo resultante que puede ser nanotubos o una mezcla de nanotubos con residuos (9). El proceso descrito se desarrolla a 1 atmósfera de presión. Otros componentes del equipo incluyen un frasco lavador para residuos (10) y una salida de gas (1 1 ). La Figura 1 1 muestra la imagen del polvo negruzco (nanotubos de carbón o una mezcla de nanotubos y residuos del proceso) obtenido. For the carbon nanotube production reaction, an aerosol-assisted vapor phase chemical deposition system (AACVD) is used, which is shown in Figure 10, where in E. Mosquera, DE Diaz-Droguett, N. Carvajal, M. Roble, M. Morel, R. Espinoza. Characterization and Hydrogen Storage in Multi-Walled Carbon Nanotubes Grown by Aerosol- Assisted CVD Method. Diamond & Related Materials 43 (2014) 66-71, the principle of operation is described. For the present invention, the method uses the AACVD technique according to the following steps and values of its variables: i) The solution (2) is placed in the ultrasonic nebulizer (1) at a frequency between 1, 7-2.5 MHz. ) of camphor and ethanol (solution A) for the purpose of generating a mist; ii) once the fog is generated, it is transported to the reactor (4) which is defined by a quartz tube (5) inserted in the furnace by means of an argon or nitrogen transport gas (3) at a flow of between 0 , 5-2 L / min; iii) the mist reacts with the catalyst or catalyst / support mixture (8), which is spread a length (7) between 4-6 cm within the reactor heating zone (6) with a length between 12 -15 cm whose temperature at that time is between 600-900Ό; iv) After 20-40 min of process, the reactor is allowed to cool to room temperature using the oven's own thermal inertia; and v) After cooling, the quartz tube (5) is dismantled from the oven and the resulting powder that can be nanotubes or a mixture of nanotubes with residues (9) is extracted. The described process is developed at 1 pressure atmosphere. Other equipment components include a waste scrubber bottle (10) and a gas outlet (1 1). Figure 1 1 shows the image of the blackish powder (carbon nanotubes or a mixture of nanotubes and process residues) obtained.
Para efectos de comparación con el Estado del Arte, se indica que el valor de la frecuencia de nebulización (1 ,7 MHz), las características del catalizador de magnetita (tamaño y pureza) o el tipo de mezcla catalizador/soporte (magnetita/zeolita), la forma de preparación de la mezcla (molienda mecánica en seco por 10 minutos), el valor de la longitud y forma de esparcimiento del catalizador o la mezcla catalizador/soporte (5 cm) dentro de la zona de calentamiento, y la longitud de la zona de calentamiento (15 cm), no se deducen de los documentos del Estado de la Técnica cercanos para obtener los nanotubos con las características obtenidas, siendo estos: E. Mosquera y
colaboradores E. Mosquera, D.E. Diaz-Droguett, N. Carvajal, M. Roble, M. Morel, R. Espinoza. Characterization and Hydrogen Storage in Multi-Walled Carbón Nanotubes Grown by Aerosol-Assisted CVD Met od. Diamond & Related Materials 43 (2014) 66-71 (fuente de carbono alcanfor, níquel como catalizador y zeolita como soporte, argón como gas transportador), E. Mosquera y colaboradores Carvajal Nicolás, Quijada Saúl, Morel Mauricio, Mosquera Edgar. Mineral Magnetite as Precursor in the synthesis of bamboo- like carbón nanotubes. Poster Congreso Material Research Society (MRS), Puerto Rico 2012. http://www.mrs.org/ndnc-2012-abstracts-c/ (consultado el 23- 09-2015). (fuente de carbono alcanfor, magnetita mineral con pureza <65,0% como catalizador y zeolita como soporte, bote de alúmina como contenedor de la mezcla catalizador/soporte, nitrógeno como gas transportador, M. Kumar y colaboradores Mukul Kumar, Yoshinori Ando. Single-wall and multi-wall carbón nanotubes from camphor-a botanical Hydrocarbon. Diamond and Related Materials 12 (2003) 1845-1850) fuente de carbono alcanfor y sustancia de hierro como catalizador), A. Khovavko y colaboradores Alexander Khovavko, Alexey Sviatenko, Víctor Kotov, Borys Bondarenko, Andriy Nebesniy, Denis Filonenko. Technology of carbón nanotubes production in gas mixtures containing carbón monoxide. Phys. Status Solidi C 10 (2013) 1 180-1 182 (uso de mineral de hierro como catalizador), G. A. Sierra y colaboradores Germán A. Sierra, Diana M. Torres. Crecimiento de nanotubos de carbono sobre el mineral limonita como catalizador. Ingeniería y Competitividad, Vol. 14, No. 2, (2012) 139-146 (uso de mineral de hierro -limonita como catalizador), y Uoo-Chang Chung y colaboradores Uoo-Chang Chung, Yong-Hwan Kim, Deok-Bo Lee, Yeon-Uk Jeong, Won-Sub Chung, Young-Rae Cho, Ik-Min Park. Catalytic mechanism for growth of carbón nanotubes under CO-H2 gas mixture. Bull. Korean Chem. Soc. Vol. 26, No. 1 (2005) 103-106 (uso de mineral de hierro- hematita como catalizador) y en documento RU2010147048 (A) (uso de
mineral de hierro con bajo contenido de hierro como catalizador). En A. Barreiro, D. Selbmann, T. Pichler, K. Biedermann, T. Gemming, M. H. Rümmeli, U. Schwaike, B. Büchner. On the effects of solution and reaction parameters for the aerosol-assisted CVD growth of long carbón nanotubes. Appl. Phys. A 82 (2006) 719-725) se puede apreciar el efecto marcado que tienen las variables/características mencionadas anteriormente sobre el desempeño del proceso AACVD y la calidad final de los nanotubos. For purposes of comparison with the State of the Art, it is indicated that the value of the fogging frequency (1, 7 MHz), the characteristics of the magnetite catalyst (size and purity) or the type of catalyst / support mixture (magnetite / zeolite ), the form of preparation of the mixture (dry mechanical grinding for 10 minutes), the value of the length and spreading form of the catalyst or the catalyst / support mixture (5 cm) within the heating zone, and the length from the heating zone (15 cm), they are not deducted from the documents of the State of the Art nearby to obtain the nanotubes with the characteristics obtained, these being: E. Mosquera and collaborators E. Mosquera, DE Diaz-Droguett, N. Carvajal, M. Roble, M. Morel, R. Espinoza. Characterization and Hydrogen Storage in Multi-Walled Carbon Nanotubes Grown by Aerosol-Assisted CVD Met od. Diamond & Related Materials 43 (2014) 66-71 (carbon source camphor, nickel as catalyst and zeolite as support, argon as carrier gas), E. Mosquera and collaborators Carvajal Nicolás, Quijada Saúl, Morel Mauricio, Mosquera Edgar. Mineral Magnetite as Precursor in the synthesis of bamboo- like carbon nanotubes. Poster Congress Material Research Society (MRS), Puerto Rico 2012. http://www.mrs.org/ndnc-2012-abstracts-c/ (accessed 09-23-2015). (Camphor carbon source, mineral magnetite with <65.0% purity as catalyst and zeolite as support, alumina canister as catalyst / support mixture container, nitrogen as carrier gas, M. Kumar and collaborators Mukul Kumar, Yoshinori Ando. Single-wall and multi-wall carbon nanotubes from camphor-a botanical Hydrocarbon Diamond and Related Materials 12 (2003) 1845-1850) source of camphor carbon and iron substance as catalyst), A. Khovavko and collaborators Alexander Khovavko, Alexey Sviatenko , Victor Kotov, Borys Bondarenko, Andriy Nebesniy, Denis Filonenko. Technology of carbon nanotubes production in gas mixtures containing carbon monoxide. Phys. Status Solidi C 10 (2013) 1 180-1 182 (use of iron ore as catalyst), GA Sierra et al. Germán A. Sierra, Diana M. Torres. Growth of carbon nanotubes on the limonite mineral as a catalyst. Engineering and Competitiveness, Vol. 14, No. 2, (2012) 139-146 (use of iron ore -limonite as a catalyst), and Uoo-Chang Chung and collaborators Uoo-Chang Chung, Yong-Hwan Kim, Deok-Bo Lee, Yeon-Uk Jeong, Won-Sub Chung, Young-Rae Cho, Ik-Min Park. Catalytic mechanism for growth of carbon nanotubes under CO-H 2 gas mixture. Bull. Korean Chem. Soc. Vol. 26, No. 1 (2005) 103-106 (use of iron-hematite ore as a catalyst) and in document RU2010147048 (A) (use of iron ore with low iron content as catalyst). In A. Barreiro, D. Selbmann, T. Pichler, K. Biedermann, T. Gemming, MH Rümmeli, U. Schwaike, B. Büchner. On the effects of solution and reaction parameters for the aerosol-assisted CVD growth of long carbon nanotubes. Appl. Phys. A 82 (2006) 719-725) the marked effect of the variables / characteristics mentioned above on the performance of the AACVD process and the final quality of the nanotubes can be seen.
