CN115069291B - Ni/VN/g-C 3 N 4 Composite photocatalyst, preparation method and application thereof - Google Patents

Abstract

The invention discloses a preparation method of Ni/VN/g‑C ₃ N ₄ composite photocatalyst, which includes the following steps: preparing porous flake g‑C ₃ N ₄ powder; preparing NiV‑LDH powder; C ₃ N ₄ powder and NiV-LDH powder are matched, and then fully mixed and then calcined and carbonized at high temperature to prepare Ni/VN/g-C ₃ N ₄ photocatalyst; the invention provides a brand-new metal Ni and VN composite serves as a noble metal-free co-catalyst for g‑C ₃ N _4. g‑C ₃ N ₄ is a typical porous nanosheet structure, which can effectively increase the number of active sites of the composite photocatalyst, while metallic nickel due to its good Metal conductivity plays the role of a charge transfer "bridge" and can quickly transfer electrons from the g‑C ₃ N ₄ valence band to VN. With their joint efforts, the Ni/VN/g‑ The charge separation efficiency and transmission efficiency of the C ₃ N ₄ composite photocatalyst improve the hydrogen production performance of the composite photocatalyst; the preparation method of the present invention has a simple process flow, easy to control conditions, low production cost, and is easy for industrial production.

Description

A Ni/VN/g-C3N4 composite photocatalyst and its preparation method and application

Technical field

The invention belongs to the technical field of functional materials, relates to photocatalytic materials, and specifically relates to a Ni/VN/g-C3N4 composite photocatalyst and its preparation method and application.

Background technique

As the energy crisis and environmental problems continue to intensify, it is increasingly urgent to develop renewable and clean energy to replace fossil fuels. Hydrogen is considered a promising alternative to fossil fuels due to its high energy density and zero emissions. In recent years, solar-driven semiconductor photocatalytic water splitting and hydrogen evolution have been considered as an ideal method to solve global environmental and energy problems. Therefore, various photocatalysts have been developed to alleviate these troublesome problems. Until now, researchers have focused on preparing hydrogen evolution photocatalysts using earth-enriched materials.

Graphitized carbon nitride (gC ₃ N ₄ ) is a stable polymer photocatalyst that is considered to be a candidate for the direct production of hydrogen using solar energy in water due to its high stability, non-toxicity, abundance and excellent optical properties. an attractive candidate material. However, the high light-induced charge recombination rate and lack of absorption above 460 nm of original gC ₃ N ₄ are still not ideal in practical applications. Then, the cocatalyst needs _to be loaded on pure _gC3N4 to achieve efficient space charge separation. It is well known that Pt has the largest work function and the lowest overpotential and is the best candidate cocatalyst for capturing electrons in _H2 production photocatalytic reactions. Given their low versatility and low cost, noble metal-based cocatalysts are too scarce and expensive to be used in large-scale energy production. The loading of cocatalysts not only promotes charge separation, but also reduces the activation energy or overpotential of the reaction. Therefore, the pursuit of a noble metal-free and highly active cocatalyst is highly desirable.

Vanadium nitride is a nitride in which nitrogen atoms occupy interstitial positions in the vanadium metal lattice. It has good electrical conductivity, stable chemical properties, and resistance to chemical corrosion. And as a cocatalyst for CdS, it can significantly improve the photocatalytic hydrogen production performance of CdS. However, the high surface energy of VN will cause it to aggregate during the preparation process, resulting in a large loss of active sites and greatly reducing the interaction with the electrolyte. opportunities for contact, thus rendering their catalytic activity unsatisfactory. Therefore, necessary methods should be explored to enrich the d-electron density of VNs. In addition, non-noble metals such as Co or Ni have also been found to effectively produce H ₂ on various semiconductor photocatalysts, and ultrafine Ni nanoparticles loaded on graphene oxide (GO) sheets have higher photocatalytic performance. There are currently no research reports on improving the photocatalytic hydrogen production efficiency of gC ₃ N ₄ and constructing a Ni/VN/gC ₃ N ₄ system.

