Method for rapidly preparing nitrogen-doped carbon nanotubes

Abstract

The invention discloses a method for rapidly preparing a nitrogen-doped carbon nanotube. The method comprises the following steps: providing a carbon felt as a carrier and a carbon source; coating the surface of the carbon felt with a catalyst to obtain the carbon felt with the surface coated with the catalyst; and by taking ammonia gas as a nitrogen source, in an ammonia gas atmosphere, electrically connecting and electrifying the carbon felt of which the surface is coated with the catalyst with a Joule heat generation device, and carrying out Joule heat reaction at high temperature to prepare the nitrogen-doped carbon nanotube. According to the method for rapidly preparing the nitrogen-doped carbon nanotube, the carbon felt is used as a carrier and a carbon source, the ferrous chloride is used as a catalyst, the ammonia gas atmosphere is used as a nitrogen source, the carbon source and the nitrogen source do not need to be additionally added, rapid heating is achieved through the Joule heat method, the reaction time is short, and the self-supporting nitrogen-doped carbon nanotube produced through a one-step method is obtained; the preparation process is environment-friendly, second-level preparation is achieved, raw materials are cheap and easy to obtain, operation danger is small, and the method is suitable for large-scale production.

Description

Technical Field

[0001] The invention belongs to the technical field of nano material preparation, and in particular relates to a method for rapidly preparing nitrogen-doped carbon nanotubes. Background Art

[0002] Carbon nanotubes have attracted widespread attention in many fields due to their unique structure and excellent properties. In order to achieve their wide application, the synthesis of high-quality carbon nanotubes is a very critical foundation. In particular, one-dimensional carbon nanotubes and their nitrogen-doped variants have received increasing attention due to their superior aspect ratio, unique electronic properties and improved surface properties. The potential application of nitrogen-doped carbon nanotubes in electrochemical energy storage and energy conversion devices further highlights the importance of their efficient synthesis. Generally, nitrogen-doped carbon nanotubes are manufactured by high-temperature pyrolysis, arc discharge, and chemical vapor deposition. However, these traditional methods often face problems such as complex operation and long reaction time, which limits their feasibility of large-scale production. Therefore, it is particularly important to develop an efficient, fast, and single-step synthesis technology for nitrogen-doped carbon nanotubes.

[0003] As an emerging synthesis technology, flash Joule heating technology has received extensive attention in the fields of inorganic materials such as carbon nanomaterials, high entropy alloys, metal carbides, and waste recycling. Due to the extremely short reaction time and extremely low energy consumption of this technology, flash Joule heating has shown significant advantages in the synthesis and modification of carbon materials. Existing patents (CN103407985A, CN116534843A, CN116654903A, etc.) use a large amount of organic solvents and nitrogen-containing polymer monomers in the process of doping carbon nanotubes, and the pre-preparation is cumbersome and has certain risks; complex catalysts or complexes containing catalytic metal components increase production costs and production difficulties; complex atmosphere environments such as methane and benzene as carbon sources, ethylenediamine as nitrogen source, and hydrogen and argon mixed gas as carrier gas make the production process dangerous and complex; the subsequent products need to be washed many times, causing pollution. Although the Joule heat method used in the literature (Small 2024, 20, 2305406) ​​greatly shortens the production time during the heating preparation, a large amount of chemical reagents are used in the pre-process of raw materials, and the precursor preparation time is as long as 15 hours, and multiple washing and centrifugation are required. More importantly, the above methods all use complex pre-treatment of nitrogen-containing organic matter as the main nitrogen source to obtain the precursor and then further dope the carbon nanotube preparation process. The operation is difficult, the production cost is high, the time is long, and there is a certain degree of danger. Moreover, none of them can quickly obtain self-supporting nitrogen-doped carbon nanotubes in one step through the flash Joule heat technology. Summary of the invention

[0004] The main purpose of the present invention is to provide a method for rapidly preparing nitrogen-doped carbon nanotubes to overcome the deficiencies in the prior art.

