Nitrogen-doped carbon nanotube as well as preparation method and application thereof

Abstract

The invention relates to the technical field of carbon materials, and particularly provides a nitrogen-doped carbon nanotube as well as a preparation method and application thereof. The preparation method of the nitrogen-doped carbon nanotube comprises the following steps: decomposing a solid-phase carbon nitrogen compound under the condition of 450-550 DEG C to obtain a reducing gas and a precursor; under the condition of 700-800 DEG C, contacting the reducing gas with a catalyst to reduce the catalyst; decomposing the precursor in an inert atmosphere at the temperature of 650-750 DEG C to obtain a gaseous carbon source and a gaseous nitrogen source; and contacting the gaseous carbon source, the gaseous nitrogen source and the reduced catalyst in an inert atmosphere at the temperature of 900-1000 DEG C. According to the method, the temperatures of the solid-phase carbon-nitrogen compound and the catalyst are independently controlled, and the pyrolysis process of the solid-phase carbon-nitrogen compound and the process of catalyzing growth of the carbon nanotube by the catalyst are coupled step by step, so that the super-long nitrogen-doped carbon nanotube is prepared.

Description

Technical Field

[0001] The invention relates to the technical field of carbon materials, and specifically provides nitrogen-doped carbon nanotubes and a preparation method and application thereof. Background Art

[0002] Studies have found that heteroatom doping can change or enhance certain properties of carbon materials. For example, nitrogen-doped carbon nanotubes have better catalytic and electrochemical properties, can replace precious metal catalysts to reduce costs, and can also be used in supercapacitors to improve their energy storage capacity.

[0003] Chemical vapor deposition (CVD) is a method for preparing nitrogen-doped carbon nanotubes with low cost and convenient operation. Conventional CVD methods can usually achieve in-situ synthesis. For example, a nitrogen source is added while adding a carbon source. The former is a combination of passing ethylene gas and injecting acetonitrile liquid, and the latter is a combination of passing acetylene gas and ammonia gas. Carbon nanotube growth and nitrogen doping are performed simultaneously, but the process needs to be first passed through hydrogen reduction activation catalyst, and the control requirements for the proportion of precursors and the time of passing through the precursors are high, and the precursors used are corrosive, toxic or dangerous. There are also existing technologies for surface modification of carbon nanotubes to achieve nitrogen doping, but the method requires a series of pretreatments to the precursors, and the steps are complicated, time-consuming, and the obtained nitrogen-doped carbon nanotubes are uneven and cannot be efficiently prepared. Therefore, it is very important to develop a convenient, safe and efficient method for preparing nitrogen-doped carbon nanotubes.

[0004] Therefore, there is an urgent need to develop a method for preparing nitrogen-doped carbon nanotubes. Summary of the invention

[0005] The present invention aims to solve one of the technical problems in the related art at least to a certain extent. To this end, one object of the present invention is to provide nitrogen-doped carbon nanotubes and a preparation method and application thereof. The method of the present invention is simple, safe, low-cost, and can be mass-produced, and can produce nitrogen-doped carbon nanotubes with long lengths.

[0006] To this end, the first aspect of the present invention provides a method for preparing nitrogen-doped carbon nanotubes, comprising the following steps:

[0007] Decomposing solid carbon and nitrogen compounds at 450° C. to 550° C. to obtain a reducing gas and a precursor; contacting the reducing gas with a catalyst at 700° C. to 800° C. to reduce the catalyst;

[0008] Decomposing the precursor under an inert atmosphere at 650° C.-750° C. to obtain a gaseous carbon source and a gaseous nitrogen source;

[0009] Under an inert atmosphere and at 900° C. to 1000° C., contacting the gaseous carbon source, the gaseous nitrogen source and the reduced catalyst, and depositing nitrogen-doped carbon nanotubes on the reduced catalyst;

[0010] The catalyst includes a soluble divalent metal hydroxide, a soluble trivalent metal hydroxide and a soluble hexavalent metal hydroxide.

[0011] The present invention uses a single solid-phase carbon-nitrogen compound as the sole carbon source and nitrogen source, independently controls the temperature of the solid-phase carbon-nitrogen compound and the catalyst, and couples the pyrolysis process of the solid-phase carbon-nitrogen compound and the process of catalytic growth of carbon nanotubes in steps, thereby achieving the purpose of efficiently growing ultra-long nitrogen-doped carbon nanotubes.

[0012] The metal components on the catalyst of the present invention are reduced to precipitate a large number of dense metal nanoparticles. The obtained metal nanoparticles can absorb and catalyze carbon source and nitrogen source molecules to eventually grow nitrogen-doped carbon nanotubes.