Contents of the invention

In view of the shortcomings of the existing technology, the purpose of the present invention is to provide a Ni/VN/gC ₃ N ₄ composite photocatalyst and its preparation method and application, to prepare a composite catalyst that effectively improves the photocatalytic hydrogen production efficiency, and the process is simple ,low cost.

In order to achieve the above object, the present invention adopts the following technical solutions to achieve it:

A preparation method of Ni/VN/gC ₃ N ₄ composite photocatalyst, including the following steps:

Step 1: Prepare porous flake gC ₃ N ₄ powder;

Step 2: Take (0.5~5) mmol nickel chloride hexahydrate, (1~3) mmol vanadium chloride, (1~5) mmol urea, (0.1~3) mmol CTAB and (0.005~0.02) g polydiene Mix propyl dimethyl ammonium chloride to obtain mixed powder C, then add 30 to 100 mL of ultrapure water, ultrasonic for 60 to 150 minutes, then stir thoroughly, then quickly pour the mixed solution into a 100 mL reaction kettle, and place Put it into an oven preheated to 120~200℃, keep it for 12~24h, and then naturally cool it to room temperature, take out the reaction kettle, centrifuge, wash, dry and grind the solution to obtain solid D, which is NiV-LDH;

Step 3: Mix (0.2-3) g of solid D and (1-12) g of porous flake gC ₃ N ₄ powder, place in 30-90 mL of ultrapure water and sonicate for 60-240 minutes, then stir thoroughly. The precipitate is obtained after centrifugation, dried and ground to obtain powder E;

Step 4: Mix powder E, N,N'-methylenebisacrylamide and dicyandiamide at a mass ratio of 1:(0.5~6):(1~8) and place them in a tube furnace. Under an argon atmosphere, raise the tube furnace to 500-700°C at a rate of 2-10°C/min, and keep it warm for 2-5 hours. After the product is naturally cooled to room temperature, take it out and grind it to obtain Ni/VN/gC ₃ N _4. Photocatalyst.

The invention also has the following technical features:

Preferably, the preparation method of porous flaky gC ₃ N ₄ powder in step one includes the following steps:

S1. Put 8~16g melamine into a white porcelain boat and place it in a tube furnace. Under the protection of argon gas, raise the temperature to 450~600°C at a heating rate of 2~10°C/min, and keep it warm for 2~4 hours. After completion of the sample Cool to room temperature naturally in the furnace, take out the sample and grind it to obtain yellow powder A, that is, block gC ₃ N ₄ ;

S2. Add 5 to 10 g of block gC ₃ N ₄ into a beaker containing 10 mL of ultrapure water, ultrasonic for 30 to 90 minutes, and finally place it in a white porcelain boat and put it into a tube furnace under an oxygen atmosphere. Raise the temperature to 350-550°C at a heating rate of 2-10°C/min and keep it warm for 30-120 minutes. After the sample is cooled to room temperature naturally in the furnace, take out the sample and grind it to obtain yellow powder B, which is a porous flake gC ₃ N ₄ .

Further, the grinding described in S1 is grinding in a mortar for 20 to 60 minutes; the grinding described in S2 is grinding in a mortar for 20 to 90 minutes.

Preferably, the sufficient stirring described in step 2 is to use a magnetic stirrer to stir for 60 to 250 minutes.

Preferably, the lotion described in step 2 is washed more than three times with ultrapure water and absolute ethanol respectively.

Preferably, the drying described in step 2 and step 3 is to dry in a vacuum drying oven for 8 to 26 hours.

Preferably, the grinding described in step two, step three and step four is to use a mortar for 30 to 120 minutes.

Preferably, the sufficient stirring in step three is to stir on a magnetic stirrer for 10 to 24 hours.

The invention also protects a Ni/VN/gC ₃ N ₄ composite photocatalyst prepared by the above method and its application in photocatalytic hydrogen production.

