A vanadium catalyst and its preparation method and application

Abstract

The invention discloses a method for preparing a vanadium catalyst, characterized in that the method comprises the following steps: S1. putting basic magnesium carbonate into a muffle furnace, and obtaining MgO powder after calcination; S2. dissolving the above-prepared MgO powder and vanadium acetylacetonate in acetone, impregnating for a period of time, drying, and grinding into powder after drying; S3. placing the ground powder in a muffle furnace for high-temperature calcination to obtain a vanadium catalyst. The invention uses an impregnation method to prepare a vanadium catalyst, uses carbon monoxide as a carbon source under normal pressure conditions, uses cheap vanadium as a catalyst, and prepares high-purity (6,5) chiral single-walled carbon nanotubes. The synthesis method is simple, the reaction time is short, it is easy to operate, it is economical and efficient, and it is conducive to large-scale production.

Description

Technical Field

[0001] The invention relates to the technical field of carbon nanotube synthesis, and in particular to a vanadium catalyst and a preparation method and application thereof. Background Art

[0002] The information disclosed in this background technology section is only intended to enhance the understanding of the overall background of the invention, and should not necessarily be regarded as an admission or any form of suggestion that the information constitutes the prior art already known to a person skilled in the art.

[0003] Since single-walled carbon nanotubes (SWNTs) were discovered in 1993, they have been one of the hot topics in the field of nanoscience, mainly due to their perfect conjugated tubular structure and outstanding physical and chemical properties. However, the inhomogeneity of the structure and properties of the currently synthesized SWNTs has seriously hindered the application of SWNTs. The synthesis of narrow-handed or even single-handed SWNTs is the key to solving this problem.

[0004] As a typical representative, high-purity (6,5) chiral single-walled carbon nanotubes have been applied in the fields of nanomedicine and solar energy. The use of high-purity (6,5) chiral single-walled carbon nanotubes can provide clear tumor imaging, and the polymer-free solar cells made with (6,5) chiral single-walled carbon nanotubes have higher power conversion efficiency. It can be seen that the direct synthesis of high-purity narrow chiral SWNTs is crucial for the application of carbon nanotubes.

[0005] The current method for synthesizing single-walled carbon nanotubes mainly uses chemical vapor deposition (CVD). The CVD method has the advantages of simple preparation process and synthesis equipment, low cost, etc. However, the regulation of catalysts and various parameters of the CVD method will affect the structure and length of single-walled carbon nanotubes, thereby affecting the chiral distribution of SWNTs. Currently, SWNTs can be prepared in batches using the CVD method, but the direct synthesis of high-purity single-chiral SWNTs cannot be achieved using the current catalyst system. Summary of the invention

[0006] In order to overcome the above problems, the present invention provides a vanadium catalyst and its preparation method and application. The present application prepares the vanadium catalyst by impregnation method, wherein V is used as a catalyst and MgO is used as a carrier, and high-purity (6,5) chiral single-walled carbon nanotubes are synthesized by CVD method, achieving the synthesis of high-purity SWNTs with narrow chirality distribution in a wide temperature range.

[0007] In order to achieve the above technical objectives, the present invention adopts the following technical solutions:

[0008] The first aspect of the present invention provides a method for preparing a vanadium catalyst, comprising the following steps:

[0009] S1. Putting basic magnesium carbonate into a muffle furnace and calcining to obtain MgO powder;

[0010] S2. The MgO powder prepared above and vanadium acetylacetonate were dissolved in acetone, immersed for a period of time, dried, and ground into powder after drying;

[0011] S3. The ground powder is placed in a muffle furnace for high-temperature calcination to obtain a vanadium catalyst.

[0012] The second aspect of the present invention provides a vanadium catalyst prepared by the above preparation method.

[0013] The third aspect of the present invention provides the use of the above vanadium catalyst in the catalytic synthesis of high-purity (6,5) chiral single-walled carbon nanotubes.

[0014] The fourth invention of the present invention provides a method for synthesizing high-purity (6,5) chiral single-walled carbon nanotubes, which is a normal-pressure CVD method and specifically comprises the following steps:

[0015] Take an appropriate amount of vanadium catalyst and put it in a quartz boat, and place the quartz boat in the middle of a high-temperature vacuum slide rail tube furnace;

[0016] Connect the gas line, open the tube furnace, introduce argon gas to remove the air in the device, and program the temperature of the tube furnace at the same time;

[0017] When the temperature of the tube furnace rises to 650-800°C, stop introducing argon and introduce CO instead to carry out the reaction. During the reaction, the reaction temperature and CO gas flow rate are maintained unchanged.