[0013] The present invention can realize one-step in-situ synthesis of nitrogen-doped carbon nanotubes. The method is simple, safe, low-cost, and can be mass-produced. Nitrogen-doped carbon nanotubes with long length, high nitrogen content, smooth and clean surface, few impurities, and high yield can be prepared.

[0014] In some embodiments of the present invention, the solid phase carbon and nitrogen compound is upstream of the catalyst.

[0015] In some embodiments of the present invention, the mass ratio of the solid carbon nitrogen compound to the catalyst is (100-150):1.

[0016] In some embodiments of the present invention, the solid-phase carbon-nitrogen compound comprises one or more of urea, cyanamide, dicyandiamide, and melamine.

[0017] In some embodiments of the present invention, the inert atmosphere is provided by one or more of argon, nitrogen, and helium.

[0018] In some embodiments of the present invention, the time for decomposing the solid phase carbon and nitrogen compounds is 0.5h-2h.

[0019] In some embodiments of the present invention, the time for decomposing the precursor is 0.5h-2h.

[0020] In some embodiments of the present invention, the time for depositing the nitrogen-doped carbon nanotubes is 0.5 h-2 h.

[0021] In some embodiments of the present invention, the soluble divalent metal includes at least one of Mg, Zn, Ca, Mn, Fe, Co, Ni and Cu.

[0022] In some embodiments of the present invention, the soluble trivalent metal includes at least one of Cr, Al, Ru, Fe, and Co.

[0023] In some embodiments of the present invention, the soluble hexavalent metal comprises tungsten and / or molybdenum.

[0024] In some embodiments of the present invention, the bulk density of the catalyst is 0.01 g / cm 3 -0.20g / cm 3 .

[0025] In some embodiments of the present invention, the method for preparing the catalyst comprises:

[0026] In the presence of a solvent, soluble divalent metal ions, soluble trivalent metal ions and soluble hexavalent metal acid radicals are mixed, the pH is adjusted to 6-11, the mixture is reacted at 25-150°C, and dried to obtain a catalyst.

[0027] The second aspect of the present invention provides nitrogen-doped carbon nanotubes prepared by the preparation method of nitrogen-doped carbon nanotubes; the length of the nitrogen-doped carbon nanotubes is 1 μm-10 μm; the nitrogen-carbon ratio (N / C) of the nitrogen-doped carbon nanotubes is 8%-9%.

[0028] The third aspect of the present invention provides the nitrogen-doped carbon nanotubes prepared by the preparation method of the nitrogen-doped carbon nanotubes and / or the use of the nitrogen-doped carbon nanotubes in at least one of (1) to (3);

[0029] (1) preparing catalytic materials;

[0030] (2) preparing sensor materials;

[0031] (3) Preparation of electrode materials.

[0032] Additional aspects and advantages of the present invention will be given in part in the following description and in part will be obvious from the following description, or will be learned through practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] The above and / or additional aspects and advantages of the present invention will become apparent and easily understood from the description of the embodiments in conjunction with the following drawings, in which:

[0034] Figure 1 This is a scanning electron microscope photo of the layered metal hydroxide synthesized in Example 1;

[0035] Figure 2 This is a scanning electron microscope photo of the nitrogen-doped carbon nanotubes obtained in Example 1;

[0036] Figure 3This is a scanning electron microscope photograph of the nitrogen-doped carbon nanotube array obtained in Example 1;

[0037] Figure 4 This is a photograph of the nitrogen-doped carbon nanotubes obtained in Example 1 taken under a transmission electron microscope with an energy dispersive X-ray spectrometer;

[0038] Figure 5 This is a scanning electron microscope photo of the nitrogen-doped carbon nanotubes obtained in Example 2 (5 μm);

[0039] Figure 6 This is a scanning electron microscope photograph of the nitrogen-doped carbon nanotubes obtained in Example 2 (1 μm);

[0040] Figure 7 This is a scanning electron microscope photo of the nitrogen-doped carbon nanotubes obtained in Example 3;

[0041] Figure 8 This is a scanning electron microscope photo of the nitrogen-doped carbon nanotubes obtained in Comparative Example 1;

[0042] Fig. 9 This is a scanning electron microscope photograph of the nitrogen-doped carbon nanotubes obtained in Comparative Example 2. DETAILED DESCRIPTION

[0043] The embodiments of the present invention are described in detail below. The embodiments described below are exemplary and are only used to explain the present invention, and should not be understood as limiting the present invention.

[0044] It should be noted that the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include one or more of the features. Further, in the description of the present invention, unless otherwise specified, the meaning of "plurality" is two or more.