[0005] In order to achieve the above-mentioned invention object, the technical solution adopted by the present invention includes: The embodiment of the present invention provides a method for rapidly preparing nitrogen-doped carbon nanotubes, which comprises: Providing carbon felt as a carrier and a carbon source; Coating a catalyst on the surface of the carbon felt to obtain a carbon felt with the catalyst coated on the surface; Ammonia is used as a nitrogen source. In an ammonia atmosphere, the carbon felt coated with a catalyst is electrically connected to a Joule heat generating device, and electricity is supplied to perform a Joule heat reaction at a high temperature to obtain nitrogen-doped carbon nanotubes.

[0006] In some embodiments, the preparation time of the nitrogen-doped carbon nanotubes is within 5 seconds.

[0007] Compared with the prior art, the beneficial effects of the present invention include: The method for rapidly preparing nitrogen-doped carbon nanotubes provided by the present invention utilizes carbon felt as a carrier and a carbon source, utilizes ferric chloride and / or ferrocene as a catalyst, and uses an ammonia atmosphere as a nitrogen source. No additional carbon source and nitrogen source need to be added. The Joule heat method is used to rapidly increase the temperature, and the reaction time is short. Self-supporting nitrogen-doped carbon nanotubes produced in a one-step process are obtained. The preparation process is environmentally friendly, can be prepared in seconds, the raw materials are cheap and readily available, the operation risk is low, and it is applicable to large-scale production. BRIEF DESCRIPTION OF THE DRAWINGS

[0008] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0009] Figure 1 This is a SEM image of the nitrogen-doped carbon nanotubes prepared in Example 1 of the present invention; Figure 2 This is a SEM energy spectrum of the nitrogen-doped carbon nanotubes prepared in Example 1 of the present invention; Figure 3 TEM image of nitrogen-doped carbon nanotubes prepared in Example 1 of the present invention; Figure 4 This is the Raman spectrum of the nitrogen-doped carbon nanotubes prepared in Example 1 of the present invention; Figure 5 This is a temperature curve diagram when preparing nitrogen-doped carbon nanotubes in Example 2 of the present invention; Figure 6This is a SEM image of the graphite felt surface after Joule heat flash evaporation in an ammonia atmosphere in Control Example 1 of the present invention. DETAILED DESCRIPTION

[0010] In view of the problems existing in the above-mentioned prior art, after long-term research and a large number of experiments, the inventors of this case proposed this technical solution, which mainly provides a method for rapidly preparing nitrogen-doped carbon nanotubes, using cheap and readily available carbon felt as a carrier and carbon source, coating ferric chloride on the surface of the carbon felt, and using ammonia as the only nitrogen source. Under the Joule heat response, the carbon felt heats up rapidly, and the carbon atoms become active under the catalytic action of ferric chloride and / or ferrocene, and growth and doping are achieved simultaneously in an ammonia atmosphere, so that self-supporting nitrogen-doped carbon nanotubes are rapidly obtained.

[0011] The technical solution, its implementation process and principle will be further explained as follows.

[0012] As one aspect of the technical solution of the present invention, a method for rapidly preparing nitrogen-doped carbon nanotubes involves: Providing carbon felt as a carrier and a carbon source; Coating a catalyst on the surface of the carbon felt to obtain a carbon felt with the catalyst coated on the surface; Ammonia is used as a nitrogen source. In an ammonia atmosphere, the carbon felt coated with a catalyst is electrically connected to a Joule heat generating device, and electricity is supplied to perform a Joule heat reaction at a high temperature to obtain nitrogen-doped carbon nanotubes.

[0013] In some specific embodiments, the catalyst may be at least one of ferric chloride, ferrocene, etc., but is not limited thereto.

[0014] In some specific embodiments, the carbon felt serves as a carrier and a carbon source, and specifically may be graphite felt (graphite fiber felt), but is not limited thereto.

[0015] In some specific embodiments, the resistance of the carbon felt is 0.5Ω~4Ω. The present invention utilizes the resistance detection function of the Joule heat generating device to feedback adjust the size of the carbon felt so that its resistance is within 0.5Ω~4Ω.

[0016] Furthermore, the carbon felt may have a thickness of 1 mm, a length of 2 to 4 cm, and a width of 1 to 2 cm, so as to obtain the required resistance.

