阅读说明：本技术 无金属的碳氮负载的碳纳米管复合材料、其制备及其用途 (Metal-free carbon-nitrogen loaded carbon nanotube composite material, preparation and application thereof ) 是由 田书博 孙晓明 徐淑慧 魏金山 孙恺 于 2021-07-13 设计创作，主要内容包括：本发明属于新型材料制备领域,尤其涉及一种无金属的碳氮负载的碳纳米管复合材料、其制备方法及其用途。所述复合材料中同时含有氮、碳、氧三种元素,所述复合材料包含：碳纳米管和包覆在所述碳纳米管上的碳氮材料层。本发明所得到的NC@CNT-T复合材料活性高,稳定性强。由于使用氧化过的CNT做载体,提高原有氮碳材料的导电性；同时经过步骤(3)的高温焙烧过程,增强了此复合材料的高度稳定性。(The invention belongs to the field of novel material preparation, and particularly relates to a metal-free carbon-nitrogen loaded carbon nano tube composite material, and a preparation method and application thereof. The composite material simultaneously contains three elements of nitrogen, carbon and oxygen, and comprises: the carbon nano tube coating structure comprises a carbon nano tube and a carbon and nitrogen material layer coated on the carbon nano tube. The NC @ CNT-T composite material obtained by the invention has high activity and strong stability. Because the oxidized CNT is used as a carrier, the conductivity of the original nitrogen-carbon material is improved; meanwhile, the high-temperature roasting process in the step (3) enhances the high stability of the composite material.)

1. A metal-free carbon-nitrogen-loaded carbon nanotube composite material is characterized by simultaneously containing three elements of nitrogen, carbon and oxygen, and comprises the following components in parts by weight: the carbon nano tube comprises an oxidized carbon nano tube and a carbon and nitrogen material layer coated on the carbon nano tube.

2. The metal-free carbon nitrogen-loaded carbon nanotube composite material according to claim 1, wherein the carbon nitrogen-loaded carbon nanotube composite material contains the following elements: the content of N is 11.0 to 34.7at percent, the content of O element is 6.3 to 11.9at percent, and the rest is C, taking the total atomic number of the composite material as a reference.

3. The method for preparing carbon nitrogen-supported carbon nanotube composite material according to claim 1, characterized by comprising the steps of:

(1) placing the single-walled carbon nanotube in strong oxidizing acid, heating for 1-3 hours at 60-80 ℃, and carrying out solid-liquid separation after the reaction is finished to obtain an oxidized carbon nanotube serving as a required CNT material;

(2) dispersing the CNT material obtained in the step (1) in a formamide solution, and performing ultrasonic treatment to obtain a hydrothermal reaction mother solution;

(3) placing the hydrothermal reaction mother liquor obtained in the step (2) in a closed reaction kettle at the temperature of 120 ℃ -;

(4) and (3) roasting the NC @ CNT material in the step (3) for 0.5-3 hours at the temperature of 400-1000 ℃ under the protection of inert gas to obtain the carbon-nitrogen-loaded carbon nanotube material.

4. The method for preparing carbon nitrogen-loaded carbon nanotube composite material according to claim 3, wherein the hydrothermal reaction temperature in the step (3) is not lower than 140 ℃.

5. The method for preparing carbon-nitrogen supported carbon nanotube composite material according to claim 3, wherein in the step (4), the inert gas is argon gas, the flow rate of the argon gas is 80mL/min, and the temperature rise rate of the calcination is 5 ℃/min.

6. The method for preparing a carbon-nitrogen-supported carbon nanotube composite material according to claim 3, wherein in the step (2), the concentration of the CNT material in the formamide solution in the step (1) is 1.3-5.8 g/L.

7. Use of the carbon nitrogen-loaded carbon nanotube composite material according to any one of claims 1 to 2 as a catalyst for the electrocatalytic reduction of oxygen to produce hydrogen peroxide, characterized in that the electrocatalytic environment is 0.1M KOH aqueous solution.

Technical Field

The invention belongs to the field of novel material preparation, and particularly relates to a metal-free carbon-nitrogen loaded carbon nano tube composite material, and a preparation method and application thereof.