[0018] After the reaction is completed, stop introducing CO, continue to introduce argon, stop the programmed temperature increase, and start cooling. When the temperature in the tubular furnace drops to room temperature, stop introducing argon to obtain a crude product of high-purity (6,5) chiral single-walled carbon nanotubes.

[0019] One or more technical solutions provided in the embodiments of the present invention have at least the following technical effects or advantages:

[0020] (1) The present invention uses an impregnation method to prepare a vanadium catalyst, using carbon monoxide as a carbon source and cheap vanadium as a catalyst under normal pressure conditions to prepare high-purity (6,5) chiral single-walled carbon nanotubes. The synthesis method is simple, the reaction time is short, the operation is easy, the operation is economical and efficient, and it is conducive to large-scale production.

[0021] (2) The present invention uses MgO as a carrier, which has the advantages of easy availability of raw materials, a wide variety, low price, and a large specific surface area. It can be removed from the sample by reacting with a weakly acidic inorganic acid solution without affecting the properties of SWNTs.

[0022] (3) The present invention uses transition metal vanadium as a catalyst and achieves a breakthrough in the catalytic growth of SWNTs, especially at a reaction temperature of 650°C, achieving the growth of (6,5) chiral single-walled carbon nanotubes with a purity of up to 67.9%, and realizing the synthesis of high-purity SWNTs with a narrow chirality distribution in a wider temperature range. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] The drawings in the specification, which constitute a part of the present application, are used to provide further understanding of the present application. The illustrative embodiments of the present application and their descriptions are used to explain the present application and do not constitute improper limitations on the present application.

[0024] Figure 1 This is the Raman spectrum of SWNTs prepared by the present invention;

[0025] Figure 2 This is a scanning electron microscope image of SWNTs prepared in the present invention;

[0026] Figure 3 This is the fluorescence spectrum of SWNTs prepared in the present invention. DETAILED DESCRIPTION

[0027] It should be noted that the following detailed descriptions are exemplary and are intended to provide further explanation of the present invention. Unless otherwise specified, all technical and scientific terms used in the present invention have the same meanings as those commonly understood by those skilled in the art to which the present invention belongs.

[0028] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit exemplary embodiments according to the present invention. As used herein, unless the context clearly indicates otherwise, the singular form is also intended to include the plural form. In addition, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components and / or combinations thereof. It should be understood that the scope of protection of the present invention is not limited to the specific embodiments described below; it should also be understood that the terms used in the embodiments of the present invention are intended to describe specific embodiments, rather than to limit the scope of protection of the present invention.

[0029] A first typical embodiment of the present invention provides a method for preparing a vanadium catalyst, comprising the following steps:

[0030] S1. Putting basic magnesium carbonate into a muffle furnace and calcining to obtain MgO powder;

[0031] S2. The MgO powder prepared above and vanadium acetylacetonate were dissolved in acetone, immersed for a period of time, dried, and ground into powder after drying;

[0032] S3. The ground powder is placed in a muffle furnace for high-temperature calcination to obtain a vanadium catalyst.

[0033] In one or more embodiments, the calcination temperature in step S1 is 360-450°C, preferably 400°C.

[0034] In one or more embodiments, the calcination time in step S1 is 80 to 100 minutes, preferably 90 minutes.

[0035] In one or more embodiments, the molar ratio of MgO to vanadium acetylacetonate is 50:1 to 200:1.

[0036] In one or more embodiments, the amount of acetone is 40 to 70 times the equivalent of the reactants.

[0037] In one or more embodiments, the immersion time is 2 to 3 hours, preferably 2 hours.

[0038] In one or more embodiments, the drying condition after dipping is: drying at 70-90° C. overnight, preferably drying at 80° C. overnight.

[0039] In one or more embodiments, the ground powder is calcined at high temperature at 800-900° C. for 4-5 h, preferably at 800° C. for 4 h.

[0040] The second typical embodiment of the present invention provides a vanadium catalyst prepared by the above preparation method. The vanadium catalyst uses vanadium as the catalyst active substance and MgO as the catalyst carrier. MgO is used as the carrier, which has the advantages of easy availability of raw materials, a wide variety, low price, and a large specific surface area. It can be removed from the sample by reacting with a weakly acidic inorganic acid solution without affecting the properties of SWNTs.

[0041] A third typical embodiment of the present invention provides the use of the above-mentioned vanadium catalyst in the catalytic synthesis of high-purity (6,5) chiral single-walled carbon nanotubes.

