Carbon nano tube simultaneously doped with nitrogen and phosphorus as well as preparation method and application of carbon nano tube

Abstract

The invention discloses a carbon nanotube simultaneously doped with nitrogen and phosphorus and a preparation method and application thereof, the preparation method comprises the following steps: (1) preparing a reaction liquid: adding acetonitrile into absolute ethyl alcohol, uniformly mixing, then adding triphenyl phosphate, uniformly mixing, then adding a catalyst, and finally performing ultrasonic treatment to obtain the reaction liquid; (2) air replacement: argon is introduced into the quartz tube reactor for air replacement; (3) heating reaction: after the replacement is completed, heating and introducing carrier gas, pumping the obtained reaction liquid into the quartz tube reactor after the temperature is increased to the reaction temperature, and starting the reaction; and (4) after the reaction is completed, stopping pumping the reaction liquid, maintaining the reaction temperature, reacting for a period of time, finally cooling to room temperature, and taking out the reactant, thereby obtaining the carbon nanotube product. The carbon nanotube doped with nitrogen and phosphorus elements prepared on the basis of the floating catalytic chemical vapor deposition method has excellent electrochemical performance; and the preparation process is easy for large-scale production and has an excellent application prospect.

Description

Technical Field

[0001] The invention belongs to the technical field of carbon nanotube preparation, and in particular relates to a carbon nanotube doped with nitrogen and phosphorus at the same time, and a preparation method and application thereof. Background Art

[0002] Nanocarbon materials are a new type of nanomaterials, mainly including carbon nanotubes, carbon nanofibers, and carbon nanospheres. Among them, carbon nanotubes have shown broad application prospects since they were discovered in 1991, due to their unique structure and excellent mechanical, electrical and chemical properties. They have attracted great attention from many scientists in the fields of materials, physics, electronics, chemistry, etc., and have become the research frontier and hotspot in the field of international new materials.

[0003] At present, the preparation of carbon nanotubes mainly includes three methods: arc discharge method, laser ablation method and chemical vapor deposition method. The arc discharge method uses graphite rods as the positive and negative electrodes, and the anode graphite rod is loaded with catalyst particles. In a vacuum reaction chamber filled with a certain inert gas, hydrogen or other gas, the solid graphite carbon source of the anode is evaporated by the high-temperature arc generated between the two electrodes, so that the carbon atoms are precipitated into tubular, granular, etc. at the cathode; the carbon nanotubes prepared by the arc discharge method have a high degree of graphitization and fewer defects, but this method has high requirements for equipment, high growth temperature and low yield. The laser ablation method, also known as the laser evaporation method, is a method of preparing carbon nanotubes by bombarding a transition metal-doped graphite target with a laser under the protection of an inert gas at a temperature of about 1200°C to form gaseous carbon atoms under the action of a catalyst; the carbon nanotubes prepared by the laser ablation method have a high purity and controllable conditions, but the equipment used is expensive and the production cost is high. Chemical vapor deposition (CVD) is a method of decomposing a carbon source in the presence of a catalyst at a relatively low temperature, causing the carbon atoms to dissolve on the catalyst particles and precipitate in the form of tubes to form carbon nanotubes. CVD is considered one of the most promising methods due to its mild reaction conditions and high yield.

