Carbon-based catalyst for promoting growth of multi-walled carbon nanotubes and method for preparing the same

Abstract

This invention discloses a carbon-based catalyst for promoting the growth of multi-walled carbon nanotubes and its preparation method, relating to the field of carbon nanotube preparation technology. The method includes the following steps: heating a polymeric carbon source under an inert gas atmosphere, holding it at that temperature, and then cooling it to room temperature to obtain a pre-carbonized product; subjecting it to Joule thermal shock under vacuum conditions, and then restoring it to atmospheric pressure to obtain polymer-derived topological defect carbon, i.e., the carbon-based catalyst for promoting the growth of multi-walled carbon nanotubes. The heteroatom removal method based on Joule thermal shock technology proposed in this invention improves the construction efficiency of topological defects in carbon catalysts. Since the catalyst is also a carbon-based material, its residue will not significantly affect the performance of carbon nanotubes, thus avoiding the problem of the metal catalyst removal process affecting the performance of carbon nanotubes. This invention solves the problems of low construction efficiency in existing carbon material topological defect construction methods and the residue left by metal catalysts in the preparation of carbon nanotubes.

Description

Technical Field

[0001] This invention relates to the field of carbon nanotube preparation technology, specifically to a carbon-based catalyst for promoting the growth of multi-walled carbon nanotubes and its preparation method. Background Technology

[0002] Carbon nanotubes, discovered in the early 1990s, are one-dimensional carbon nanomaterials with excellent mechanical properties, electrical / thermal conductivity, and chemical stability. They have been widely used in fields such as conductive agents / reinforcing agents for composite materials and conductive agents for lithium-ion batteries. Currently, the mainstream technology for producing carbon nanotubes is the low-cost, high-volume chemical vapor deposition (CVD) method. This method requires the use of transition metal-based catalysts such as iron, cobalt, and nickel. Therefore, the product must be purified to remove the influence of these catalysts on the final product's performance. Acid treatment is a common method for removing these catalysts. However, this method not only damages the structure of carbon nanotubes to some extent, affecting their performance, but it also cannot remove some catalysts encapsulated by carbon impurities. Topological defect carbons, rich in non-hexagonal topological defects such as pentagons, heptagons, and octagons, possess excellent catalytic activity. These defects belong to high-energy states and can induce local charge rearrangement in the carbon substrate, thus serving as excellent catalytic active sites for promoting carbon nanotube growth. If topological defect carbons are used as catalysts to promote the growth of multi-walled carbon nanotubes, since the catalyst is also a carbon-based material, the trace amounts of such catalyst residues will have a negligible impact on the performance of carbon nanotubes. Therefore, developing novel carbon-based catalysts that do not affect the performance of carbon nanotubes even if residues are present is essential for the large-scale preparation of high-quality carbon nanotubes by chemical vapor deposition.

[0003] However, current methods for constructing topological defects in carbon materials suffer from low construction efficiency. This is because, while constructing topological defects, other defects are inevitably introduced. For example, ball milling and chemical in-situ etching introduce numerous edge defects and oxygen-containing functional groups, respectively. In recent years, researchers have proposed a method for efficiently constructing topological defects by removing heteroatoms from the carbon matrix (heteroatom removal method). Theoretically, the removal of heteroatoms will form dangling bonds in the carbon matrix, and the rearrangement of these dangling bonds will form specific topological defects, potentially achieving efficient construction of topological defects. However, this method requires execution at extremely high temperatures (≥1000℃) for several hours (2-4 hours). Carbon materials tend to graphitize under prolonged high-temperature processing. When heteroatoms are removed, adjacent carbon atoms may rearrange to form a graphitized structure, making it difficult to form topological defect structures. Summary of the Invention

[0004] To address the aforementioned technical problems, the present invention aims to provide a carbon-based catalyst for promoting the growth of multi-walled carbon nanotubes and its preparation method, thereby solving the problems of low construction efficiency and residues in existing carbon material topological defect construction methods and the presence of metal catalysts in the preparation of carbon nanotubes.

[0005] The technical solution of this invention to solve the above-mentioned technical problems is as follows: A method for preparing a carbon-based catalyst to promote the growth of multi-walled carbon nanotubes is provided, comprising the following steps:

[0006] (1) Under an inert gas atmosphere, a polymeric carbon source is heated and kept at that temperature, and then cooled to room temperature to obtain a pre-carbonized product.

