CN110694633B

CN110694633B - CVD preparation method of single-walled carbon nanotube

Info

Publication number: CN110694633B
Application number: CN201911006484.XA
Authority: CN
Inventors: 刘磊; 于树磊; 李杭; 李锐杰; 王恩哥
Original assignee: Peking University
Current assignee: Peking University
Priority date: 2019-10-22
Filing date: 2019-10-22
Publication date: 2021-07-23
Anticipated expiration: 2039-10-22
Also published as: CN110694633A

Abstract

A Fe-Mo/MgO catalyst and its preparing process and the single-wall carbon nanotube CVD preparing process are disclosed, which features that the formula of Fe-Mo bimetal catalyst based on MgO load is optimized to greatly reduce the content of Mg element in catalyst and lower the cost of preparing catalyst, and the CH in the CVD growth of carbon nanotube is used₄、H₂And the optimal combination of inert gas flux is explored, and the macro-quantitative preparation of the single-walled carbon nanotubes (SWNTs) is realized.

Description

CVD preparation method of single-walled carbon nanotube

Technical Field

The invention belongs to the technical field of material physics, particularly relates to a CVD preparation method of a single-walled carbon nanotube, and particularly relates to a method for massively preparing the single-walled carbon nanotube by a CVD method by using a Fe-Mo/MgO catalyst.

Background

The carbon nano tube has very wide application prospect in the fields of composite materials, electrochemical electrode materials, flexible electrode materials, field emission devices, nano electronic devices and the like due to excellent properties such as very high Young modulus and tensile strength, high thermal conductivity, high electron mobility, regular pore structure in the tube, huge specific surface area and the like. The demand of the industry for high quality, high purity carbon nanotubes has steadily increased. Among them, since the carbon nanotube has a typical one-dimensional tubular structure and has both semiconductivity and metallicity, and since sp²The hybridized C-C single bond has an electron movement speed of 1/300 light speed and up to 20000cm²The electron mobility of the electrode material is more remarkable when the single-walled carbon nanotubes (SWNTs) are used as the electrode material. Therefore, how to effectively realize the macro preparation of the single-walled carbon nanotube has important significance for the large-scale application of the single-walled carbon nanotube.

At present, the methods for growing single-walled carbon nanotubes mainly include arc discharge, laser evaporation catalytic deposition (CVD), and Chemical Vapor Deposition (CVD). The first two methods are quite complex to operate, and they require the evaporation of a solid carbon source into carbon atoms at a high temperature of more than 3000 ℃, which severely limits the number of carbon nanotubes that can be synthesized; in addition, the carbon nanotubes grown by evaporating carbon atoms are highly entangled and mixed with other carbon impurities and metal catalysts, so that the application range is severely limited. However, the Chemical Vapor Deposition (CVD) method for preparing carbon nanotubes has very significant advantages. The CVD preparation SWNTs equipment is simple and has good maneuverability, the CVD preparation SWNTs is generally carried out under normal pressure, the growth temperature of the SWNTs is low, the use requirement on instruments and equipment is lower, the process flow is simple, the growth can be effectively controlled, and the method is beneficial to industrial application. Nevertheless, the CVD method for mass production of SWNTs still has serious problems, such as very low yield of SWNTs, very high cost for catalyst preparation, etc. Therefore, the technical scheme of the conventional CVD method for massively preparing the SWNTs still has very wide progress space, and further optimization is still needed.

The CVD growth of the carbon nano tube by adopting the Fe-Mo bimetallic catalyst based on MgO load is taken as a research object, and the obvious defects existing in the preparation of the single-walled carbon nano tube by the current CVD method are summarized as follows: the CVD growth product of carbon nanotubes has very low SWNTs yield, and there are a large number of bamboo-like, bulky multi-walled carbon nanotubes (MWNTs). In addition, the surface of the SWNTs prepared by the existing CVD method is often covered with a certain amount of amorphous carbon, so that the separation and purification process of the SWNTs product is more complicated. Meanwhile, the preparation cost of the catalyst adopted in the current technical scheme of the CVD growth of the carbon nano tube is generally very high, and the preparation process of the catalyst is complex. These factors greatly limit the macro-quantitative preparation of SWNTs.

