CN112299395A

CN112299395A - High metallic, hydrophilic, polymer-free Carbon Nanotube (CNT) sheets and uses thereof

Info

Publication number: CN112299395A
Application number: CN202010745076.2A
Authority: CN
Inventors: 李春红
Original assignee: Individual
Current assignee: Individual
Priority date: 2020-07-29
Filing date: 2020-07-29
Publication date: 2021-02-02

Abstract

The invention discloses a carbon nano tube film which has high conductivity, good hydrophilicity, no high polymer material and high tensile strength. More particularly, the disclosed systems and methods relate to an ordered aqueous layer near the surface of individual carbon nanotubes and subsequent use of chlorosulfonic acid (HClSO)₃) And densifying the carbon nanotube membrane under the condition of increasing the temperature. The surface aperture of the densified carbon nano tube is reduced, and the tensile strength and the electric conductivity are obviously improved. The carbon nanotube film of this disclosure has excellent surface anti-contamination properties when used as a filtration membrane. The film is also excellentThe electromagnetic wave interference shielding material.

Description

High metallic, hydrophilic, polymer-free Carbon Nanotube (CNT) sheets and uses thereof

Technical Field

The present invention generally relates to high metallic, hydrophilic, polymer-free Carbon Nanotube (CNT) sheets, and methods for making the same. Highly metallic, hydrophilic, polymer-free Carbon Nanotube (CNT) sheets can be used as filtration membranes without adsorbing surface fouling, while being useful as excellent electromagnetic interference (EMI) shielding materials.

Background

By virtue of their uniqueness, mechanical strength, chemical stability, and resistance to high temperatures and organic solvents, each CNT sheet is expected to be future proof in many applications. In addition to being flexible and lightweight in shape, they can also conduct electricity and heat. However, it is difficult to transfer these characteristics of each CNT to a large-area CNT sheet.

Powders have been used to prepare polymer composite films, and CNT powders can be dispersed in a solvent or mixed with a polymer to form functional groups with certain chemical or physical properties. Generally, it is difficult to uniformly functionalize CNTs because of the varying amounts of amorphous carbon present and the varying degrees of aggregation and binding. Covalent CNTs can generate functional groups with certain chemical or physical properties, depending on the delicate chemical treatments, which further destroy the surface structure of the CNTs. It can also be done by physical means (e.g. sonication), which usually helps the CNT dispersion into the solvent, but also further disrupts the CNT structure, and CNT powder dispersion and uniformity will also be difficult to control.

Composite membranes always have the limitations of polymers. For example, many composite films lack the chemical stability and mechanical strength of CNTs because of the absence of polymers. Degradation of the polymer in the CNT composite film over time may also lead to leaching of degradation products and CNTs for health and safety considerations.

Without a polymer binder, it would be a difficult task to prepare CNT films with sufficient tensile strength. Bucky paper is an example of a CNT film that is prepared using dispersed CNT powder rather than a polymer binder. However, Bucky paper is generally weak and lacks the physical strength required for many applications due to cracking of the film and the absence of CNTs in the film.

Inc. has successfully prepared durable CNT films, tapes, from CNT powders without using conventional polymers as binders. This process requires the dissolution of CNT powder in chlorosulfonic acid and then extrusion of the solution to obtain aligned CNT fibers and films. The technique is most suitable for producing CNT threads, yarns and narrow bands (< = 4 cm wide) with a thickness of 10 to 100 [ mu ] m.

Another method for producing CNT sheets without using a polymer binder is Floating Catalyst Chemical Vapor Deposition (FCCVD). In the FCCVD process, pristine CNTs grown in situ in a high temperature furnace (about 1000 ℃ C. and 1200 ℃ C.) are deposited on the substrate surface and then physically compressed to form a sheet. Currently, only a few companies can produce such pristine CNT sheets with a size of 1 m x 1 m or more. Nanocomp Technologies inc and sco creative nanocarbon limited are two companies with this capability.

However, pristine CNT sheets have varying amounts of amorphous carbon along the individual CNT surfaces and channels. The as-grown CNTs of the CNT sheet vary in crystallinity, diameter and length during the growth process. Variations in CNT sheet properties are manifested in differences in CNT mass, e.g., irreproducible hydrophobicity, poor electrical conductivity, and tensile strength.