[0004] The floating catalytic chemical vapor deposition method is an improved method of the chemical vapor deposition method. It is a process in which carbon source and catalyst are volatilized into gaseous state and various elements are cracked out, and then carbon nanotubes are formed under the catalytic action of the catalyst. It has the advantages of simple process, in-situ preparation of catalyst, and easy realization of continuous production. In the prior art, the patent document CN114538416 B adopts the floating catalytic chemical vapor deposition method to introduce carbon dioxide with mild oxidizing properties under high temperature conditions to promote carbon source conversion and maintain catalyst activity. At the same time, it can also play a role in supplementing carbon source, improve preparation efficiency and product yield; the improved floating catalyst chemical vapor deposition method provided by the master's thesis (Guo Shuyu. Controllable preparation of semiconductor single-walled carbon nanotubes by floating catalyst chemical vapor deposition method [D]. Northeastern University, 2019.) uses benzyl alcohol as the carbon source, and by adjusting and optimizing the growth parameters of carbon nanotubes, high-quality carbon nanotubes with relatively uniform diameter distribution, high purity, good structural integrity and high G / D ratio are obtained. The surface inertness of carbon nanotubes makes them poorly soluble, which affects the efficiency of chemical reactions. Therefore, the modification of carbon nanotubes has become very important. For example, patent document CN102757031B provides a method for preparing nitrogen-phosphorus modified and doped carbon nanotubes, but it is prepared based on the traditional chemical vapor deposition method. How to prepare carbon nanotubes modified with different elements based on floating catalytic chemical vapor deposition to give them rich properties is still worth studying. Summary of the invention

[0005] In view of the shortcomings of the prior art, the purpose of the present invention is to provide a carbon nanotube doped with nitrogen and phosphorus and a preparation method and application thereof. The carbon nanotube doped with nitrogen and phosphorus elements prepared by floating catalytic chemical vapor deposition has excellent electrochemical properties; and the preparation process is easy to scale up production and has excellent application prospects.

[0006] In order to achieve the above object, the present invention adopts the following technical solution:

[0007] In a first aspect, the present invention provides a method for preparing carbon nanotubes doped with nitrogen and phosphorus, comprising the following steps:

[0008] (1) preparing a reaction solution: adding acetonitrile to anhydrous ethanol, mixing well, then adding triphenyl phosphate, mixing well, then adding a catalyst, and finally ultrasonically treating to obtain a reaction solution for later use;

[0009] (2) Air replacement: Argon gas is introduced into the quartz tube reactor to replace the air;

[0010] (3) Heating reaction: After the replacement is completed, the temperature is increased and a carrier gas is introduced. When the temperature reaches the reaction temperature, the reaction solution obtained in step (1) is pumped into a quartz tube reactor to start the reaction;

[0011] (4) After the reaction is completed, stop pumping the reaction liquid, maintain the reaction temperature for a period of time, and finally cool to room temperature, take out the reactant, and obtain the carbon nanotube product.

[0012] As a further preferred embodiment of the technical solution of the present invention, in step (1), the catalyst is a mixture of ferrocene and cobalt nitrate.

[0013] As a further preferred embodiment of the technical solution of the present invention, in step (1), the mass ratio of acetonitrile, anhydrous ethanol and triphenyl phosphate is 0.2-0.8:1:0.04-0.09; in the reaction solution, the concentration of ferrocene is 0.005-0.02 g / mL, and the concentration of cobalt nitrate is 0.001-0.015 g / mL.

[0014] As a further preferred embodiment of the technical solution of the present invention, in step (2), the flow rate of argon gas is 150 to 250 sccm.

[0015] As a further preferred embodiment of the technical solution of the present invention, in step (3), the heating rate is 5-50°C / min, the carrier gas is a mixture of hydrogen and argon, the flow rate of hydrogen is 50-200sccm, and the flow rate of argon is 200-400sccm.

[0016] As a further preferred embodiment of the technical solution of the present invention, in step (3), the reaction temperature is 750-850° C., the reaction time is 0.5-5 h, and the pumping rate of the reaction solution is 0.05-0.2 mL / min.

[0017] As a further preferred embodiment of the technical solution of the present invention, in step (4), the reaction temperature is maintained for a reaction time of 10 to 60 minutes.

[0018] As a further preferred embodiment of the technical solution of the present invention, in step (4), the cooling process is: first stop the introduction of hydrogen and keep introducing argon until cooling to room temperature.

[0019] In a second aspect, the present invention also aims to protect the carbon nanotube product prepared by the above method.