[0007] (2) The pre-carbonized product obtained in step (1) is subjected to Joule thermal shock under vacuum conditions, and then restored to normal pressure to obtain polymer-derived topological defect carbon, i.e. carbon-based catalyst that promotes the growth of multi-walled carbon nanotubes.

[0008] Based on the above technical solution, the present invention can be further improved as follows:

[0009] Furthermore, in step (1), the inert gas is argon or nitrogen.

[0010] Furthermore, in step (1), the flow rate of the inert gas is 100 sccm.

[0011] Furthermore, in step (1), the polymeric carbon source is polyaniline, polypyrrole, polythiophene, polytetrafluoroethylene or polyvinylidene fluoride.

[0012] The beneficial effects of adopting the above-mentioned further technical solution are as follows: using a polymer containing a single heteroatom as a precursor, the heteroatom doping state of its derived carbon will tend to be uniform, which will promote the uniformity of the derived topological defect structure after the heteroatom is removed, which is beneficial to the precise control of the topological defect structure in the carbon matrix.

[0013] Furthermore, in step (1), the polymeric carbon source is heated to 400-900℃.

[0014] Further, heat to 400-900℃ at a heating rate of 5-10℃ / min.

[0015] Furthermore, heat to 400-900℃ at a heating rate of 10℃ / min.

[0016] Further, heat to 400-900℃ at a heating rate of 5℃ / min.

[0017] Furthermore, in step (1), the temperature is maintained for 1-3 hours.

[0018] Furthermore, in step (1), after the heat preservation is completed, the temperature is further cooled to room temperature in an inert gas atmosphere.

[0019] Furthermore, in step (2), the vacuum condition is -0.09 MPa.

[0020] Furthermore, in step (2), the peak temperature of the Joule thermal shock is 1300-2200℃.

[0021] Furthermore, in step (2), the peak temperature of the Joule thermal shock is 1400-2200℃.

[0022] Furthermore, in step (2), the Joule thermal shock conditions are: voltage 8-32V, current 55-85A, thermal shock mode is time pulse mode, heating time 1200-3600ms, cooling time 500ms, and number of shocks 8-80 times.

[0023] Furthermore, in step (2), the Joule thermal shock conditions are: voltage 24-32V, current 55-85A, thermal shock mode is time pulse mode, heating time 1200-3600ms, cooling time 500ms, and number of shocks 20-80 times.

[0024] Furthermore, in step (2), the Joule thermal shock conditions are: voltage 24V, current 65A, thermal shock mode is time pulse mode, heating time 3600ms, cooling time 500ms, and number of shocks 20.

[0025] Furthermore, in step (2), the Joule thermal shock conditions are: voltage 32V, current 55A, thermal shock mode is time pulse mode, heating time 1200ms, cooling time 500ms, and number of shocks 80 times.

[0026] Furthermore, in step (2), the Joule thermal shock conditions are: voltage 32V, current 85A, thermal shock mode is time pulse mode, heating time 1200ms, cooling time 500ms, and number of shocks 40.

[0027] The present invention also provides a carbon-based catalyst for promoting the growth of multi-walled carbon nanotubes prepared by the above method.

[0028] The present invention also provides the application of the above-mentioned carbon-based catalyst for promoting the growth of multi-walled carbon nanotubes in promoting the growth of multi-walled carbon nanotubes.

[0029] Furthermore, the method for promoting the growth of multi-walled carbon nanotubes includes the following steps:

[0030] S1: Pre-activation of the catalyst: Under an inert gas atmosphere, the carbon-based catalyst for promoting the growth of multi-walled carbon nanotubes as described in claim 8 is heated and kept at a certain temperature to obtain a pre-activated catalyst.

[0031] S2: In the pre-activated catalyst obtained in step S1, a mixture of inert gas and carbon source gas is introduced, and catalytic growth is carried out at 650-950℃ to obtain multi-walled carbon nanotubes.

[0032] Furthermore, in step S1, the inert gas is argon or nitrogen.

[0033] Furthermore, in step S1, the flow rate of the inert gas is 100 sccm.