There are pi-pi interactions and van der waals forces between adjacent CNTs. However, this attractive force between the native carbon nanotubes is significantly reduced by the presence of amorphous carbon and air. When pressure is present together, the resulting pristine CNT sheet typically lacks the necessary tensile strength and hydrophilicity, and pore size within the sheet is also difficult to control. Without the necessary tensile strength, the pristine CNT sheet will always be susceptible to film cracking and CNT loss. Therefore, a process flow is urgently needed to manufacture CNT sheets having desired physical (tensile) strength without CNT deletion. Such pure CNT flakes are resistant to high temperatures, scaling, corrosion and organic solvents and are not easily degraded if a polymer is not used as a binder. Therefore, they will find application in the difficult conditions under which common membranes typically fail.

Disclosure of Invention

One embodiment of the present subject matter provides a method of densifying a CNT sheet or film without mechanical compression. Immediately after annealing at high temperature, the CNT sheet is treated with a concentrated acid such as phosphoric acid or sulfuric acid at high temperature. After washing with water, the resulting sheet was dried in air and further densified at high temperature in an atmosphere of chlorosulfonic acid (HClSO 3). Dense CNT sheets have hydrophilicity, mechanical strength, and durability, and do not adhere to other solid surfaces (such as teflon, nylon membranes, and metal block surfaces). No loss of CNTs was seen after pressing the dense CNT sheet on the teflon or polypropylene surface. The dense CNT thin film or sheet appeared silvery and the conductivity increased (between 5x 105S/m and 1 x 106S/m).

In another embodiment, the annealed purified CNT sheet will be stored in air for an extended period of time and then treated with a concentrated acid such as phosphoric acid or sulfuric acid at elevated temperatures. After rinsing with water, the sheet was dried and further densified under high temperature conditions in an atmosphere of HClSO3 to obtain silver durable CNT sheets.

In another embodiment, the purified CNT sheet is treated with SO3 NEt3 complex at elevated temperatures immediately after annealing. After rinsing with water, the sheets were dried and further densified under high temperature conditions in an atmosphere of HClSO3 to give densified CNT sheets with improved tensile strength and electrical conductivity.

Drawings

FIG. 1 (A) is a cross-sectional view of alternating positive and negative charges (or partial charges) across the surface of a single CNT (only one molecular layer is shown for simplicity); (B) alternating charge distribution along the CNT surface; (C) due to the charge separation on the surface of the CNTs, a thin and ordered water layer (only one molecular layer is shown for simplicity) is formed around each CNT. A nanogap exists between the surface of the CNT and the water layer. Air or water vapor may be present in the nanogap.

Fig. 2 (a) shows that the total surface area is reduced by the presence of an aqueous layer, which is in order of coverage and connects adjacent CNTs together. When air or water vapor is present in the nanogap, adjacent CNTs do not easily approach. (B) Dehydration in the presence of HClSO3 results in a more ordered and dense aqueous layer with increased charge separation, which in turn causes more charge separation at the CNT surface. The increase in charge separation results in an increase in the attraction between the CNTs. Thinning of the ordered water layer further densifies the adjacent CNTs, making the CNT film or sheet more dense (only one molecular layer shown for simplicity) although not shown in figure (B), residual water molecules may be present between the dense CNTs. Densification may also be promoted during dehydration when air or water vapor is removed from the nanogap, thereby forming a vacuum gap.

FIG. 3 (A) the chlorosulfonic acid (HClSO 3) molecule is highly polar, with a partial positive charge at the "H" end and a partial negative charge at the "O" end; (B) after high temperature annealing, the CNTs become more polarized with charge separation. When treated with hciso 3, an ordered molecular layer of hciso 3 forms around the surface of individual CNTs. Due to the high polarity of HClSO3, the CNTs within the layer become more polarized, and the attractive forces between adjacent CNTs increase significantly, resulting in densification of the CNT sheet. Subsequent washing with water can form an ordered water layer structure as shown in figure 2B.