[0042] A fourth typical embodiment of the present invention provides a method for synthesizing high-purity (6,5) chiral single-walled carbon nanotubes, the method being a normal pressure CVD method, specifically comprising the following steps:

[0043] Take an appropriate amount of vanadium catalyst and put it in a quartz boat, and place the quartz boat in the middle of a high-temperature vacuum slide rail tube furnace;

[0044] Connect the gas line, open the tube furnace, introduce argon gas to remove the air in the device, and program the temperature of the tube furnace at the same time;

[0045] When the temperature of the tube furnace rises to 650-800°C, stop introducing argon and introduce CO instead to carry out the reaction. During the reaction, the reaction temperature and CO gas flow rate are maintained unchanged.

[0046] After the reaction is completed, stop introducing CO, continue to introduce argon, stop the programmed temperature increase, and start cooling. When the temperature in the tubular furnace drops to room temperature, stop introducing argon to obtain a crude product of high-purity (6,5) chiral single-walled carbon nanotubes.

[0047] In one or more embodiments, the rate of the programmed temperature increase is 18-22°C / min, preferably 20°C / min.

[0048] In one or more embodiments, the gas flow rate of the introduced argon gas is 300 sccm.

[0049] In one or more embodiments, the CO gas flow rate is 300 sccm.

[0050] In one or more embodiments, the reaction time is 20 to 40 minutes, preferably 30 minutes.

[0051] In order to enable those skilled in the art to more clearly understand the technical solution of the present invention, the technical solution of the present invention will be described in detail below in conjunction with specific embodiments.

[0052] Example 1

[0053] Preparation of vanadium catalyst:

[0054] Place basic magnesium carbonate in a muffle furnace and calcine at 400°C for 90 minutes to obtain MgO; dissolve 1g MgO and 0.2g vanadium acetylacetonate in 50ml acetone, soak for 2h, place in an oven, dry at 80°C overnight, and grind the dried solid into powder in a mortar; place 1g of the powder in a muffle furnace and calcine at 800°C for 4h to obtain 0.8g vanadium catalyst.

[0055] Example 2

[0056] Preparation of vanadium catalyst:

[0057] Place basic magnesium carbonate in a muffle furnace and calcine at 360°C for 90 minutes to obtain MgO; dissolve 2g MgO and 0.3g vanadium acetylacetonate in 50ml acetone, soak for 2h, place in an oven, dry at 80°C overnight, and grind the dried solid into powder in a mortar; place 2g of the powder in a muffle furnace and calcine at 800°C for 4h to obtain 1.5g vanadium catalyst.

[0058] Example 3

[0059] Preparation of vanadium catalyst:

[0060] Place basic magnesium carbonate in a muffle furnace and calcine at 450°C for 90 minutes to obtain MgO; dissolve 3g MgO and 0.12g vanadium acetylacetonate in 50ml acetone, soak for 2h, place in an oven, dry at 80°C overnight, and grind the dried solid into powder in a mortar; place 3g of the powder in a muffle furnace and calcine at 800°C for 4h to obtain 2.6g vanadium catalyst.

[0061] Example 4

[0062] (6,5) Preparation of chiral single-walled carbon nanotubes:

[0063] 0.5 g of the vanadium catalyst prepared in Example 1 was put into a quartz boat, and the quartz boat was placed in the middle of a high-temperature vacuum slide-rail tube furnace. The gas path was connected, the tube furnace was turned on, and argon was introduced at a flow rate of 300 sccm to exclude air in the device. At the same time, the tube furnace was set to perform a temperature program at a rate of 20° C. / min. When the temperature rose to 650° C., the introduction of argon was stopped, and CO was introduced at a flow rate of 300 sccm to react. During the reaction, the reaction temperature and the gas flow rate of CO were maintained unchanged. After reacting for 35 minutes, the introduction of CO was stopped first, and then argon was introduced at a flow rate of 300 sccm, the temperature program was stopped, and the temperature began to decrease. When the temperature in the tube furnace dropped to room temperature, the introduction of argon was stopped, and 0.6 g of a crude product of high-purity (6,5) chiral single-walled carbon nanotubes was obtained.

[0064] like Figure 1 As shown in Figure 1, under different lasers, Raman spectroscopy shows the successful growth of high-quality single-walled carbon nanotubes. -1 The radial breathing (RBM) peak appears in the range of 1350 cm-1, which confirms that the grown carbon nanotubes are single-walled carbon nanotubes. The diameter can be calculated based on the position of the RBM peak. It can be seen that the diameter distribution is narrow and the tube diameter is relatively small, 1350 cm-1. -1 The peaks on the left and right are the D peaks of carbon nanotubes, 1580 cm -1 The left and right are G peaks. The value of G / D can confirm the degree of graphitization of carbon nanotubes, which means that the quality of the grown single-walled carbon nanotubes is high.

