Preparation method and application of cobalt-doped porous carbon nitride nanosheet

Abstract

The invention relates to a preparation method and application of a cobalt-doped porous carbon nitride nanosheet, and the preparation method comprises the following steps: (1) taking a nitrogen source and a cobalt source as raw materials, grinding the nitrogen source and the cobalt source, uniformly mixing, calcining at high temperature, naturally cooling to room temperature, washing the calcined substances of the nitrogen source and the cobalt source, and drying in vacuum to obtain the cobalt-doped carbon nitride nanosheet; and (2) dispersing the cobalt-doped carbon nitride nanosheet obtained in the step (1) in hydrazine hydrate for heating reaction, washing the cobalt-doped carbon nitride nanosheet to be neutral after the heating reaction is finished, and finally performing vacuum drying to obtain the cobalt-doped porous carbon nitride nanosheet. The cobalt-doped porous carbon nitride nanosheet prepared by the method disclosed by the invention is a catalytic material which is high in response capability to visible light, high in yield of hydrogen peroxide prepared by photocatalysis, good in decomposition inhibition performance and capable of being repeatedly used, and is suitable for the field of new energy products.

Description

Technical Field

[0001] The present invention relates to the technical field of new energy functional materials, and particularly relates to a preparation method and application of cobalt-doped porous carbon nitride nanosheets. Background Art

[0002] With the rapid development of the economy, traditional resources have been over-consumed. There is an urgent need for humans to find green and renewable energy sources, such as hydrogen energy, wind energy, tidal energy, etc. Compared with hydrogen energy, hydrogen peroxide is regarded as a more promising sustainable energy carrier. This is because the energy density of hydrogen peroxide is similar to that of hydrogen, but its transportation and storage are safer. Currently, the main routes for synthesizing hydrogen peroxide are the anthraquinone process and the direct synthesis method. The former requires multiple steps of hydrogenation / oxidation reaction steps, highly relies on high energy input, and is prone to generating toxic by-products; the latter requires the participation of precious metals, is expensive, and the reaction conditions are dangerous and difficult to precisely control.

[0003] Photocatalysis provides an efficient and energy-saving way for the production of hydrogen peroxide through the photochemical reaction of water and oxygen driven by sunlight. So far, many photocatalysts have been used in the field of photocatalysis, such as carbon nitride, titanium dioxide, tungsten oxide, bismuth vanadate, cadmium sulfide, molybdenum sulfide, organic polymers, etc. Due to the presence of sp 2 -hybridized carbon and nitrogen, carbon nitride can establish a conjugated electron structure, has a suitable conduction band potential (-1.1 eV vs. NHE) and valence band potential (1.6 eV vs. NHE), and is a commonly used photocatalytic material. However, as a typical non-metal catalyst, the biggest limitation of carbon nitride is the high recombination rate of photo-generated electron-hole pairs and the lack of surface active sites, resulting in insufficient performance. Therefore, in most carbon nitride-hydrogen peroxide production systems, small molecular weight organic substances are often added as electron donors to enable more electrons to participate in the reaction to prepare hydrogen peroxide, but this will undoubtedly increase the cost and involve the generation of by-products.

[0004] In order to improve the photocatalytic performance of carbon nitride, a variety of strategies have been developed, such as morphology regulation, surface passivation, element doping, metal deposition, and heterostructure construction. Designing carbon nitride with different morphologies is conducive to expanding the specific surface area, improving the charge transfer efficiency, and thus promoting surface catalytic reactions. Two-dimensional carbon nitride nanosheets, especially porous carbon nitride nanosheets, show superiority in improving the separation of carriers and providing abundant reaction sites. In addition, the photocatalytic preparation of hydrogen peroxide is a dynamic process, including the in situ production and in situ decomposition of hydrogen peroxide. Even if the photocatalyst can produce a large amount of hydrogen peroxide, hydrogen peroxide has a strong tendency to induce decomposition on its surface. Hydrogen peroxide stabilizers, such as sodium pyrophosphate and ethylenediaminetetraacetic acid, are usually added to the reaction system. These stabilizers can interact with hydrogen peroxide molecules to form relatively stable complexes to inhibit the decomposition of hydrogen peroxide. In summary, the existing carbon nitride materials have problems such as rapid recombination of photogenerated carriers, insufficient surface active sites, reverse decomposition of hydrogen peroxide, and low catalytic efficiency in the process of photocatalytic preparation of hydrogen peroxide, which need to be solved urgently.