FIG. 4 Scanning Electron Microscope (SEM) image (A) of a pristine CNT sheet showing the presence of a substantial amount of amorphous carbon attached to individual CNTs; (B) after annealing at 1000 ℃ for 4 hours, there was little residual particulate or amorphous carbon.

Fig. 5 a monolithic flexible carbon nanotube sheet that (a) is dark black before densification and (B) exhibits a sparkling silver gray color after densification.

Fig. 6 is an SEM image (a) of CNT flakes after densification in the presence of HClSO3 at 80,000x magnification; (B) magnification 320,000x, showed substantial agglomeration and visible pores less than 100 nm.

FIG. 7 shows the tensile strength of the densified carbon nanotube film exceeding 800 MPa, and the inset shows the tensile strength of the undensified carbon nanotube film, which is very low.

FIG. 8 shows that the conductivity of the carbon nanotube film densified by chlorosulfonic acid is sharply increased to approximately 1X 106S/m.

FIG. 9X-band electromagnetic interference (EMI) shielding effect (A) of carbon nanotube films after different processing methods; (B) densified carbon nanotube films of different thicknesses.

FIG. 10 illustrates the densified carbon nanotube film before and after an X-band electromagnetic interference (EMI) shielding effect (A) high temperature high humidity treatment; and (B) before and after the strong acid and strong base are soaked for a long time, the EMI shielding effect is not changed after the carbon nanotube film is stored in a harsh environment for 30 days, and the chemical stability and the structural stability of the densified carbon nanotube film are shown.

Detailed Description

Inert gas atmosphere here means a chemically inert gaseous medium. The inert gas may be selected from nitrogen and noble gases including helium, neon, argon, krypton and xenon. The inert gas may be doped with a small amount of hydrogen to remove traces of oxygen from the inert atmosphere.

Without being bound by any particular theory, various aspects of the invention and its uses are described below.

Consists of aromatic structures and each individual CNT can be considered as a giant molecule. According to molecular orbital theory, one 2p orbital per carbon atom participates in the recombination of 2p orbitals to form the molecular pi orbital. Each molecule pi-orbital has a specific number of nodes. The higher the energy level, the more nodes the pi orbital has. When electrons fill the pi orbitals, they will be in the pi orbitals and have more and more nodes. In an electronic cloud distribution, these nodes may be interpreted as "+" or "-". In essence, electrons in high energy pi orbitals can be considered to be more closely located around some carbon atoms, but far from others. Thus, even though the entire CNT molecule is charge neutral, there is a partial positive charge around some carbon atoms and a local negative charge around others on the entire CNT surface. This inhomogeneous electron density distribution, although small, may account for the differences in 13C nuclear magnetic chemical shifts of aromatic molecules (e.g., pyr). Recent spectral evidence also indicates that the electron density distribution in CNT and graphene materials is not uniform. The non-uniform electron density distribution across the CNT surface can be interpreted as having a strong dipole or alternating positive and negative charges (or partial charges) (fig. 1A and 1B). Due to this charge separation, even if the hydrophilic chemical functional groups on the surface of the CNTs do not perfectly interact with water molecules, the CNTs entangled in the CNT sheet preferentially interact with polar molecules (such as water molecules), showing hydrophilicity.

The presence of amorphous carbon disrupts the ordered charge separation along the CNT surface. Amorphous carbon also promotes the hydrophobicity of CNTs by keeping air pockets on the CNT surface. Removing the amorphous carbon content of the pristine CNT sheet results in CNTs that are cleaner, more crystalline, less structural defects, and have a fairly high degree of uniformity in tube diameter, surface smoothness, and crystallinity.

In this purified CNT sheet, an adsorbed layer of water is formed around each CNT, creating a nanogap between the CNT surface and the water layer (fig. 1C). Air or water vapor is present in the nanogap space. Treatment of the purified CNT flakes with concentrated sulfuric acid further stabilizes the adsorption of the aqueous layer. It is expected that the aqueous layer becomes more ordered due to the permeation promoting action of sulfate ions. As the water layer approaches the CNT surface, it becomes more and more ordered. Adjacent CNTs are minimally linked together by the water layer surface (fig. 2A). However, since air or water vapor occupies the nanogap, the resistance may increase as the CNTs approach each other.