[0017] In some specific embodiments, the method for rapidly preparing nitrogen-doped carbon nanotubes specifically includes: coating a catalyst on the surface of a carbon felt, and folding the carbon felt along a width or length direction to form a space enclosing the catalyst.

[0018] In some specific embodiments, the method for rapidly preparing nitrogen-doped carbon nanotubes specifically comprises: sealingly and electrically connecting the folded carbon felt to a Joule heat generating device, and placing the folded carbon felt in a reaction chamber of a reaction device.

[0019] In some specific embodiments, the method for rapidly preparing nitrogen-doped carbon nanotubes further comprises: introducing ammonia or a mixture of ammonia and an inert gas into the reaction chamber, controlling the ammonia concentration to 20% to 100% with a flow meter, and maintaining continuous ventilation.

[0020] In some specific embodiments, the method for rapidly preparing nitrogen-doped carbon nanotubes further comprises: first evacuating the reaction chamber, then introducing an inert gas (such as argon) to replace the inert atmosphere, and then introducing ammonia for more than 3 minutes at a flow ratio of 1:4, 1:2, 1:1 or 1:0 to the inert gas, so that the atmosphere in the reaction chamber is a mixed atmosphere of ammonia and argon, and the ventilation state is maintained during the generation of Joule heat.

[0021] In some specific implementation schemes, the discharge voltage of the Joule heat generating device is controlled to be 20V~60V, the current is 20~60A, the discharge time is 1~5s, and the pulse parameter conditions are 1~5 pulses, and the interruption time of each pulse is 1~5s.

[0022] In some specific embodiments, the peak temperature of the Joule heat reaction is 2900°C.

[0023] In some specific embodiments, the preparation time of the nitrogen-doped carbon nanotubes is within 5 seconds.

[0024] Furthermore, the diameter of the nitrogen-doped carbon nanotubes prepared by the present invention is above 100 nm.

[0025] Furthermore, in the nitrogen-doped carbon nanotubes prepared by the present invention, the nitrogen element is evenly distributed in the carbon material, and the content of the doped nitrogen element is 10-40wt%. The nitrogen doping ratio is easy to adjust, which is specifically achieved by controlling the ratio of ammonia and inert gas in the atmosphere.

[0026] In summary, the present invention uses carbon felt as a carbon source and carrier, uses ferric chloride and / or ferrocene as a catalyst, and uses an ammonia atmosphere as a nitrogen source. It is unnecessary to add a carbon source and a nitrogen source separately, and uses the Joule heat method to quickly heat up, and the reaction time is short. A one-step method of rapid Joule heat preparation of a self-supporting nitrogen-doped carbon nanotube composite material is also possible. At the same time, the preparation process is environmentally friendly, low-cost, the production time is measured in seconds, and the production risk is low.

[0027] The technical scheme of the present invention is further described in detail below in conjunction with several preferred embodiments and accompanying drawings. Obviously, the described embodiments are only a part of embodiments of the present invention, rather than all embodiments. It should be pointed out that the embodiments described below are intended to facilitate the understanding of the present invention, and do not have any limiting effect on them. Based on the embodiments in the present invention, all other embodiments obtained by ordinary technicians in the art without making creative work belong to the scope of protection of the present invention. The experimental methods for which specific conditions are not indicated in the following examples are usually according to conventional conditions, or according to the conditions recommended by the manufacturer. The experimental materials used in the embodiments used below, if not otherwise specified, can all be purchased by conventional biochemical reagent companies.

[0028] Example 1 (1) Cut the commercial 1mm thick graphite felt into suitable size, and use the resistance detection function of the Joule heat generating device to feedback and adjust the size of the graphite felt so that the resistance is within 0.5Ω~4Ω.

[0029] (2) Coat 30 mg of FeCl2 powder on the cut graphite felt and fold the graphite felt along the width direction to form a cavity to enclose the powder.

[0030] (3) Fix the graphite felt on the sample stage of the Joule heat generating device and transfer the sample stage to the quartz tube.