Compared with the existing CVD preparation method, the invention reduces the Mg content in the catalyst and optimizes the carbon-containing gas (CH) by optimizing the formula of the catalyst₄) And hydrogen (H)₂) And inert gas flux, the macro-quantitative preparation of the carbon nano tube can be realized, the carbon yield in the growth product is close to 2 times, and more importantly, the proportion of the single-walled carbon nano tubeIs very considerable. In the research of the invention, the formula of the Fe-Mo bimetallic catalyst (abbreviated as Fe-Mo/MgO) based on MgO load is optimized, so that the high yield of SWNTs in the CVD growth product is realized on the premise of greatly reducing the content of Mg element in the catalyst. The catalyst formula not only reduces the preparation cost of the catalyst, but also realizes the purpose of improving the yield of SWNTs in CVD growth products. While in the present invention by CVD growth of carbon nanotubes₄、H₂And inert gas flux, and summing up the optimal technical scheme in the CVD growth process of the carbon nano tube by adopting the catalyst for reducing the content of Mg element, thereby realizing the macro-quantitative preparation of the SWNTs.

Disclosure of Invention

The invention aims to provide a method for industrially and massively preparing high-quality single-walled carbon nanotubes.

In order to achieve the purpose, the invention adopts the technical scheme that:

a preparation method of Fe-Mo/MgO catalyst is characterized by comprising the following steps:

s1, preparing ferric nitrate nonahydrate, anhydrous magnesium acetate, ammonium molybdate tetrahydrate, citric acid and ammonium nitrate;

s2, determining the mass of each compound raw material according to the metal atom molar ratio of Mo, Fe and Mg in the catalyst formula, and weighing the compound raw materials on a molecular weight;

s3, preparing the weighed compound into a uniform aqueous solution;

s4, heating the solution until the solution is boiled and becomes yellow loose solid;

s5, primary grinding and roasting;

and S6, further grinding after finishing the roasting to obtain light yellow powder, namely the required catalyst.

Preferably, in step S2, the ratio of each compound raw material is further required to satisfy the mass ratio of metal catalyst component/redox agent of 1.4 to 1.5.

Preferably, in step S3, the weighed compound is poured into a beaker and dissolved with deionized water, and then ultrasonic treatment is performed for 10min to 20min to completely dissolve the solute, so as to prepare a uniform aqueous solution.

Preferably, in step S4, the solution is heated in an electric furnace for 20-30 min until it is boiled to become a yellow loose solid.

Preferably, in step S5, the yellow loose solid is primarily ground and then placed in a tube furnace to be baked at 600 to 700 ℃ for 300 to 360 min.

A CVD preparation method of single-walled carbon nanotubes is characterized by comprising the following steps:

s21, preparing the Fe-Mo/MgO catalyst by the preparation method of any one of claims 1-5, and placing the catalyst on a baking device;

s22, before the growth starts, vacuumizing a pipeline of the CVD growth system, and flushing the pipeline with inert gas until the pipeline is in an atmospheric pressure state;

s23, heating the baking device to 800-850 ℃, and simultaneously using H₂Reducing the catalyst;

s24, placing the reduced catalyst powder sample in CH₄Heating and growing at 800-850 ℃ in the atmosphere to obtain a black powder sample, namely a single-walled carbon nanotube product mixed with a catalyst;

and S25, purifying the single-walled carbon nanotube product.

Preferably, in step S22, the vacuum pump is operated for 5min to 15min to vacuumize, the pressure in the pipeline is stabilized at 0.1Pa to 5.0Pa, then the vacuum pump is closed, and the pipeline is flushed with inert gas until the pressure is in the atmospheric pressure state.

Preferably, in step S23, the temperature of the hearth of the tube furnace is raised to 800-850 ℃ within 40-50 min, and reducing gas H is introduced into the growth system within 7-10 min of the last temperature raising process₂。

Preferably, in step S23, the inert gas flux is adjusted to 200sccm to 500sccm before the start of the temperature raising stage of the tube furnace so that the system is in a stable state at the start of the growth process.

Preferably, in step S24, the heating growth time is 20min to 25 min.

Preferably, in step S24, CH₄The flux is 200sccm to 230 sccm.

Preferably, in step S24, the inert gas is used as the carrier gas, and the inert gas flux is 500sccm to 750 sccm.

Preferably, the baking apparatus is a CVD tube furnace.

