A method for preparing single-walled carbon nanotubes by a plasma-assisted chemical vapor deposition method
By introducing plasma technology and ferric sulfate compound into chemical vapor deposition, the crystallization and polymerization of carbon atoms are promoted, solving the problems of high preparation cost and difficulty in mass production, and realizing the low-cost large-scale production of high-quality single-walled carbon nanotubes.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- 厦门华碳科技有限公司
- Filing Date
- 2024-03-20
- Publication Date
- 2026-06-26
Smart Images
Figure CN118289746B_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of nanomaterial preparation technology, and in particular to a method for preparing single-walled carbon nanotubes by plasma-assisted chemical vapor deposition. Background Technology
[0002] Single-walled carbon nanotubes (SUVs) can be viewed as a coiled structure of monolayer graphite, with an all-carbon covalent bond structure. They exhibit low surface defects and high crystallinity, demonstrating superior comprehensive properties, including ultra-high mechanical strength, excellent electrical conductivity, and high thermal conductivity. Therefore, SUVs show great market competitiveness in fields such as electrochemical catalytic energy storage, catalysis, composite materials, and functional coatings. Currently, the main methods for preparing SUVs include: arc burning, laser methods, chemical vapor deposition, and plasma methods.
[0003] Chemical vapor deposition (CVD) is a commonly used method for preparing carbon nanomaterials. It involves introducing one or more precursors of the desired material into a reaction chamber under gaseous conditions, where a chemical reaction occurs under appropriate temperature, pressure, and atmosphere, ultimately depositing the desired thin film material onto a substrate surface. This method converts the carbon source gas into carbon nanotubes under suitable reaction conditions. During CVD, a metal catalyst is typically used, deposited on the substrate to form a catalyst particle. Then, the carbon source gas is introduced into the reaction chamber and decomposed at high temperature. The decomposition products are adsorbed by the catalyst and rearranged on the surface, forming single-walled carbon nanotubes. Plasma ionization (PLA), by controlling reaction conditions and catalyst selection, can prepare high-purity single-walled carbon nanotubes and reduce the presence of impurities. Furthermore, PLA offers good controllability; the morphology, size, and structural properties of single-walled carbon nanotubes can be controlled by parameters such as plasma density, gas composition, and reaction temperature. In addition, PLA has a higher yield compared to other methods, producing more products in the same time frame. Compared to other methods, plasma-assisted chemical vapor deposition (PVD) offers advantages in several aspects, including enhanced catalyst activity, improved carbon nanotube quality, and control over carbon nanotube size and morphology. The presence of plasma can enhance catalyst activity, promote the decomposition of carbon source gas and the growth of carbon nanotubes, thereby increasing growth rate and yield. However, the high solvent cost of PVD hinders large-scale production. Therefore, to address these issues, we propose a plasma-assisted PVD method for preparing single-walled carbon nanotubes. This method saves on solvent costs, achieves Raman G / D ratios exceeding 120 for the prepared single-walled carbon nanotubes, and enables large-scale production. Summary of the Invention
[0004] In view of this, the purpose of this invention is to propose a method for preparing single-walled carbon nanotubes by plasma-assisted chemical vapor deposition. The preparation method is simple, can save solvent costs, and can more effectively achieve large-scale mass production, thus effectively solving the technical problems in the background art.
[0005] Technical effects: This invention adds controllable current and voltage plasma to the chemical vapor deposition (CVD) process. The plasma promotes the polymerization and growth of carbon atoms by providing a high energy field and catalytic activation. Furthermore, the invention employs a combination of ferric sulfate and iron-containing inorganic compounds in the CVD process. The addition of sulfur promotes the crystallization and arrangement of carbon atoms. This combination reduces costs while achieving a Raman G / D ratio of over 120 for single-walled carbon nanotubes, thus enabling large-scale mass production.