[0031] (4) After completing the sealed electrical connection between the sample stage and the outside world, close the valves of the gas washing bottle and the quartz tube, turn on the vacuum pump to evacuate the tube, and judge the vacuum level in the quartz tube according to the indication of the vacuum gauge. Then, introduce argon gas, replace the atmosphere in the quartz tube with argon gas, and then introduce ammonia gas for more than 3 minutes to make the atmosphere in the tube ammonia gas. Keep the tube ventilated during the reaction.

[0032] (5) The voltage, current and pulse parameters were set through the control end of the Joule heat generating device. The discharge voltage was set to 20 V and 44 V, and the pulses were pulsed five times in turn. The discharge time was 5 s. The quartz tube device emitted strong light, and the peak temperature reached 2900 °C, thus producing nitrogen-doped carbon nanotubes.

[0033] The SEM image of the nitrogen-doped carbon nanotubes prepared in this example is as follows: Figure 1 As shown in the figure, it can be seen that the carbon nanotubes grow on the graphite felt fibers as a substrate.

[0034] Figure 2 This is the SEM energy spectrum of the nitrogen-doped carbon nanotubes. It can be seen from the figure that the N element is evenly distributed, which is consistent with the C element distribution of the carbon nanotubes. At the same time, it is further confirmed that the obtained sample is a nitrogen-doped carbon nanotube with a nitrogen doping content of 40wt%.

[0035] Figure 3TEM image of the nitrogen-doped carbon nanotubes. From this image, it can be seen that the diameter of the obtained nitrogen-doped carbon nanotubes is above 100 nm.

[0036] Figure 4 is the Raman spectrum of the nitrogen-doped carbon nanotubes. D / I G It can be seen that the synthesized nitrogen-doped carbon nanotubes have large defects, which is consistent with the expectations of doping.

[0037] Example 2 (1) Cut the commercial 1mm thick graphite felt into suitable size, and use the resistance detection function of the Joule heat generating device to feedback and adjust the size of the graphite felt so that the resistance is within 0.5Ω~4Ω.

[0038] (2) Coat 30 mg of FeCl2 powder on the cut graphite felt, fold the graphite felt along the width direction to form a chamber to enclose the powder, and cut two smaller pieces of graphite felt to wrap the two ends of the folded graphite felt to reduce the contact resistance between the graphite felt and the sample stage electrode.

[0039] (3) Fix the graphite felt on the sample stage of the Joule heat generating device and transfer the sample stage to the quartz tube.

[0040] (4) After completing the sealed electrical connection between the sample stage and the outside world, close the valves of the gas washing bottle and the quartz tube, turn on the vacuum pump to evacuate the tube, and judge the vacuum level in the quartz tube according to the indication of the vacuum gauge. Then, introduce argon gas, replace the atmosphere in the quartz tube with argon gas, and then introduce ammonia gas. Use a flow meter to adjust the flow of the two atmospheres so that the atmosphere in the tube is a mixed gas of ammonia and argon gas. The flow ratio is ammonia: argon = 50:50 sccm. The nitrogen doping content obtained under this mixed atmosphere is 30wt%.

[0041] (5) The voltage, current and pulse parameters are set through the control end of the Joule heat generating device. The discharge voltage is set to 20 V and 44 V, and the pulses are pulsed five times in turn. The discharge time is 5 s. The quartz tube device emits strong light and the peak temperature reaches 2900 °C.

[0042] Figure 5 This is the temperature curve when preparing nitrogen-doped carbon nanotubes in this embodiment. It can be seen from the figure that the Joule heat rises very quickly and the peak temperature is close to 3000°C.

[0043] Example 3 (1) Cut the commercial 1mm thick graphite felt into suitable size, and use the resistance detection function of the Joule heat generating device to feedback and adjust the size of the graphite felt so that the resistance is within 0.5Ω~4Ω.

[0044] (2) Coat 30 mg of FeCl2 powder on the cut graphite felt, fold the graphite felt along the width direction to form a chamber to enclose the powder, and cut two smaller pieces of graphite felt to wrap the two ends of the folded graphite felt to reduce the contact resistance between the graphite felt and the sample stage electrode.

[0045] (3) Fix the graphite felt on the sample stage of the Joule heat generating device and transfer the sample stage to the quartz tube.