La Tabla 4 resume el rendimiento y aprovechamiento de la materia prima carbonosa logrados con el método bajo las condiciones descritas para la obtención de nanotubos de carbono tipo pared múltiple (MWCNT). Table 4 summarizes the yield and use of the carbonaceous raw material achieved with the method under the conditions described for obtaining multiple wall carbon nanotubes (MWCNT).
Tabla 4. Rendimiento y aprovechamiento de la materia prima carbonosa. Table 4. Performance and utilization of carbonaceous raw material.
Etapa 2: Purificación de Nanotubos de Carbono de Pared Múltiple (MWCNT) Obtenidos por AACVD
Otro aspecto de la invención corresponde al método de purificación, y la selección de variables junto con sus valores para purificar los nanotubos de carbono de pared múltiple (MWCNT) obtenidos por la técnica AACVD. Stage 2: Purification of Multiple Wall Carbon Nanotubes (MWCNT) Obtained by AACVD Another aspect of the invention corresponds to the purification method, and the selection of variables together with their values to purify the multi-walled carbon nanotubes (MWCNT) obtained by the AACVD technique.
Para la presente invención, el método para la remoción de impurezas y condicionamiento de los nanotubos de carbono para su aplicación en almacenamiento de hidrógeno se muestra en La Figura 12. For the present invention, the method for removal of impurities and conditioning of carbon nanotubes for application in hydrogen storage is shown in Figure 12.
Paso 1 : Tratamiento térmico. Se colocan entre 400-558 mg de los nanotubos obtenidos en un horno tubular (marca Nabetrtherm RHTH 12-600/16 con velocidad de calentamiento Ι δΌΛτπη) a una temperat ura de entre 400-550Ό por 1 -3 horas. Posteriormente, se deja enfriar hasta temperatura ambiente entre 6-12 horas. El objetivo con este paso es lograr la eliminación del carbono amorfo A. Reyhani, S. Z. Mortazavi, S. Mirershadi, A. Z. Moshfegh, P. Parvin, A. Nozad. Hydrogen storage in decorated multiwalled carbón nanotubes by Ca, Co, Fe, Ni, and Pd nanoparticles under ambient conditions. J. Phys. Chem. C. 1 15 (201 1 ) 6994-7001 . Step 1: Heat treatment. They are placed between 400-558 mg of the nanotubes obtained in a tubular furnace (Nabetrtherm RHTH brand 12-600 / 16 with heating rate Ι δΌΛτπη) at a temperature of between 400-550Ό for 1-3 hours. Subsequently, it is allowed to cool to room temperature between 6-12 hours. The objective with this step is to achieve the elimination of amorphous carbon A. Reyhani, S. Z. Mortazavi, S. Mirershadi, A. Z. Moshfegh, P. Parvin, A. Nozad. Hydrogen storage in decorated multiwalled carbon nanotubes by Ca, Co, Fe, Ni, and Pd nanoparticles under ambient conditions. J. Phys. Chem. C. 1 15 (201 1) 6994-7001.
Paso 2: Tratamiento con solución de ácido fluorhídrico (HF) en baño ultrasónico. Se colocan las muestras provenientes del paso 1 en solución de ácido fluorhídrico (con una concentración entre el 20-60% y en una relación HF:CNT de entre 1 :3 a 3:5 en función al volumen) bajo baño ultrasónico (marca ELMASONIC E 30 H) a una frecuencia de entre 25-40 kHz durante 1 -3 horas. Posteriormente se deja en reposo la solución resultante entre 10-30 minutos en una campana de extracción, tiempo luego del cual, se procede a retirar el líquido sobrenadante con micro pipetas descartables. Este paso se realiza a presión de 101 ,3 KPa (1 atmósfera) y temperatura ambiente (25Ό). El objetivo con este paso es lograr la eliminación de los alumino-silicatos de la zeolita A. Reyhani, S. Z. Mortazavi, S. Mirershadi, A. Z. Moshfegh, P. Parvin, A. Nozad. Hydrogen storage in decorated multiwalled carbón nanotubes by Ca, Co, Fe, Ni, and Pd nanoparticles under ambient conditions. J. Phys. Chem. C. 1 15
(201 1 ) 6994-7001 y de la magnetita mineral Libro Química. Raymond Chang, Kenneth A. Goldsby, 1 1 edición editorial Me Graw Hill, 2013. Step 2: Treatment with hydrofluoric acid (HF) solution in ultrasonic bath. The samples from step 1 are placed in hydrofluoric acid solution (with a concentration between 20-60% and in a HF: CNT ratio between 1: 3 to 3: 5 depending on volume) under ultrasonic bath (ELMASONIC brand E 30 H) at a frequency between 25-40 kHz for 1 -3 hours. Subsequently, the resulting solution is allowed to stand for 10-30 minutes in an extraction hood, after which time, the supernatant liquid is removed with disposable micro pipettes. This step is performed at a pressure of 101.3 KPa (1 atmosphere) and room temperature (25Ό). The objective with this step is to achieve the removal of alumino-silicates from zeolite A. Reyhani, SZ Mortazavi, S. Mirershadi, AZ Moshfegh, P. Parvin, A. Nozad. Hydrogen storage in decorated multiwalled carbon nanotubes by Ca, Co, Fe, Ni, and Pd nanoparticles under ambient conditions. J. Phys. Chem. C. 1 15 (201 1) 6994-7001 and of the mineral magnetite Chemical Book. Raymond Chang, Kenneth A. Goldsby, 1 1 editorial edition Me Graw Hill, 2013.
Paso 3: Lavado y centrifugado. Las muestras provenientes del paso 2 se someten a un ciclo de lavado-centrifugado hasta llegar a un pH neutro. Como agente lavador se utiliza agua desionizada y cada centrifugado se realiza por 4 minutos a 3500 rpm en un equipo ELCEMCC60CLA # IVlicrocentrifuga para tubos eppendorf de 1 ,5 mi Prisma (Labnet USA). Una vez se alcanza el pH neutro, se realiza un último lavado con etanol. Step 3: Wash and spin. The samples from step 2 are subjected to a wash-spin cycle until they reach a neutral pH. As a washing agent, deionized water is used and each centrifuge is carried out for 4 minutes at 3500 rpm in an ELCEMCC60CLA # IV anti-centrifuge equipment for eppendorf tubes of 1.5 m Prism (Labnet USA). Once the neutral pH is reached, a final wash with ethanol is performed.