[0045] The first aspect of the present invention provides a method for preparing nitrogen-doped carbon nanotubes, comprising the following steps:

[0046] Decomposing solid carbon and nitrogen compounds at 450° C. to 550° C. to obtain a reducing gas and a precursor; contacting the reducing gas with a catalyst at 700° C. to 800° C. to reduce the catalyst;

[0047] Decomposing the precursor under an inert atmosphere at 650° C.-750° C. to obtain a gaseous carbon source and a gaseous nitrogen source;

[0048] Under an inert atmosphere and at 900° C. to 1000° C., contacting the gaseous carbon source, the gaseous nitrogen source and the reduced catalyst, and depositing nitrogen-doped carbon nanotubes on the reduced catalyst;

[0049] The catalyst includes a soluble divalent metal hydroxide, a soluble trivalent metal hydroxide and a soluble hexavalent metal hydroxide.

[0050] The present invention uses a single solid-phase carbon-nitrogen compound as the sole carbon source and nitrogen source, independently controls the temperature of the solid-phase carbon-nitrogen compound and the catalyst, and couples the pyrolysis process of the solid-phase carbon-nitrogen compound and the process of catalytic growth of carbon nanotubes in steps, thereby achieving the purpose of efficiently growing ultra-long nitrogen-doped carbon nanotubes.

[0051] The metal components on the catalyst of the present invention are reduced to precipitate a large number of dense metal nanoparticles. The obtained metal nanoparticles can absorb and catalyze carbon source and nitrogen source molecules to eventually grow nitrogen-doped carbon nanotubes.

[0052] The present invention can realize one-step in-situ synthesis of nitrogen-doped carbon nanotubes. The method is simple, safe, low-cost, and can be mass-produced. Nitrogen-doped carbon nanotubes with long length, high nitrogen content, smooth and clean surface, few impurities, and high yield can be prepared.

[0053] In some embodiments of the present invention, the solid phase carbon and nitrogen compound is upstream of the catalyst.

[0054] In some embodiments of the present invention, the catalyst is at the downwind port, and the solid carbon and nitrogen compound is at the upwind port of the catalyst. The decomposition products of the solid carbon and nitrogen compound can reach the downwind port and then contact the catalyst.

[0055] In some embodiments of the present invention, the mass ratio of the solid carbon nitrogen compound to the catalyst is (100-150): 1. The present invention uses a solid carbon nitrogen compound precursor as both the sole carbon source and the sole nitrogen source for carbon nanotube growth; it undergoes two processes when heated: when heated to a certain temperature, it pyrolyzes and releases a large amount of reducing gas; and when further heated, it decomposes to form a gas that can provide a carbon source and a nitrogen source.

[0056] In some embodiments of the present invention, the solid-phase carbon-nitrogen compound comprises one or more of urea, cyanamide, dicyandiamide, and melamine.

[0057] Solid carbon and nitrogen compound precursors can be pyrolyzed at a certain temperature and release reducing gases, as well as carbon sources required for carbon nanotube growth and nitrogen sources required for nitrogen doping. Taking dicyandiamide as an example, it will undergo two processes when heated: 1. It pyrolyzes and releases a large amount of reducing ammonia gas at a temperature of 450°C to 550°C to form C3N4; 2. When it reaches 650°C, the C3N4 obtained in process 1 further decomposes to form carbon source and nitrogen source gases.

[0058] In some embodiments of the present invention, the reducing gas includes one or more of hydrogen, ammonia, and carbon monoxide. The reducing gas is mainly used to reduce and activate the transition metal component supported in the catalyst to obtain transition metal nanoparticles.

[0059] In some embodiments of the present invention, the inert atmosphere is provided by one or more of argon, nitrogen, and helium; the gas flow rate is 20 sccm-100 sccm.

[0060] The catalyst of the present invention is used to meet the needs of growing nitrogen-doped carbon nanotubes from a solid-phase carbon-nitrogen source. The catalyst is designed to have a lamellar structure in which the lamellar layers are not obviously stacked, and the structure can provide sufficient space for the growth of nitrogen-doped carbon nanotubes. Specifically, the lamellar structure catalyst can be hydrotalcite, vermiculite, mica, magnesium oxide or silicon dioxide; a transition metal component is loaded on the surface or inside of the catalyst, and the loaded transition metal component can be one or more of Fe, Co and Ni.

[0061] In some preferred embodiments of the present invention, soluble divalent metal ions, soluble trivalent metal ions and soluble hexavalent metal acid radicals are mixed and the pH is adjusted to 7-11.