[0020] In a third aspect, the present invention also aims to protect the use of the above-mentioned carbon nanotubes in the preparation of electrochemical materials.

[0021] Compared with the prior art, the present invention has the following beneficial effects:

[0022] (1) The present invention creatively implements a floating catalytic chemical vapor deposition method to produce a carbon nanotube product, and the obtained carbon nanotube product has excellent electrochemical properties. Moreover, based on the advantage of the floating catalytic chemical vapor deposition method that is easy to produce continuously, the carbon nanotube product in the present invention can be produced continuously and on a large scale, and has good application prospects.

[0023] (2) The method for preparing carbon nanotubes provided by the present invention uses acetonitrile as the N source, triphenyl phosphate as the P source, and anhydrous ethanol as the C source, taking into account the solubility of each substance, avoiding the use of aromatic substances such as benzene and xylene, and reducing the toxicity risk; the performance of the carbon nanotube product after doping and reaction is greatly improved; I D / I G Large, with many defects and better activity.

[0024] (3) In the method for preparing carbon nanotubes provided by the present invention, the catalyst is repeatedly screened, and a composite system of ferrocene and cobalt nitrate is used, which greatly improves the catalytic performance. The optimal usage ratio of the two is about 2:1.

[0025] (4) The method for preparing carbon nanotubes provided by the present invention repeatedly optimizes the process parameters, carrier types, etc. to obtain the best production process conditions.

[0026] In summary, the preparation of nitrogen and phosphorus co-doped carbon nanotubes based on the floating catalytic chemical vapor deposition method of the present invention is creatively proposed by the applicant, the preparation method is easy to implement, the obtained product has good performance and has potential application value. DETAILED DESCRIPTION

[0027] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0028] Unless otherwise specified, all commodities in this invention are purchased through market channels.

[0029] A method for preparing carbon nanotubes doped with nitrogen and phosphorus comprises the following steps:

[0030] (1) preparing a reaction solution: adding acetonitrile to anhydrous ethanol, mixing well, then adding triphenyl phosphate, mixing well, then adding a catalyst, and finally ultrasonically treating to obtain a reaction solution for later use;

[0031] (2) Air replacement: Argon gas is introduced into the quartz tube reactor to replace the air;

[0032] (3) Heating reaction: After the replacement is completed, the temperature is increased and a carrier gas is introduced. When the temperature reaches the reaction temperature, the reaction solution obtained in step (1) is pumped into a quartz tube reactor to start the reaction;

[0033] (4) After the reaction is completed, stop pumping the reaction liquid, maintain the reaction temperature for a period of time, and finally cool to room temperature, take out the reactant, and obtain the carbon nanotube product.

[0034] In the above technical scheme, the preparation of carbon nanotubes is based on the floating catalytic chemical vapor deposition method, which has the advantages of simple process, in-situ preparation of catalyst, and easy to realize continuous production. In order to improve the reaction activity and comprehensive performance of carbon nanotubes, the applicant creatively proposed to dope and modify carbon nanotubes in the floating catalytic chemical vapor deposition method around doping modification. Specifically, after repeated screening, the carbon source was selected as anhydrous ethanol, which on the one hand overcomes the disadvantages of high toxicity and pollution when xylene and benzene are used as carbon sources, and on the other hand, is conducive to the dissolution of cobalt nitrate; after repeated screening, the applicant selected acetonitrile as the nitrogen source and triphenyl phosphate as the phosphorus source, which not only ensured the effect of carbon nanotube modification, but also ensured the solubility of triphenyl phosphate.

[0035] In the above technical scheme, the quartz tube reactor is a common laboratory instrument and equipment, which has been used and reported in many floating catalytic chemical vapor deposition methods. Its specific structure is not described in the present invention; similarly, the peristaltic pump involved in the pumping of the reaction liquid is also a conventional equipment on the market, and the present invention does not make specific requirements on its model and structure.