Compared with the existing technology, the present invention has the following technical effects:

The invention provides a brand-new metal Ni and VN composite as a noble metal-free co-catalyst for gC ₃ N ₄ and its preparation method. gC ₃ N ₄ is a typical porous nanosheet structure, and the pores on the surface of gC ₃ N ₄ nanosheets It can effectively increase the number of active sites of the composite photocatalyst. When sunlight irradiates gC ₃ N ₄ , its valence band electrons will be excited to the conduction band. VN has good electron adsorption capacity due to its unique electronic structure, which can It is very good at attracting the photogenerated electrons accumulated in the conduction band of gC ₃ N ₄ , and metal nickel plays the role of a charge transfer "bridge" due to its good metal conductivity, and can quickly transfer the electrons in the valence band of gC ₃ N ₄ Transferred to VN, with their joint efforts, the charge separation efficiency and transmission efficiency of the Ni/VN/gC ₃ N ₄ composite photocatalyst are greatly improved, thereby improving the hydrogen production performance of the composite photocatalyst;

In the process of preparing the Ni/VN/gC ₃ N ₄ composite photocatalytic material, the present invention adopts a solid-phase sintering method to avoid the introduction of heterogeneous atoms during the composite process, and NiV-LDH and gC ₃ are added before carbonization. N ₄ compounding makes the composite photocatalyst grow firmly, the process is simple, the conditions are easy to control, and the production cost is low, making it easy for industrial production.

Description of drawings

Figure 1 is an X-ray diffraction analysis chart of Ni/VN/gC ₃ N ₄ prepared in Example 1 of the present invention;

Figure 2 is a scanning electron microscope image at 500nm of Ni/VN/gC ₃ N ₄ prepared in Example 1 of the present invention;

Figure 3 is a graph showing the hydrogen production performance of Ni/VN/gC ₃ N ₄ prepared in Example 1 of the present invention under visible light.

Detailed ways

The specific content of the present invention will be further explained in detail below with reference to the examples.

Example 1:

Step 1: Prepare porous flake gC ₃ N ₄ powder;

S1, put 12g of melamine into a white porcelain boat, place it in a tube furnace, under argon protection, heat it up to 550°C at a heating rate of 5°C/min, and keep it for 4 hours. After the end, the sample is naturally cooled to room temperature in the furnace. , take out the sample and grind it in a mortar for 50 minutes to obtain yellow powder A, which is block gC ₃ N ₄ ;

S2. Add 8g of block gC ₃ N ₄ into a beaker containing 10 mL of ultrapure water, ultrasonic for 40 minutes, and finally place it in a white porcelain boat and put it into a tube furnace, under an oxygen atmosphere, at 4°C/min The heating rate was increased to 400°C and kept for 60 minutes. After the sample was cooled to room temperature naturally in the furnace, the sample was taken out and ground in a mortar for 40 minutes to obtain yellow powder B, which is porous flake gC ₃ N ₄ .

Step 2: Mix 3 mmol nickel chloride hexahydrate, 1 mmol vanadium chloride, 2 mmol urea, 0.5 mmol CTAB and 0.005 g polydiallyldimethylammonium chloride to obtain mixed powder C, then add 40 mL of ultrapure water , first ultrasonic for 70 minutes, then stir on a magnetic stirrer for 80 minutes, then quickly pour the mixture into a 100mL reaction kettle, put it into an oven preheated to 160°C, and keep it warm for 12 hours. After completion, naturally cool to room temperature and take it out. In the reaction kettle, centrifuge the solution, wash it with ultrapure water and absolute ethanol three times or more, place it in a vacuum drying box and dry it at 80°C for 24 hours, and grind it with a mortar for 60 minutes to obtain solid D, which is NiV-LDH;

Step 3: Mix 2g of solid D and 7g of porous flake gC ₃ N ₄ powder, place it in 30 mL of ultrapure water and sonicate for 60 minutes, stir on a magnetic stirrer for 14 hours, and then centrifuge to get the precipitate, and put it in a vacuum Dry in a drying box for 24 hours and grind in a mortar for 60 minutes to obtain powder E;

Step 4: Mix powder E, N,N'-methylenebisacrylamide and dicyandiamide at a mass ratio of 1:0.6:4 and place them in a tubular furnace, and place the tubular furnace under an argon atmosphere. The furnace was raised to 600°C at a rate of 5°C/min and kept for 2 hours. After the product was naturally cooled to room temperature, it was taken out and ground in a mortar for 40 minutes to obtain the Ni/VN/gC ₃ N ₄ photocatalyst.