[0062] In some preferred embodiments of the present invention, the solvent may be a liquid having a diluting effect on soluble divalent metal ions, soluble trivalent metal ions and soluble hexavalent metal ions, for example, may be water.

[0063] In some embodiments of the present invention, the time for decomposing the solid phase carbon and nitrogen compounds is 0.5 h to 2 h. As an example, the time for decomposing the solid phase carbon and nitrogen compounds can be 0.5 h, 1 h, 1.5 h, or 2 h.

[0064] In some embodiments of the present invention, the time for decomposing the precursor is 0.5 h-2 h. As an example, the time for decomposing the precursor can be 0.5 h, 1 h, 1.5 h, or 2 h.

[0065] In some embodiments of the present invention, the time for depositing the nitrogen-doped carbon nanotubes is 0.5 h to 2 h. As an example, the time for depositing the nitrogen-doped carbon nanotubes can be 0.5 h, 1 h, 1.5 h, or 2 h.

[0066] In some embodiments of the present invention, the soluble divalent metal includes at least one of Mg, Zn, Ca, Mn, Fe, Co, Ni and Cu.

[0067] In some preferred embodiments of the present invention, the soluble divalent metal comprises a first soluble divalent metal and a second soluble divalent metal;

[0068] The first soluble divalent metal includes at least one of Fe, Co, Ni and Cu;

[0069] The second soluble divalent metal includes at least one of Mg, Zn, Ca, and Mn.

[0070] In some preferred embodiments of the present invention, the molar ratio of the first soluble divalent metal to the second soluble divalent metal is (0.002-1):1.

[0071] In some embodiments of the present invention, the soluble trivalent metal includes at least one of Cr, Al, Ru, Fe, and Co.

[0072] In some preferred embodiments of the present invention, the soluble trivalent metal comprises a first soluble trivalent metal and a second soluble trivalent metal;

[0073] The first soluble trivalent metal includes at least one of Ru, Fe, and Co;

[0074] The second soluble trivalent metal includes at least one of Cr and Al.

[0075] In some preferred embodiments of the present invention, the molar ratio of the first soluble trivalent metal to the second soluble trivalent metal is (0.002-1):1.

[0076] In some embodiments of the present invention, the soluble hexavalent metal comprises tungsten and / or molybdenum.

[0077] In some embodiments of the present invention, the bulk density of the catalyst is 0.01 g / cm 3 -0.20g / cm 3 .

[0078] In some embodiments of the present invention, the method for preparing the catalyst comprises:

[0079] In the presence of a solvent, soluble divalent metal ions, soluble trivalent metal ions and soluble hexavalent metal acid radicals are mixed, the pH is adjusted to 6-11, the mixture is reacted at 25-150°C, and dried to obtain a catalyst.

[0080] In some embodiments of the present invention, the soluble divalent metal ions include Mg 2+ 、Zn 2+ , Ca 2+ , Mn 2+ , Fe 2+ 、Co 2+ 、Ni 2+ and Cu 2+ At least one of .

[0081] In some preferred embodiments of the present invention, the soluble divalent metal ions include Fe 2+ 、Co 2+ 、Ni 2+ and Cu 2+ At least one of .

[0082] In some embodiments of the present invention, the soluble divalent metal ions are present in the form of soluble divalent metal salts; the anions in the soluble divalent metal salts include Cl - 、NO3 - 、SO4 2- At least one of .

[0083] In some embodiments of the present invention, the soluble trivalent metal ions include Cr 3+ 、Al 3+ 、Ru 3+ , Fe 3+ 、Co 3+ At least one of .

[0084] In some embodiments of the present invention, the soluble trivalent metal ions include Ru 3+ , Fe 3+ 、Co 3+ At least one of .

[0085] In some embodiments of the present invention, the soluble trivalent metal ion exists in the form of a soluble trivalent metal salt; the anion in the soluble trivalent metal salt includes Cl - 、NO3 - 、SO4 2- At least one of .

[0086] In some embodiments of the present invention, the soluble hexavalent metal acid radicals include tungstate and / or molybdate.

[0087] In some embodiments of the present invention, the soluble hexavalent metal acid radical exists in the form of a soluble hexavalent metal acid salt; the soluble hexavalent metal salt includes ammonium molybdate and / or sodium molybdate.

[0088] In some embodiments of the present invention, the molar ratio of the soluble divalent metal ions to the soluble trivalent metal ions is (0.1-10):1, preferably (0.5-3):1; in other embodiments of the present invention, the molar ratio of the divalent to trivalent metal ions is 0.6:1, 2.2:1, 2.4:1 or 1.2:1.