Paso 4: secado. Las muestras provenientes del paso 3 se secan al ambiente durante 30-50 horas dentro de un recipiente (vaso beaker). Step 4: drying. The samples from step 3 are dried in the environment for 30-50 hours in a container (beaker).
Paso 5: Tratamiento con solución de ácido clorhídrico (HCI). Se colocan las muestras provenientes del paso 4 en solución de ácido clorhídrico (con una concentración entre 30-45% y en una relación HCLCNT de entre 1 :3 a 3:5 en función al volumen) durante 20-30 hoas horas en estado estacionario. Posteriormente se procede a retirar el líquido sobrenadante con micro pipetas descartables. El objetivo con este paso es lograr la eliminación del hierro presente en los nanotubos Mauricio Morel (2013). Síntesis de Nanocompuestos Magnéticos con Polímeros Conjugados: Estudio de sus Propiedades Magnéticas y Ópticas. Tesis de doctorado en Ciencia de los Materiales, Facultad de Ciencias Físicas y Matemáticas (Universidad de Chile). Step 5: Treatment with hydrochloric acid (HCI) solution. The samples from step 4 are placed in hydrochloric acid solution (with a concentration between 30-45% and in an HCLCNT ratio between 1: 3 to 3: 5 depending on volume) for 20-30 hours at steady state . Subsequently, the supernatant liquid is removed with disposable micro pipettes. The objective with this step is to achieve the elimination of iron present in nanotubes Mauricio Morel (2013). Synthesis of Magnetic Nanocomposites with Conjugated Polymers: Study of their Magnetic and Optical Properties. PhD thesis in Materials Science, Faculty of Physical and Mathematical Sciences (University of Chile).
Paso 6: Lavado y centrifugado. Las muestras provenientes del paso 5 se someten a un ciclo de lavado-centrifugado hasta llegar a un pH neutro. Como agente lavador se utiliza agua desionizada y cada centrifugado se realiza por 4 minutos a 3500 rpm en ELCEMCC60CLA # Microcentrifuga para tubos eppendorf de 1 ,5 mi Prisma (Labnet USA). Una vez que se alcanza el pH neutro, se realiza un último lavado con etanol.
Paso 7: El sólido resultante del paso 6 se seca en un horno con un sistema de vacío (-0,1 MPa) marca Leybold (Mod: D1 ,6B) a una temperatura de 80Ό por 1 hora. Step 6: Wash and spin. The samples from step 5 are subjected to a wash-spin cycle until they reach a neutral pH. As a washing agent, deionized water is used and each centrifuge is performed for 4 minutes at 3500 rpm in ELCEMCC60CLA # Microcentrifuge for eppendorf tubes of 1, 5 mi Prism (Labnet USA). Once the neutral pH is reached, a final wash with ethanol is performed. Step 7: The solid resulting from step 6 is dried in an oven with a vacuum system (-0.1 MPa) Leybold brand (Mod: D1, 6B) at a temperature of 80Ό for 1 hour.
Para efectos de comparación con el Estado del Arte, se indica que la secuencia de pasos sugeridos dentro del método purificación (7 pasos), las variables y los valores asociados a cada uno de dichos pasos (cantidad de material, tiempo, temperatura, presión), no se deducen de los documentos del Estado de la Técnica cercanos, siendo estos: Yue-Ying Fan y colaboradores Yue-Ying Fan, Adam Kaufmann, Alexander Mukasyan, Arvind Varma. Single- and multi-wall carbón nanotubes produced using the floating catalyst method: Synthesis, purification and hydrogen up-take. Carbón 44 (2006) 2160-2170. (tratamiento térmico y tratamiento con HCI), H. Igarashi y colaboradores Hideyuki Igarashi, Hiroto Murakami, Yoichi Murakami, Shigeo Maruyama, Naotoshi Nakashima. Purification and characterization of zeolite-supported single-walled carbón nanotubes catalytically synthesized from ethanol. Chemical Physics Letters 392 (2004) 529-532. (tratamiento térmico y tratamiento con HF), Sang Kyu Choi y colaboradores Sang Kyu Choi, Seung-Beck Lee. Role of thermal treatment on the structural behavior of the are SWCNTs in the purification system process. Current Applied Physics 9 (2009) 658-662 (tratamiento térmico y tratamiento con HCI), y CN102897747 (A) (tratamiento con HCI y filtración), y tampoco de los métodos de purificación utilizados en nanotubos para aplicaciones en almacenamiento de hidrógeno descritas al inicio en [C. Liu, Y. Y. Fan, M. Liu, H. T. Cong, H. M. Cheng, M. S. Dresselhaus. Hydrogen Storage in Single- Walled Carbón Nanotubes at Room Temperature. Science 286, 1 127 (1999), Chen P, Wu X, Lin J, Tan KL. High H2 uptake by alkali-doped carbón nanotubes under ambient pressure and modérate temperatures. Science 285 (1999) 91 -93, Ralph T. Yang. Hydrogen storage by alkali-doped carbón nanotubes-revisited. Carbón 38 (2000) 623-626, A Züttel, Ch Nützenadel, P
Sudan, Ph Mauron, Ch Emmenegger, S Rentsch, L Schlapbach, A Weidenkaff, T Kiyobayashi. Hydrogen sorption by carbón nanotubes and other carbón nanostructures. Journal of Alloys and Compounds 330-332 (2002) 676-682, M. Hirscher, M. Becher, M. Haluska, U. Dettlaff-Weglikowska, A. Quintel, G.S. Duesberg, Y.-M. Choi, P. Downes, M. Hulmán, S. Roth, I. Stepanek, P. Bernier. Hydrogen storage in sonicated carbón materials. Applied Physics A 72 (2001 ) 129-132, W.Z. Huang, X.B. Zhang, J.P. Tu, F.Z. Kong, J.X. Ma, F. Liu, H.M. Lu, CP. Chen. The effect of pretreatments on hydrogen adsorption of multi-walled carbón nanotubes. Mater. Chem. Phys. 78 (2002) 144-148, L. Ci, H. Zhu, B. Wei, C. Xu, D. Xu. Annealing amorphous carbón nanotubes for their application in hydrogen storage. Appl. Surf. Sci. 205 (2003) 39-43, P.-X. Hou, S.-T. Xu, Z. Ying, Q.-H. Yang, C. Liu, H.-M. Cheng. Hydrogen adsorption/desorption behavior of multiwalled carbón nanotubes with different diameters. Carbón 41 (2003) 2471-2476, K. Shen, H. Xu, Y. Jiang, T. Pietra. The role of carbón nanotube structure in purification and hydrogen adsorption. Carbón 42 (2004) 2315-2322, C. Liu, Y. Chen, C-Z. Wu, S-T. Xu, H-M. Cheng. Hydrogen storage in carbón nanotubes revisited. Carbón 48 (2010) 452-455, A. Reyhani, S. Z. Mortazavi, S. Mirershadi, A. Z. Moshfegh, P. Parvin, A. Nozad. Hydrogen storage in decorated multiwalled carbón nanotubes by Ca, Co, Fe, Ni, and Pd nanoparticles under ambient conditions. J. Phys. Chem. C. 1 15 (201 1 ) 6994- 7001 , K-S. Lin, Y-J. Mai, S-R. Li, C-W. Shu, C-H. Wang. Characterization and hydrogen storage of surface-modified multiwalled carbón nanotubes for fuel cell application. Journal of Nanomaterials 2012 (2012) 1-12), y otros tales como: documento KR20030003890 (A), documento US6869583 (B2), y documento KR201 10044367 (A). For purposes of comparison with the State of the Art, it is indicated that the sequence of steps suggested within the purification method (7 steps), the variables and the values associated with each of said steps (amount of material, time, temperature, pressure) , are not deduced from the documents of the State of the Art nearby, these being: Yue-Ying Fan and collaborators Yue-Ying Fan, Adam Kaufmann, Alexander