[0034] Furthermore, in step S1, the temperature is increased to 650-950℃.

[0035] Furthermore, in step S1, the temperature is increased to 800-950°C.

[0036] Furthermore, in step S1, heating is carried out at a heating rate of 5-10℃ / min.

[0037] Furthermore, in step S1, heating is performed at a heating rate of 10°C / min.

[0038] Furthermore, in step S1, the temperature is maintained for 0.5-1 hour.

[0039] Furthermore, in step S1, the temperature is maintained for 0.5 hours.

[0040] Furthermore, in step S2, catalytic growth is carried out at 800-950℃.

[0041] Furthermore, in step S2, catalytic growth is carried out for 0.5-3 hours.

[0042] Furthermore, in step S2, catalytic growth is carried out for 1-2 hours.

[0043] Furthermore, in step S2, the total flow rate of the inert gas and the carbon source gas is 100 sccm.

[0044] Furthermore, in step S2, the flow rate ratio of the inert gas to the carbon source gas is 1-9:1-9.

[0045] Furthermore, in step S2, the flow rate ratio of the inert gas to the carbon source gas is 3:7.

[0046] Furthermore, in step S2, the flow rate ratio of the inert gas to the carbon source gas is 1:1.

[0047] Furthermore, in step S2, the flow rate ratio of the inert gas to the carbon source gas is 6:4.

[0048] The beneficial effects of adopting the above-mentioned further technical solutions are as follows: the pre-activation of carbon catalyst can eliminate the influence of trace oxygen heteroatoms in carbon matrix and improve the activity of catalyst; during the catalytic growth process, the diameter of carbon nanotubes can be controlled by controlling the flow rate ratio of inert gas to carbon source gas.

[0049] Furthermore, in step S2, the inert gas is argon or nitrogen.

[0050] Furthermore, in step S2, the carbon source gas is acetylene, ethylene, methane, or propylene.

[0051] The present invention has the following beneficial effects:

[0052] 1. This invention addresses the problems existing in the construction of topological defects in carbon materials using the aforementioned heteroatom removal method by proposing an improvement using Joule thermal shock technology. This improved method uses a special polymer as the carbon source, pre-carbonizing it; then, the pre-carbonized product undergoes Joule thermal shock treatment to rapidly remove heteroatoms from the carbon matrix. After removal, topological defects are constructed in the carbon matrix, yielding polymer-derived topological defect carbon. The advantage of this improved heteroatom removal method is that the instantaneous heat treatment at extremely high temperatures achieves rapid removal of heteroatoms from the carbon matrix, while avoiding the problem of defect structure rearrangement into graphitized structures caused by prolonged high-temperature treatment, thus achieving efficient construction of topological defect structures in the carbon matrix.

[0053] 2. Regarding the preparation of carbon nanotubes by vapor deposition, the removal of metal catalysts in this process can significantly affect the performance of carbon nanotubes. This invention proposes to prepare carbon nanotubes using topological defect carbon as a catalyst. This process avoids the impact of catalyst removal on the performance of carbon nanotubes.

[0054] 3. The heteroatom removal method based on Joule thermal shock technology proposed in this invention can not only achieve rapid removal of heteroatoms in the carbon matrix, but also avoid the problem of defect structure rearrangement into graphitized structure under long-term high-temperature treatment, thereby improving the construction efficiency of topological defects. The process for preparing carbon nanotubes by vapor deposition using topological defect carbon as a catalyst proposed in this invention has no significant impact on the performance of carbon nanotubes because the catalyst is also a carbon-based material, thus avoiding the problem of the performance of carbon nanotubes being affected by the removal process of metal catalysts. Attached Figure Description

[0055] Figure 1 Here is a high-resolution TEM image of the catalyst prepared in Example 1;

[0056] Figure 2 The Raman spectrum of the catalyst prepared in Example 1 is shown below.

[0057] Figure 3 SEM image of the multi-walled carbon nanotubes prepared in Example 1;

[0058] Figure 4 SEM image of the carbon nanotubes prepared in Comparative Example 1.