[0006] The further defined technical solution of the present invention is: a method for preparing single-walled carbon nanotubes by plasma-assisted chemical vapor deposition, comprising the following steps: weighing an inorganic iron compound in proportion and placing it on a carrier, and introducing a gaseous carbon source and an inert gas in a high-temperature environment, and then obtaining single-walled carbon nanotubes under constant current and high-voltage plasma torch conditions; wherein the inorganic iron compound includes ferric sulfate and iron-containing inorganic compounds.
[0007] The beneficial effects of this invention are:
[0008] (1) The present invention provides a method for preparing single-walled carbon nanotubes by plasma-assisted chemical vapor deposition, comprising the following steps: weighing an inorganic iron compound in proportion and placing it on a carrier, and introducing a gaseous carbon source and an inert gas in a high-temperature environment, and then obtaining single-walled carbon nanotubes under the conditions of a constant current and a high-voltage plasma torch; the present invention mainly adds a plasma torch that can control the current and voltage under the conditions of chemical vapor deposition, wherein the plasma torch promotes the polymerization and growth of carbon atoms by providing a high energy field and catalyst activation, thereby helping to form the structure of single-walled carbon nanotubes. The inorganic iron compound includes ferric sulfate and iron-containing inorganic compounds, wherein the addition of sulfur can promote the crystallization and arrangement of carbon atoms, thereby effectively controlling the diameter and morphology of single-walled carbon nanotubes, and thus improving the stability and high-temperature resistance of single-walled carbon nanotubes.
[0009] (2) The inorganic iron compounds in this invention include ferric sulfate and iron-containing inorganic compounds, including ferric chloride, ferric oxide, and ferric nitrate. The molar ratio of ferric sulfate to iron-containing inorganic compounds is 1:0.5-2. Controlling the amount of inorganic iron compounds is beneficial to the reaction between the gaseous carbon source and the inert gas components, promoting the crystallization and arrangement of carbon atoms, thereby effectively controlling the diameter, length, and morphology of single-walled carbon nanotubes. This invention effectively reduces production costs by using ferric sulfate and iron-containing inorganic compounds in a chemical vapor deposition process, while also having a high Raman G / D ratio. Attached Figure Description
[0010] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained from these drawings without creative effort.
[0011] Figure 1 This is a schematic diagram of the apparatus for preparing single-walled carbon nanotubes by plasma-assisted chemical vapor deposition in this invention.
[0012] Figure 2 This is a transmission electron microscope image of the single-walled carbon nanotubes prepared in Example 1 of this invention;
[0013] Figure 3 This is a transmission electron microscope image of the single-walled carbon nanotubes prepared in Example 2 of this invention;
[0014] Figure 4 This is a transmission electron microscope image of the single-walled carbon nanotubes prepared in Example 3 of this invention;
[0015] Figure 5 This is a transmission electron microscope image of the single-walled carbon nanotubes prepared in Comparative Example 1 in this invention.
[0016] Figure 6 This is a schematic diagram of the Raman spectrum of the single-walled carbon nanotubes prepared in Example 1 of this invention;
[0017] Figure 7 This is a schematic diagram of the Raman spectrum of the single-walled carbon nanotubes prepared in Example 2 of this invention;
[0018] Figure 8 This is a schematic diagram of the Raman spectrum of the single-walled carbon nanotubes prepared in Example 3 of this invention;
[0019] Figure 9 This is a schematic diagram of the Raman spectrum of the single-walled carbon nanotubes prepared in Comparative Example 1 in this invention;
[0020] Reference numerals: 1. First gas channel; 2. Second gas channel; 3. Plasma torch; 4. Reaction unit; 41. Corundum magnetic boat; Detailed Implementation
[0021] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to represent selected embodiments of the invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.
[0022] This invention provides a method for preparing single-walled carbon nanotubes using plasma-assisted chemical vapor deposition, comprising the following steps:
[0023] S1, inorganic iron compounds were weighed in proportion and placed on a support, and a gaseous carbon source and an inert gas were introduced under high temperature. Then, under constant current and high-pressure plasma torch conditions, single-walled carbon nanotubes were obtained.