[0036] In step (1) of the above-mentioned process for preparing carbon nanotubes, the catalyst is a mixture of ferrocene and cobalt nitrate. This catalyst composite system is obtained by the applicant after repeated screening. For example, other composite systems such as ferrocene and cobaltocene, ferric nitrate and cobalt nitrate have better catalytic effects.

[0037] Furthermore, in the above step (1), the mass ratio of acetonitrile, anhydrous ethanol, and triphenyl phosphate after optimized coupling is 0.2-0.8:1:0.04-0.09, and the amount of each substance can be flexibly adjusted within this range. It should be noted that in the reaction solution, the concentration of ferrocene is 0.005-0.02 g / mL, and the concentration of cobalt nitrate is 0.001-0.015 g / mL. In the catalyst compound system, the catalytic effect is better when the amount of iron is higher than the amount of cobalt, and the optimal mass ratio of the two is about 2:1.

[0038] In step (2) of the above-mentioned process for preparing carbon nanotubes, the flow rate of the argon gas introduced for replacement can be flexibly adjusted, and the preferred range is 150 to 250 sccm; more preferably, it is 180 sccm.

[0039] In step (3) of the above-mentioned process for preparing carbon nanotubes, the heating rate is 5 to 50°C / min. It is understood that the heating rate can be 5°C / min, 6°C / min, 7°C / min, 8°C / min, 9°C / min, 10°C / min, 11°C / min, 12°C / min, 13°C / min, 14°C / min, 15°C / min, 20°C / min, 25°C / min, 30°C / min, 35°C / min, 40°C / min, 45°C / min, 50°C / min or any value within the above range. The carrier gas is a mixture of hydrogen and argon, and the flow ratio of argon to hydrogen is about 2 to 3, more preferably, 2.5:1. Specifically, the flow rate of hydrogen is 50 to 200 sccm, and the flow rate of argon is 200 to 400 sccm; for example, when the flow rate of argon is 350 sccm, the flow rate of hydrogen is about 140 sccm.

[0040] In step (3) of the above-mentioned process for preparing carbon nanotubes, the reaction temperature is also important. The optimized range of the reaction temperature in the present preparation process is 750-850°C, and the reaction time is 0.5-5h; of course, the more preferred reaction temperature is 790°C; the preferred reaction time is about 35min. During the reaction, the pumping rate of the reaction solution is 0.05-0.2mL / min. It can be understood that the pumping rate can be 0.05mL / min, 0.06mL / min, 0.07mL / min, 0.08mL / min, 0.09mL / min, 0.1mL / min, 0.11mL / min, 0.12mL / min, 0.13mL / min, 0.14mL / min, 0.15mL / min or any value within the above range; more preferably, the pumping rate is 0.12mL / min.

[0041] In step (4) of the above-mentioned process for preparing carbon nanotubes, the reaction is maintained for a period of time after the reaction is completed, which is conducive to the full reaction of the material system. Specifically, the reaction temperature is maintained for a reaction time of 10 to 60 minutes. It can be understood that the above-mentioned time can be a value among 10 minutes, 15 minutes, 20 minutes, 25 minutes, 30 minutes, 35 minutes, 40 minutes, 45 minutes, 50 minutes, 55 minutes, 60 minutes or any value within the above-mentioned range; more preferably, it is 25 minutes.

[0042] In step (4) of the above-mentioned process for preparing carbon nanotubes, during cooling, the introduction of hydrogen is first stopped, and then the introduction of argon is maintained until cooling to room temperature.

[0043] After the carbon nanotubes are prepared, they can be used for preparing electrochemical materials. The application form is not specifically limited in the present invention, such as working electrodes.

[0044] In order to more specifically present the advantages and properties of the carbon nanotubes prepared by the present invention, the present invention provides the following examples for further description.