[0059] Figure 5 SEM image of the carbon nanotubes prepared in Comparative Example 2;

[0060] Figure 6 This is a SEM image of the carbon nanotubes prepared in Comparative Example 3. Detailed Implementation

[0061] The principles and features of the present invention are described below with reference to the accompanying drawings. The examples given are for illustrative purposes only and are not intended to limit the scope of the invention. Unless otherwise specified in the examples, conventional conditions or conditions recommended by the manufacturer should be followed. Reagents or instruments whose manufacturers are not specified are all commercially available products.

[0062] Example 1:

[0063] A carbon-based catalyst for promoting the growth of multi-walled carbon nanotubes, the preparation method of which includes the following steps:

[0064] (1) Argon gas was passed through at room temperature for 1 hour to remove air. The argon gas flow rate was 100 sccm. Under this inert gas atmosphere, the polymer carbon source (polyaniline) was placed in a tube furnace and heated to 500°C at a heating rate of 10°C / min. The temperature was held for 2 hours and then cooled to room temperature under an inert gas atmosphere to obtain the pre-carbonized product.

[0065] (2) Spread the pre-carbonized product obtained in step (1) evenly between two layers of carbon cloth (WOS1011), fix it on the thermal shock stage, and seal the edges with ceramic clamps; then, put the stage into the glass vacuum chamber, align the carbon cloth with the infrared thermometer on the top of the vacuum chamber, connect the wires to both ends of the stage and fix them; then close the vacuum chamber and turn on the vacuum pump to evacuate.

[0066] The pre-carbonized product obtained in step (1) was subjected to Joule thermal shock under vacuum (-0.09 MPa). The Joule thermal shock conditions were: voltage 24V, current 65A, thermal shock mode time pulse mode, heating time 3600ms, cooling time 500ms, and number of shocks 20. The peak temperature of the Joule thermal shock was 1400℃. After the thermal shock, the vacuum was removed to obtain polymer-derived topological defect carbon, which is a carbon-based catalyst that promotes the growth of multi-walled carbon nanotubes.

[0067] A method for promoting the growth of multi-walled carbon nanotubes includes the following steps:

[0068] S1: Pre-activation of the catalyst: At room temperature, argon gas was passed through for 0.5 h to remove air. The argon gas flow rate was 100 sccm. Under this inert gas atmosphere, the carbon-based catalyst that promotes the growth of multi-walled carbon nanotubes was placed in a tube furnace and heated to 800℃ at a heating rate of 10℃ / min and held for 0.5 h to obtain the pre-activated catalyst.

[0069] S2: In the pre-activated catalyst obtained in step S1, a mixture of argon and carbon source gas (acetylene) is introduced (the total flow rate of argon and carbon source gas is 100 sccm, and the flow rate ratio of argon and carbon source gas is 3:7), and catalytic growth is carried out at 800℃ for 2 hours to obtain multi-walled carbon nanotubes.

[0070] Example 2:

[0071] A carbon-based catalyst for promoting the growth of multi-walled carbon nanotubes, the preparation method of which includes the following steps:

[0072] (1) Argon gas was passed through at room temperature for 1 hour to remove air. The argon gas flow rate was 100 sccm. Under this inert gas atmosphere, the polymer carbon source (polypyrrole) was placed in a tube furnace and heated to 900°C at a heating rate of 10°C / min. The temperature was held for 1 hour and then cooled to room temperature under an inert gas atmosphere to obtain the pre-carbonized product.

[0073] (2) Spread the pre-carbonized product obtained in step (1) evenly between two layers of carbon cloth (WOS1011), fix it on the thermal shock stage, and seal the edges with ceramic clamps; then, put the stage into the glass vacuum chamber, align the carbon cloth with the infrared thermometer on the top of the vacuum chamber, connect the wires to both ends of the stage and fix them; then close the vacuum chamber and turn on the vacuum pump to evacuate.

[0074] The pre-carbonized product obtained in step (1) was subjected to Joule thermal shock under vacuum (-0.09 MPa). The Joule thermal shock conditions were: voltage 32V, current 55A, thermal shock mode time pulse mode, heating time 1200ms, cooling time 500ms, and number of shocks 80. The peak temperature of the Joule thermal shock was 1600℃. After the thermal shock, the vacuum was removed to obtain polymer-derived topological defect carbon, which is a carbon-based catalyst that promotes the growth of multi-walled carbon nanotubes.

