A Ni-Fe2P / CoP3 / g-C3N4 composite photocatalyst, its preparation method and application

Abstract

This invention discloses a Ni-Fe2P / CoP3 / g-C3N4 composite photocatalyst, its preparation method, and its application. The preparation method includes two-step calcination in a muffle furnace to prepare sheet-like nano-g-C3N4, followed by hydrothermal synthesis of a precursor by mixing nickel acetate, cobalt chloride hexahydrate, ferric chloride hexahydrate, hexadecyltrimethylammonium bromide, urea, and the g-C3N4 prepared in step one, and then phosphating in one step to obtain the composite photocatalytic material. The entire preparation process is simple, the conditions are easy to control, the production cost is low, and it is easy to industrialize. The prepared Ni-Fe2P / CoP3 / g-C3N4 composite photocatalyst exhibits a hydrogen production rate of up to 16.666 mmol / g under visible light irradiation for four hours, demonstrating excellent photocatalytic hydrogen evolution efficiency.

Description

Technical Field

[0001] This invention belongs to the field of functional materials technology, and relates to composite photocatalysts, specifically to a Ni-Fe2P / CoP3 / g-C3N4 composite photocatalyst, its preparation method, and its application. Background Technology

[0002] In order to reduce the emission of harmful gases and the consumption of non-renewable energy, the development of eco-friendly, inexpensive and sustainable energy is urgently needed in the world today. Hydrogen molecules, as an ideal energy carrier, have received widespread attention in the world energy crisis of the 21st century due to their environmental protection and high energy efficiency. Semiconductor photocatalytic water splitting under visible light irradiation is a green and friendly way to convert solar energy into renewable hydrogen energy. It can directly convert intermittent renewable solar energy into chemical energy, which plays an indispensable role in promoting the industrialization of hydrogen. Semiconductor photocatalytic materials have high photocatalytic activity and stability, and their potential application in solar hydrogen production has attracted much attention [1]. Among the various semiconductors explored as photocatalyst candidates, polymeric organic carbon nitride (g-C3N4, CN) with visible light response and robustness has received widespread attention. Two-dimensional CN (CNNS) can not only expand its specific surface area, but more importantly, due to the shortening of the diffusion distance, it suppresses the possibility of bulk recombination of charge carriers. However, the inherent low charge separation rate and lack of catalytic sites of CN still limit the full utilization of charge carriers to trigger the generation of hydrogen. Despite increasing research on CN, its photocatalytic hydrogen evolution efficiency remains low, primarily because photogenerated electrons and holes readily recombine before migrating to the catalyst surface and reacting with reactants [8-10]. To address this issue, various strategies have been employed to improve CN photocatalytic efficiency, including morphology modification, elemental doping, heterojunction construction, and cocatalyst modification. Highly efficient and stable cocatalysts can not only lower the activation barrier and accelerate reaction kinetics but also improve charge separation and provide more active catalytic sites for hydrogen evolution by capturing charge carriers. One of the most comprehensive strategies currently employed is the introduction of noble metals / complexes such as Pt and Au as cocatalysts on the CN surface. Although noble metals exhibit the best efficiency in photocatalysis, their practical application potential is limited due to their scarcity and high cost. Therefore, there is an urgent need to explore highly active and low-cost noble metal alternatives.

[0003] In recent years, the hydrogen evolution activity of several CN cocatalysts, including oxides, sulfides, and phosphides of transition metals (such as iron, cobalt, nickel, molybdenum, and tungsten), has been improved. Transition metal phosphides (TMPs), in particular, have shown improved activity. TMPs can be viewed as phosphorus (P) atoms doped into the transition metal lattice. DFT calculations have demonstrated that P atoms play a crucial role in hydrogen evolution response (HER) in TMPs. During HER, electrons in the transition metal tend to transfer from metal atoms to the more electronegative phosphorus atoms, allowing the more electronegative P atoms to attract electrons from the metal atoms. Therefore, negatively charged phosphorus atoms can effectively capture protons during HER. Consequently, p-rich phosphides exhibit better catalytic activity than metal-rich phosphides. However, the catalytic activity of CoP3 is still insufficient for practical applications and requires further improvement. To further enhance the HER catalytic activity of TMPs, heterogeneous atom doping is an effective strategy. It can modulate the local electronic and atomic structure of TMPs, improve electron transport, and increase the density of active sites, thereby effectively improving HER performance. Bimetallic phosphides (BMPs), as derivatives of TMPs, possess advantages such as tunable electronic structure, good electronic conductivity, low hydrogen evolution overpotential, and low carrier transfer impedance. Compared to monometallic phosphides, bimetallic atoms have a higher positive charge, which can significantly increase the number of hydride ion accepting active sites. Simultaneously, the large number of negatively charged P atoms can effectively capture protons through electrostatic attraction, thereby promoting photocatalytic activity. Summary of the Invention