Background

Hydrogen peroxide (H)₂O₂) Is a multifunctional and important chemical substance, is an important component of modern industry, and has wide application in the fields of medicine, environmental protection and the like. At present, H₂O₂Is prepared by reacting anthraquinone with H₂Hydrogenation, followed by O in an organic solvent₂Oxidized and generated indirectly. Although the anthraquinone process is capable of producing large quantities of H at high concentrations₂O₂It requires elaborate, large-scale equipment, is energy intensive and costly, and produces large amounts of waste. Furthermore, the direct synthesis of H from hydrogen and oxygen₂O₂Is thermodynamically spontaneous and can provide continuous production of H₂O₂And therefore, the method has a wide prospect. However, H₂And O₂Is potentially explosive and is also explosive to H₂O₂And H₂O₂The yield of (a) is low, which hinders practical application of the route. Therefore, there is a great need for other direct, efficient, and economical methods for producing H₂O₂。

For H₂O₂One safe, attractive and promising strategy for production is electrochemical oxygen reduction via a two-electron pathway. However, the electrochemical oxygen reduction process also has a competitive four-electron pathway to produce H₂O, competitive side reactions further reduce H₂O₂Resulting in a lower coulombic efficiency. Thus, the efficiency of the electrochemical process depends to a large extent on the identification of cost-effective catalysts with high activity and selectivity

Therefore, there is an urgent need to develop a high activity and selectivity catalyst for electrocatalytic oxygen reduction to produce H₂O₂. The present invention has been made to solve the above problems.

Disclosure of Invention

The invention provides a metal-free carbon-nitrogen-loaded carbon nanotube (NC @ CNT-T) composite material, which simultaneously contains three elements of nitrogen, carbon and oxygen, and comprises the following components in parts by weight: the carbon nano tube comprises an oxidized carbon nano tube and a carbon and nitrogen material layer coated on the carbon nano tube.

Preferably, in the NC @ CNT-T composite material, the content of each element is as follows: the content of N is 11.0 to 34.7at percent, the content of O is 6.3 to 11.9at percent, and the rest is C, taking the total atomic number of the composite material as a reference.

at% is the unit of atomic percentage. In the present invention, the atomic percentage of a certain element is the percentage of the number of atoms of the element to the total number of atoms of each element in the composite material of the present invention.

In a second aspect, the present invention provides a method for preparing the NC @ CNT-T composite material according to the first aspect, comprising the steps of:

(1) placing the single-walled carbon nanotube in strong oxidizing acid, heating for 1-3 hours at 60-80 ℃, and carrying out solid-liquid separation after the reaction is finished to obtain an oxidized carbon nanotube serving as a CNT material;

(2) dispersing the CNT material obtained in the step (1) in a formamide solution, and performing ultrasonic treatment to obtain a hydrothermal reaction mother solution;

(3) placing the hydrothermal reaction mother liquor obtained in the step (2) in a closed reaction kettle at the temperature of 120 ℃ -;

(4) and (4) roasting the NC @ CNT material obtained in the step (3) at the temperature of 400-1000 ℃ under the protection of inert gas for 0.5-3 hours to obtain the NC @ CNT-T material.

In the step (1), after the carbon nanotubes are subjected to slight oxidation treatment, oxygen-containing functional groups on the surfaces of the carbon nanotubes are increased, so that the carbon nanotubes can be better dispersed in the formamide solution in the step (2).

Preferably, the strong oxidizing acid is selected from: sulfuric acid, nitric acid or perchloric acid.

Preferably, in the step (2), the concentration of the CNT material in the formamide solution in the step (1) is 1.3-5.8 g/L.

Preferably, the heating temperature is 75-80 deg.C, and the heating time is 2 h.

Preferably, in the step (3), the temperature of the hydrothermal reaction is not lower than 140 ℃.

Preferably, in the step (4), the inert gas is argon, the flow rate of the argon is 80mL/min, and the heating rate of the high-temperature carbonization is 5 ℃/min.

In a third aspect, the present invention provides the use of the NC @ CNT-T composite of any one of the first aspects as a catalyst for the electrocatalytic reduction of oxygen to produce hydrogen peroxide in an electrocatalytic environment of 0.1M aqueous KOH.

Preferably, the material can improve the catalytic activity and stability of the reaction of oxygen reduction to produce hydrogen peroxide.

Of course, other uses of the present invention are possible and yet to be developed.

Compared with the prior art, the invention has the following beneficial effects:

1. the NC @ CNT-T composite material obtained by the invention has high activity and strong stability. Because the oxidized CNT is used as a carrier, the conductivity of the original nitrogen-carbon material is improved; meanwhile, the high-temperature roasting process in the step (3) enhances the high stability of the composite material.