Subsequent treatment with chlorosulfonic acid (HClSO 3) further thins and polarizes the ordered aqueous layer, further enhancing CNT charge separation by relaying the electric field changes. Thus, the attractive forces between adjacent CNTs are significantly increased to densify the CNTs in the CNT sheet (FIG. 2B). It is also possible to gradually remove water vapor in the nanogap, resulting in a vacuum gap that further promotes the densification of the CNTs. The resulting CNT sheet has higher tensile strength, becomes stronger, and does not lose individual CNTs.

Another possibility is that the concentrated sulfuric acid forms a layer around individual CNTs within the purified CNT sheet. After washing with water, an ordered water layer forms around the CNTs. When treated with chlorosulfonic acid, the aqueous layer becomes thinner and more polar. This polarization in the aqueous layer results in greater charge separation within the CNTs. Thus, the CNTs have a greater attraction to each other, which brings the CNTs closer together, thereby densifying the CNTs into a CNT sheet.

Another possibility is that chlorosulfonic acid (a molecule of strong dipole, fig. 3A) completely removes the ordered water layer near the surface of the CNTs, and then an ordered layer of chlorosulfonic acid forms very close to the surface of the CNTs (fig. 3B). Since chlorosulfonic acid is highly polar, the chlorosulfonic acid layer enhances charge separation in individual CNTs. By being more attractive to each other, the CNTs densify to form a durable CNT sheet with improved tensile strength.

During FCCVD for the production of CNT sheets, CNTs in the furnace grow very fast (typically in a few seconds) at high temperatures (1000 ℃ to 1200 ℃) while the growing CNTs are simultaneously pulled out of the furnace. Amorphous carbon is inevitably formed in this process. There may also be many structural defects in the film-formed CNTs. After the CNT is wound and pressed into a CNT sheet, a lot of amorphous carbon is embedded into the sheet structure (fig. 4A).

Amorphous carbon and structural defects in the sheet also present some challenges:

1) the physical strength of the film is compromised due to weak adhesion between individual CNTs;

2) CNT loss may occur due to adhesion of CNTs to other surfaces;

3) the surface deposition of polymer or small molecule CNTs is made difficult by the presence of tiny air pockets in the sheet structure;

4) the quality of CNT sheets is difficult to control because amorphous carbon and structural defects easily affect CNT surface properties.

Therefore, it is necessary to purify CNTs by removing amorphous carbon and repairing structural defects in CNTs.

Annealing the CNT sheet at 1000 ℃ or higher for 1 to 8h under an inert atmosphere can effectively remove amorphous carbon from the pristine CNT sheet and result in CNTs with a rather smooth surface (fig. 4B) and possibly improved crystallinity. It is speculated that the annealing process also helps to repair structural defects in the CNTs, so that the CNTs in the CNT sheet become fairly uniform. In some examples, the temperature of the sintering anneal may be between 600 ℃ and 1400 ℃. In some examples, the temperature of the sintering anneal may be between 800 ℃ and 1200 ℃. The time for the sintering annealing can be shortened at a higher temperature and can be prolonged appropriately at a lower temperature.

Based on molecular orbital theory and spectroscopic evidence, there is charge separation in CNT molecules. Greater charge separation corresponds to higher CNT hydrophilicity. One way to increase the charge separation is to increase the energy level of the pi electrons in the CNT molecules. Because of the large number of pi orbitals, the energy gap between the Highest Occupied Molecular Orbital (HOMO) and the Lowest Unoccupied Molecular Orbital (LUMO) is relatively small. Thus, thermal treatment of CNT molecules results in the transition of pi electrons from the HOMO to the LUMO. As higher energy levels of LUMO have more nodes, more pi electrons in LUMO correspond to greater charge separation in CNT molecules. Thus, the purified CNT sheet has a high hydrophilicity after annealing under an inert atmosphere and can be used for water filtration at a large flux rate. However, such CNT sheets are easily broken under high shear or pressure. When such sheets are pressed against a hard surface, such as teflon, loss of CNTs is often observed.