[0024] Preferably, the inorganic iron compound includes ferric sulfate and iron-containing inorganic compounds, with a molar ratio of ferric sulfate to iron-containing inorganic compounds of 1:0.5-2. The addition of sulfur promotes the crystallization and arrangement of carbon atoms, effectively controlling the diameter, length, and morphology of single-walled carbon nanotubes. Simultaneously, sulfur and carbon form sulfides, enhancing the stability and high-temperature resistance of the carbon nanotubes. Preferably, the iron-containing inorganic compounds include ferric chloride, ferric oxide, and ferric nitrate.
[0025] Preferably, the gaseous carbon source is one or more of methane, ethylene, and carbon monoxide, and the inert gas is one or two of argon and nitrogen. Preferably, the gaseous carbon source is methane, and the inert gas is a mixture of argon and nitrogen.
[0026] Preferably, the high-temperature environment is set at 950-1250℃, which is conducive to the pyrolysis of carbon source to generate carbon nanotubes under the action of catalyst.
[0027] Preferably, the constant current is 200-240A, and the pressure under high-pressure conditions is 4-16 kPa. This setting is beneficial for providing a high energy field and catalyst activation, thereby promoting the polymerization and growth of carbon atoms, which is conducive to the formation of single-walled carbon nanotubes. If the voltage is greater than 16 kPa or the current is greater than 240A, it may lead to an excessive increase in the high energy field and catalyst activation, resulting in an excessively rapid polymerization and formation rate of carbon atoms, leading to structural instability or uncontrolled growth of carbon nanotubes. If the voltage is less than 4 kPa or the current is less than 200A, it may lead to insufficient high energy field and catalyst activation, failing to provide enough energy and activation for carbon atoms, resulting in the inability to polymerize and grow carbon atoms, thus failing to form high-quality single-walled carbon nanotubes.
[0028] S2, the single-walled carbon nanotubes obtained in step S1 are placed in an environment with a certain temperature and air is introduced for oxidation. Then, an acidic substance is added and stirred to obtain purified single-walled carbon nanotubes.
[0029] Preferably, the temperature in a certain temperature environment is 610-630℃, and the oxidation time is 3-4 hours. This certain temperature environment and oxidation setting are beneficial for removing impurities from the surface of single-walled carbon nanotubes.
[0030] Preferably, the acidic substance is one or more of concentrated sulfuric acid, concentrated hydrochloric acid, or aqua regia, which is beneficial for removing metal catalyst impurities from single-walled carbon nanotubes. This process helps increase the activity of MWCNTs and remove impurities. First, the MWCNTs are purified, and then hydroxyl, carboxyl, and other groups can be added to the surface of the carbon nanotubes, thereby increasing the dispersibility of the carbon nanotubes in water.
[0031] Preferably, the stirring temperature is 60-80℃ and the stirring time is 16-18h. Those skilled in the art can adjust the stirring temperature and stirring time within this range according to actual needs.
[0032] Example 1
[0033] A method for preparing single-walled nanotubes using plasma-assisted chemical vapor deposition, wherein the apparatus for preparation is as follows: Figure 1 As shown, it includes the following steps:
[0034] (1) Preparation of single-walled carbon nanotubes: 1 mol of ferric sulfate and 0.5 mol of ferric chloride were placed on the corundum magnetic boat 41. The reaction unit 4 was heated to 1000℃. 3000 sccm of methane was introduced through the second gas channel 2 and 500 sccm of nitrogen was introduced through the first gas channel 1. Then, under the conditions of constant current 210A and pressure of plasma torch 3 of 5KPa, single-walled carbon nanotubes were directly generated on the corundum magnetic boat to obtain single-walled carbon nanotubes.
[0035] (2) Preparation of purified single-walled carbon nanotubes: Take out the single-walled carbon nanotubes from step (1), place them at a temperature of 620℃, and then oxidize them by passing air through them for 3 hours; then add 5M concentrated sulfuric acid and stir for 16 hours to remove impurities by acidification twice, thereby removing metal impurities from the single-walled carbon nanotubes and obtaining purified single-walled carbon nanotubes.