[0045] Example 1

[0046] A method for preparing carbon nanotubes doped with nitrogen and phosphorus comprises the following steps:

[0047] (1) preparing a reaction solution: adding acetonitrile to anhydrous ethanol, mixing well, then adding triphenyl phosphate, mixing well, then adding a catalyst (ferrocene and cobalt nitrate), and finally ultrasonically treating for 10 minutes to obtain a reaction solution for standby use; wherein the mass ratio of acetonitrile, anhydrous ethanol, and triphenyl phosphate is 0.5:1:0.06, and the concentration of ferrocene in the reaction solution is 0.014 g / mL, and the concentration of cobalt nitrate is 0.007 g / mL;

[0048] (2) Air replacement: Argon gas at a flow rate of 180 sccm was introduced into the quartz tube reactor for air replacement;

[0049] (3) Heating reaction: After the replacement is completed, the temperature is raised and a carrier gas (a mixture of argon and hydrogen with flow rates of 350 sccm and 140 sccm, respectively) is introduced. When the temperature is raised to a reaction temperature of 790°C at a heating rate of 6°C / min, the reaction solution obtained in step (1) is pumped into the quartz tube reactor at a rate of 0.12 mL / min and the reaction is started for 35 min.

[0050] (4) After the reaction is completed, stop pumping the reaction liquid, maintain the reaction temperature for 25 minutes, and finally stop passing hydrogen and keep passing argon until it cools to room temperature. Then take out the reactants to obtain carbon nanotube products.

[0051] Example 2

[0052] A method for preparing carbon nanotubes doped with nitrogen and phosphorus comprises the following steps:

[0053] (1) preparing a reaction solution: adding acetonitrile to anhydrous ethanol, mixing well, then adding triphenyl phosphate, mixing well, then adding a catalyst (ferrocene and cobalt nitrate), and finally ultrasonically treating for 10 minutes to obtain a reaction solution for standby use; wherein the mass ratio of acetonitrile, anhydrous ethanol, and triphenyl phosphate is 0.5:1:0.06, and the concentration of ferrocene in the reaction solution is 0.014 g / mL, and the concentration of cobalt nitrate is 0.007 g / mL;

[0054] (2) Air replacement: Argon gas at a flow rate of 180 sccm was introduced into the quartz tube reactor for air replacement;

[0055] (3) Heating reaction: After the replacement is completed, the temperature is raised and a carrier gas (a mixture of argon and hydrogen with flow rates of 350 sccm and 140 sccm, respectively) is introduced. When the temperature is raised to a reaction temperature of 795°C at a heating rate of 6°C / min, the reaction solution obtained in step (1) is pumped into a quartz tube reactor at a rate of 0.11 mL / min and the reaction is started for 40 minutes;

[0056] (4) After the reaction is completed, stop pumping the reaction liquid, maintain the reaction temperature for 20 minutes, and finally stop passing hydrogen and keep passing argon until it cools to room temperature. Then take out the reactants to obtain carbon nanotube products.

[0057] Example 3

[0058] A method for preparing carbon nanotubes doped with nitrogen and phosphorus comprises the following steps:

[0059] (1) preparing a reaction solution: adding acetonitrile to anhydrous ethanol, mixing well, then adding triphenyl phosphate, mixing well, then adding a catalyst (ferrocene and cobalt nitrate), and finally ultrasonically treating for 10 minutes to obtain a reaction solution for standby use; wherein the mass ratio of acetonitrile, anhydrous ethanol, and triphenyl phosphate is 0.5:1:0.06, and the concentration of ferrocene in the reaction solution is 0.014 g / mL, and the concentration of cobalt nitrate is 0.007 g / mL;

[0060] (2) Air replacement: Argon gas at a flow rate of 150 sccm was introduced into the quartz tube reactor for air replacement;

[0061] (3) Heating reaction: After the replacement is completed, the temperature is raised and a carrier gas (a mixture of argon and hydrogen with flow rates of 340 sccm and 150 sccm, respectively) is introduced. When the temperature is raised to a reaction temperature of 800°C at a heating rate of 5°C / min, the reaction solution obtained in step (1) is pumped into the quartz tube reactor at a rate of 0.11 mL / min and the reaction is started for 40 minutes;

[0062] (4) After the reaction is completed, stop pumping the reaction liquid, maintain the reaction temperature for 20 minutes, and finally stop passing hydrogen and keep passing argon until it cools to room temperature. Then take out the reactants to obtain carbon nanotube products.