[0005] The patent application publication number CN 114192178 A discloses a preparation method and application of a cobalt-containing carbon nitride catalyst, which comprises calcining urea, cyanamide, dicyandiamide or melamine precursors to obtain a carbon nitride material; then dispersing the carbon nitride material into an aqueous solution of a Co(II) inorganic salt, adding an aqueous solution of an inorganic base, stirring, solid-liquid separation, and then washing, drying and calcining the separated solid to obtain a cobalt-containing carbon nitride catalyst. The catalyst is used in an intermittent reactor to efficiently catalyze the selective oxidation of ethylbenzene to synthesize acetophenone under solvent-free conditions. The raw materials in this patent are cheap and easy to obtain, the method is simple, the cycle is short, the catalyst is easy to recover, and the reuse effect is good. However, unlike the present patent application, which prepares cobalt-containing carbon nitride nanosheets by a one-step calcination method, the patent undergoes two calcinations to obtain cobalt-containing carbon nitride. First, a cyanide-containing precursor (urea, cyanamide, dicyandiamide or melamine) is calcined to obtain carbon nitride, which is then dispersed in a cobalt-containing inorganic salt (Co(NO 3 ) 2 、CoSO 4 ,CoBr 2 or Co(OAc) 2 ) aqueous solution, and calcined again to obtain the final product. Therefore, on the basis of improving the calcination method, this patent application prepares cobalt-doped porous carbon nitride nanosheets by hydrazine hydrate treatment, which has a better effect in the photocatalytic preparation of hydrogen peroxide and is conducive to increasing the yield of hydrogen peroxide. Summary of the invention

[0006] The purpose of the present invention is to address the problems existing in the background technology and to provide a preparation method and application of cobalt-doped porous carbon nitride nanosheets.

[0007] To achieve the above object, the present invention provides the following technical solution: A preparation method of cobalt-doped porous carbon nitride nanosheets, which comprises the following steps: (1) Using a nitrogen source and a cobalt source as raw materials, the nitrogen source and the cobalt source are ground and mixed evenly, and then calcined at high temperature. After naturally cooling to room temperature, the calcined product of the nitrogen source and the cobalt source is washed and vacuum dried to obtain cobalt-doped carbon nitride nanosheets; (2) The cobalt-doped carbon nitride nanosheets obtained in step (1) are dispersed in hydrazine hydrate for a heating reaction. After the heating reaction is completed, the cobalt-doped carbon nitride nanosheets are washed to neutrality, and finally vacuum dried to obtain cobalt-doped porous carbon nitride nanosheets.

[0008] The cobalt-doped carbon nitride nanosheets are prepared by a one-step calcination method, and its chemical formula structure is as Figure 1 shown. Cobalt is anchored on the carbon nitride skeleton through covalent bonds (Co-O and Co-N), that is, cobalt is introduced into the carbon nitride skeleton through bidentate ligands to form strong coordination centers to change the heterocyclic structure of carbon nitride. This one-step calcination method can broaden the light absorption range of carbon nitride, increase the electron density, and promote charge separation and transfer. After treatment with hydrazine hydrate, the porous defects on the surface of the nanosheets can be increased, further promoting charge separation and transfer and improving the photocatalytic performance.

[0009] Preferably, in step (1), the nitrogen source is one of urea, melamine and thiourea; the cobalt source is one of cobalt acetylacetonate, cobalt nitrate and cobalt chloride.

[0010] Preferably, in step (1), the mass ratio of the cobalt source to the nitrogen source is 1:200~1:1000.

[0011] Preferably, in step (1), the calcination is carried out in a high-temperature furnace, the calcination temperature is 350 °C~750 °C, and the calcination time is 0.5 h~5 h.