Mukasyan, Arvind Varma. Single- and multi-wall carbon nanotubes produced using the floating catalyst method: Synthesis, purification and hydrogen up-take. Coal 44 (2006) 2160-2170. (heat treatment and treatment with HCI), H. Igarashi and collaborators Hideyuki Igarashi, Hiroto Murakami, Yoichi Murakami, Shigeo Maruyama, Naotoshi Nakashima. Purification and characterization of zeolite-supported single-walled carbon nanotubes catalytically synthesized from ethanol. Chemical Physics Letters 392 (2004) 529-532. (heat treatment and HF treatment), Sang Kyu Choi and collaborators Sang Kyu Choi, Seung-Beck Lee. Role of thermal treatment on the structural behavior of the are SWCNTs in the purification system process. Current Applied Physics 9 (2009) 658-662 (heat treatment and HCI treatment), and CN102897747 (A) (HCI treatment and filtration), and neither of the purification methods used in nanotubes for hydrogen storage applications described in start in [C. Liu, YY Fan, M. Liu, HT Cong, HM Cheng, MS Dresselhaus. Hydrogen Storage in Single- Walled Carbon Nanotubes at Room Temperature. Science 286, 1 127 (1999), Chen P, Wu X, Lin J, Tan KL. High H2 uptake by alkali-doped carbon nanotubes under ambient pressure and modérate temperatures. Science 285 (1999) 91-93, Ralph T. Yang. Hydrogen storage by alkali-doped carbon nanotubes-revisited. Coal 38 (2000) 623-626, A Züttel, Ch Nützenadel, P Sudan, Ph Mauron, Ch Emmenegger, S Rentsch, L Schlapbach, A Weidenkaff, T Kiyobayashi. Hydrogen surprise by carbon nanotubes and other carbon nanostructures. Journal of Alloys and Compounds 330-332 (2002) 676-682, M. Hirscher, M. Becher, M. Haluska, U. Dettlaff-Weglikowska, A. Quintel, GS Duesberg, Y.-M. Choi, P. Downes, M. Hulmán, S. Roth, I. Stepanek, P. Bernier. Hydrogen storage in sonicated carbon materials. Applied Physics A 72 (2001) 129-132, WZ Huang, XB Zhang, JP Tu, FZ Kong, JX Ma, F. Liu, HM Lu, CP. Chen. The effect of pretreatments on hydrogen adsorption of multi-walled carbon nanotubes. Mater. Chem. Phys. 78 (2002) 144-148, L. Ci, H. Zhu, B. Wei, C. Xu, D. Xu. Annealing amorphous carbon nanotubes for their application in hydrogen storage. Appl. Surf. Sci. 205 (2003) 39-43, P.-X. Hou, S.-T. Xu, Z. Ying, Q.-H. Yang, C. Liu, H.-M. Cheng Hydrogen adsorption / desorption behavior of multiwalled carbon nanotubes with different diameters. Coal 41 (2003) 2471-2476, K. Shen, H. Xu, Y. Jiang, T. Pietra. The role of carbon nanotube structure in purification and hydrogen adsorption. Coal 42 (2004) 2315-2322, C. Liu, Y. Chen, CZ. Wu, ST. Xu, HM. Cheng Hydrogen storage in carbon nanotubes revisited. Coal 48 (2010) 452-455, A. Reyhani, SZ Mortazavi, S. Mirershadi, AZ Moshfegh, P. Parvin, A. Nozad. Hydrogen storage in decorated multiwalled carbon nanotubes by Ca, Co, Fe, Ni, and Pd nanoparticles under ambient conditions. J. Phys. Chem. C. 1 15 (201 1) 6994-7001, KS. Lin, YJ. Mai, SR. Li, CW. Shu, CH. Wang. Characterization and hydrogen storage of surface-modified multiwalled carbon nanotubes for fuel cell application. Journal of Nanomaterials 2012 (2012) 1-12), and others such as: document KR20030003890 (A), document US6869583 (B2), and document KR201 10044367 (A).
La Tabla 5 resume la eficiencia del proceso de purificación de los nanotubos de carbono tipo pared múltiple obtenidos a partir de la técnica AACVD.
Tabla 5. Rendimiento y eficiencia del proceso de purificación de los nanotubos de carbono de pared múltiple. Table 5 summarizes the efficiency of the purification process of multiple-wall carbon nanotubes obtained from the AACVD technique. Table 5. Performance and efficiency of the purification process of multiple wall carbon nanotubes.
Pruebas de Adsorción de Hidrógeno de los Nanotubos de Carbono de Pared Múltiple (MWCNT) Obtenidos por Método AACVD y Purificados Hydrogen Adsorption Tests of Multiple Wall Carbon Nanotubes (MWCNT) Obtained by AACVD Method and Purified
Las pruebas de adsorción de hidrógeno para los nanotubos de carbono de pared múltiple (MWCNT) obtenidos por técnica AACVD antes y después del tratamiento de purificación se llevaron a cabo depositando en la superficie de una microbalanza de cristal de cuarzo (QC) a temperatura ambiente, dichos nanotubos en suspensión. Dicha suspensión se obtiene al dispersar los MWCNT en alcohol isopropilico por sonicación utilizando un baño ultrasónico por 7 minutos. Posterior al depósito, el QC se ubica en la cabeza un sistema de microbalanza de cristal de cuarzo (modelo SQM-310) y se coloca dentro de una cámara de vacío. La cámara se bombea hasta 933,3 Pa (7x10"6 Torr) usando bombas turbo y rotatorias que operan en serie. Una válvula de compuerta colocada entre la cámara y la bomba turbo aisla la cámara de vacío, lo que permite presurizar con H2 (99,995 %, 02 < 5 ppm, H20 < 8 ppm, C02 + CO < 4 ppm, N2 < 20 ppm y THC < 5 ppm) inyectándolo a través de una válvula de aguja. El cambio de masa sobre la adsorción de hidrógeno se determina monitoreando in situ los cambios en la frecuencia de resonancia del QC en
función del tiempo mientras que la muestra se expone al hidrógeno durante 8 minutos. Después de la exposición al H2, la cámara se bombea de nuevo a 933,3 Pa (7x10"6 Torr), y el proceso se repite inyectando hidrógeno hasta alcanzar la presión mayor. Las presiones entre 400 Pa y 7,3 KPa (3 y 55 Torr) se monitorean con un medidor capacitivo (Baratron de MKS Instruments) para los diferentes ciclos de hidrogenación. Hydrogen adsorption tests for multiple wall carbon nanotubes (MWCNT) obtained by AACVD technique before and after the purification treatment were carried out by depositing on the surface of a quartz crystal microbalance (QC) at room temperature, said nanotubes in suspension. Said suspension is obtained by dispersing the MWCNT in isopropyl alcohol by sonication using an ultrasonic bath for 7 minutes. After the deposit, the QC is located on the head a quartz crystal microbalance system (model SQM-310) and is placed inside a vacuum chamber. The chamber is pumped up to 933.3 Pa (7x10 "6 Torr) using turbo and rotary pumps that operate in series. A gate valve placed between the chamber and the turbo pump isolates the vacuum chamber, allowing pressurization with H 2 (99.995%, 0 2 <5 ppm, H 2 0 <8 ppm, C0 2 + CO <4 ppm, N 2 <20 ppm and THC <5 ppm) by injecting it through a needle valve. hydrogen adsorption is determined by monitoring in situ changes in the resonance frequency of the QC in function of time while the sample is exposed to hydrogen for 8 minutes. After exposure to H 2 , the chamber is pumped back to 933.3 Pa (7x10 "6 Torr), and the process is repeated by injecting hydrogen until the highest pressure is reached. Pressures between 400 Pa and 7.3 KPa ( 3 and 55 Torr) are monitored with a capacitive meter (Baratron from MKS Instruments) for the different hydrogenation cycles.