When the CNT sheet is thinner than 50 μm, the physical method of densifying the CNT sheet is not effective. The loss of CNTs is also a problem because CNTs adhere when pressed to a flat surface. The length of the CNTs in the CNT sheet also varies, which may have a significant effect on the interactions between CNTs. When the adhesion between CNTs is not strong enough, the loss of CNTs during processing becomes more severe. There is a need for molecular methods to produce CNT flakes that are physically robust without the use of polymeric binders and mechanical bonding.

With the removal of surface amorphous carbon and the increased charge separation resulting from high temperature processing, the annealed CNT molecules have a strong attraction to polar molecules (e.g. water). A perfect CNT molecule does not have any surface functional groups that interact with water molecules. It is anticipated that as more water molecules get closer to the CNT surface, hydrogen bonding between them will result in the formation of an ordered water layer, thereby forming gaps between the ordered water layer and the CNT surface. When the CNT charge separation is higher, the gaps are most likely smaller and the water layer is thicker and more ordered. Thus, the heat-treated CNT flakes exhibit a high degree of hydrophilicity. Over time and with dissipation of energy, the degree of charge separation decreases and the attraction between the CNTs and the water layer decreases. Thus, the water layer becomes irregular and moves away from the CNT surface, increasing the gap size. The CNT surface appears more hydrophobic as water molecules move away from the CNT surface.

The charge separation enhancement by means of high temperature treatment alone is not sufficient to densify the CNTs enough. Other highly polar molecules (e.g., molecules more polar than water) that are used to form an ordered layer "wrap" around the surface of the CNT can further enhance charge separation in the CNT. Thus, treating the annealed CNT sheet with a protonic acid, including H2SO4 or H3PO4, may make it appear more hydrophilic. Treating the carbon nanotube sheet with a protonic acid at elevated temperatures can reduce the effective treatment time. In some cases, the treatment time may be 30 minutes. However, the increase in charge separation achieved during concentrated or phosphoric acid treatment is not sufficient to densify CNTs into durable CNT flakes, probably due to the buffering capacity from the ordered aqueous layer adjacent to the CNT surface.

Chlorosulfonic acid is highly hygroscopic and polar. When the CNT sheet is treated with chlorosulfonic acid, the water layer is gradually thinned and removed, and the formation of a chlorosulfonic acid layer around the surface of each CNT greatly enhances charge separation in the CNT. Since chlorosulfonic acid is slowly removed upon heating, the individual CNTs become more closely located due to increased attraction. Thus, the CNTs densify to form a durable and robust CNT sheet. Unlike dark pristine CNT sheets, the dense CNT sheets appear silver gray. SEM images showed that the pore size in the dense CNT sheet was reduced to 100 nm or less, and the binding was uniform (fig. 5). SEM photographs showed that the densified carbon nanotube film had a pore size of 10 nm or less and the nanotubes were uniformly bundled (fig. 6). Extensive conjugation between dense CNTs further stabilizes charge separation across the CNT sheet. Extensive charge separation may be responsible for the metallic luster of the dense CNT sheet.

The dense CNT board has a tensile strength of 300 to 450 MPa (the tensile strength of the pristine CNT board is 60 to 120 MPa) compared to a pristine CNT board having the same areal density (FIG. 7). Tensile strength and other properties can be related to many factors, such as the original carbon nanotube mass, individual carbon nanotube diameters (from about 2 nm to about 50 nm), nanotube diameter size distribution, amount of amorphous carbon content, and areal density (from about 2 g/m2 to 25 g/m 2). In some cases, the original carbon nanotube film sheet may lose about 30% of its weight after being subjected to a high temperature annealing process.

The dense CNT sheet is also thinner (< 5 μm vs. -20 μm) and the conductivity is higher, the conductivity reaching 5x 105S/m to 1 x 106S/m (from about 5x 104S/m). Rsq < 0.5 Ω in the pristine CNT sheet, and has an enhanced EMI shielding effect (55 dB vs. 40 dB in the pristine CNT sheet) in the X-band (8 GHz to 12.5 GHz).