Preferably, in step S24, the CH₄Atmosphere is high-purity CH₄Inert gas, H₂A mixture of (a).

Preferably, in step S23, the temperature rise rate in the temperature rise process is about 18.5 ℃/min to 19.5 ℃/min.

Preferably, in step S23, H₂The atmosphere time is 7 min-10 min.

Preferably, in step S23, H₂Atmosphere H₂The flux is in direct proportion to the feeding amount of the catalyst.

Preferably, in step S24, the CH₄The air intake rate of (2) is 12L/h to 13.8L/h.

Preferably, the growth temperature is 800-850 ℃, and the growth time is 20-25 min.

The beneficial effects of the invention are as follows: the novel formula of the catalyst for reducing the content of Mg element obviously improves the yield of SWNTs in the CVD growth product of the carbon nano tube, and simultaneously realizes the simplification of the production process and the great reduction of the production cost. The link of preparing the catalyst does not relate to high-temperature reaction, the experimental method is simple, the operation flow is easy, the large-scale production in a factory can be realized, and the industrial macro preparation of the single-walled carbon nanotube is realized. The improved chemical vapor deposition method in the technical scheme only needs low high-purity CH₄Gas flux as carbon source, small amount of H₂The conversion of the catalyst to the final product can be achieved as a reducing agent. By applying CH to the carbon source gas at different stages in the CVD growth process of carbon nanotubes₄Reducing gas H₂And the gas flux of the inert gas carrier gas is accurately regulated, and the high-quality, high-purification and macro-preparation of the SWNTs are realized by different combinations of the gas fluxes of the three gases at different growth stages. In view of the above, it is desirable to provide,the technical scheme of the invention can ensure the yield of SWNTs and the growth quality of the SWNTs, accurately control the production cost and has no pollution to the environment.

In addition, in the growth product obtained by the carbon nano tube CVD growth experiment according to the technical scheme shown by the invention, a large amount of SWNTs exist, the content of coarse MWNTs is greatly reduced, and the appearance is flexible. According to the characterization results obtained by a plurality of characterization means, the tube bundle diameter of the SWNTs product is 10 nm-20 nm.

The invention has the advantages that:

1. the invention relates to a method for massively preparing a single-walled carbon nanotube by a CVD method by using a Fe-Mo/MgO catalyst;

2. the catalyst prepared by the method greatly reduces the content of Mg element, accurately controls and reduces the production cost in the preparation process of the catalyst.

3. The technical scheme provided by the invention is simple and effective, and the yield of SWNTs in the CVD growth product can be greatly improved by accurately controlling the gas flux on the basis of improving the formula of the catalyst.

4. The technical scheme provided by the invention has strong operability, can be used for large-scale production in a factory, and realizes the industrial macro preparation of the single-walled carbon nanotube.

5. The yield of carbon in the growth product obtained by the CVD method is close to 2 times, and the purity of the single-walled carbon nanotube is very considerable.

Drawings

FIG. 1 is a flow diagram of catalyst preparation;

FIG. 2 is a schematic diagram of a single-walled carbon nanotube preparation system;

FIG. 3 is an SEM image of the catalyst from run one of example 1;

FIG. 4 is an SEM image of the catalyst from run two of example 1;

FIG. 5 is an SEM image of CVD-grown single-walled carbon nanotubes of experiment one of example 2;

FIG. 6 is an SEM image of CVD-grown single-walled carbon nanotubes of experiment two of example 2;

FIG. 7 is an SEM image of CVD-grown single-walled carbon nanotubes of experiment three of example 2;

figure 8 is an SEM image of CVD grown single-walled carbon nanotubes from experiment four of example 2.

Detailed Description

The invention is described in further detail below with reference to specific examples, which are commercially available from the open literature unless otherwise specified.

As shown in fig. 1: the preparation of the metal active catalyst involves four steps: preparing a mixed solution, synthesizing by low-temperature combustion, sintering and grinding powder. As shown in fig. 2: the preparation system of the single-walled carbon nanotube comprises hydrogen (H) which is communicated in sequence₂) Gas source 10, methane (CH)₄) The gas source 20 and the inert gas source 30 are connected with the gas inlet end of the tube furnace through a gas mass flow meter, and the vacuum mechanical pump 40 and the exhaust port 50 are communicated with the gas outlet end.