[0063] Comparative Example 1

[0064] Compared with Example 1, in Comparative Example 1, only ferrocene is used as the catalyst, and the total amount of the catalyst is the same as that of Example 1. Specifically, a method for preparing carbon nanotubes doped with nitrogen and phosphorus comprises the following steps:

[0065] (1) preparing a reaction solution: adding acetonitrile to anhydrous ethanol, mixing well, then adding triphenyl phosphate, mixing well, then adding a catalyst (ferrocene), and finally subjecting the mixture to ultrasonic treatment for 10 minutes to obtain a reaction solution for later use; wherein the mass ratio of acetonitrile, anhydrous ethanol, and triphenyl phosphate is 0.5:1:0.06;

[0066] (2) Air replacement: Argon gas at a flow rate of 180 sccm was introduced into the quartz tube reactor for air replacement;

[0067] (3) Heating reaction: After the replacement is completed, the temperature is raised and a carrier gas (a mixture of argon and hydrogen with flow rates of 350 sccm and 140 sccm, respectively) is introduced. When the temperature is raised to a reaction temperature of 790°C at a heating rate of 6°C / min, the reaction solution obtained in step (1) is pumped into the quartz tube reactor at a rate of 0.12 mL / min and the reaction is started for 35 min.

[0068] (4) After the reaction is completed, stop pumping the reaction liquid, maintain the reaction temperature for 25 minutes, and finally stop passing hydrogen and keep passing argon until it cools to room temperature. Then take out the reactants to obtain carbon nanotube products.

[0069] Comparative Example 2

[0070] Compared with Example 1, the catalyst cobalt ferric nitrate in Comparative Example 2 is replaced by cobaltocene, and the rest is the same. Specifically, a method for preparing carbon nanotubes doped with nitrogen and phosphorus comprises the following steps:

[0071] (1) preparing a reaction solution: adding acetonitrile to anhydrous ethanol, mixing well, then adding triphenyl phosphate, mixing well, then adding a catalyst (ferrocene and cobaltocene), and finally ultrasonically treating for 10 minutes to obtain a reaction solution for standby use; wherein the mass ratio of acetonitrile, anhydrous ethanol, and triphenyl phosphate is 0.5:1:0.06, and the concentration of ferrocene in the reaction solution is 0.014 g / mL, and the concentration of cobaltocene is 0.007 g / mL;

[0072] (2) Air replacement: Argon gas at a flow rate of 180 sccm was introduced into the quartz tube reactor for air replacement;

[0073] (3) Heating reaction: After the replacement is completed, the temperature is raised and a carrier gas (a mixture of argon and hydrogen with flow rates of 350 sccm and 140 sccm, respectively) is introduced. When the temperature is raised to a reaction temperature of 790°C at a heating rate of 6°C / min, the reaction solution obtained in step (1) is pumped into the quartz tube reactor at a rate of 0.12 mL / min and the reaction is started for 35 min.

[0074] (4) After the reaction is completed, stop pumping the reaction liquid, maintain the reaction temperature for 25 minutes, and finally stop passing hydrogen and keep passing argon until it cools to room temperature. Then take out the reactants to obtain carbon nanotube products.