[0089] In some embodiments of the present invention, the molar ratio of the soluble divalent metal ions to the soluble hexavalent metal acid radicals is (1-6):(0.01-0.1). In other embodiments of the present invention, the molar ratio of the soluble divalent metal ions to the soluble hexavalent metal acid radicals is 5.3:0.1, 6:0.1, 1:0.01, 1.1:0.01 or 4:1.

[0090] In some preferred embodiments of the present invention, the soluble divalent metal ions include a first soluble divalent metal ion and a second soluble divalent metal ion;

[0091] The first soluble divalent metal ion includes Fe 2+ 、Co 2+ 、Ni 2+ and Cu 2+ At least one of;

[0092] The second soluble divalent metal ion comprises Mg 2+ 、Zn 2+ , Ca 2+ , Mn 2+ At least one of .

[0093] In some preferred embodiments of the present invention, the soluble trivalent metal ions include a first soluble trivalent metal ion and a second soluble trivalent metal ion;

[0094] The first soluble trivalent metal ion includes Ru 3+ , Fe 3+ 、Co 3+ At least one of;

[0095] The second soluble trivalent metal ion includes Cr 3+ 、Al 3+ At least one of .

[0096] In some preferred embodiments of the present invention, the molar ratio of the first soluble divalent metal ion to the second soluble divalent metal ion is (0.002-1):1.

[0097] In some preferred embodiments of the present invention, the molar ratio of the first soluble trivalent metal ion to the second soluble trivalent metal ion is (0.002-1):1.

[0098] In some embodiments of the present invention, the reaction time is 0.1 h-36 h.

[0099] In some embodiments of the present invention, the mixing is performed under stirring conditions; the stirring speed is 10 rpm-600 rpm, preferably 300-500 rpm.

[0100] In some embodiments of the present invention, the drying temperature is 80°C-90°C.

[0101] In some embodiments of the present invention, the mixing specifically comprises:

[0102] Mix soluble divalent metal ions, soluble trivalent metal ions and solvent, adjust the pH to 6-11, and obtain a first mixed solution; mix soluble hexavalent metal acid radicals and solvent to obtain a second mixed solution; mix the first mixed solution and the second mixed solution, and adjust the pH to 6-11.

[0103] In some embodiments of the present invention, the pH is adjusted with a base; the base is preferably present in the form of a solution, and the concentration of the base in the base solution is 0.1 mol / L-20 mol / L.

[0104] In some embodiments of the present invention, the base includes at least one of sodium hydroxide, potassium hydroxide, sodium bicarbonate, sodium carbonate, ammonium bicarbonate, ammonium carbonate, urea and aqueous ammonia.

[0105] In some embodiments of the present invention, the concentration of metal ions in the metal ion solution is 0.005 mol / L-2 mol / L.

[0106] The second aspect of the present invention provides nitrogen-doped carbon nanotubes prepared by the preparation method of nitrogen-doped carbon nanotubes; the length of the nitrogen-doped carbon nanotubes is 1 μm-10 μm; the nitrogen-carbon ratio (N / C) of the nitrogen-doped carbon nanotubes is 8%-9%.

[0107] The nitrogen-doped carbon nanotubes obtained by the invention have long length, high nitrogen content, smooth and clean surface, few impurities and high yield.

[0108] The third aspect of the present invention provides the nitrogen-doped carbon nanotubes prepared by the preparation method of the nitrogen-doped carbon nanotubes and / or the use of the nitrogen-doped carbon nanotubes in at least one of (1) to (3);

[0109] (1) preparing catalytic materials;

[0110] (2) preparing sensor materials;

[0111] (3) Preparation of electrode materials.

[0112] The scheme of the present disclosure will be explained below in conjunction with the examples. Those skilled in the art will appreciate that the following examples are only used to illustrate the present disclosure and should not be considered to limit the scope of the present disclosure. Where specific techniques or conditions are not indicated in the examples, the techniques or conditions described in the literature in this area or the product instructions are used. Where the manufacturers of reagents or instruments are not indicated, they are all conventional products that can be obtained commercially.

[0113] Example 1

[0114] The method for preparing nitrogen-doped carbon nanotubes of this embodiment comprises the following steps:

[0115] (1) Dissolve 0.05 mol magnesium sulfate, 0.02 mol aluminum sulfate, 0.005 mol iron nitrate and 0.003 mol nickel nitrate in 1 L of water and stir to form solution A; dissolve 0.001 mol sodium molybdate in water and stir to form solution B; dissolve 1.1 mol urea in water and stir to form solution C. Add solution A and solution C at a drop rate of 6 mL / min until the end point pH is 7-10, then set the reaction temperature to 115°C, stir at 300 rpm, react for 2 hours, add solution B dropwise to the mixed solution of A and C, pH is still 7-10, and continue stirring and reacting for 8 hours under the same conditions. Then, let stand and age at 115°C for 10 hours. After the reaction is completed, the product is filtered and washed to neutrality. The solid is dried in a forced air drying oven at 80°C and ground to obtain a layered metal hydroxide with separate layers and no obvious layer assembly. The bulk density of the powder is 0.02 g / cm 3 .