[0004] To address the shortcomings of existing technologies, the present invention aims to provide a Ni-Fe2P / CoP3 / g-C3N4 composite photocatalyst, its preparation method, and its application. Ni-Fe2P / CoP3 nanosheets are uniformly dispersed on g-C3N4 nanosheets, increasing the specific surface area and surface active sites of the product, effectively promoting the separation and transport of photogenerated charges, and improving hydrogen production efficiency.

[0005] To achieve the above objectives, the present invention employs the following technical solution:

[0006] A method for preparing a Ni-Fe2P / CoP3 / g-C3N4 composite photocatalyst includes the following steps:

[0007] Step 1: Preparation of sheet-like nano-g-C3N4;

[0008] Step 2: Nickel acetate, cobalt chloride hexahydrate, ferric chloride hexahydrate, hexadecyltrimethylammonium bromide, urea, and g-C3N4 prepared in Step 1 are mixed in a mass ratio of (0.1-2):(0.5-4):(0.2-3):(1-3):(1-5):(3-8) and placed in a beaker. Deionized water is added at a mass ratio of g-C3N4 to deionized water of 1:10, and methanol is added at a volume ratio of deionized water to methanol of 1:3. After ultrasonication until uniform dispersion, pyrrole at 1% of the mass of g-C3N4 is added. After stirring until uniform dispersion, the mixed solution is quickly poured into the lining of the reaction vessel.

[0009] Step 3: Seal the reaction vessel and place it in a vacuum drying oven. Keep it at 100-180℃ for 10-20 hours. After the temperature inside the oven drops to room temperature, remove the reaction vessel and cool it. Then pour out the reaction solution and centrifuge to separate it. Wash the precipitate and dry it to obtain the reaction precursor C.

[0010] Step 4: Place the reaction precursor C and sodium hypophosphite in a white porcelain boat at a mass ratio of 1:(1-20), put it into a tube furnace, and raise the temperature to 300-550℃ at a rate of 5-20℃ / min under the protection of an inert atmosphere. Hold the temperature for 2-4 hours. After the product cools down, take it out and grind it to obtain the Ni-Fe2P / CoP3 / g-C3N4 composite photocatalyst.

[0011] The present invention also has the following technical features:

[0012] Preferably, the preparation and release of g-C3N4 in step one includes the following steps:

[0013] S1. Melamine is placed in a white porcelain boat, the heating rate is set to 2-10℃ / min, the temperature is 450-650℃, the holding time is 2-5h, and calcination is carried out. After calcination, the sample is allowed to cool naturally and then ground.

[0014] S2. The sample obtained in step S1 is placed in a porcelain boat for secondary calcination. The heating rate is set to 5-10℃ / min, the calcination temperature is 150-450℃, and the holding time is 0.5-3h. After secondary calcination, the sample is naturally cooled in the furnace and ground to obtain light yellow powder A, i.e., flake g-C3N4.

[0015] Preferably, the grinding in steps S1 and S2 is performed by grinding in a mortar and pestle for 30 to 60 minutes.

[0016] Preferably, the ultrasound time in step two is 45 to 125 minutes.

[0017] Preferably, the stirring time in step two is 120 to 720 minutes.

[0018] Preferably, the washing in step three involves washing with deionized water and anhydrous ethanol 3 to 5 times respectively.

[0019] Preferably, the drying in step three is performed in a vacuum drying oven at 80°C for 8–24 hours.

[0020] Preferably, the grinding in step four is performed by grinding in a mortar and pestle for 30 to 90 minutes.