Example 1: a preparation method of a novel Fe-Mo/MgO series catalyst comprises the following steps:

firstly, preparing ferric nitrate nonahydrate, anhydrous magnesium acetate, ammonium molybdate tetrahydrate, citric acid and ammonium nitrate;

(II) determining the mass of each compound raw material according to the metal atom mole ratio of Mo, Fe and Mg in the catalyst formula and the mass of the metal catalyst component/the mass of the redox agent being 1.4-1.5, respectively weighing the compound raw materials on a molecular weight by using weighing paper, wherein the medicine formula is shown in Table 1;

TABLE 1 medicine proportioning table (molar ratio of components)

The component ratio of each catalyst, wherein CA represents citric acid (C)₆H₈O₇) In units of grams; NN stands for ammonium nitrate in grams. The ratio between the metal atoms is a molar ratio.

Pouring the weighed compound particles into a beaker, dissolving the compound particles by using deionized water, and then carrying out ultrasonic treatment for 10-20 min to completely dissolve solute to prepare a uniform aqueous solution;

heating the solution by an electric furnace for 20-30 min until the solution is boiled to become yellow loose solid;

fifthly, after primary grinding, putting the mixture into a tube furnace, and roasting the mixture for 300-360 min at the temperature of 600-700 ℃;

sixthly, further grinding the roasted product to obtain light yellow powder which is the needed catalyst;

the catalyst obtained in this example was a pale yellow powder and was characterized by Scanning Electron Microscopy (SEM) as shown in figure 4.

Test one: the preparation of the Fe-Mo/MgO catalyst by using the novel catalyst formula in the test is carried out according to the following steps:

firstly, putting five compounds of ferric nitrate nonahydrate, anhydrous magnesium acetate, ammonium molybdate tetrahydrate, citric acid and ammonium nitrate on a laboratory bench in a certain sequence;

0.7500g of citric acid, 0.2500g of ammonium nitrate, 0.0129g of ammonium molybdate tetrahydrate, 0.2949g of ferric nitrate and 1.1566g of anhydrous magnesium acetate are weighed on a molecular weight scale by using weighing paper;

and (III) pouring the weighed compound particles into a beaker, adding 50ml of deionized water for dissolving, and carrying out ultrasonic treatment for 10min to completely dissolve the solute, wherein the solution is light yellow.

And (IV) heating the solution for 30min by using an electric furnace, and boiling the solution to form yellow loose solid.

And fifthly, primarily grinding the obtained solid, and then putting the solid into a tube furnace to be roasted for 350min at the constant temperature of 600 ℃.

And (VI) after the roasting is finished, further grinding the obtained yellow solid by using an agate mortar to obtain light yellow powder, namely the required catalyst.

And (2) test II: the preparation of the Fe-Mo/MgO catalyst by using the novel catalyst formula in the test is carried out according to the following steps:

firstly, preparing five compounds of ferric nitrate nonahydrate, anhydrous magnesium acetate, ammonium molybdate tetrahydrate, citric acid and ammonium nitrate, and sequentially placing the five compounds on a laboratory table;

3.7776g of citric acid, 1.2592g of ammonium nitrate, 0.0260g of ammonium molybdate tetrahydrate, 0.5898g of ferric nitrate and 6.9394g of anhydrous magnesium acetate are weighed on a molecular weight scale by using weighing paper;

and (III) pouring the weighed compound particles into a beaker, adding 100ml of deionized water for dissolving, and carrying out ultrasonic treatment for 20min to completely dissolve the solute, wherein the solution is light yellow.

And (IV) heating the solution for 25min by using an electric furnace, and boiling the solution to form yellow loose solid.

And fifthly, primarily grinding the obtained solid, and then putting the solid into a tube furnace to be roasted for 300min at the constant temperature of 650 ℃.

As shown in fig. 4, it can be seen from the above-mentioned methods of the first to second tests that the catalyst powder prepared by the present embodiment exhibits very fine granular shapes.

Example 2: a technical scheme for growing high-purity SWNTs by a CVD method based on a novel Fe-Mo/MgO series catalyst comprises the following steps:

preparing an aqueous solution by using five compounds of ferric nitrate nonahydrate, anhydrous magnesium acetate, ammonium molybdate tetrahydrate, citric acid and ammonium nitrate as solutes, and preparing catalyst powder by a wet chemistry and self-propagating high-temperature synthesis method.