The long-term stability of the shielding effect is critical to ensure proper operation of the electronic device, especially in harsh external environments, such as long-term high temperature and high humidity and strong acid and base environments. The EMI shielding effect of the densified carbon nanotube film was substantially unchanged after 30 days of storage under high temperature (85 oC) and high humidity (85% relative humidity) (Figure 10A), indicating that the stability of the densified carbon nanotube film is far better than that of metal alkylenes (MXene) EMI shielding materials. The EMI shielding effect of the densified carbon nanotube film was also unchanged (Figure 10B) by soaking in sulfuric acid (pH = 0) and aqueous sodium hydroxide (pH = 14), respectively, for one month, indicating that the densified carbon nanotube film had very good corrosion resistance. These excellent characteristics are not achieved by the conventional metallic materials in combination. Therefore, the densified carbon nanotube film does not contain a high-molecular adhesive, is used as an EMI shielding material, and has breakthrough significance in the fields of wearable intelligent electronic products and 5G communication equipment.

The dense CNT sheet is hydrophilic and can be used as a water filtration membrane. According to the thickness and the pore diameter of the sheet, the flux rate can reach 451L/(m 2. h) at 0.1 MPa, 1068.4L/(m 2. h) at 0.2 MPa, 2693.8L/(m 2. h) at 0.3 MPa and 2863.7L/(m 2. h) at 0.4 MPa. The dense CNT sheets with smaller pores have a retention of more than 50% when used to filter Bovine Serum Albumin (BSA) solution (1 g/L), indicating that they are very effective in removing contaminants from water.

The dense CNT sheet has excellent bare film permeability for various gases, for example, 293,000 GPU for N2, 269,000 GPU for O2, and 672,000 GPU for He. Bare membrane selectivity indicates that the knoop flow passes through the membrane. Thus, dense CNT sheets can be used to remove particulates from air and other gases.

Examples

A sheet of crude CNT from the FCCVD process (13.09 mg, areal density of about 6 g/m2, size 5 cm x 5 cm) was heated in a tube furnace at 1000 ℃ for 4 hours under an inert atmosphere (2% H298% N2). Cooled to room temperature under an inert atmosphere and then weighed (10.61 mg, 19% weight loss). The CNT sheet was stored in air for about 3 weeks, then placed in an erlenmeyer flask and treated with a drop of concentrated sulfuric acid (21.3 mg, 11.6 μ L) by a pipette tip. The flask was capped with a stopper and placed on a hot plate at 110 ℃ for 24 hours. The CNT sheet was cooled to room temperature and rinsed with deionized water (DI), then dried in air for 3 days, and then weighed (10.43 mg). The dried CNT sheet was placed in an erlenmeyer flask and treated with chlorosulfonic acid (62.58 mg, 35.7 μ L) by a pipette tip. The flask was stoppered and held at room temperature for 1 hour, then heated at 110 ℃ for 96 hours. After cooling to room temperature, the CNT sheet was rinsed with deionized water and dried in air (11.76 mg). The flakes appeared soft with a silvery luster. When pressed against the polyethylene surface and the PTFE surface, no loss of CNTs was seen, indicating densification of the CNTs in the sheet.

A sheet of crude CNT from the FCCVD process (11.01 mg, areal density of about 6 g/m2, size 5 cm x 5 cm) was heated in a tube furnace at 1000 ℃ for 4 hours under an inert atmosphere (2% H298% N2), cooled to room temperature under an inert atmosphere and weighed (7.96 mg, 27.7% weight loss). Immediately, the CNT sheet was placed in a conical flask and treated with concentrated sulfuric acid (16.0 mg, 8.8 μ L) by a pipette tip. The flask was capped with a stopper and placed on a hot plate at 110 ℃ for 24 hours. The CNT sheet was cooled to room temperature, rinsed with deionized water, and dried in air for 3 days, and then weighed (8.13 mg). The dried CNT sheet was placed in a conical flask and treated with chlorosulfonic acid (96.24 mg, 55 μ L) by a pipette tip. The flask was stoppered and held at room temperature for 1 hour, then heated at 110 ℃ for 96 hours. After cooling to room temperature, the CNT sheet was rinsed with deionized water and dried in air (8.97 mg). The sheet appeared soft and metallic. When pressed against polyethylene and PTFE surfaces, no loss of CNTs was seen, indicating densification of CNTs in the sheet.