[0021] This invention also protects a Ni-Fe2P / CoP3 / g-C3N4 composite photocatalyst prepared by the method described above and its application in photocatalytic hydrogen evolution.

[0022] Compared with the prior art, the present invention has the following technical effects:

[0023] The g-C3N4 prepared in this invention is in the form of nanosheets, which increases its specific surface area and active sites during photocatalytic hydrogen production, thereby effectively improving hydrogen production efficiency. The prepared Ni-Fe2P / CoP3 exhibits a three-dimensional nanosheet structure composed of stacked nanosheets. This structure is beneficial to increasing the specific surface area and surface active sites of the Ni-Fe2P / CoP3 / g-C3N4 composite photocatalyst, so as to effectively promote the separation and transport of photogenerated charges. The prepared Ni-Fe2P / CoP3 / g-C3N4 composite photocatalyst has a hydrogen production of up to 16.666 mmol / g in four hours under visible light irradiation, showing excellent photocatalytic hydrogen evolution efficiency.

[0024] Furthermore, this invention combines hydrothermal and solid-state sintering methods. First, carbon nitride is prepared, then all raw materials are mixed and synthesized through hydrothermal synthesis of the precursor, followed by one-step phosphating to obtain the composite photocatalytic material. The entire preparation process is simple, the conditions are easy to control, the production cost is low, and it is easy to industrialize. Attached Figure Description

[0025] Figure 1 X-ray diffraction pattern of Ni-Fe2P / CoP3 / g-C3N4 prepared in Example 1;

[0026] Figure 2 The scan image shows the Ni-Fe2P / CoP3 / g-C3N4 prepared in Example 1;

[0027] Figure 3 The hydrogen evolution performance diagram is shown for Ni-Fe2P / CoP3 / g-C3N4 prepared in Example 1. Detailed Implementation

[0028] The specific content of the present invention will be further explained in detail below with reference to the embodiments.

[0029] Example 1:

[0030] Step 1: First, place 9g of melamine in a white porcelain boat, set the calcination temperature to 500℃, hold for 5 hours, and raise the temperature at a rate of 10℃ / min. After calcination, allow the sample to cool naturally, grind it for 40 minutes, and then place it back into the porcelain boat for a second calcination. Set the calcination temperature to 150℃, hold for 2 hours, and raise the temperature at a rate of 5℃ / min. After the second calcination, allow the sample to cool naturally in the furnace and grind it for 45 minutes to obtain light yellow powder A, i.e., thin-flake nano-g-C3N4.

[0031] Step 2: Mix nickel acetate, cobalt chloride hexahydrate, ferric chloride hexahydrate, hexadecyltrimethylammonium bromide, urea, and powder A in a mass ratio of 0.8:1.5:1:1.2:1.5:3, with 1g of thin-film nano-g-C3N4, to obtain mixed powder B. Then add 10mL of deionized water and 30mL of methanol, sonicate for 95min, then add 0.01g of pyrrole, and stir on a magnetic stirrer for 150min. Then quickly pour the mixture into the lining of a 100mL reaction vessel.

[0032] Step 3: Set the working temperature of the vacuum drying oven to 160℃. After the temperature inside the drying oven reaches the set temperature, place the sealed reaction vessel into the oven and keep it at that temperature for 12 hours. After the temperature inside the oven drops to room temperature, remove the reaction vessel and cool it. Pour out the cooled reaction solution and centrifuge it. Wash it three times with deionized water and anhydrous ethanol respectively to obtain a precipitate. Then place it in a vacuum drying oven at 80℃ for 14 hours to obtain solid C, i.e., the precursor.

[0033] Step 4: Place the solid C precursor and sodium hypophosphite in a white porcelain boat at a mass ratio of 1:15, put it in a tube furnace, and raise the temperature to 350°C at a rate of 10°C / min under an inert atmosphere. Hold the temperature for 3 hours. After the product cools down, take it out and grind it for 60 minutes to obtain the Ni-Fe2P / CoP3 / g-C3N4 photocatalyst.