Lab Solar 6A model equipment was used to test the photocatalytic effect of Ni/VN/gC ₃ N ₄ . The specific test process includes weighing 50 mg of composite photocatalyst and 10 mL of xylitol oligosaccharide, and placing them in a glass reaction vessel containing 90 mL of ultrapure water, and illuminating them for 4 hours.

Figure 1 is an X-ray diffraction analysis chart of Ni/VN/gC ₃ N ₄ prepared in Example 1; the abscissa is the 2θ angle, and the ordinate is the absorption intensity. 13° and 27° respectively correspond to the (100) crystal plane and (002) crystal plane of gC ₃ N ₄ , and Ni/VN/gC ₃ N ₄ can also accurately correspond to Ni PDF#04-0850 and VN PDF#35 -0768, indicating the successful preparation of Ni/VN/gC ₃ N ₄ composite photocatalyst;

Figure 2 is a scanning electron microscope image at 500nm of Ni/VN/gC ₃ N ₄ prepared in Example 1; from Figure 2, it can be clearly observed that Ni-VN has a smaller flake structure than carbon nitride and is evenly dispersed On gC ₃ N ₄ nanosheets;

Figure 3 is a diagram of the hydrogen production performance of Ni/VN/gC ₃ N ₄ prepared in Example 1 under visible light. As can be seen from Figure 3, the catalyst has excellent hydrogen production performance and a stable hydrogen production rate. The hydrogen production capacity in four hours can be Reached 1669μmol/g.

Example 2:

Step 1: Prepare porous flake gC ₃ N ₄ powder;

S1, put 10g of melamine into a white porcelain boat, place it in a tube furnace, under argon protection, heat it up to 600°C at a heating rate of 10°C/min, and keep it for 2 hours. After the end, the sample is naturally cooled to room temperature in the furnace. , take out the sample and grind it in a mortar for 60 minutes to obtain yellow powder A, that is, block gC ₃ N ₄ ;

S2. Take another 10g of block gC ₃ N ₄ and add it to a beaker containing 10mL of ultrapure water. Ultrasonic for 30 minutes. Finally, place it in a white porcelain boat and put it into a tube furnace. Under an oxygen atmosphere, heat at 2°C/min. The heating rate was increased to 550°C and kept for 60 minutes. After the sample was cooled to room temperature naturally in the furnace, the sample was taken out and ground in a mortar for 40 minutes to obtain yellow powder B, which is porous flake gC ₃ N ₄ .

Step 2: Mix 3mmol nickel chloride hexahydrate, 1mmol vanadium chloride, 4mmol urea, 2mmol CTAB and 0.01g polydiallyldimethylammonium chloride to obtain mixed powder C, then add 60mL of ultrapure water. First ultrasonic for 60 minutes, then stir on a magnetic stirrer for 60 minutes, then quickly pour the mixture into a 100 mL reaction kettle, put it into an oven preheated to 140°C, and keep it warm for 14 hours. After completion, naturally cool to room temperature and take out the reaction. kettle, centrifuge the solution, wash it more than three times with ultrapure water and absolute ethanol, dry it in a vacuum drying box for 18 hours, and grind it with a mortar for 40 minutes to obtain solid D, which is NiV-LDH;

Step 3: Mix 1g of solid D and 2g of porous flake gC ₃ N ₄ powder, place in 30 mL of ultrapure water and sonicate for 60 minutes, place on a magnetic stirrer and stir for 14 hours, then centrifuge to obtain the precipitate, and place in a vacuum Dry in a drying box for 18 hours and grind in a mortar for 50 minutes to obtain powder E;

Step 4: Mix the powder E, N,N'-methylenebisacrylamide and dicyandiamide in a mass ratio of 1:2:6 and place them in a tube furnace. Put the tube in an argon atmosphere. The furnace was raised to 550°C at a rate of 5°C/min and kept for 3 hours. After the product was naturally cooled to room temperature, it was taken out and ground in a mortar for 60 minutes to obtain the Ni/VN/gC ₃ N ₄ photocatalyst.