La relación entre la masa que se adiciona al QC, Am, debido a la adsorción de H2 en los MWCNT y el cambio en la frecuencia de resonancia, Af, se representa por la ecuación de Sauerbrey's (T. G. Sauerbrey. Verwendug von Schwingquarzen zur Wágung dünner Schichten und zur Microwágung. Z. Phys. 155 (1959) 206-222, V. M. Mecea. From quartz crystal microbalance to fundamental principies of mass measurements. Analytical Lett. 38 (2005) 753- 767 y R. Lucklum, P. Hauptmann. The quartz microbalance: mass sensitivity, viscoelasticity and acoustic amplification. Sensor and Actuators B 70 (2000) 30- 36). The relationship between the mass that is added to the QC, Am, due to the adsorption of H 2 in the MWCNT and the change in the resonance frequency, Af, is represented by the Sauerbrey ' s equation (TG Sauerbrey. Verwendug von Schwingquarzen zur Wágung dünner Schichten und zur Microwágung. Z. Phys. 155 (1959) 206-222, VM Mecea. From quartz crystal microbalance to fundamental principies of mass measurements. Analytical Lett. 38 (2005) 753-767 and R. Lucklum, P Hauptmann The quartz microbalance: mass sensitivity, viscoelasticity and acoustic amplification Sensor and Actuators B 70 (2000) 30-36).
La Figura 13 muestra los resultados frente al comportamiento de adsorción de hidrógeno (H2) en función de la presión para los nanotubos de carbono sin el procesos de purificación, entre tanto, la Figura 14 muestra los resultados frente al comportamiento de adsorción de hidrógeno (H2) en función de la presión para los nanotubos de carbono con el procesos de purificación. Figure 13 shows the results against the hydrogen adsorption behavior (H 2 ) as a function of the pressure for the carbon nanotubes without the purification process, meanwhile, Figure 14 shows the results against the hydrogen adsorption behavior ( H 2 ) depending on the pressure for carbon nanotubes with the purification process.
De la Figura 13 se puede observar que la máxima capacidad de adsorción peso de Hidrógeno Adsorbido fue de 1 ,76 para las muestras sin purificar para M2, lo cual está muy por debajo del valor logrado luego de la purificación. Si bien es cierto, destaca el potencial de crecer nanotubos de pared múltiple sin utilizar un soporte de zeolita (100% mineral de magnetita), estos no son apropiados para su aplicación en adsorción de hidrógeno. From Figure 13 it can be seen that the maximum adsorption capacity of Adsorbed Hydrogen weight was 1.76 for the unpurified samples for M2, which is well below the value achieved after purification. While it is true, it highlights the potential to grow multiple wall nanotubes without using a zeolite support (100% magnetite mineral), these are not suitable for application in hydrogen adsorption.
De la Figura 14 se observa que las muestras M2 y M3 se encuentran en valores en una escala de los 0,1 -3,5 en peso de Hidrógeno Adsorbido. La muestra M1 , demuestra un proceso de adsorción creciente a medida que aumenta la presión, esto se debe a la combinación de método de síntesis- material de partida y proceso de purificación. La muestra de M3, se llevó a cabo bajo una purificación diferente donde solo se utilizó ácido clorhídrico concentrado y luego se pasó a la parte de adsorción de hidrógeno, si bien, la adsorción mejoró en un par de puntos respecto al nanotubo de carbono sin purificar, este se encuentra muy por debajo respecto de las muestras M1 y M2. Este efecto se debe principalmente a un proceso de purificación incompleto, que al dejar impurezas presentes del tipo zeolita disminuyen la propiedad de adsorción. From Figure 14 it can be seen that the samples M2 and M3 are found in values on a scale of 0.1-3.5 by weight of Adsorbed Hydrogen. Sample M1 demonstrates an increasing adsorption process as the pressure increases, this is due to the combination of synthesis method-starting material and purification process. The M3 sample was carried out under a different purification where only concentrated hydrochloric acid was used and then passed to the hydrogen adsorption part, although the adsorption improved by a couple of points with respect to the unpurified carbon nanotube , this is well below the samples M1 and M2. This effect is mainly due to an incomplete purification process, which by leaving present impurities of the zeolite type decreases the adsorption property.
Ejemplo Example
Obtención de nanotubos de carbono de pared múltiple para adsorción de hidrogeno
Paso 1: Preparación de la fuente de carbono (solución A) Obtaining multiple wall carbon nanotubes for hydrogen adsorption Step 1: Preparation of the carbon source (solution A)
Se toman aproximadamente 2,0 gr de Alcanfor (Ci0H16O) con 95% pureza, se mezclan con 10ml de alcohol isopropilico (10 mi a 2% p/p) en un agitador magnético por 5 minutos. Approximately 2.0 g of Camphor (Ci 0 H 16 O) with 95% purity are taken, mixed with 10 ml of isopropyl alcohol (10 ml at 2% w / w) on a magnetic stirrer for 5 minutes.
Paso 2: Preparación de mezcla catalizador/soporte Step 2: Preparation of catalyst / support mixture
Se realiza una molienda mecánica en seco en mortero de ágata por 10 minutos de mineral de magnetita con 98% fase magnetita malla 325 (menor a 45μηι) con una Zeolita (tamiz molecular: álcali-metal alumino silicato/calcio, grado cromatografo, linde/Coast engineering I abo rato ry/Redondo Beach CA-USA) en una proporción de 66% a 34%, respectivamente. A dry mechanical grinding is performed in agate mortar for 10 minutes of magnetite ore with 98% magnetite phase 325 mesh (less than 45μηι) with a Zeolite (molecular sieve: alkali-metal alumina silicate / calcium, chromatograph grade, edge / Coast engineering I abo ry time / Redondo Beach CA-USA) in a proportion of 66% to 34%, respectively.
Paso 3: Obtención de nanotubos por técnica AACVD Step 3: Obtaining nanotubes by AACVD technique
1 ) Se coloca en el nebulizador ultrasónico a una frecuencia entre 1 ,7 MHz la solución de alcanfor y etanol (solución A) con el propósito de generar una niebla; 2) se transporta la niebla al reactor (tubo de cuarzo insertado en el horno) por medio de un gas transportador (argón o nitrógeno con 99.99% de pureza) a un flujo de 1 L/min; 3) la neblina reacciona con el catalizador o la mezcla catalizador/soporte, el cual se encuentra esparcido una longitud de entre 5 cm dentro de la zona de calentamiento del reactor con longitud de entre 15 cm cuya temperatura en ese momento es de entre 800Ό; 4) Luego de 30 min de proceso, se deja enfriar el reactor a temperatura ambiente utilizando la propia inercia térmica del horno; y 5) se extrae el polvo resultante (mezcla de nanotubos con residuos). El proceso descrito se desarrolla a 1 atmósfera de presión. 1) The camphor and ethanol solution (solution A) is placed in the ultrasonic nebulizer at a frequency between 1.7 MHz for the purpose of generating a mist; 2) the mist is transported to the reactor (quartz tube inserted in the oven) by means of a transport gas (argon or nitrogen with 99.99% purity) at a flow of 1 L / min; 3) the mist reacts with the catalyst or catalyst / support mixture, which is spread a length of between 5 cm within the heating zone of the reactor with a length of between 15 cm whose temperature at that time is between 800Ό; 4) After 30 min of process, the reactor is allowed to cool to room temperature using the oven's own thermal inertia; and 5) the resulting powder is extracted (mixture of nanotubes with residues). The described process is developed at 1 pressure atmosphere.