[0034] The photocatalytic effect of Ni-Fe2P / CoP3 / g-C3N4 was tested using a LabSolar 6A instrument. The specific test procedure included weighing 55 mg of the composite photocatalyst and 10 mL of isopropanol, and then placing them into a glass reaction vessel containing 90 mL of deionized water, followed by irradiation for 4 hours.

[0035] Figure 1The image shows the X-ray diffraction pattern of Ni-Fe2P / CoP3 / g-C3N4 prepared in Example 1, where the horizontal axis represents the 2θ angle and the vertical axis represents the diffraction peak intensity. The peaks at 13° and 27° correspond to the (100) and (002) crystal planes of g-C3N4, respectively. Furthermore, Ni-Fe2P / CoP3 / g-C3N4 accurately corresponds to CoP3 PDF#29-0496 and Fe2P PDF#51-0943, indicating the successful preparation of the Ni-Fe2P / CoP3 / g-C3N4 photocatalyst.

[0036] Figure 2 The scanning chromatogram of Ni-Fe2P / CoP3 / g-C3N4 prepared in Example 1; as shown. Figure 2 As shown, the added g-C3N4 exhibits a nanosheet structure, while Ni-Fe2P / CoP3 exhibits a three-dimensional nanosheet structure composed of stacked nanosheets and grows on the surface of carbon nitride.

[0037] Figure 3 The hydrogen evolution performance diagram of Ni-Fe2P / CoP3 / g-C3N4 prepared in Example 1 is shown below; Figure 3 As shown in Figure b, the composite photocatalyst prepared by this invention exhibits excellent hydrogen evolution performance, with a hydrogen production of up to 16.666 mmol / g within four hours under visible light irradiation.

[0038] Example 2:

[0039] Step 1: First, place 10g of melamine in a white porcelain boat, set the calcination temperature to 600℃, hold for 2 hours, and raise the temperature at a rate of 10℃ / min. After calcination, allow the sample to cool naturally, grind it for 50 minutes, and then place it back into the porcelain boat for a second calcination. Set the calcination temperature to 250℃, hold for 1 hour, and raise the temperature at a rate of 5℃ / min. After the second calcination, allow the sample to cool naturally in the furnace and grind it for 40 minutes to obtain light yellow powder A, i.e., flaky nano-g-C3N4.

[0040] Step 2: Mix nickel acetate, cobalt chloride hexahydrate, ferric chloride hexahydrate, cetyltrimethylammonium bromide, urea, and powder A in a mass ratio of 0.5:1:0.8:1.6:1:4, with 0.8g of flake nano g-C3N4, to obtain mixed powder B. Then add 15mL of deionized water and 45mL of methanol, sonicate for 75min, then add 0.008g of pyrrole, and stir on a magnetic stirrer for 120min. Then quickly pour the mixture into the lining of a 100mL reaction vessel.

[0041] Step 3: Set the working temperature of the vacuum drying oven to 180℃. After the temperature inside the drying oven reaches the set temperature, place the sealed reaction vessel into the oven and keep it warm for 10 hours. After the temperature inside the oven drops to room temperature, remove the reaction vessel and cool it. Pour out the cooled reaction solution and centrifuge it. Wash it four times with deionized water and anhydrous ethanol respectively to obtain a precipitate. Then put it into the vacuum drying oven at 80℃ for 8 hours to obtain solid C, i.e., the precursor.

[0042] Step 4: Place the solid C precursor and sodium hypophosphite in a white porcelain boat at a mass ratio of 1:8, put it in a tube furnace, and raise the temperature to 400℃ at a rate of 8℃ / min under the protection of an inert atmosphere. Hold the temperature for 2 hours. After the product cools down, take it out and grind it for 55 minutes to obtain the Ni-Fe2P / CoP3 / g-C3N4 photocatalyst.

[0043] The photocatalytic effect of Ni-Fe2P / CoP3 / g-C3N4 was tested using a LabSolar 6A instrument. The specific test procedure included weighing 60 mg of photocatalyst and 10 mL of isopropanol, and then placing them into a glass reaction vessel containing 90 mL of ultrapure water, followed by irradiation for 4 hours.