[0036] Example 2
[0037] A method for preparing single-walled carbon nanotubes using plasma-assisted chemical vapor deposition, wherein the apparatus for preparation is as follows: Figure 1 As shown, it includes the following steps:
[0038] (1) Preparation of single-walled carbon nanotubes: 1 mol of ferric sulfate and 1 mol of ferric oxide were placed on the corundum magnetic boat 41. The reaction unit 4 was heated to 1100℃. 3000 sccm of ethylene was introduced through the second gas channel 2 and 500 sccm of argon was introduced through the first gas channel 1. Then, under the conditions of constant current 220A and plasma torch 3 pressure of 10 kPa, single-walled carbon nanotubes were directly generated on the corundum magnetic boat to obtain single-walled carbon nanotubes.
[0039] (2) Preparation of purified single-walled carbon nanotubes: Take out the single-walled carbon nanotubes from step (1), place them at a temperature of 620℃, and then oxidize them by passing air through them for 3 hours; then add 5M concentrated sulfuric acid and stir for 17 hours to remove impurities by acidification twice, thereby removing metal impurities from the single-walled carbon nanotubes and obtaining purified single-walled carbon nanotubes.
[0040] Example 3
[0041] A method for preparing single-walled carbon nanotubes using plasma-assisted chemical vapor deposition, wherein the apparatus for preparation is as follows: Figure 1 As shown, it includes the following steps:
[0042] (1) Preparation of single-walled carbon nanotubes: 1 mol of ferric sulfate and 2 mol of ferric nitrate were placed on the corundum magnetic boat 41. The reaction unit 4 was heated to 1200℃. 3000 sccm of methane was introduced through the second gas channel 2 and 250 sccm of nitrogen and 250 sccm of argon were introduced through the first gas channel 1. Then, under the conditions of constant current 220A and plasma torch 3 pressure of 15KPa, single-walled carbon nanotubes were directly generated on the corundum magnetic boat to obtain single-walled carbon nanotubes.
[0043] (2) Preparation of purified single-walled carbon nanotubes: Take out the single-walled carbon nanotubes from step (1), place them at a temperature of 620℃, and then oxidize them by passing air through them for 3 hours; then add 5M concentrated sulfuric acid and stir for 18 hours to remove impurities by acidification twice, thereby removing metal impurities from the single-walled carbon nanotubes and obtaining purified single-walled carbon nanotubes.
[0044] Comparative Example 1
[0045] A method for preparing single-walled carbon nanotubes using plasma-assisted chemical vapor deposition, wherein the apparatus for preparation is as follows: Figure 1 As shown, it includes the following steps:
[0046] (1) Preparation of single-walled carbon nanotubes: 2 mol of ferric sulfate was placed on the corundum magnetic boat 41, the reaction unit 4 was heated to 1200℃, 3000 sccm of methane was introduced through the second gas channel 2, and 250 sccm of nitrogen and 250 sccm of argon were introduced through the first gas channel 1. Then, under the conditions of constant current 220A and plasma torch 3 pressure of 15KPa, single-walled carbon nanotubes were directly generated on the corundum magnetic boat to obtain pre-purified single-walled carbon nanotubes.
[0047] (2) Preparation of purified single-walled carbon nanotubes: Take out the single-walled carbon nanotubes from step (1), place them at a temperature of 620℃, and then oxidize them by passing air through them for 3 hours; then add 5M concentrated sulfuric acid and stir for 18 hours to remove impurities by acidification twice, thereby removing the metal impurities from the single-walled carbon nanotubes and obtaining single-walled carbon nanotubes.
[0048] Application Example 1
[0049] In this application example 1, the purified single-walled carbon nanotubes prepared in Examples 1, 2, 3, and Comparative Example 1 were cut into 1cm × 1cm sizes and tested under a transmission electron microscope. The resulting transmission electron microscope (TEM) images of Examples 1, 2, 3, and Comparative Example 1 are shown below. Figure 2 , Figure 3 , Figure 4 as well as Figure 5 ;Depend on Figure 2 , Figure 3 , Figure 4 As can be seen, the SEM images of Examples 1, 2, and 3 show relatively uniform particle size distribution and smooth surfaces. The SEM image of Comparative Example 1 shows relatively non-uniform particle size distribution and rough surfaces.