Los nanotubos de carbono de pared múltiple (MWCNT) obtenidos presentan una morfología de aglomerado, con longitud promedio de 1 .5 μηι, diámetro promedio 30 nm, espesores de multipared entre 4,5-7,0 nm y cada nanotubo se compone de entre 15-20 nanotubos concéntricos. Tienen adheridos en las paredes externas nanopartículas de óxidos de hierro con tamaños 20-30 nm, y
presentan una mezcla de fases (carbón amorfo, nanotubos de carbono de pared múltiple, óxidos de hierro y zeolita). Tienen una relación simetría/desorden (IG/ID) a partir de Raman de 1 ,02. The multiple-wall carbon nanotubes (MWCNT) obtained have an agglomerate morphology, with an average length of 1.5 microns, average diameter 30 nm, multipared thicknesses between 4.5-7.0 nm and each nanotube is composed of 15-20 concentric nanotubes. Nanoparticles of iron oxides with sizes 20-30 nm are attached to the outer walls, and they present a mixture of phases (amorphous carbon, multi-walled carbon nanotubes, iron oxides and zeolite). They have a symmetry / disorder (IG / ID) ratio from Raman of 1, 02.
Posteriormente los nanotubos de carbono se someten a un tratamiento de purificación que consiste de Subsequently the carbon nanotubes undergo a purification treatment consisting of
Paso 4: Tratamiento térmico. Step 4: Heat treatment.
Se colocan entre 500 mg de los nanotubos obtenidos en el paso 3 un horno tubular con velocidad de calentamiento 15ΌΛηίη a u na temperatura de entre 450Ό por 1 hora. Posteriormente, se deja enfriar h asta temperatura ambiente por 1 1 horas. A tubular oven with heating rate 15 velocidadηίη at a temperature of between 450ΌΛ for 1 hour is placed between 500 mg of the nanotubes obtained in step 3. Subsequently, it is allowed to cool to room temperature for 11 hours.
Paso 5: Tratamiento con solución de ácido fluorhídrico (HF) en baño ultrasónico. Step 5: Treatment with hydrofluoric acid (HF) solution in ultrasonic bath.
Se colocan las muestras provenientes del paso 4 en solución de ácido fluorhídrico (con una concentración entre el 40% y en una relación HF:CNT de entre 1 :3 en función al volumen) bajo baño ultrasónico (marca ELMASONIC E 30 H) a una frecuencia de entre 37 kHz durante 1 hora. Posteriormente se deja en reposo la solución resultante por 20 minutos en una campana de extracción, tiempo luego del cual, se procede a retirar el líquido sobrenadante con micro pipetas descartables. Este paso se realiza a presión de 1 atmósfera y temperatura ambiente (25Ό). The samples from step 4 are placed in hydrofluoric acid solution (with a concentration between 40% and in an HF: CNT ratio between 1: 3 depending on volume) under ultrasonic bath (ELMASONIC E 30 H mark) at a frequency between 37 kHz for 1 hour. Subsequently, the resulting solution is allowed to stand for 20 minutes in an extraction hood, after which time, the supernatant liquid is removed with disposable micro pipettes. This step is performed at a pressure of 1 atmosphere and room temperature (25Ό).
Paso 6: Lavado y centrifugado. Step 6: Wash and spin.
Las muestras provenientes del paso 5 se someten a un ciclo de lavado- centrifugado hasta llegar a un pH neutro. Como agente lavador se utiliza agua desionizada y cada centrifugado se realiza por 4 minutos a 3500 rpm en un equipo ELCEMCC60CLA # Microcentrifuga para tubos eppendorf de 1 .5 mi Prisma (Labnet USA). Una vez se alcanza el pH neutro, se realiza un último lavado con etanol.
Paso 7: secado. Las muestras provenientes del paso 6 se secan al ambiente durante 48 horas dentro de un recipiente (por ejemplo un vaso beaker). The samples from step 5 are subjected to a wash-spin cycle until they reach a neutral pH. As a washing agent, deionized water is used and each centrifuge is performed for 4 minutes at 3500 rpm in an ELCEMCC60CLA # Microcentrifuge for eppendorf tubes of 1 .5 mi Prism (Labnet USA). Once the neutral pH is reached, a final wash with ethanol is performed. Step 7: drying. The samples from step 6 are dried in the environment for 48 hours in a container (for example a beaker).
Paso 8: Tratamiento con solución de ácido clorhídrico (HCI). Step 8: Treatment with hydrochloric acid (HCI) solution.
Se colocan las muestras provenientes del paso 7 en solución de ácido clorhídrico (con una concentración entre 37% y en una relación HCI:CNT de 1 :3 en función al volumen) durante 24 horas en estado estacionario. Posteriormente se procede a retirar el líquido sobrenadante con micro pipetas descartables. The samples from step 7 are placed in hydrochloric acid solution (with a concentration between 37% and in an HCI: CNT ratio of 1: 3 as a function of volume) for 24 hours at steady state. Subsequently, the supernatant liquid is removed with disposable micro pipettes.
Paso 9: Lavado y centrifugado. Step 9: Wash and spin.
Las muestras provenientes del paso 8 se someten a un ciclo de lavado- centrifugado hasta llegar a un pH neutro. Como agente lavador se utiliza agua desionizada y cada centrifugado se realiza por 4 minutos a 3500 rpm en ELCEMCC60CLA # Microcentrifuga para tubos eppendorf de 1 ,5 mi Prisma (Labnet USA). Una vez se alcanza el pH neutro, se realiza un último lavado con etanol. The samples from step 8 are subjected to a wash-spin cycle until they reach a neutral pH. As a washing agent, deionized water is used and each centrifuge is performed for 4 minutes at 3500 rpm in ELCEMCC60CLA # Microcentrifuge for eppendorf tubes of 1, 5 mi Prism (Labnet USA). Once the neutral pH is reached, a final wash with ethanol is performed.
Paso 10: secado Step 10: drying
El sólido resultante del paso 9 se seca en un horno con un sistema de vacío (- 0,1 MPa) marca Leybold (Mod: D1 ,6B) a una temperatura de 80Ό por 1 hora. Los nanotubos de carbono de pared múltiple (MWCNT) luego de la purificación presentan como elemento constituyente al carbono, morfología global tipo espiral y una superficie corrugada que se extiende desde las capas externas a las más internas, así como la desaparición de las nanopartículas adheridas en las paredes de estos. Presentan una elevada cristalinidad producto de la eliminación del carbón amorfo, con una relación simetría/desorden (IG/ID) a partir de Raman de 0,63, y un área superficial BET entre 70,5-650,3 m2/g determinado por adsorción de N2 a -196Ό (77,1 Ή).