Example 3:

Step 1: Prepare porous flake gC ₃ N ₄ powder;

S1, put 14g of melamine into a white porcelain boat, place it in a tube furnace, under argon protection, heat it up to 600°C at a heating rate of 6°C/min, and keep it for 2 hours. After the end, the sample is naturally cooled to room temperature in the furnace. , take out the sample and grind it in a mortar for 40 minutes to obtain yellow powder A, that is, block gC ₃ N ₄ ;

S2. Add 8g of block gC ₃ N ₄ into a beaker containing 10 mL of ultrapure water, ultrasonic for 60 minutes, and finally place it in a white porcelain boat and put it into a tube furnace, under an oxygen atmosphere, at 6°C/min The heating rate was increased to 500°C and kept for 80 minutes. After that, the sample was naturally cooled to room temperature in the furnace. The sample was taken out and ground in a mortar for 40 minutes to obtain yellow powder B, which is porous flake gC ₃ N ₄ .

Step 2: Mix 3mmol nickel chloride hexahydrate, 2mmol vanadium chloride, 4mmol urea, 1.2mmol CTAB and 0.02g polydiallyldimethylammonium chloride to obtain mixed powder C, then add 60mL of ultrapure water , first ultrasonic for 60 minutes, then stir on a magnetic stirrer for 120 minutes, then quickly pour the mixture into a 100mL reaction kettle, put it into an oven preheated to 160°C, and keep it warm for 16 hours. After completion, naturally cool to room temperature and take it out. In the reaction kettle, centrifuge the solution, wash it three times or more with ultrapure water and absolute ethanol, dry it in a vacuum drying oven for 18 hours, and grind it with a mortar for 60 minutes to obtain solid D, which is NiV-LDH;

Step 3: Mix 1g of solid D and 6g of porous flake gC ₃ N ₄ powder, place in 40 mL of ultrapure water and sonicate for 60 minutes, place on a magnetic stirrer and stir for 10 hours, then centrifuge to obtain the precipitate, and place in a vacuum Dry in a drying box for 18 hours and grind in a mortar for 40 minutes to obtain powder E;

Step 4: Mix powder E, N,N'-methylenebisacrylamide and dicyandiamide in a mass ratio of 1:2:4 and place them in a tube furnace. Put the tube in an argon atmosphere. The furnace was raised to 650°C at a rate of 5°C/min and kept for 3 hours. After the product was naturally cooled to room temperature, it was taken out and ground in a mortar for 40 minutes to obtain the Ni/VN/gC ₃ N ₄ photocatalyst.

Example 4:

Step 1: Prepare porous flake gC ₃ N ₄ powder;

S1, put 8g of melamine into a white porcelain boat, place it in a tube furnace, under argon protection, raise the temperature to 450°C at a heating rate of 2°C/min, and keep it for 3 hours. After the end, the sample is naturally cooled to room temperature in the furnace. , take out the sample and grind it in a mortar for 20 minutes to obtain yellow powder A, that is, block gC ₃ N ₄ ;

S2. Add 5g of block gC ₃ N ₄ into a beaker containing 10 mL of ultrapure water, ultrasonic for 80 minutes, and finally place it in a white porcelain boat and put it into a tube furnace under an oxygen atmosphere at 5°C/min. The heating rate was increased to 350°C, and the temperature was maintained for 120 minutes. After the completion of the sample, the sample was naturally cooled to room temperature in the furnace. The sample was taken out and ground in a mortar for 20 minutes to obtain yellow powder B, which is porous flake gC ₃ N ₄ .