[0075] Comparative Example 3

[0076] Compared with Example 1, the dosage ratio of the catalyst in Comparative Example 3 was adjusted, that is, the ratio of the two was adjusted to 1:1. Specifically, a method for preparing carbon nanotubes doped with nitrogen and phosphorus comprises the following steps:

[0077] (1) preparing a reaction solution: adding acetonitrile to anhydrous ethanol, mixing well, then adding triphenyl phosphate, mixing well, then adding a catalyst (ferrocene and cobalt nitrate), and finally ultrasonically treating for 10 minutes to obtain a reaction solution for standby use; wherein the mass ratio of acetonitrile, anhydrous ethanol, and triphenyl phosphate is 0.5:1:0.06, and the concentration of ferrocene in the reaction solution is 0.0105 g / mL, and the concentration of cobalt nitrate is 0.0105 g / mL;

[0078] (2) Air replacement: Argon gas at a flow rate of 180 sccm was introduced into the quartz tube reactor for air replacement;

[0079] (3) Heating reaction: After the replacement is completed, the temperature is raised and a carrier gas (a mixture of argon and hydrogen with flow rates of 350 sccm and 140 sccm, respectively) is introduced. When the temperature is raised to a reaction temperature of 790°C at a heating rate of 6°C / min, the reaction solution obtained in step (1) is pumped into the quartz tube reactor at a rate of 0.12 mL / min and the reaction is started for 35 min.

[0080] (4) After the reaction is completed, stop pumping the reaction liquid, maintain the reaction temperature for 25 minutes, and finally stop passing hydrogen and keep passing argon until it cools to room temperature. Then take out the reactants to obtain carbon nanotube products.

[0081] Comparative Example 4

[0082] Compared with Example 1, in Comparative Example 4, phosphorus modification is not performed, that is, the addition of triphenyl phosphate is omitted. Specifically, a method for preparing carbon nanotubes doped with nitrogen and phosphorus comprises the following steps:

[0083] (1) preparing a reaction solution: adding acetonitrile to anhydrous ethanol, mixing well, then adding a catalyst (ferrocene and cobalt nitrate), and finally ultrasonically treating for 10 min to obtain a reaction solution for later use; wherein the mass ratio of acetonitrile to anhydrous ethanol is 0.5:1, and the concentration of ferrocene in the reaction solution is 0.014 g / mL, and the concentration of cobalt nitrate is 0.007 g / mL;

[0084] (2) Air replacement: Argon gas at a flow rate of 180 sccm was introduced into the quartz tube reactor for air replacement;

[0085] (3) Heating reaction: After the replacement is completed, the temperature is raised and a carrier gas (a mixture of argon and hydrogen with flow rates of 350 sccm and 140 sccm, respectively) is introduced. When the temperature is raised to a reaction temperature of 790°C at a heating rate of 6°C / min, the reaction solution obtained in step (1) is pumped into the quartz tube reactor at a rate of 0.12 mL / min and the reaction is started for 35 min.

[0086] (4) After the reaction is completed, stop pumping the reaction liquid, maintain the reaction temperature for 25 minutes, and finally stop passing hydrogen and keep passing argon until it cools to room temperature. Then take out the reactants to obtain carbon nanotube products.

[0087] Next, the carbon nanotube products prepared in Example 1 and Comparative Examples 1 to 4 were subjected to performance tests, as follows:

[0088] The obtained carbon nanotube product was first washed with 6 mol / L hydrochloric acid and dried, then heated and refluxed with concentrated nitric acid for 2.5 h, and finally filtered, washed, and dried to complete the purification of the carbon nanotubes. First, Raman analysis was performed on the purified carbon nanotubes to calculate I D / I G Next, the purified carbon nanotubes (2.5 μg) were added to 450 μL of anhydrous ethanol, and after oscillation and dispersion, 5 μL was added dropwise to the glassy carbon electrode and dried at room temperature. Subsequently, the electrode obtained above was used as the working electrode, the Ag / AgCl electrode was used as the reference electrode, and the platinum ring electrode was used as the auxiliary electrode. A linear scan was performed in an oxygen-saturated 0.1 mol / L KOH solution at a scan rate of 5 mV / s to obtain the oxygen reduction catalytic performance data of the catalyst. The specific results are shown in Table 1.