And (II) before the growth begins, vacuumizing a pipeline of the CVD growth system by using a vacuum pump (a mechanical vacuum pump or a molecular pump), and stabilizing the pressure in the pipeline to be 0.1-5.0 Pa by operating the vacuum pump for 5-15 min. Then the vacuum pump is closed, and the pipeline is flushed by inert gas until the state of atmospheric pressure is reached;

and thirdly, adjusting the flux of the inert gas to 200 sccm-500 sccm before the temperature rise stage of the tubular furnace is started, so that the system is in a stable state when the growth process is started.

(IV) starting the tube furnace to raise the temperature to the growth temperature, and simultaneously using H₂The catalyst is reduced. Said H₂The flux is proportional to the amount of catalyst charged, as shown in table 2. The temperature of the hearth of the tubular furnace is increased to 800-850 ℃ in 40-50 min, and the temperature is increased in the process of temperature increaseFinally, introducing reducing gas H into the growth system for 8-10 min₂. In the process, the iron oxide and the molybdenum oxide are all coated with H₂Reducing the solution into simple substance. Wherein a portion of the molybdenum in contact with the iron forms an iron-molybdenum alloy with the iron, but a majority of the molybdenum remains in the elemental phase around the iron-molybdenum alloy particles.

TABLE 2

H₂Empirical formula between throughput and catalyst inventory:

wherein:

q represents H₂Flux, in sccm;

m represents the catalyst charge in g.

(V) placing the reduced catalyst powder sample in CH₄Heating and growing at 800-850 deg.c for 20-25 min in atmosphere, CH₄The flux is 200 sccm-230 sccm, wherein the inert gas is used as the carrier gas, and the inert gas flux is 500 sccm-750 sccm at this stage. When cracking CH₄During the preparation, carbon is formed on the surface of the iron-molybdenum alloy phase, carbon atoms are dissolved in the alloy phase, then deposition is generated at the interface of the carrier and the iron-molybdenum alloy phase through bulk phase diffusion, the iron-molybdenum alloy particles are jacked up, so that the active metal particles are separated from the MgO carrier, and the cylindrical single-walled carbon nanotubes randomly distributed in the carrier are generated.

And (VI) obtaining a black powder sample after the growth is finished, namely the SWNTs product mixed with the catalyst. Because of the obvious optical contrast between the carbon nano tube and the residual catalyst, the appearance of the single-walled carbon nano tube can be clearly seen through the direct observation of a scanning electron microscope.

(VII) if necessary, purifying the SWNTs product.

The single-walled carbon nanotubes obtained in this example were black powders and represented by SEM and the like as shown in fig. 7.

Test one: the macro preparation of single-walled carbon nanotubes by a Chemical Vapor Deposition (CVD) method of this experiment was carried out according to the following steps:

first, 0.2g of the catalyst powder prepared in example 1 was spread in a quartz boat, the quartz boat was placed in the center of a quartz tube of a tube furnace, and an inlet tube and an outlet tube were connected to both ends of the quartz tube, respectively, and the quartz tube was sealed and kept airtight.

Pumping out air in the pipeline by using a mechanical vacuum pump, enabling the system pressure to be kept at 1.8Pa by using the mechanical vacuum pump for 8min, and then flushing the whole pipeline by using high-purity Ar (99.999%);

regulating the Ar flux to 300sccm before the beginning of the temperature rising stage of the tubular furnace, and rising the furnace temperature of the tubular furnace from the room temperature of 20 ℃ to the growth temperature of 850 ℃ within 45 min;

(IV) introducing H of 400sccm into the pipeline after the last 10min of the temperature rise stage of the tubular furnace, namely the tubular furnace works for 35min₂Reducing the catalyst powder;

fifthly, after the furnace temperature reaches 850 ℃, the Ar flux is adjusted to 750sccm, and meanwhile, 210sccm CH is continuously introduced into the pipeline₄The time of the growth stage of the carbon nano tube is 21 min;

(VI) after the growth process is finished, closing CH₄. And after the Ar atmosphere is reduced to a lower temperature, taking out the quartz boat containing the catalyst, and collecting, observing and characterizing the quartz boat.