[0046] (4) After completing the sealed electrical connection between the sample stage and the outside world, close the valves of the gas washing bottle and the quartz tube, turn on the vacuum pump to evacuate the tube, and judge the vacuum level in the quartz tube according to the indication of the vacuum gauge. Then, introduce argon gas, replace the atmosphere in the quartz tube with argon gas, and then introduce ammonia gas. Use a flow meter to adjust the flow of the two atmospheres so that the atmosphere in the tube is a mixed gas of ammonia and argon gas. The flow ratio is ammonia: argon = 30:70 sccm. The nitrogen doping content obtained under this mixed atmosphere is 24wt%.

[0047] (5) The voltage, current and pulse parameters are set through the control end of the Joule heat generating device. The discharge voltage is set to 20 V and 44 V, and the pulses are pulsed five times in turn. The discharge time is 5 s. The quartz tube device emits strong light and the peak temperature reaches 2900 °C.

[0048] Example 4 (1) Cut the commercial 1mm thick graphite felt into suitable size, and use the resistance detection function of the Joule heat generating device to feedback and adjust the size of the graphite felt so that the resistance is within 0.5Ω~4Ω.

[0049] (2) Coat 30 mg of FeCl2 powder on the cut graphite felt, fold the graphite felt along the width direction to form a chamber to enclose the powder, and cut two smaller pieces of graphite felt to wrap the two ends of the folded graphite felt to reduce the contact resistance between the graphite felt and the sample stage electrode.

[0050] (3) Fix the graphite felt on the sample stage of the Joule heat generating device and transfer the sample stage to the quartz tube.

[0051] (4) After completing the sealed electrical connection between the sample stage and the outside world, close the valves of the gas washing bottle and the quartz tube, turn on the vacuum pump to evacuate the tube, and judge the vacuum level in the quartz tube according to the indication of the vacuum gauge. Then, introduce argon gas, replace the atmosphere in the quartz tube with argon gas, and then introduce ammonia gas. Use a flow meter to adjust the flow of the two atmospheres so that the atmosphere in the tube is a mixed gas of ammonia and argon gas. The flow ratio is ammonia: argon = 20:80 sccm. The nitrogen doping content obtained under this mixed atmosphere is 18%wt.

[0052] (5) The voltage, current and pulse parameters are set through the control end of the Joule heat generating device. The discharge voltage is set to 20 V and 44 V, and the pulses are pulsed five times in turn. The discharge time is 5 s. The quartz tube device emits strong light and the peak temperature reaches 2900 °C.

[0053] Example 5 (1) Cut the commercial 1mm thick graphite felt into suitable size, and use the resistance detection function of the Joule heat generating device to feedback and adjust the size of the graphite felt so that the resistance is within 0.5Ω~4Ω.

[0054] (2) Spread 30 mg of ferrocene powder on the cut graphite felt, fold the graphite felt along the width direction to form a chamber to enclose the powder, and cut two smaller pieces of graphite felt to wrap the two ends of the folded graphite felt to reduce the contact resistance between the graphite felt and the sample stage electrode.

[0055] (3) Fix the graphite felt on the sample stage of the Joule heat generating device and transfer the sample stage to the quartz tube.

[0056] (4) After completing the sealed electrical connection between the sample stage and the outside world, close the valves of the gas washing bottle and the quartz tube, turn on the vacuum pump to evacuate the tube, and judge the vacuum level in the quartz tube according to the indication of the vacuum gauge. Then, introduce argon gas, replace the atmosphere in the quartz tube with argon gas, and then introduce ammonia gas. Use a flow meter to adjust the flow of the two atmospheres so that the atmosphere in the tube is a mixed gas of ammonia and argon. The flow ratio is ammonia:argon = 20:80sccm. The nitrogen doping content obtained under this mixed atmosphere is 18wt%.

[0057] (5) The voltage, current and pulse parameters are set through the control end of the Joule heat generating device. The discharge voltage is set to 20 V and 44 V, and the pulses are pulsed five times in turn. The discharge time is 5 s. The quartz tube device emits strong light and the peak temperature reaches 2900 °C.