[0089] Table 1

[0090] Starting potential / V Half-wave potential / V <![CDATA[I D / I G ]]> Example 1 -0.009 -0.088 1.24 Comparative Example 1 -0.028 -0.145 1.05 Comparative Example 2 -0.016 -0.112 1.15 Comparative Example 3 -0.013 -0.105 1.17 Comparative Example 4 -0.039 -0.176 0.98

[0091] As can be seen from Table 1, the carbon nanotubes prepared in the present application exhibit excellent oxygen reduction catalytic performance, and the onset potential and half-wave potential are shifted compared with the comparative example; and the I D / I G The larger value indicates that after nitrogen and phosphorus co-modification, there are more lattices and the degree of graphitization is relatively lower.

[0092] The present invention illustrates the technical concept of the present invention through the above-mentioned embodiments, but the present invention is not limited to the above-mentioned embodiments, that is, it does not mean that the present invention must rely on the above-mentioned embodiments to be implemented. Those skilled in the art should understand that any improvement of the present invention, equivalent replacement of individual raw materials of the product of the present invention, addition of auxiliary components, selection of specific methods, etc., all fall within the protection scope and disclosure scope of the present invention.

Claims

1. A method for preparing carbon nanotubes doped with nitrogen and phosphorus, characterized in that: The steps include: (1) preparing a reaction solution: adding acetonitrile to anhydrous ethanol, mixing well, then adding triphenyl phosphate, mixing well, then adding a catalyst, and finally ultrasonically treating to obtain a reaction solution for later use; (2) Air replacement: Argon gas is introduced into the quartz tube reactor to replace the air; (3) Heating reaction: After the replacement is completed, the temperature is increased and a carrier gas is introduced. When the temperature reaches the reaction temperature, the reaction solution obtained in step (1) is pumped into a quartz tube reactor to start the reaction; (4) After the reaction is completed, stop pumping the reaction liquid, maintain the reaction temperature for a period of time, and finally cool to room temperature, take out the reactant, and obtain the carbon nanotube product.

2. The method for preparing carbon nanotubes doped with nitrogen and phosphorus according to claim 1, characterized in that: In step (1), the catalyst is a mixture of ferrocene and cobalt nitrate.

3. The method for preparing carbon nanotubes doped with nitrogen and phosphorus according to claim 2, characterized in that: In step (1), the mass ratio of acetonitrile, anhydrous ethanol and triphenyl phosphate is 0.2-0.8:1:0.04-0.09; in the reaction solution, the concentration of ferrocene is 0.005-0.02 g / mL, and the concentration of cobalt nitrate is 0.001-0.015 g / mL.

4. The method for preparing carbon nanotubes doped with nitrogen and phosphorus according to claim 1, characterized in that: In step (2), the flow rate of argon gas is 150-250 sccm.

5. The method for preparing carbon nanotubes doped with nitrogen and phosphorus according to claim 1, characterized in that: In step (3), the heating rate is 5-50°C / min, the carrier gas is a mixture of hydrogen and argon, the flow rate of hydrogen is 50-200sccm, and the flow rate of argon is 200-400sccm.

6. The method for preparing carbon nanotubes doped with nitrogen and phosphorus according to claim 1, characterized in that: In step (3), the reaction temperature is 750-850° C., the reaction time is 0.5-5 h, and the pumping rate of the reaction solution is 0.05-0.2 mL / min.

7. The method for preparing carbon nanotubes doped with nitrogen and phosphorus according to claim 1, characterized in that: In step (4), the reaction temperature is maintained for a reaction time of 10 to 60 minutes.

8. The method for preparing carbon nanotubes doped with nitrogen and phosphorus according to claim 1, characterized in that: In step (4), the cooling process is as follows: first stop the introduction of hydrogen and continue to introduce argon until cooling to room temperature.

9. A carbon nanotube prepared by the method according to any one of claims 1 to 8.

10. Use of the carbon nanotubes according to claim 9 in preparing electrochemical materials.