[0075] A method for promoting the growth of multi-walled carbon nanotubes includes the following steps:

[0076] S1: Pre-activation of the catalyst: At room temperature, argon gas was passed through for 0.5 h to remove air. The argon gas flow rate was 100 sccm. Under this inert gas atmosphere, the carbon-based catalyst that promotes the growth of multi-walled carbon nanotubes was placed in a tube furnace and heated to 950°C at a heating rate of 10°C / min. The temperature was then maintained for 0.5 h to obtain the pre-activated catalyst.

[0077] S2: In the pre-activated catalyst obtained in step S1, a mixture of argon and carbon source gas (ethylene) is introduced (the total flow rate of argon and carbon source gas is 100 sccm, and the flow rate ratio of argon and carbon source gas is 1:1), and catalytic growth is carried out at 950℃ for 1 h to obtain multi-walled carbon nanotubes.

[0078] Example 3:

[0079] A carbon-based catalyst for promoting the growth of multi-walled carbon nanotubes, the preparation method of which includes the following steps:

[0080] (1) Argon gas was passed through at room temperature for 1 hour to remove air. The argon gas flow rate was 100 sccm. Under this inert gas atmosphere, the polymer carbon source (polythiophene) was placed in a tube furnace and heated to 400°C at a heating rate of 5°C / min. The temperature was held for 3 hours and then cooled to room temperature under an inert gas atmosphere to obtain the pre-carbonized product.

[0081] (2) Spread the pre-carbonized product obtained in step (1) evenly between two layers of carbon cloth (WOS1011), fix it on the thermal shock stage, and seal the edges with ceramic clamps; then, put the stage into the glass vacuum chamber, align the carbon cloth with the infrared thermometer on the top of the vacuum chamber, connect the wires to both ends of the stage and fix them; then close the vacuum chamber and turn on the vacuum pump to evacuate.

[0082] The pre-carbonized product obtained in step (1) was subjected to Joule thermal shock under vacuum (-0.09 MPa). The Joule thermal shock conditions were: voltage 32V, current 85A, thermal shock mode time pulse mode, heating time 1200ms, cooling time 500ms, and number of shocks 40. The peak temperature of the Joule thermal shock was 2200℃. After the thermal shock, the vacuum was removed to obtain polymer-derived topological defect carbon, which is a carbon-based catalyst that promotes the growth of multi-walled carbon nanotubes.

[0083] A method for promoting the growth of multi-walled carbon nanotubes includes the following steps:

[0084] S1: Pre-activation of the catalyst: At room temperature, argon gas was passed through for 0.5 h to remove air. The argon gas flow rate was 100 sccm. Under this inert gas atmosphere, the carbon-based catalyst that promotes the growth of multi-walled carbon nanotubes was placed in a tube furnace and heated to 850°C at a heating rate of 10°C / min and held for 1 h to obtain the pre-activated catalyst.

[0085] S2: In the pre-activated catalyst obtained in step S1, a mixture of argon and carbon source gas (methane) is introduced (the total flow rate of argon and carbon source gas is 100 sccm, and the flow rate ratio of argon and carbon source gas is 6:4), and catalytic growth is carried out at 850℃ for 1.5 h to obtain multi-walled carbon nanotubes.

[0086] Comparative Example 1:

[0087] A carbon-based catalyst, the preparation method of which includes the following steps:

[0088] Step (2) is excluded; the rest is the same as in Example 1.

[0089] A method for promoting the growth of multi-walled carbon nanotubes includes the following steps:

[0090] The above-mentioned carbon-based catalyst was used to promote the growth of multi-walled carbon nanotubes, and the rest was the same as in Example 1.

[0091] Comparative Example 2:

[0092] A carbon-based catalyst, the preparation method of which includes the following steps:

[0093] Step (2) is excluded; the rest is the same as in Example 2.

[0094] A method for promoting the growth of multi-walled carbon nanotubes includes the following steps:

[0095] The above-mentioned carbon-based catalyst was used to promote the growth of multi-walled carbon nanotubes, and the rest was the same as in Example 2.

[0096] Comparative Example 3:

[0097] A carbon-based catalyst, the preparation method of which includes the following steps:

[0098] Step (2) is excluded; the rest is the same as in Example 3.