[0050] Application Example 2
[0051] In this application example 2, the purified single-walled carbon nanotubes prepared in Examples 1, 2, and 3, as well as Comparative Example 1, were ground into powder and placed on the sample stage of a Raman spectrometer for testing. Figure 6 As can be seen from the data, the Raman G / D ratio of the single-walled carbon nanotubes in Example 1 is 126.9. Figure 7 It can be seen that the Raman G / D ratio of the single-walled carbon nanotubes in Example 2 is 128, which is... Figure 8 It can be seen that the Raman G / D ratio of the single-walled carbon nanotubes in Example 3 is 146.6. Figure 9 It can be seen that the Raman G / D ratio of the single-walled carbon nanotube in Comparative Example 1 is 56.6.
[0052] Depend on Figure 6 , Figure 7 , Figure 8 as well as Figure 9 It can be seen that Examples 1, 2 and 3 all have high Raman G / D ratios, with the single-walled carbon nanotubes in Example 3 having the highest Raman G / D ratio. This indicates that the combined use of ferric sulfate and iron-containing inorganic compounds is beneficial to improving the Raman G / D ratio of single-walled carbon nanotubes, thereby reducing defects and improving lattice quality.
[0053] This invention discloses a method for preparing single-walled carbon nanotubes using plasma-assisted chemical vapor deposition (CVD). This method primarily involves adding plasma with controllable current and voltage under CVD conditions, and employing a combination of ferric sulfate and iron-containing inorganic compounds in the CVD process to effectively reduce costs. The resulting single-walled carbon nanotubes exhibit a Raman G / D ratio exceeding 120. The addition of sulfur promotes the crystallization and arrangement of carbon atoms, thereby effectively controlling the diameter, length, and morphology of the single-walled carbon nanotubes. Furthermore, sulfur can form sulfides with carbon, increasing the stability of the carbon nanotubes.
[0054] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the invention by those skilled in the art. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the invention should be included within the scope of protection of the invention.
Claims
1. A method for preparing single-walled carbon nanotubes by plasma-assisted chemical vapor deposition, characterized in that, Includes the following steps: Inorganic iron compounds were weighed out in proportion and placed on a support. A gaseous carbon source and an inert gas were introduced into the high-temperature environment. Then, under the conditions of constant current and high-voltage plasma torch, single-walled carbon nanotubes were obtained. The inorganic iron compounds include ferric sulfate and iron-containing inorganic compounds, with a molar ratio of ferric sulfate to iron-containing inorganic compounds of 1:0.5-2; the iron-containing inorganic compounds are ferric chloride, ferric oxide, or ferric nitrate; the temperature under the high-temperature conditions is 950-1250℃, the constant current is 200-240A, and the pressure under the high-pressure conditions is 4-16KPa; The single-walled carbon nanotubes are placed in an environment at a certain temperature, and air is introduced for oxidation. Then, an acidic substance is added and stirred to obtain purified single-walled carbon nanotubes. The temperature in the environment at a certain temperature is 610-630℃, and the acidic substance is one or more of concentrated sulfuric acid, concentrated hydrochloric acid, and aqua regia.
2. The method for preparing single-walled carbon nanotubes by plasma-assisted chemical vapor deposition according to claim 1, characterized in that, The gaseous carbon source is one or more of methane, ethylene, and carbon monoxide, and the inert gas is one or two of argon and nitrogen.
3. The method for preparing single-walled carbon nanotubes by plasma-assisted chemical vapor deposition according to claim 1, characterized in that, The oxidation time is 3-4 hours.
4. The method for preparing single-walled carbon nanotubes by plasma-assisted chemical vapor deposition according to claim 1, characterized in that, The stirring temperature is 60-80℃, and the stirring time is 16-18h.