[0012] Preferably, in step (2), the volume of the hydrazine hydrate is 5 mL~50 mL.

[0013] Preferably, in step (2), the amount of the cobalt-doped carbon nitride nanosheets is 20 mg~200 mg.

[0014] Preferably, in step (2), the temperature of the heating reaction is 50 °C~250 °C; the heating reaction time is 1 h~5 h.

[0015] Preferably, in step (1), the specific operations of washing and vacuum drying are: washing the calcined product to neutrality with deionized water, and drying in a vacuum drying oven for 5 h~20 h, and setting the drying temperature to 50 °C~100 °C.

[0016] The present invention also provides an application of cobalt-doped porous carbon nitride nanosheets, and the cobalt-doped porous carbon nitride nanosheets are used as photocatalysts.

[0017] Preferably, the cobalt-doped porous carbon nitride nanosheets are used as photocatalysts in the photocatalytic preparation of hydrogen peroxide.

[0018] The photocatalytic preparation of hydrogen peroxide is a dynamic process, accompanied by the generation and decomposition of hydrogen peroxide. To clarify the generation process of hydrogen peroxide, hydrogen peroxide preparation experiments and hydrogen peroxide decomposition experiments were carried out respectively. Compared with pure carbon nitride, the hydrogen peroxide yield of cobalt-doped carbon nitride nanosheets obtained by one-step calcination method increased slightly, because most of the hydrogen peroxide produced by using pure carbon nitride was decomposed, resulting in less remaining hydrogen peroxide in the system. Compared with the above two materials, the hydrogen peroxide yield of cobalt-doped porous carbon nitride nanosheets treated with hydrazine hydrate increased significantly, because the hydrogen peroxide generated in the reaction system was not easily decomposed, making the remaining hydrogen peroxide more. Therefore, a synergistic effect is generated between the porous structure and the supported cobalt metal, which can activate the electronic structure of the active site, improve the hydrogen peroxide yield and avoid its in-situ decomposition.

[0019] Compared with the prior art, the beneficial effects of the present invention are as follows: (1) The preparation method of the cobalt-doped porous carbon nitride nanosheets of the present invention is simple, the required raw materials are easy to obtain, and the operation is simple; (2) In the cobalt-doped porous carbon nitride nanosheets of the present invention, cobalt metal is implanted into the carbon nitride framework through a bidentate ligand to form a strong coordination center, thereby changing the structure of the heterocycle and making electrons more evenly distributed throughout the structure, improving the electron transport performance of the material; (3) The morphology structure of the cobalt-doped porous carbon nitride nanosheets of the present invention is a two-dimensional porous structure, and the advantages of this structure are as follows: the porous structure increases the internal surface area, exposes more catalytic active sites on the surface, and makes full contact with the reactants, greatly improving the efficiency of the catalytic reaction; the porous structure provides a fast diffusion channel for the reactants and products, accelerates the transport of substances inside the catalyst, reduces the mass transfer resistance, and enables the reaction to proceed better; a synergistic effect is generated between the porous structure and the supported cobalt metal, which can activate the electronic structure of the active site, improve the hydrogen peroxide yield and avoid its in-situ decomposition; (4) The cobalt-doped porous carbon nitride nanosheets of the present invention are a catalytic material with strong visible light response ability, high efficiency in photocatalytic preparation of hydrogen peroxide, stable performance, and can be reused multiple times. Description of the Drawings

[0020] Figure 1 It is the chemical structure diagram of the cobalt-doped carbon nitride prepared in the present invention; Figure 2This is the scanning electron microscope (SEM) image of cobalt-doped carbon nitride nanosheets in Example 1 of the present invention; Figure 3 This is the transmission electron microscope (TEM) image of cobalt-doped carbon nitride nanosheets in Example 1 of the present invention; Figure 4 This is the SEM image of cobalt-doped porous carbon nitride nanosheets in Example 2 of the present invention; Figure 5 This is the TEM image of cobalt-doped porous carbon nitride nanosheets in Example 2 of the present invention; Figure 6 This is the effect diagram of photocatalytic production of hydrogen peroxide by cobalt-doped carbon nitride nanosheets, cobalt-doped porous carbon nitride nanosheets and carbon nitride prepared in Example 1 and Example 2 of the present invention; Figure 7 This is the effect diagram of photocatalytic decomposition of hydrogen peroxide by cobalt-doped carbon nitride nanosheets, cobalt-doped porous carbon nitride nanosheets and carbon nitride prepared in Example 1 and Example 2 of the present invention; Figure 8 This is the cyclic effect diagram of photocatalytic production of hydrogen peroxide by cobalt-doped porous carbon nitride nanosheets prepared in Example 2 of the present invention. Detailed implementation manners