2. At present, formamide is generally used, and metal participates in the use, and the formamide and the metal are subjected to copolymerization reaction to obtain the metal nitrogen carbon material. The invention unexpectedly discovers that an NC-T material obtained by roasting after formamide autopolymerization reaction without metal has extremely high selectivity of electrochemically generating hydrogen peroxide, and is not available in other reported carbon materials.

3. The preparation method has the advantages of low cost and low toxicity of raw materials, simple reaction operation and high preparation efficiency of the NC @ CNT-T composite material.

4. In example 37, the present inventors have found that the difference in oxygen content directly affects the efficiency of the final hydrogen peroxide generation, and that the content of oxygen in the catalyst can be changed by adjusting the calcination temperature T, thereby improving the activity of the catalyst and improving the stability of the active sites. The concrete expression is as follows: the higher the calcination temperature T, the lower the oxygen content of the catalyst, the average H₂O₂The lower the selectivity.

5. The NC @ CNT-T composite catalyst synthesized by the invention has the characteristics of simple preparation method, easy operation and economic cost, and compared with the traditional anthraquinone method, the method for producing hydrogen peroxide by using the catalyst in the cathodic oxygen reduction reaction has the characteristics of directness, high efficiency, economy, safety and environmental protection.

Drawings

FIG. 1 is a schematic process flow diagram of the preparation method of the NC @ CNT-T composite material.

FIG. 2 is a schematic process flow diagram of the preparation method of the NC-T material.

FIG. 3 is a Scanning Electron Microscope (SEM) characterization image of carbon materials prepared in preferred examples 29 to 32 of the present invention and comparative examples 1 to 3.

FIG. 4 is a Transmission Electron Microscope (TEM) characterization image of carbon materials prepared in preferred examples 29 to 32 of the present invention and comparative examples 1 to 3.

FIG. 5 is a high resolution spectrum of preferred embodiments 29-32 of the present invention.

FIG. 6 is an X-ray diffraction (XRD) pattern of carbon materials produced in preferred examples 29 to 32 of the present invention and comparative examples 1 to 3.

FIG. 7 is a graph showing ORR polarization curves of potassium hydroxide solutions on rotating disks for 2 electrodes prepared in example 29 and comparative example 2.

FIG. 8 is a graph showing H calculated for 2 kinds of electrodes prepared in example 29 and comparative example 2₂O₂Selectivity profile of (a).

Detailed Description

The present invention is further illustrated by the following examples, but is not limited to these examples. The experimental methods not specified in the examples are generally commercially available according to the conventional conditions and the conditions described in the manual, or according to the general-purpose equipment, materials, reagents and the like used under the conditions recommended by the manufacturer, unless otherwise specified. The starting materials required in the following examples and comparative examples are all commercially available.

Examples 1 to 36

The method of the present invention is described in detail with reference to the flow chart of the manufacturing process shown in fig. 1.

Step a, preparing a mixed acid solution with strong oxidizing property, namely 65 percent of HNO₃15mL and 98% H₂SO₄45mL of the solution was mixed well, and then 500mg of the purchased single-walled carbon nanotube was added thereto, followed by stirring at 75 ℃ for 3 hours. And after the reaction is finished, performing solid-liquid separation by using a centrifugal mode, washing the carbon tube by water for multiple times, and then freeze-drying overnight to obtain the carbon oxide nanotube CNT.

And step b, taking formamide as a solvent, adding 250mg of the dried carbon oxide nanotube into 70mL of formamide, and performing ultrasonic treatment until the carbon oxide nanotube is uniformly dispersed to obtain a hydrothermal reaction mother liquor. Care should be taken that the container is kept completely dry, mainly considering that the autopolymerization of formamide cannot take place in the presence of water.

And c, putting the hydrothermal reaction mother liquor into a closed reaction kettle for hydrothermal reaction. The hydrothermal reaction was carried out under the following conditions: the temperatures and times are shown in Table 1 below, and the pressures are the self-generated pressures. In the hydrothermal reaction process, formamide generates self-polymerization reaction on the surface of the carbon tube. And after the hydrothermal reaction is finished, cooling the sealed container to room temperature, opening the container, taking out the solid material, and washing the solid material with deionized water or ethanol to obtain the black solid material NC @ CNT without formamide residues.