Pruebas de adsorción de hidrogeno de los nanotubos de carbono de pared múltiple The solid resulting from step 9 is dried in an oven with a vacuum system (-0.1 MPa) Leybold brand (Mod: D1, 6B) at a temperature of 80Ό for 1 hour. The multiple-walled carbon nanotubes (MWCNT) after purification have as a constituent element carbon, global spiral morphology and a corrugated surface that extends from the outer layers to the innermost, as well as the disappearance of the nanoparticles adhered to the walls of these. They have a high crystallinity resulting from the removal of amorphous carbon, with a symmetry / disorder (IG / ID) ratio from 0.63 to Raman, and a BET surface area between 70.5-650.3 m 2 / g determined by adsorption of N 2 to -196Ό (77.1 Ή). Hydrogen adsorption tests of multiple wall carbon nanotubes
Paso 1: Los nanotubos de carbono de pared múltiple (MWCNT) obtenidos después del tratamiento de purificación se depositan en suspensión en la superficie de una microbalanza de cristal de cuarzo (QC) a 25Ό, donde dicha suspensión se obtiene al dispersar los MWCNT en alcohol isopropilico por sonicación utilizando un baño ultrasónico por 7 minutos. Step 1: The multi-walled carbon nanotubes (MWCNT) obtained after the purification treatment are deposited on the surface of a quartz crystal microbalance (QC) at 25Ό, where said suspension is obtained by dispersing the MWCNT in alcohol Sonopropyl isopropyl using an ultrasonic bath for 7 minutes.
Paso 2: Posterior al depósito, el QC se ubica en la cabeza un sistema de microbalanza de cristal de cuarzo (modelo SQM-310) y se coloca dentro de una cámara de vacío. La cámara se bombea hasta 101 ,3 (7x10"6 Torr) usando bombas turbo y rotatorias que operan en serie. Una válvula de compuerta colocada entre la cámara y la bomba turbo aisla la cámara de vacío, lo que permite presurizar con H2 (Indura, 99,995 %, 02 < 5 ppm, H20 < 8 ppm, C02 + CO < 4 ppm, N2 < 20 ppm y THC < 5 ppm) inyectándolo a través de una válvula de aguja. Step 2: After the deposit, the QC is located on the head of a quartz crystal microbalance system (model SQM-310) and placed inside a vacuum chamber. The chamber is pumped up to 101, 3 (7x10 "6 Torr) using turbo and rotary pumps that operate in series. A gate valve placed between the chamber and the turbo pump isolates the vacuum chamber, allowing pressurization with H 2 ( Indura, 99.995%, 0 2 <5 ppm, H 2 0 <8 ppm, C0 2 + CO <4 ppm, N 2 <20 ppm and THC <5 ppm) by injecting it through a needle valve.
Paso 3: Se determina el cambio de masa sobre la adsorción de hidrógeno monitoreando in-situ los cambios en la frecuencia de resonancia del QC en función del tiempo mientras que la muestra se expone al hidrógeno durante 8 minutos. Step 3: The change in mass on hydrogen adsorption is determined by monitoring in situ changes in the resonance frequency of the QC as a function of time while the sample is exposed to hydrogen for 8 minutes.
Paso 4: Después de la exposición al H2, la cámara se bombea de nuevo a 101 ,3 KPa (7x10"6 Torr), y el proceso se repite inyectando hidrógeno hasta alcanzar la presión mayor. Las presiones entre 399,6 Pa a 732,6 Pa (3 y 55 Torr) se monitorean con un medidor capacitivo (Baratron de MKS Instruments) para los diferentes ciclos de hidrogenación. Step 4: After exposure to H 2 , the chamber is pumped back to 101.3 KPa (7x10 "6 Torr), and the process is repeated by injecting hydrogen until the highest pressure is reached. Pressures between 399.6 Pa a 732.6 Pa (3 and 55 Torr) are monitored with a capacitive meter (Baratron from MKS Instruments) for the different hydrogenation cycles.
Paso 5: Se utiliza la ecuación de Sauerbrey's (ec. 1 ) para el cálculo de la masa de hidrogeno adsorbida en el nanotubo de carbono.
El valor de adsorción en peso de hidrógeno determinado por el método descrito fue de 3,5 para los nanotubos de carbono de pared múltiple purificados, mientras que el valor obtenido para la misma muestra de MWCNT sin purificar fue de 0,5.
Step 5: The Sauerbrey ' s equation (ec. 1) is used to calculate the mass of adsorbed hydrogen in the carbon nanotube. The adsorption value by weight of hydrogen determined by the described method was 3.5 for the purified multi-wall carbon nanotubes, while the value obtained for the same sample of unpurified MWCNT was 0.5.
Claims
1 . Método en dos etapas para obtener nanotubos de carbono de pared múltiple (MWCNT) para adsorción de hidrógeno caracterizado porque comprende las siguientes etapas: one . Two-stage method for obtaining multiple-wall carbon nanotubes (MWCNT) for hydrogen adsorption characterized in that it comprises the following stages:
a) obtener nanotubos por técnica de deposición química en fase vapor asistida por aerosol (AACVD) utilizando como catalizador mineral magnetita y una solución de alcanfor/alcohol como fuente de carbono, el que a su vez comprende los siguientes pasos: a) obtain nanotubes by chemical vapor deposition technique (AACVD) using magnetite mineral catalyst and a camphor / alcohol solution as carbon source, which in turn comprises the following steps:
a.1 ) preparar la fuente de carbono que comprende mezclar alcanfor (Ci0H16O) con alcohol isopropilico, con agitación en una proporción 1 :5 p/v de alcanfor: alcohol isopropilico, a.1) prepare the carbon source comprising mixing camphor (Ci 0 H 16 O) with isopropyl alcohol, with stirring in a 1: 5 w / v ratio of camphor: isopropyl alcohol,
a.2) preparar la mezcla catalizador/soporte donde el catalizador es magnetita mineral de tamaño menor a 45 μηι y el soporte es zeolita, y ambos se mezclan en estado sólido mediante molienda mecánica en seco, y a.2) Prepare the catalyst / support mixture where the catalyst is mineral magnetite smaller than 45 μηι and the support is zeolite, and both are mixed in a solid state by dry mechanical grinding, and
a.3) obtener nanotubos por deposición química en fase vapor asistida por aerosol (AACVD), donde dicha etapa comprende los pasos de: a.3) obtain nanotubes by chemical deposition in the vapor-assisted vapor phase (AACVD), where said stage comprises the steps of:
i) generar una niebla al colocar en un nebulizador ultrasónico, una solución de alcanfor y etanol; i) generate a fog by placing in a ultrasonic nebulizer a solution of camphor and ethanol;
ii) transportar la niebla generada en la etapa i) a un reactor por medio de un gas transportador, ii) transport the mist generated in step i) to a reactor by means of a transporting gas,
iii) hacer reaccionar la neblina con la mezcla catalizador/soporte que se encuentra esparcida dentro de la zona de calentamiento del reactor, donde la proporción de longitud de mezcla esparcida a longitud de zona de calentamiento del reactor es 1 :3, cuya temperatura está en el rango de 750- 850eC, iii) reacting the mist with the catalyst / support mixture that is scattered within the heating zone of the reactor, where the ratio of mixing length spread to the heating zone length of the reactor is 1: 3, whose temperature is at the range of 750-850 e C,
iv) dejar enfriar el reactor a temperatura ambiente utilizando la propia inercia térmica del horno; y
v) posterior al enfriamiento, se desarticula el tubo de cuarzo del horno y se extrae el polvo resultante (mezcla de nanotubos con residuos), y donde esta subetapa se desarrolla a 101 ,3Pa de presión; y iv) allow the reactor to cool to room temperature using the oven's own thermal inertia; Y v) after cooling, the quartz tube is dismantled from the oven and the resulting powder is extracted (mixture of nanotubes with residues), and where this sub-stage develops at 101, 3Pa of pressure; Y
b) purificar los nanotubos obtenidos por tratamiento térmico y tratamiento con ácidos que comprende los pasos: b) purify the nanotubes obtained by heat treatment and acid treatment comprising the steps:
b.1 ) tratamiento térmico que consiste en colocar los nanotubos obtenidos en un horno tubular a una temperatura entre 400-500sC, y se dejan enfriar hasta temperatura ambiente para eliminar el carbono amorfo; b.1) heat treatment consisting of placing the nanotubes obtained in a tubular oven at a temperature between 400-500 s C, and allowing them to cool to room temperature to remove amorphous carbon;
b.2) tratamiento con solución de ácido fluorhídrico (HF) en baño ultrasónico donde los nanotubos se colocan en solución de ácido fluorhídrico bajo baño ultrasónico , y posteriormente, se dejan en la solución resultante para luego retirar el líquido sobrenadante, esta etapa se realiza a presión de 101 ,3 KPa y temperatura ambiente, 25CC, y se elimina el alumino-silicato de la zeolit a; b.2) treatment with hydrofluoric acid (HF) solution in an ultrasonic bath where the nanotubes are placed in hydrofluoric acid solution under an ultrasonic bath, and subsequently, they are left in the resulting solution to then remove the supernatant liquid, this stage is performed at a pressure of 101.3 KPa and room temperature, 25 C C, and the alumino silicate is removed from the zeolit a;
b.3) lavado y centrifugado, donde los nanotubos se someten a un ciclo de lavado- centrifugado hasta llegar a un pH neutro usando agua desionizada como agente de lavado, y se centrifugan, donde dicho lavado y centrifugado se repiten, realizándose un último lavado con etanol; b.3) washing and centrifuging, where the nanotubes are subjected to a wash-spin cycle until they reach a neutral pH using deionized water as a washing agent, and centrifuged, where said washing and spinning are repeated, with a final wash with ethanol;
b.4) secado, los nanotubos se secan al ambiente; b.4) drying, the nanotubes are dried in the environment;
b.5) tratamiento con solución de ácido clorhídrico (HCI), los nanotubos se colocan en solución de ácido clorhídrico en estado estacionario, y posteriormente se procede a retirar el líquido sobrenadante para eliminar el hierro presente; b.5) treatment with hydrochloric acid (HCI) solution, the nanotubes are placed in stationary hydrochloric acid solution, and then the supernatant is removed to remove the iron present;
b.6) lavado y centrifugado, donde los nanotubos se someten a un ciclo de lavado-centrifugado hasta llegar a un pH neutro usando agua desionizada como agente de lavado y repitiéndose cada ciclo lavado-centrifugado, para luego, realizar un último lavado con etanol; y b.6) washing and spinning, where the nanotubes are subjected to a wash-spin cycle until they reach a neutral pH using deionized water as a washing agent and repeating each wash-spin cycle, then perform a final wash with ethanol ; Y
b.7) secado de los nanotubos en un horno con un sistema de vacío. b.7) drying the nanotubes in an oven with a vacuum system.
2. El método de la reivindicación 1 caracterizado porque la magnetita mineral comprende más del 80% de magnetita.
2. The method of claim 1 characterized in that the mineral magnetite comprises more than 80% magnetite.
3. El método de la reivindicación 2 caracterizado porque la magnetita mineral comprende 80% de magnetita, 20% silicatos y óxidos de hierro. 3. The method of claim 2 characterized in that the mineral magnetite comprises 80% magnetite, 20% silicates and iron oxides.
4. El método de la reivindicación 2 caracterizado porque la magnetita mineral comprende 98% fase magnetita, 2% silicatos y hematita. 4. The method of claim 2 characterized in that the mineral magnetite comprises 98% magnetite phase, 2% silicates and hematite.
5. El método de la reivindicación 1 caracterizado porque la proporción magnetita a soporte es 100: 0 a 50:50. 5. The method of claim 1 characterized in that the magnetite to support ratio is 100: 0 to 50:50.
6. El método de la reivindicación 5 caracterizado porque la proporción magnetita a soporte es 100: 0. 6. The method of claim 5 characterized in that the magnetite to support ratio is 100: 0.
7. El método de la reivindicación 5 caracterizado porque la proporción magnetita a soporte es 66:34. 7. The method of claim 5 characterized in that the magnetite to support ratio is 66:34.
8. El método de la reivindicación 1 caracterizado porque en la etapa a.3.ii) el reactor es un tubo de cuarzo insertado en el horno. 8. The method of claim 1 characterized in that in step a.3.ii) the reactor is a quartz tube inserted in the oven.
9. El método de la reivindicación 1 caracterizado porque en la etapa a.3.ii) el gas transportador es argón o nitrógeno. 9. The method of claim 1 characterized in that in step a.3.ii) the transport gas is argon or nitrogen.
10. El método de la reivindicación 9 caracterizado porque el gas transportador es argón con 99,99% de pureza. 10. The method of claim 9 characterized in that the carrier gas is argon with 99.99% purity.
1 1 . El método de la reivindicación 9 caracterizado porque el gas transportador tiene un flujo de 1 L/min. eleven . The method of claim 9 characterized in that the transport gas has a flow of 1 L / min.
12. El método de la reivindicación 1 caracterizado porque la proporción fuente de carbono a mezcla de catalizador es 4:1 . 12. The method of claim 1 characterized in that the source ratio of carbon to catalyst mixture is 4: 1.
13. El método de la reivindicación 1 caracterizado porque la proporción fuente de carbono a mezcla de catalizador/soporte es 2:5. 13. The method of claim 1 characterized in that the source ratio of carbon to catalyst / support mixture is 2: 5.
14. El método de la reivindicación 1 caracterizado porque en la etapa b.ii) dicho ácido fluorhídrico es ácido fluorhídrico al 40%. 14. The method of claim 1 characterized in that in step b.ii) said hydrofluoric acid is 40% hydrofluoric acid.
15. El método de la reivindicación 14 caracterizado porque en la etapa b.ii) la relación HF:nanotubo de carbono (CNT) es de 1 :3, en volumen. 15. The method of claim 14 characterized in that in step b.ii) the ratio HF: carbon nanotube (CNT) is 1: 3, by volume.
16. El método de la reivindicación 1 caracterizado porque en la etapa b.v) dicho ácido clorhídrico es ácido clorhídrico al 37%.
16. The method of claim 1 characterized in that in step bv) said hydrochloric acid is 37% hydrochloric acid.
17. El método de la reivindicación 16 caracterizado porque en la etapa b.v) la relación HF:nanotubo de carbono (CNT) de 1 :3, en volumen 17. The method of claim 16 characterized in that in step b.v) the ratio HF: carbon nanotube (CNT) of 1: 3, by volume
18. El método de la reivindicación 17 caracterizado porque en la etapa b.v) la relación HChnanotubo de carbono (CNT) de 1 :3, en volumen. 18. The method of claim 17 characterized in that in step b.v) the ratio HChnanotube of carbon (CNT) of 1: 3, by volume.
19. El método de la reivindicación 1 caracterizado porque en la etapa a.3.i), dicha neblina se genera a una frecuencia de 1 ,7KHz. 19. The method of claim 1 characterized in that in step a.3.i), said mist is generated at a frequency of 1.7KHz.
20. El método de la reivindicación 1 caracterizado porque en la etapa a.3.iii), la temperatura de reacción de la neblina en la mezcla catalizador/soporte es 800eC. 20. The method of claim 1 characterized in that in step a.3.iii), the reaction temperature of the mist in the catalyst / support mixture is 800 e C.
21 . El método de la reivindicación 1 caracterizado porque en la etapa b.i), dicho tratamiento térmico se realiza a 450eC. twenty-one . The method of claim 1 characterized in that in step bi), said heat treatment is carried out at 450 e C.
22. El método de la reivindicación 1 porque dicho baño ultrasónico se realiza a 37 KHz.
22. The method of claim 1, wherein said ultrasonic bath is performed at 37 KHz.
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