[0021] The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments, so that those skilled in the art can better understand the present invention and be able to implement it, but the embodiments cited are not intended to limit the present invention.

[0022] Example 1: The preparation of cobalt-doped carbon nitride nanosheets is specifically carried out as follows: Cobalt-doped carbon nitride nanosheets are prepared by thermal polymerization. First, 10 g of urea and a certain amount of cobalt(II) acetylacetonate are placed in a mortar and ground thoroughly until completely homogeneous. Then, the above-ground powder is transferred to a 100 mL covered crucible and calcined at 550 °C for 2 h, with a heating rate of 5 °C min -1 . After natural cooling to room temperature, it is washed three times with deionized water and dried in a vacuum drying oven at 60 °C for 12 h. By changing the addition amount of cobalt(II) acetylacetonate, carbon nitride nanosheets and cobalt-doped carbon nitride nanosheets with different cobalt doping amounts are obtained in turn. The cobalt-doped carbon nitride nanosheets are prepared by a one-step calcination method, and its chemical structure is as Figure 1 shown.

[0023] Attached Figure 2 and attached Figure 3 are the SEM and TEM images of cobalt-doped carbon nitride nanosheets respectively. From attached Figure 2 and attached Figure 3 it can be seen that the prepared cobalt-doped carbon nitride nanosheets exhibit a smooth two-dimensional sheet structure on the surface.

[0024] Example 2: Preparation of cobalt-doped porous carbon nitride nanosheets, the specific steps are as follows: Disperse the obtained cobalt-doped carbon nitride nanosheets in 20 mL of hydrazine hydrate and react at 110 °C for 2 h. Subsequently, wash repeatedly with deionized water until neutral. Finally, dry in a vacuum drying oven at 60 °C for 12 h to obtain cobalt-doped porous carbon nitride nanosheets. Cobalt-doped porous carbon nitride nanosheets are obtained by treatment with hydrazine hydrate.

[0025] Appendix Figure 4 and Appendix Figure 5 are the SEM and TEM images of cobalt-doped porous carbon nitride nanosheets respectively. Through Appendix Figure 4 and Appendix Figure 5 it can be seen that a uniform and dense porous structure appears on the two-dimensional cobalt-doped porous carbon nitride nanosheets.

[0026] Example 3: Photocatalytic preparation of hydrogen peroxide, the specific steps are as follows: Disperse 30 mg of the catalyst cobalt-doped porous carbon nitride nanosheets prepared in Example 1 and Example 2 in 50 mL of pure water by ultrasonic dispersion respectively, and stir for 30 min to reach the adsorption-desorption equilibrium. Then, use a 300 W xenon lamp as the light source, and use a condensation circulation system to keep the temperature of the photocatalytic reaction system at 10 °C. The photocatalytic reaction continues for 1 h under stirring conditions, and samples are taken once every 15 min. Finally, the amount of hydrogen peroxide produced under illumination is quantitatively detected by iodometry and ultraviolet-visible spectrophotometer. To verify the ability of photocatalytic decomposition of hydrogen peroxide, replace the above-mentioned ultrapure water with an aqueous hydrogen peroxide solution (1 mM), and the rest of the operations are the same as above.

[0027] Appendix Figure 6 is the effect diagram of photocatalytic preparation of hydrogen peroxide by the prepared carbon nitride, cobalt-doped carbon nitride nanosheets and cobalt-doped porous carbon nitride nanosheets. From Figure 6 it can be seen that the efficiency of photocatalytic preparation of hydrogen peroxide by cobalt-doped porous carbon nitride nanosheets is significantly higher than that of carbon nitride and cobalt-doped carbon nitride nanosheets.