And d, placing the obtained NC @ CNT in a porcelain boat, heating to the calcining temperature shown in the following table 1 at the heating rate shown in the following table 1 under the protection of inert gas, keeping the temperature for a period of time at the temperature, and naturally cooling to the room temperature after the reaction is finished to obtain the required NC @ CNT-T composite material (T represents the calcining temperature). Elemental content analysis of the target product was performed and found to consist of nitrogen, carbon and oxygen.

TABLE 1

Examples 4, 8, 12, 16, 20, 24, 28, 32 and 36 above represent NC @ CNT obtained without high temperature calcination in step d.

Comparative examples 1 to 2

In addition, referring to fig. 2, for comparison, the present comparative examples 1 to 2 provide a specific method of preparing a nitrocarbon material: the difference from the embodiment is that no carbon tube is added in the whole synthesis process, namely formamide is directly placed in a hydrothermal reaction kettle for reaction for 12 hours at 180 ℃, and after the reaction is finished, solid-liquid separation is carried out to obtain a black solid material; and then, under the protection of inert gas, heating to the calcining temperature shown in the table 2 at the heating rate shown in the table 2, keeping the temperature at the temperature for a period of time, and naturally cooling to room temperature after the reaction is finished to obtain the required NC-T nitrogen-carbon material (T represents the calcining temperature). Elemental content analysis of the target product was performed and found to consist of nitrogen, carbon and oxygen.

TABLE 2

The above comparative example 2 represents the obtained black solid material without high-temperature calcination.

Comparative example 3

The CNT obtained in step a of the example was used as the comparative example 3.

The products prepared in the above preferred examples 29 to 32 and comparative examples 1 to 3 were characterized and the results were as follows:

FIG. 3 is a Scanning Electron Microscope (SEM) characterization image of carbon materials prepared in preferred examples 29 to 32 of the present invention and comparative examples 1 to 3, which all show the morphology of carbon tubes.

FIG. 4 is a Transmission Electron Microscope (TEM) characterization image of carbon materials prepared in preferred examples 29 to 32 of the present invention and comparative examples 1 to 3, each showing the morphology of a carbon tube.

FIG. 5 is a high resolution spectrum of preferred embodiments 29-32 of the present invention, all containing nitrogen, indicating successful encapsulation of nitrocarbon materials.

FIG. 6 is an X-ray diffraction (XRD) pattern of the carbon materials obtained in preferred examples 29 to 32 of the present invention and comparative examples 1 to 3, which shows that only the peak of carbon exists.

The electron microscope analysis proves that formamide successfully wraps the carbon tubes in the products prepared in the embodiments 29 to 32, and the original tubular shape of the carbon tubes is kept (see fig. 3 and 4).

Example 37

The products obtained in the above preferred examples 29 to 32 and comparative examples 1 to 3 were used for the preparation of rotating disk electrodes by the following method: 3.3mg of the catalyst materials prepared in examples 1 to 4 and comparative examples 1 to 2 were dispersed in 980. mu.L of isopropyl alcohol, respectively, 20. mu.L of 5% Nafion solution was added, mixed uniformly, and subjected to ultrasonic treatment for 30 min. 6 mu L of the prepared active material solution is uniformly dripped on a glassy carbon electrode. The active material solution is dried after dropping and then tested, and preferably the comparison results are shown in table 3 below. The Ppm units in the table are mg/L.

TABLE 3

Note: and (3) testing conditions are as follows: the linear sweep voltammograms were tested in 0.1mol/L KOH solution under saturation with oxygen at 1600rpm and a sweep rate of 5 mv/s. Comparative example 2 is not listed here because conductivity is almost nonexistent.

Fig. 7 is a plot of LSV in KOH solution for 2 electrodes prepared in example 29 and comparative example 2.

FIG. 8 is H calculated from the following equation and the LSV curve of FIG. 6 for 2 kinds of electrodes prepared in example 29 and comparative example 2₂O₂Selectivity diagram of (a):

as can be seen from Table 3 and FIGS. 7 and 8, comparative examples 1-2, i.e., NC-T materials, according to the present invention also have good H₂O₂Selectivity, but its conductivity is very poor; in contrast, in examples 29 to 32 in which carbon nanotubes were added, the conductivity became significantly better and a plateau of limiting current appeared. In particular, example 29, namely NC @ CNT-400The selectivity of the large voltage interval is over 90%, and the conductivity is better than that of the comparative example 1.

In addition, the materials used in the invention are all cheap pure carbon materials, so that the method is more suitable for producing H than the commercial anthraquinone method₂O₂The method of (3) has a greater cost advantage.