Step 2: Mix 0.5 mmol nickel chloride hexahydrate, 3 mmol vanadium chloride, 1 mmol urea, 0.1 mmol CTAB and 0.02 polydiallyldimethylammonium chloride to obtain mixed powder C, then add 30 mL of ultrapure water , first ultrasonic for 90 minutes, then stir on a magnetic stirrer for 180 minutes, then quickly pour the mixture into a 100 mL reaction kettle, put it into an oven preheated to 120°C, and keep it warm for 20 hours. After completion, naturally cool to room temperature and take it out. In the reaction kettle, centrifuge the solution, wash it three times or more with ultrapure water and absolute ethanol, dry it in a vacuum drying oven for 8 hours, and grind it with a mortar for 30 minutes to obtain solid D, which is NiV-LDH;

Step 3: Mix 3g of solid D and 1g of porous flake gC ₃ N ₄ powder, place it in 60 mL of ultrapure water and sonicate for 120 minutes, stir on a magnetic stirrer for 20 hours, and then centrifuge to get the precipitate, and put it in a vacuum Dry in a drying box for 8 hours and grind in a mortar for 30 minutes to obtain powder E;

Step 4: Mix the powder E, N,N'-methylenebisacrylamide and dicyandiamide at a mass ratio of 1:0.5:8 and place them in a tube furnace. Put the tube in an argon atmosphere. The furnace was raised to 500°C at a rate of 2°C/min and maintained for 4 hours. After the product was naturally cooled to room temperature, it was taken out and ground in a mortar for 30 minutes to obtain the Ni/VN/gC ₃ N ₄ photocatalyst.

Example 5:

Step 1: Prepare porous flake gC ₃ N ₄ powder;

S1, put 16g of melamine into a white porcelain boat, place it in a tube furnace, under argon protection, heat it up to 500°C at a heating rate of 8°C/min, and keep it for 3 hours. After the end, the sample is naturally cooled to room temperature in the furnace. , take out the sample and grind it in a mortar for 30 minutes to obtain yellow powder A, which is block gC ₃ N ₄ ;

S2. Add 6g of block gC ₃ N ₄ into a beaker containing 10 mL of ultrapure water, ultrasonic for 90 minutes, and finally place it in a white porcelain boat and put it into a tube furnace, in an oxygen atmosphere, at 10°C/min The heating rate was increased to 450°C and kept for 30 minutes. After the sample was cooled to room temperature naturally in the furnace, the sample was taken out and ground in a mortar for 90 minutes to obtain yellow powder B, which is porous flake gC ₃ N ₄ .

Step 2: Mix 5 mmol nickel chloride hexahydrate, 1 mmol vanadium chloride, 5 mmol urea, 3 mmol CTAB and 0.01g polydiallyldimethylammonium chloride to obtain mixed powder C, then add 100 mL of ultrapure water. First ultrasonic for 150 minutes, then stir on a magnetic stirrer for 250 minutes, then quickly pour the mixture into a 100 mL reaction kettle, put it into an oven preheated to 200°C, and keep it warm for 24 hours. After completion, naturally cool to room temperature and take out the reaction. kettle, centrifuge the solution, wash it more than three times with ultrapure water and absolute ethanol, dry it in a vacuum drying box for 26 hours, and grind it with a mortar for 120 minutes to obtain solid D, which is NiV-LDH;

Step 3: Mix 0.2g of solid D and 12g of porous flake gC ₃ N ₄ powder, place it in 90 mL of ultrapure water and sonicate for 240 minutes, stir on a magnetic stirrer for 24 hours, and then centrifuge to get the precipitate. Put it in Dry in a vacuum drying oven for 26 hours and grind in a mortar for 120 minutes to obtain powder E;

Step 4: Mix the powder E, N,N'-methylenebisacrylamide and dicyandiamide at a mass ratio of 1:6:1 and place them in a tube furnace. Put the tube in an argon atmosphere. The furnace was raised to 700°C at a rate of 10°C/min and maintained for 5 hours. After the product was naturally cooled to room temperature, it was taken out and ground in a mortar for 120 minutes to obtain the Ni/VN/gC ₃ N ₄ photocatalyst.