As shown in fig. 5, a large amount of SWNTs can be seen from the SEM characterization of the growth product obtained after the growth by the present technical scheme, indicating that the SWNTs in the growth product is very high.

And (2) test II: the macro preparation of single-walled carbon nanotubes by a Chemical Vapor Deposition (CVD) method of this experiment was carried out according to the following steps:

(I) 0.02g of the catalyst powder prepared in example 1 was spread in a quartz boat, the quartz boat was placed in the center of a quartz tube of a tube furnace, and an inlet tube and an outlet tube were connected to both ends of the quartz tube, respectively, to keep the tube sealed.

Pumping air in the pipeline by using a molecular pump, keeping the system pressure at 0.4Pa by using the molecular pump within 12min, and then flushing the whole pipeline by using Ar;

regulating the Ar flux to 400sccm before the beginning of the temperature rise stage of the tubular furnace, starting the tubular furnace, raising the temperature of the tubular furnace from 20 ℃ at room temperature to 830 ℃ at the growth temperature, and raising the temperature for 42 min;

(IV) introducing H of 40sccm into the pipeline after the last 10min of the temperature rise stage of the tubular furnace, namely the tubular furnace works for 32min₂Reducing the catalyst powder;

(V) continuously introducing 205sccm CH into the pipeline after the furnace temperature reaches 850 DEG C₄Continuously growing the carbon nano tube for 24min, wherein the flux of Ar serving as carrier gas is 500 sccm;

(VI) after the growth process is finished, closing CH₄. And after the Ar atmosphere is reduced to a lower temperature, taking out the quartz boat containing the catalyst, and collecting the growth product for observation and characterization.

As shown in fig. 6, the growing product obtained after growth by the present solution can be seen by SEM characterization of the very polymorphic bundles of SWNTs, indicating that the proportion of SWNTs in the growing product is very high.

And (3) test III: the macro preparation of single-walled carbon nanotubes by a Chemical Vapor Deposition (CVD) method of this experiment was carried out according to the following steps:

taking 0.1g of the catalyst powder prepared in the example 1, flatly spreading the catalyst powder in a quartz boat, putting the quartz boat in the center of a quartz tube of a tube furnace, and respectively connecting an air inlet pipe and an air outlet pipe to two ends of the quartz tube to ensure that the pipeline is in a sealed state.

Pumping out air in the pipeline by using a mechanical vacuum pump, keeping the system pressure at 4.4Pa within 10min by using the mechanical vacuum pump, and then flushing the whole pipeline by using Ar;

regulating the Ar flux to 500sccm before the beginning of the temperature rise stage of the tubular furnace, starting the tubular furnace, raising the temperature of the tubular furnace from 20 ℃ at room temperature to 840 ℃ at the growth temperature, and raising the temperature for 44 min;

(IV) introducing 200sccm of H into the pipeline after the last 9min of the temperature rise stage of the tubular furnace, namely 35min of the operation of the tubular furnace₂Reducing the catalyst powder;

(V) keeping the furnace temperature at 850 DEG CContinuously introducing CH of 220sccm into the pipeline₄Continuously growing the carbon nano tube for 23min, wherein the flux of Ar serving as carrier gas is 600 sccm;

(VI) after the growth process is finished, closing CH₄. After the Ar atmosphere is reduced to a lower temperature, the quartz boat containing the catalyst is taken out, and the grown product is collected to prepare an SEM sample for observation and characterization.

As shown in fig. 7, it can be seen by SEM characterization that there are a considerable number of bundles of SWNTs in the CVD grown product, indicating that the proportion of SWNTs in the grown product is very high.

And (4) testing: the macro preparation of single-walled carbon nanotubes by a Chemical Vapor Deposition (CVD) method of this experiment was carried out according to the following steps:

(I) 0.2g of the catalyst powder prepared in example 1 was spread in a quartz boat, the quartz boat was placed in the center of a quartz tube of a tube furnace, and an inlet tube and an outlet tube were connected to both ends of the quartz tube, respectively, to keep the tube sealed.