[0116] (2) 2 g of dicyandiamide is placed in the low temperature zone of the upper tuyere of a tubular furnace, and 20 mg of the layered metal hydroxide obtained in step (1) is placed as a catalyst in the high temperature zone of the lower tuyere of the tubular furnace.

[0117] (3) Nitrogen gas was passed through the gas path and the tube furnace for 10 minutes to remove the air so as to maintain an inert atmosphere in the chamber, and 60 sccm of nitrogen gas was continuously passed through during the subsequent preparation of nitrogen-doped carbon nanotubes.

[0118] (4) The high temperature zone where the catalyst is located is heated to 750°C. After reaching the temperature, the low temperature zone where the dicyandiamide is located is heated to 450°C and maintained for 50 minutes to obtain ammonia and a precursor. The catalyst is reduced with ammonia. The reduced catalyst is loaded with a catalyst having an average particle size of 5 nm and an average density of 1.12×10 15 m -2 of Fe nanoparticles.

[0119] (5) The high temperature zone where the catalyst is located is heated to 900°C. After reaching the temperature, the low temperature zone is heated to 700°C and maintained for 1 hour to decompose the precursor to form a carbon source gas and a nitrogen source gas. The carbon source gas and the nitrogen source gas reach the high temperature zone under the action of nitrogen. Under the action of the catalyst, nitrogen-doped carbon nanotubes are formed after 1 hour.

[0120] The layered metal hydroxide (catalyst) and nitrogen-doped carbon nanotubes used in the examples were characterized by scanning electron microscopy (SEM) and energy dispersive X-ray spectrometry (EDS). Figure 1-4 As shown in Table 1. Figure 1 It can be seen that Figure 1 This is the SEM image of the synthesized layered metal hydroxide, which has a layered structure and basic regular hexagonal shape characteristics; Figure 2 This is a SEM image of nitrogen-doped carbon nanotubes synthesized by the catalyst at low magnification. The length of the nitrogen-doped carbon nanotubes is more than 2 microns, and they show two growth structures: mesh interweaving and array. Figure 3 This is an enlarged SEM image of the synthesized nitrogen-doped carbon nanotubes with an array growth structure; Figure 4 This is a transmission electron microscope (TEM) image of a single nitrogen-doped carbon nanotube obtained in conjunction with an EDS spectrum. The synthesized nitrogen-doped carbon nanotube has a bamboo-like structural feature, and the EDS spectrum of carbon and nitrogen proves that it is a nitrogen-doped carbon nanotube.

[0121] Table 1 Element content data of X-ray photoelectron spectroscopy (XPS) of nitrogen-doped carbon nanotubes

[0122]

[0123] As can be seen from Table 1, the carbon nanotubes are nitrogen-doped carbon nanotubes, and the nitrogen-to-carbon ratio (N / C) is 8.67 Atom %.

[0124] Example 2

[0125] The method for preparing nitrogen-doped carbon nanotubes of this embodiment comprises the following steps:

[0126] (1) The preparation method of the layered composite metal catalyst of this embodiment is carried out by referring to the method in Example 1. The difference from Example 1 is that the iron nitrate of this embodiment is replaced by cobalt nitrate of the same amount of substance, and the other steps are carried out by referring to step (1) of Example 1.

[0127] (2) 2 g of melamine is placed in the low temperature zone of the upper tuyere of a tubular furnace, and 20 mg of the layered metal hydroxide obtained in step (1) is placed as a catalyst in the high temperature zone of the lower tuyere of the tubular furnace.

[0128] (3) First, argon gas was passed through for 10 minutes to remove the air in the gas path and the tube furnace to maintain an inert atmosphere in the chamber, and 40 sccm of argon gas was continuously passed through during the subsequent preparation process of nitrogen-doped carbon nanotubes.

[0129] (4) The high temperature zone where the catalyst is located is heated to 750°C. After reaching the temperature, the low temperature zone where the melamine is located is heated to 450°C and maintained for 30 minutes to obtain ammonia and a precursor. The catalyst is reduced with ammonia. The reduced catalyst is loaded with a particle size of 6.2 nm and an average density of 1.52×10 15 m -2 of Co nanoparticles.