[0058] Example 6 Compared with Example 1, the present embodiment is different in that: the voltage and current and pulse parameter settings are performed through the control end of the Joule heat generating device, the discharge voltage is set to 20V and 60V pulsed 3 times in turn, the discharge time is 1s, the quartz tube device emits strong light, the peak temperature reaches 2900°C, and nitrogen-doped carbon nanotubes are obtained.

[0059] Example 7 The present embodiment is different from the embodiment 5 in that the voltage, current and pulse parameters are set by controlling the Joule heat generating device, the discharge voltage is set to 20V and 60V pulsed once alternately, the discharge time is 2s, the quartz tube device emits strong light, the peak temperature reaches 2900°C, and nitrogen-doped carbon nanotubes are obtained.

[0060] Comparative Example 1 This comparative example is basically the same as Example 1, except that an ammonia environment without a catalyst is used.

[0061] It is impossible to obtain nitrogen-doped carbon nanotubes grown in one step. Figure 6 This is the SEM image of the carbon felt prepared in this control example. It can be seen that no carbon nanotubes grow on the surface of the carbon felt in this control example.

[0062] In addition, the inventors of this case also referred to the aforementioned embodiments and conducted experiments with other raw materials, process operations, and process conditions described in this specification, and obtained relatively ideal results.

[0063] It should be understood that the above are only specific application examples of the present invention and do not constitute any limitation on the protection scope of the present invention. Any technical solution formed by equivalent transformation or equivalent replacement falls within the protection scope of the present invention.

Claims

1. A method for rapidly preparing nitrogen-doped carbon nanotubes, characterized in that: include: Providing carbon felt as a carrier and a carbon source; Coating a catalyst on the surface of the carbon felt to obtain a carbon felt with the catalyst coated on the surface; Ammonia is used as a nitrogen source. In an ammonia atmosphere, the carbon felt coated with a catalyst is electrically connected to a Joule heat generating device, and electricity is supplied to perform a Joule heat reaction at a high temperature to obtain nitrogen-doped carbon nanotubes.

2. The method for rapidly preparing nitrogen-doped carbon nanotubes according to claim 1, characterized in that: The carbon felt includes graphite felt; and / or the catalyst includes ferric chloride and / or ferrocene.

3. The method for rapidly preparing nitrogen-doped carbon nanotubes according to claim 1, characterized in that: The carbon felt has a resistance of 0.5Ω~4Ω.

4. The method for rapidly preparing nitrogen-doped carbon nanotubes according to claim 1, characterized in that: include: The catalyst is coated on the surface of the carbon felt, and the carbon felt is folded along the width or length direction to form a space enclosing the catalyst.

5. The method for rapidly preparing nitrogen-doped carbon nanotubes according to claim 4, characterized in that: include: The folded carbon felt is sealed and electrically connected to a Joule heat generating device and is placed in a reaction chamber of a reaction device.

6. The method for rapidly preparing nitrogen-doped carbon nanotubes according to claim 5, characterized in that: include: Ammonia or a mixture of ammonia and inert gas is introduced into the reaction chamber, and the ammonia concentration is controlled to be 20%~100%, and continuous ventilation is maintained.

7. The method for rapidly preparing nitrogen-doped carbon nanotubes according to claim 1 or 5, characterized in that: The discharge voltage of the Joule heat generating device is controlled to be 20~60V, the current is 20~60A, the discharge time is 1~5s, and the pulse parameter conditions are 1~5 pulses, and the interruption time of each pulse is 1~5s.

8. The method for rapidly preparing nitrogen-doped carbon nanotubes according to claim 7, characterized in that: The peak temperature of the Joule heat reaction is 2900°C.

9. The method for rapidly preparing nitrogen-doped carbon nanotubes according to claim 1, characterized in that: The preparation time of the nitrogen-doped carbon nanotubes is within 5 seconds.

10. The method for rapidly preparing nitrogen-doped carbon nanotubes according to claim 1, characterized in that: The diameter of the nitrogen-doped carbon nanotube is greater than 100 nm, and the content of nitrogen doped in the nitrogen-doped carbon nanotube is 10% to 40%.

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