Claims (9)

1. Ni/VN/g-C ₃ N ₄ The preparation method of the composite photocatalyst is characterized by comprising the following steps:

step one, preparing porous flaky g-C ₃ N ₄ Powder;

mixing (0.5-5) mmol of nickel chloride hexahydrate, (1-3) mmol of vanadium chloride, (1-5) mmol of urea, (0.1-3) mmole CTAB and (0.005-0.02) g of polydiallyl dimethyl ammonium chloride to obtain mixed powder C, adding 30-100 mL of ultrapure water, performing ultrasonic treatment for 60-150 min, fully stirring, rapidly pouring the mixed solution into a 100mL reaction kettle, putting into an oven which is preheated to 120-200 ℃, preserving heat for 12-24 h, naturally cooling to room temperature after finishing, taking out the reaction kettle, centrifuging, washing, drying and grinding the solution to obtain solid D, namely NiV-LDH;

step three, taking (0.2-3) g of solid D and (1-12) g of porous flaky g-C ₃ N ₄ Mixing the powder, placing the mixture into 30-90 mL of ultrapure water, performing ultrasonic treatment for 60-240 min, fully stirring, centrifuging to obtain precipitate, drying and grinding to obtain powder E;

step four, proportioning powder E, N, N' -methylene bisacrylamide and dicyandiamide according to the mass ratio of 1 (0.5-6) (1-8), placing the mixture into a tube furnace, heating the tube furnace to 500-700 ℃ at the speed of 2-10 ℃/min under the argon atmosphere, preserving heat for 2-5 hours, taking out and grinding after the product is naturally cooled to room temperature, thus obtaining Ni/VN/g-C ₃ N ₄ A photocatalyst;

porous sheet-shaped g-C in the step one ₃ N ₄ The preparation method of the powder comprises the following steps:

s1, placing 8-16 g of melamine into a white porcelain boat, placing the white porcelain boat into a tubular furnace, heating to 450-600 ℃ at a heating rate of 2-10 ℃/min under the protection of argon, preserving heat for 2-4 hours, naturally cooling a sample to room temperature along with the furnace after the completion of the heating, taking out the sample, and grinding to obtain yellow powder A, namely a block g-C ₃ N ₄ ；

S2, taking 5-10 g of block g-C ₃ N ₄ Adding into a beaker filled with 10mL of ultrapure water, carrying out ultrasonic treatment for 30-90 min, finally placing the beaker into a white porcelain boat, placing the porcelain boat into a tube furnace, heating to 350-550 ℃ at a heating rate of 2-10 ℃/min under an oxygen atmosphere, preserving heat for 30-120 min, naturally cooling the sample to room temperature along with the furnace after the completion of the heating, taking out the sample, and grinding to obtain yellow powder B, namely porous flaky g-C ₃ N ₄ 。

2. Ni/VN/g-C according to claim 1 ₃ N ₄ The preparation method of the composite photocatalyst is characterized in that grinding in S1 is carried out in a mortar for 20-60 min; the grinding in S2 is grinding for 20-90 min in a mortar.

3. Ni/VN/g-C according to claim 1 ₃ N ₄ The preparation method of the composite photocatalyst is characterized in that the full stirring in the second step is stirring for 60-250 min by adopting a magnetic stirrer.

4. Ni/VN/g-C according to claim 1 ₃ N ₄ The preparation method of the composite photocatalyst is characterized in that the lotion in the second step is washed for more than three times by adopting ultrapure water and absolute ethyl alcohol respectively.

5. Ni/VN/g-C according to claim 1 ₃ N ₄ The preparation method of the composite photocatalyst is characterized in that the drying in the second step and the third step is that the composite photocatalyst is put into a vacuum drying oven to be dried for 8-26 hours.

6. Ni/VN/g-C according to claim 1 ₃ N ₄ The preparation method of the composite photocatalyst is characterized in that grinding in the second step, the third step and the fourth step is grinding for 30-120 min by adopting a mortar.

7. Ni/VN/g-C according to claim 1 ₃ N ₄ A preparation method of a composite photocatalyst,the method is characterized in that the full stirring in the step three is carried out by placing the mixture on a magnetic stirrer for stirring for 10-24 hours.

8. Ni/VN/g-C prepared by the method according to any one of claims 1-7 ₃ N ₄ A composite photocatalyst.

9. A Ni/VN/g-C as in claim 8 ₃ N ₄ The application of the composite photocatalyst in the photocatalytic hydrogen production.