[0130] (5) The high temperature zone where the catalyst is located is heated to 900°C. After reaching the temperature, the low temperature zone is heated to 700°C and maintained for 1 hour to decompose the precursor to form a carbon source gas and a nitrogen source gas. The carbon source gas and the nitrogen source gas reach the high temperature zone under the action of nitrogen. Under the action of the catalyst, nitrogen-doped carbon nanotubes are formed in 30 minutes. The obtained nitrogen-doped carbon nanotubes are as follows Figure 5 , 6 shown. Figure 5 , 6 The SEM images of the nitrogen-doped carbon nanotubes of this embodiment at low magnification and high magnification are shown respectively. The length of the nitrogen-doped carbon nanotubes is more than 1 micron.

[0131] Example 3

[0132] The method for preparing nitrogen-doped carbon nanotubes of this embodiment comprises the following steps:

[0133] (1) The preparation method of the layered composite metal catalyst of this embodiment is carried out by referring to the method in Example 1. The difference from Example 1 is that in this embodiment, ferric nitrate is replaced by ferrous nitrate of the same amount of substance, and the other steps are carried out by referring to step (1) of Example 1.

[0134] (2) 2 g of dicyandiamide is placed in the low temperature zone of the upper tuyere of a tubular furnace, and 20 mg of the layered metal hydroxide obtained in step (1) is placed as a catalyst in the high temperature zone of the lower tuyere of the tubular furnace.

[0135] (3) First, nitrogen gas was passed through the gas path and the tube furnace for 10 minutes to remove the air so as to maintain an inert atmosphere in the chamber, and then 100 sccm of nitrogen gas was continuously passed through the furnace during the subsequent preparation of nitrogen-doped carbon nanotubes.

[0136] (4) The high temperature zone where the catalyst is located is heated to 800°C. After reaching the temperature, the low temperature zone where the dicyandiamide is located is heated to 450°C and maintained for 100 minutes to obtain ammonia and a precursor. The catalyst is reduced with ammonia. The reduced catalyst is loaded with a catalyst having an average particle size of 4 nm and an average density of 1.65×10 14 m -2 of Fe nanoparticles.

[0137] (5) The high temperature zone where the catalyst is located is heated to 1000°C. After reaching the temperature, the low temperature zone is heated to 700°C and maintained for 1 hour to decompose the precursor to form a carbon source gas and a nitrogen source gas. The carbon source gas and the nitrogen source gas reach the high temperature zone under the action of nitrogen. Under the action of the catalyst, nitrogen-doped carbon nanotubes are formed after 1 hour. The obtained nitrogen-doped carbon nanotubes are as follows: Figure 7 shown. Figure 7 The SEM image of the nitrogen-doped carbon nanotubes of this embodiment at a high magnification is shown in FIG. The length of the nitrogen-doped carbon nanotubes is more than 1 micron.

[0138] Comparative Example 1

[0139] The preparation method of nitrogen-doped carbon nanotubes in this comparative example is different from that in Example 1 only in that the catalyst and dicyandiamide are placed in the same place in this comparative example, and the remaining steps are carried out with reference to the method in Example 1, specifically comprising the following steps:

[0140] (1) 20 mg of catalyst and 2 g of dicyandiamide were placed in the same temperature zone, and nitrogen was passed through the gas path and the tube furnace for 10 minutes to remove the air so that the chamber maintained an inert atmosphere. During the entire growth preparation process, 60 sccm of nitrogen was continuously passed through.

[0141] (2) Without step-by-step coupled heating, the temperature zone where the catalyst and dicyandiamide are located is first heated to 450°C and maintained for 2 hours, and then heated to 750°C for 1 hour to obtain nitrogen-doped carbon nanotubes. The obtained nitrogen-doped carbon nanotubes are as follows Figure 8 shown. Figure 8 This is a SEM image of the nitrogen-doped carbon nanotubes obtained in Comparative Example 1. It can be seen that the nitrogen-doped carbon nanotubes obtained in this comparative example are shorter and significantly sparser than those in the example, indicating a lower yield.

[0142] Comparative Example 2

[0143] The preparation method of nitrogen-doped carbon nanotubes in this comparative example is different from that in Example 2 only in that the catalyst and dicyandiamide are placed in the same place in this comparative example, and the remaining steps are carried out with reference to the method in Example 2, specifically comprising the following steps:

[0144] (1) 20 mg of catalyst and 2 g of melamine were placed in the same temperature zone. Nitrogen was passed through the gas path and the tube furnace for 10 minutes to remove the air so that the chamber maintained an inert atmosphere. During the entire growth preparation process, 40 sccm of argon was continuously passed through.