A sheet of crude CNT from the FCCVD process (12.03 mg, areal density of about 6 g/m2, size 5 cm x 5 cm) was heated in a tube furnace at 1000 ℃ for 4 hours under an inert atmosphere (2% H298% N2), cooled to room temperature under an inert atmosphere and weighed (8.26 mg, 31.3% weight loss). The CNT sheet was immediately placed on a Teflon bulk substrate and treated with solid SO3 NEt3 complex (12.15 mg). The solid complex is dispersed on the CNT sheet. Subsequently, the CNT sheet on the teflon block was placed in a vacuum oven at 100 ℃ for 24 hours. The CNT sheet was cooled to room temperature and rinsed with deionized water (5 ×) and dried in air for 3 days, then weighed (8.35 mg). Dried CNT pellets were placed in Erlenmyer flasks and treated with chlorosulfonic acid (100.2 mg, 57.2 μ L) by pipette tips. The flask was stoppered and held at room temperature for 1 hour, then heated at 110 ℃ for 96 hours. After cooling to room temperature, the CNT sheet was rinsed with deionized water and dried in air (9.16 mg). The flakes appeared soft with a metallic luster. When pressed against polyethylene and PTFE surfaces, no loss of CNTs was seen, indicating densification of CNTs in the sheet.

The densified carbon nanotube film has surface contamination resistance and is very effective for filtering water. Thus, water filters made from densified carbon nanotube membranes are suitable for use in biopharmaceutical applications, including fermentation processes. The membrane can also be used as an inner shell, a septum and an outer shell of a reaction vessel or device. The densified carbon nanotube membrane can also be used for the ultrapure water preparation process in the biopharmaceutical industry.

Claims

1. A preparation process is used for producing a purified carbon nanotube film and comprises the following steps:

placing the carbon nanotube membrane in an inert atmosphere;

heating the carbon nanotube film and cooling the carbon nanotube film to room temperature.

2. The process of claim 1, wherein the elevated temperature is about 800 to 1200 degrees celsius.

3. The process of claim 1, wherein the inert atmosphere comprises 1 to 5% hydrogen.

4. A process for densifying carbon nanotubes in a carbon nanotube membrane, comprising the steps of:

contacting the carbon nanotube membrane with a solution comprising a protic acid;

washing the membrane with a volume of protic solvent; the protic solvent is then removed.

5. A process for densifying carbon nanotubes in a carbon nanotube membrane, comprising:

mixing solid SO₃NEt₃Melting the composite compound on the carbon nanotube film;

washing the membrane with a volume of protic solvent;

the protic solvent is then removed.

6. A process according to any one of claims 1 to 5, further comprising contacting the carbon nanotube film with HClSO₃And (4) contacting.

7. A densified carbon nanotube membrane produced by the process of any one of claims 1-5.

8. A method for shielding electromagnetic radiation comprising covering an article in need of shielding with the densified carbon nanotube film of claim 7.

9. A method of filtering a fluid comprising passing the liquid through the densified carbon nanotube membrane of claim 7.

10. The method of filtering a fluid of claim 9, the fluid being water.

11. The method of filtering a fluid of claim 9, the fluid being a gas.

12. A method of protecting a surface of an article from corrosion comprising covering the surface of the article with the densified carbon nanotube film of claim 7 and contacting the surface with a corrosive substance.

13. The method of protecting a surface of an article from corrosion according to claim 12, the corrosive substance being a protic acid or an alkaline solution.

14. A method for protecting a surface of an object from fouling comprising covering the surface of the object with a densified carbon nanotube film of claim 7 and contacting the surface with a fouling material.

15. A method of protecting a surface of an object from fouling in accordance with claim 14, the fouling material being a fermentation or biological fluid.

16. A method of protecting a surface of an object from fouling in accordance with claim 14, the fouling material being a fluid in a heat exchanger.