[0099] A method for promoting the growth of multi-walled carbon nanotubes includes the following steps:

[0100] The above-mentioned carbon-based catalyst was used to promote the growth of multi-walled carbon nanotubes, and the rest was the same as in Example 3.

[0101] Test case

[0102] 1. The carbon-based catalyst for promoting the growth of multi-walled carbon nanotubes prepared in Example 1 was subjected to TEM detection. The results are shown in […]. Figure 1 .

[0103] Depend on Figure 1 It is known that the topological defect carbon catalyst obtained after Joule thermal shock has a large number of non-six-membered ring topological defect structures in its carbon matrix.

[0104] 2. The carbon-based catalyst for promoting the growth of multi-walled carbon nanotubes prepared in Example 1 was subjected to Raman spectroscopy. The results are shown below. Figure 2 .

[0105] Depend on Figure 2 It can be seen that, comparing the Raman spectra of pre-carbonized derived carbon and topological defect carbon subjected to Joule thermal shock, the latter's I... D / I G The difference is much greater than the former, because a large number of heteroatoms in the carbon matrix are removed after Joule thermal shock, which at the same time forms a rich topological defect structure.

[0106] III. The multi-walled carbon nanotubes prepared in Example 1 were subjected to SEM analysis. The results are shown below. Figure 3 .

[0107] Depend on Figure 3 It can be seen that carbon nanotubes with a diameter of about 30-60 nm were prepared by vapor deposition using topological defect carbon as a catalyst.

[0108] IV. The samples obtained after the catalytic experiments of Comparative Examples 1, 2, and 3 were characterized by SEM. The results are shown in the figure. Figure 4-6 .

[0109] Depend on Figure 4-6 It is known that derived carbon that has not undergone Joule thermal shock treatment cannot catalyze the growth of carbon nanotubes under the same conditions.

[0110] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a carbon-based catalyst for promoting the growth of multi-walled carbon nanotubes, characterized in that, Includes the following steps: (1) Under an inert gas atmosphere, the polymer carbon source is heated and kept at a certain temperature, and then cooled to room temperature to obtain a pre-carbonized product; (2) The pre-carbonized product obtained in step (1) is subjected to Joule thermal shock under vacuum conditions, and then restored to normal pressure to obtain polymer-derived topological defect carbon, i.e. carbon-based catalyst that promotes the growth of multi-walled carbon nanotubes. In step (1), the polymeric carbon source is polyaniline, polypyrrole, polythiophene, polytetrafluoroethylene or polyvinylidene fluoride; In step (1), the polymeric carbon source is heated to 400-900℃; In step (1), keep warm for 1-3 hours; In step (2), the peak temperature of the Joule thermal shock is 1300-2200℃; In step (2), the Joule thermal shock conditions are: voltage 8-32V, current 55-85A, thermal shock mode is time pulse mode, heating time 1200-3600ms, cooling time 500ms, and number of shocks 8-80 times.

2. The carbon-based catalyst for promoting the growth of multi-walled carbon nanotubes prepared by the method of claim 1.

3. The application of the carbon-based catalyst for promoting the growth of multi-walled carbon nanotubes as described in claim 2 in promoting the growth of multi-walled carbon nanotubes.

4. The application of the carbon-based catalyst for promoting the growth of multi-walled carbon nanotubes according to claim 3 in promoting the growth of multi-walled carbon nanotubes, characterized in that, The method for promoting the growth of multi-walled carbon nanotubes includes the following steps: S1: Pre-activation of catalyst: Under an inert gas atmosphere, the carbon-based catalyst for promoting the growth of multi-walled carbon nanotubes as described in claim 2 is heated and kept at a certain temperature to obtain a pre-activated catalyst. S2: In the pre-activated catalyst obtained in step S1, a mixture of inert gas and carbon source gas is introduced, and catalytic growth is carried out at 650-950℃ to obtain multi-walled carbon nanotubes.

5. The application of the carbon-based catalyst for promoting the growth of multi-walled carbon nanotubes according to claim 4 in promoting the growth of multi-walled carbon nanotubes, characterized in that, In step S2, the carbon source gas is acetylene, ethylene, methane, or propylene.

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