[0145] (2) Without step-by-step coupled heating, the temperature zone where the catalyst and melamine are located is first heated to 450°C and maintained for 30 minutes, and then heated to 900°C for 1 hour to obtain nitrogen-doped carbon nanotubes. The obtained nitrogen-doped carbon nanotubes are as follows Fig. 9 shown. Fig. 9This is the SEM image of the nitrogen-doped carbon nanotubes obtained in Comparative Example 2. It can be seen that only a very small amount of carbon nanotubes can be obtained in this comparative example.

[0146] In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "example", "specific example", "some implementation schemes" or "some examples" etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art may combine and combine the different embodiments or examples described in this specification and the features of the different embodiments or examples, unless they are contradictory.

[0147] Although the embodiments of the present invention have been shown and described above, it is to be understood that the above embodiments are exemplary and are not to be construed as limitations of the present invention. A person skilled in the art may change, modify, replace and vary the above embodiments within the scope of the present invention.

Claims

1. A method for preparing nitrogen-doped carbon nanotubes, characterized in that: The following steps are involved: Decomposing solid carbon and nitrogen compounds at 450° C. to 550° C. to obtain a reducing gas and a precursor; contacting the reducing gas with a catalyst at 700° C. to 800° C. to reduce the catalyst; Decomposing the precursor under an inert atmosphere at 650° C.-750° C. to obtain a gaseous carbon source and a gaseous nitrogen source; Under an inert atmosphere and at 900° C. to 1000° C., contacting the gaseous carbon source, the gaseous nitrogen source and the reduced catalyst, and depositing nitrogen-doped carbon nanotubes on the reduced catalyst; The catalyst includes a soluble divalent metal hydroxide, a soluble trivalent metal hydroxide and a soluble hexavalent metal hydroxide.

2. The method for preparing nitrogen-doped carbon nanotubes according to claim 1, characterized in that: The solid phase carbon and nitrogen compound is upstream of the catalyst.

3. The method for preparing nitrogen-doped carbon nanotubes according to claim 1, characterized in that: The mass ratio of the solid phase carbon nitrogen compound to the catalyst is (100-150):

1.

4. The method for preparing nitrogen-doped carbon nanotubes according to claim 1, characterized in that: The solid phase carbon-nitrogen compound comprises one or more of urea, cyanamide, dicyandiamide and melamine.

5. The method for preparing nitrogen-doped carbon nanotubes according to claim 1, characterized in that: The inert atmosphere is provided by one or more of argon, nitrogen and helium.

6. The method for preparing nitrogen-doped carbon nanotubes according to claim 1, characterized in that: The time for decomposing the solid phase carbon and nitrogen compounds is 0.5h-2h; and / or, The time for decomposing the precursor is 0.5h-2h; and / or, The time for depositing the nitrogen-doped carbon nanotubes is 0.5 h-2 h.

7. The method for preparing nitrogen-doped carbon nanotubes according to claim 1, characterized in that: The soluble divalent metal includes at least one of Mg, Zn, Ca, Mn, Fe, Co, Ni and Cu; and / or, The soluble trivalent metal includes at least one of Cr, Al, Ru, Fe and Co; and / or, The soluble hexavalent metal includes tungsten and / or molybdenum.

8. The method for preparing nitrogen-doped carbon nanotubes according to claim 1, characterized in that: The bulk density of the catalyst is 0.01 g / cm 3 -0.20g / cm 3 .

9. The method for preparing nitrogen-doped carbon nanotubes according to claim 1, characterized in that: The preparation method of the catalyst comprises: In the presence of a solvent, soluble divalent metal ions, soluble trivalent metal ions and soluble hexavalent metal acid radicals are mixed, the pH is adjusted to 6-11, the mixture is reacted at 25-150°C, and dried to obtain a catalyst.

10. The nitrogen-doped carbon nanotubes prepared by the method for preparing nitrogen-doped carbon nanotubes according to any one of claims 1 to 9; the length of the nitrogen-doped carbon nanotubes is 1 μm-10 μm; the nitrogen-to-carbon ratio of the nitrogen-doped carbon nanotubes is 8%-9%.

11. Use of the nitrogen-doped carbon nanotubes prepared by the method for preparing nitrogen-doped carbon nanotubes according to any one of claims 1 to 9 and / or the nitrogen-doped carbon nanotubes according to claim 10 in at least one of (1) to (3); (1) preparing catalytic materials; (2) preparing sensor materials; (3) Preparation of electrode materials.

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