[0065] like Figure 2 As shown, a large number of carbon nanotubes can be seen in the center of the scanning electron microscope, which is an intuitive representation of the successful growth of single-walled carbon nanotubes.

[0066] like Figure 3As shown in Figure 2, fluorescence spectroscopy can characterize the chiral distribution of single-walled carbon nanotubes and roughly calculate the purity of each chiral single-walled carbon nanotube. From the fluorescence spectrum, we can see the high intensity of (6,5) tubes, which strongly proves that the catalyst we prepared is highly selective for (6,5) tubes.

[0067] Example 5

[0068] (6,5) Preparation of chiral single-walled carbon nanotubes:

[0069] 0.5 g of the vanadium catalyst prepared in Example 1 was put into a quartz boat, and the quartz boat was placed in the middle of a high-temperature vacuum slide-rail tube furnace. The gas path was connected, the tube furnace was turned on, and argon was introduced at a flow rate of 300 sccm to exclude air in the device. At the same time, the tube furnace was set to perform a programmed temperature increase at a rate of 20° C. / min. When the temperature rose to 700° C., the introduction of argon was stopped, and CO was introduced at a flow rate of 300 sccm to react. During the reaction, the reaction temperature and the gas flow rate of CO were maintained unchanged. After reacting for 35 minutes, the introduction of CO was stopped first, and then argon was introduced at a flow rate of 300 sccm, the programmed temperature increase was stopped, and the temperature began to decrease. When the temperature in the tube furnace dropped to room temperature, the introduction of argon was stopped, and 0.65 g of a crude product of high-purity (6,5) chiral single-walled carbon nanotubes was obtained.

[0070] Example 6

[0071] (6,5) Preparation of chiral single-walled carbon nanotubes:

[0072] 0.5 g of the vanadium catalyst prepared in Example 1 was put into a quartz boat, and the quartz boat was placed in the middle of a high-temperature vacuum slide-rail tube furnace. The gas path was connected, the tube furnace was turned on, and argon was introduced at a flow rate of 300 sccm to exclude the air in the device. At the same time, the tube furnace was set to perform a programmed temperature increase at a rate of 20° C. / min. When the temperature rose to 800° C., the introduction of argon was stopped, and CO was introduced at a flow rate of 300 sccm to react. During the reaction, the reaction temperature and the gas flow rate of CO were maintained unchanged. After reacting for 35 minutes, the introduction of CO was stopped first, and then argon was introduced at a flow rate of 300 sccm, the programmed temperature increase was stopped, and the temperature began to decrease. When the temperature in the tube furnace dropped to room temperature, the introduction of argon was stopped, and 0.66 g of a crude product of high-purity (6,5) chiral single-walled carbon nanotubes was obtained.

[0073] Comparative Example 1

[0074] (6,5) Preparation of chiral single-walled carbon nanotubes:

[0075] 0.5 g of MgO prepared in Comparative Example 1 was put into a quartz boat, and the quartz boat was placed in the middle of a high-temperature vacuum slide rail tube furnace. The gas path was connected, the tube furnace was turned on, and argon was introduced at a flow rate of 300 sccm to remove the air in the device. At the same time, the tube furnace was set to perform a programmed temperature increase at a rate of 20°C / min. When the temperature rose to 650°C, the introduction of argon was stopped, and CO was introduced at a flow rate of 300 sccm to react. During the reaction, the reaction temperature and the gas flow rate of CO were maintained unchanged. After reacting for 35 minutes, the introduction of CO was stopped first, and then argon was introduced at a flow rate of 300 sccm, the programmed temperature increase was stopped, and the temperature began to decrease. When the temperature in the tube furnace dropped to room temperature, the introduction of argon was stopped. It was found that the addition of MgO alone could not catalyze the formation of (6,5) chiral single-walled carbon nanotubes.