[0028] Appendix Figure 7 is the effect diagram of photocatalytic decomposition of hydrogen peroxide by the prepared carbon nitride, cobalt-doped carbon nitride nanosheets and cobalt-doped porous carbon nitride nanosheets. From Figure 7 it can be seen that the efficiency of photocatalytic inhibition of hydrogen peroxide decomposition by cobalt-doped porous carbon nitride nanosheets is significantly higher than that of carbon nitride and cobalt-doped carbon nitride nanosheets.

[0029] Appendix Figure 8 is the cyclic effect diagram of photocatalytic preparation of hydrogen peroxide by cobalt-doped porous carbon nitride nanosheets. FromFigure 8 It can be seen that after being used five times, the material still exhibits a high hydrogen peroxide production, indicating its good cycling stability and suitability for the preparation of hydrogen peroxide.

[0030] Obviously, the above embodiments are merely examples given for clear illustration and are not limitations on the implementation manners. For those of ordinary skill in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to enumerate all the implementation manners here. And the obvious changes or modifications derived therefrom still fall within the protection scope of the present invention.

Claims

1. A method for preparing cobalt-doped porous carbon nitride nanosheets, characterized in that: The following steps are involved: (1) Using a nitrogen source and a cobalt source as raw materials, grinding the nitrogen source and the cobalt source, mixing them evenly, and then calcining them at high temperature; after naturally cooling to room temperature, washing the calcined nitrogen source and the cobalt source, and vacuum drying them to obtain cobalt-doped carbon nitride nanosheets; (2) The cobalt-doped carbon nitride nanosheets obtained in step (1) are dispersed in hydrazine hydrate for heating reaction. After the heating reaction is completed, the cobalt-doped carbon nitride nanosheets are washed to neutrality, and finally vacuum dried to obtain cobalt-doped porous carbon nitride nanosheets.

2. The method for preparing a cobalt-doped porous carbon nitride nanosheet according to claim 1, characterized in that: In step (1), the nitrogen source is one of urea, melamine and thiourea; the cobalt source is one of cobalt acetylacetonate, cobalt nitrate and cobalt chloride.

3. The method for preparing cobalt-doped porous carbon nitride nanosheets according to claim 1, characterized in that: In step (1), the mass ratio of the cobalt source to the nitrogen source is 1:200 to 1:1000.

4. The method for preparing a cobalt-doped porous carbon nitride nanosheet according to claim 1, characterized in that: In step (1), calcination is carried out in a high temperature furnace at a calcination temperature of 350°C to 750°C and a calcination time of 0.5 h to 5 h.

5. The method for preparing cobalt-doped porous carbon nitride nanosheets according to claim 1, characterized in that: In step (2), the volume of the hydrazine hydrate is 5 mL to 50 mL.

6. The method for preparing cobalt-doped porous carbon nitride nanosheets according to claim 5, characterized in that: In step (2), the amount of the cobalt-doped carbon nitride nanosheets is 20 mg to 200 mg.

7. The method for preparing cobalt-doped porous carbon nitride nanosheets according to claim 1, characterized in that: In step (2), the heating reaction temperature is 50 °C to 250 °C; the heating reaction time is 1 h to 5 h.

8. The method for preparing cobalt-doped porous carbon nitride nanosheets according to claim 7, characterized in that: In step (1), the specific operations of washing and vacuum drying are: washing the calcined product with deionized water until it is neutral, and drying it in a vacuum drying oven for 5 h to 20 h, with the drying temperature set at 50 °C to 100 °C.

9. A use of a cobalt-doped porous carbon nitride nanosheet according to any one of claims 1 to 8, characterized in that: The cobalt-doped porous carbon nitride nanosheets are used as photocatalysts.

10. The use of a cobalt-doped porous carbon nitride nanosheet according to claim 9, characterized in that: The cobalt-doped porous carbon nitride nanosheet is used as a photocatalyst in the photocatalytic preparation of hydrogen peroxide.

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