Pumping air in the pipeline by using a molecular pump, keeping the system pressure at 1.6Pa by using the molecular pump within 8min, and then flushing the whole pipeline by using Ar;

regulating the Ar flux to 360sccm before the beginning of the temperature rise stage of the tubular furnace, starting the tubular furnace, raising the temperature of the tubular furnace from the room temperature of 20 ℃ to the growth temperature of 820 ℃, and raising the temperature for 43 min;

(IV) introducing H of 400sccm into the pipeline after the last 8min of the temperature rise stage of the tubular furnace, namely the tubular furnace works for 35min₂Continuously maintaining for 8min, and reducing the catalyst powder;

(V) continuously introducing 230sccm CH into the pipeline after the furnace temperature reaches 850 DEG C₄Continuously growing the carbon nano tube for 20min, wherein the flux of Ar serving as carrier gas is 700 sccm;

As shown in fig. 8, under SEM, we can see that the tube bundles of SWNTs in the grown product obtained after growth by the present technical solution occupy a very high proportion, and the coarse MWNTs in the grown product are very few, indicating that the SWNTs growth effect achieved by the technical solution is very good.

Claims

1. A CVD preparation method of single-walled carbon nanotubes is characterized by comprising the following steps:

the preparation of the Fe-Mo/MgO catalyst comprises the following steps:

s2, determining the mass of each compound raw material according to the metal atom molar ratio of Mo, Fe and Mg in the catalyst formula of 0.1:1:33.3, and weighing the compound raw materials respectively;

s3, preparing the weighed compound into a uniform aqueous solution;

s5, primary grinding and roasting;

s6, further grinding after roasting to obtain light yellow powder, namely the required catalyst;

in step S2, the mixture ratio of each compound raw material is also required to satisfy the condition that the mass ratio of the metal catalyst component/the mass ratio of the redox agent is 1.4-1.5;

the preparation of single-walled carbon nanotubes using the prepared Fe-Mo/MgO-based catalyst comprises the steps of:

s21, placing the prepared Fe-Mo/MgO catalyst on a baking device;

s22, before the growth starts, vacuumizing a pipeline of the CVD growth system, and then flushing the pipeline with inert gas until the pipeline is in an atmospheric pressure state, wherein the method specifically comprises the following steps: vacuumizing for 5-15 min by using a vacuum pump, stabilizing the pressure in the pipeline to 0.1-5.0 Pa, then closing the vacuum pump, and flushing the pipeline by using inert gas until the pipeline is in an atmospheric pressure state;

s23, heating the baking device to 800-850 ℃, and simultaneously using H₂The reduction catalyst specifically comprises: the temperature of the hearth of the tubular furnace is raised to 800-850 ℃ within 40-50 min, and the reducibility is introduced into the growth system within 7-10 min of the last temperature raising processGas H₂；H₂The flux and the catalyst feeding amount satisfy the formula:

wherein: q represents H₂Flux, in sccm; m represents the feeding amount of the catalyst and the unit is g;

and S25, purifying the single-walled carbon nanotube product.

2. The method as claimed in claim 1, wherein the inert gas flux is adjusted to 200sccm to 500sccm before the start of the temperature-raising stage of the tube furnace so that the system is in a stable state at the start of the growth process in step S23.

3. The method according to claim 1, wherein the heating growth time in step S24 is 20-25 min.

4. The method of claim 1, wherein in step S24, CH₄The flux is 200sccm to 230 sccm.

5. The method of claim 1, wherein the baking apparatus is a CVD tube furnace.

6. The method according to claim 1, wherein in step S24, the CH₄Atmosphere is high-purity CH₄Inert gas, H₂A mixture of (a).

7. The method according to claim 1, wherein in step S23, the temperature rise rate of the temperature rise process is 18.5 ℃/min to 19.5 ℃/min.

8. The method according to claim 1, wherein in step S24, the CH₄The air intake rate of (2) is 12L/h to 13.8L/h.

9. The method of claim 1, wherein in step S3, the weighed compound is poured into a beaker and dissolved in deionized water, and then ultrasonic treatment is performed for 10min to 20min to completely dissolve the solute, thereby preparing a uniform aqueous solution.

10. The method of claim 1, wherein in step S4, the solution is heated in an electric furnace for 20-30 min until boiling to become a yellow loose solid.

11. The method according to claim 1, wherein in step S5, the yellow loose solid is primarily ground and then placed in a tube furnace and calcined at 600-700 ℃ for 300-360 min.