[0076] Comparative Example 2

[0077] The cobalt catalyst prepared in Example 1 of CN109433208A was used to catalyze the synthesis of single-walled carbon nanotubes:

[0078] 0.5 g of the cobalt catalyst prepared in Example 1 of CN109433208A was put into a quartz boat, and the quartz boat was placed in the middle of a high-temperature vacuum slide rail tube furnace. The gas path was connected, the tube furnace was turned on, and argon was introduced at a flow rate of 300 sccm to exclude the air in the device. At the same time, the tube furnace was set to perform a programmed temperature increase at a rate of 20°C / min. When the temperature rose to 650°C, the introduction of argon was stopped, and CO was introduced at a flow rate of 300 sccm to react. During the reaction, the reaction temperature and the gas flow rate of CO were maintained unchanged. After reacting for 35 minutes, the introduction of CO was stopped first, and then argon was introduced at a flow rate of 300 sccm, the programmed temperature increase was stopped, and the temperature began to decrease. When the temperature in the tube furnace dropped to room temperature, the introduction of argon was stopped, and the final product was ordinary single-walled carbon nanotubes.

[0079] Compared with cobalt catalysts, the advantages of the present invention are mainly reflected in two aspects. First, the quality of single-walled carbon nanotubes. The single-walled carbon nanotubes of the present invention have higher quality at the same low temperature. From the comparison results of Raman characterization, it can be seen that the present invention has a higher G / D ratio, which proves that the single-walled carbon nanotubes grown by the present invention have smaller defects and higher quality; second, the chiral selectivity of single-walled carbon nanotubes. The selectivity of the present invention for (6,5) tubes is as high as 67.9%, which is much higher than that of Comparative Document 1.

Claims

1. Use of a vanadium catalyst in the catalytic synthesis of high-purity (6,5) chiral single-walled carbon nanotubes, characterized in that: High-purity (6,5) chiral single-walled carbon nanotubes were prepared by atmospheric pressure CVD method with carbon monoxide as carbon source and vanadium catalyst. The preparation method of the vanadium catalyst comprises the following steps: S1. Putting basic magnesium carbonate into a muffle furnace and calcining to obtain MgO powder; S2. The MgO powder prepared above and vanadium acetylacetonate were dissolved in acetone, immersed for a period of time, dried, and ground into powder after drying; S3. The ground powder is placed in a muffle furnace and calcined at high temperature to obtain a vanadium catalyst; The molar ratio of MgO to vanadium acetylacetonate is 50:1 to 200:1; The conditions for high-temperature calcination of the ground powder are: calcination at 800-900° C. for 4-5 hours.

2. The use according to claim 1, characterized in that The calcination temperature in step S1 is 360-450°C; Alternatively, the calcination time in step S1 is 80 to 100 minutes.

3. The use according to claim 1, characterized in that The calcination temperature in step S1 is 400°C.

4. The use according to claim 1, characterized in that The calcination time in step S1 is 90 minutes.

5. The use according to claim 1, characterized in that The amount of acetone is 40 to 70 times the equivalent of the reactants.

6. The use according to claim 1, characterized in that The immersion time is 2 to 3 hours; Alternatively, the drying condition after the dipping is: drying at 70-90° C. overnight.

7. The use according to claim 1, characterized in that The immersion time is 2 hours.

8. The use according to claim 1, characterized in that The drying condition after the dipping is: drying at 80° C. overnight.

9. The use according to claim 1, characterized in that The conditions for high-temperature calcination of the ground powder are: calcination at 800° C. for 4 hours.

10. A method for synthesizing high-purity (6,5) chiral single-walled carbon nanotubes, characterized in that: The method is a normal pressure CVD method, which specifically comprises the following steps: Take an appropriate amount of the vanadium catalyst according to any one of claims 1 to 9 and put it in a quartz boat, and place the quartz boat in the middle of a high-temperature vacuum slide rail tube furnace; Connect the gas line, open the tube furnace, introduce argon gas to remove the air in the device, and program the temperature of the tube furnace at the same time; When the temperature of the tube furnace rises to 650-800°C, stop introducing argon and introduce CO instead for reaction. During the reaction, the reaction temperature and CO gas flow rate are maintained unchanged. After the reaction is completed, stop introducing CO, continue to introduce argon, stop the programmed temperature increase, and start cooling. When the temperature in the tubular furnace drops to room temperature, stop introducing argon to obtain a crude product of high-purity (6,5) chiral single-walled carbon nanotubes.

11. The method according to claim 10, characterized in that The rate of the programmed temperature rise is 18-22°C / min; Or, the gas flow rate of the introduced argon gas is 300 sccm; Alternatively, the gas flow rate of CO is 300 sccm.

12. The method according to claim 10, characterized in that The rate of the programmed temperature increase is 20°C / min.

13. The method according to claim 10, characterized in that The reaction time is 20 to 40 minutes.

14. The method according to claim 10, characterized in that The reaction time is 30 min.

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