[0044] Example 3:

[0045] Step 1: First, place 12g of melamine into a white porcelain boat, set the calcination temperature to 650℃, hold for 3 hours, and raise the temperature at a rate of 5℃ / min. After calcination, allow the sample to cool naturally, grind it for 40 minutes, and then place it back into the porcelain boat for a second calcination. Set the calcination temperature to 350℃, hold for 1.5 hours, and raise the temperature at a rate of 7℃ / min. After the second calcination, allow the sample to cool naturally in the furnace and grind it for 60 minutes to obtain light yellow powder A, i.e., flaky nano-g-C3N4.

[0046] Step 2: Mix nickel acetate, cobalt chloride hexahydrate, ferric chloride hexahydrate, cetyltrimethylammonium bromide, urea, and powder A in a mass ratio of 1.2:2:3:1.5:2.4:4.5, with 1.2g of flake nano-g-C3N4, to obtain mixed powder B. Then add 12mL of deionized water and 36mL of methanol, sonicate for 120min, then add 0.015g of pyrrole, and stir on a magnetic stirrer for 150min. Then quickly pour the mixture into the lining of a 100mL reaction vessel.

[0047] Step 3: Set the working temperature of the vacuum drying oven to 180℃. After the temperature inside the drying oven reaches the set temperature, place the sealed reaction vessel into the oven and keep it warm for 10 hours. After the temperature inside the oven drops to room temperature, remove the reaction vessel and cool it. Pour out the cooled reaction solution and centrifuge it. Wash it five times with deionized water and anhydrous ethanol respectively to obtain a precipitate. Then put it into the vacuum drying oven at 80℃ for 12 hours to obtain solid C, i.e., the precursor.

[0048] Step 4: Place the solid C precursor and sodium hypophosphite in a white porcelain boat at a mass ratio of 1:15, put it in a tube furnace, and raise the temperature to 500℃ at a rate of 10℃ / min under the protection of an inert atmosphere. Hold the temperature for 2 hours. After the product cools down, take it out and grind it for 80 minutes to obtain the Ni-Fe2P / CoP3 / g-C3N4 photocatalyst.

[0049] The photocatalytic effect of Ni-Fe2P / CoP3 / g-C3N4 was tested using a LabSolar 6A instrument. The specific test procedure included weighing 55 mg of photocatalyst and 15 mL of isopropanol, and then placing them into a glass reaction vessel containing 85 mL of ultrapure water and irradiating with light for 4 hours.

[0050] Example 4:

[0051] Step 1: First, place 10g of melamine in a white porcelain boat, set the calcination temperature to 450℃, hold for 2 hours, and raise the temperature at a rate of 2℃ / min. After calcination, allow the sample to cool naturally, grind it for 30 minutes, and then place it back into the porcelain boat for a second calcination. Set the calcination temperature to 450℃, hold for 0.5 hours, and raise the temperature at a rate of 10℃ / min. After the second calcination, allow the sample to cool naturally in the furnace and grind it for 30 minutes to obtain light yellow powder A, i.e., flaky nano-g-C3N4.

[0052] Step 2: Mix nickel acetate, cobalt chloride hexahydrate, ferric chloride hexahydrate, cetyltrimethylammonium bromide, urea, and powder A in a mass ratio of 0.1:0.5:0.2:1:1:3, with 0.8g of flake nano g-C3N4, to obtain mixed powder B. Then add 15mL of deionized water and 45mL of methanol, sonicate for 40min, then add 0.008g of pyrrole, and stir on a magnetic stirrer for 720min. Then quickly pour the mixture into the lining of a 100mL reaction vessel.

[0053] Step 3: Set the working temperature of the vacuum drying oven to 150℃. After the temperature inside the drying oven reaches the set temperature, place the sealed reaction vessel into the oven and keep it warm for 15 hours. After the temperature inside the oven drops to room temperature, remove the reaction vessel and cool it. Pour out the cooled reaction solution and centrifuge it. Wash it four times with deionized water and anhydrous ethanol respectively to obtain a precipitate. Then put it into the vacuum drying oven at 80℃ for 12 hours to obtain solid C, i.e., the precursor.

[0054] Step 4: Place the solid C precursor and sodium hypophosphite in a white porcelain boat at a mass ratio of 1:1, put it in a tube furnace, and raise the temperature to 300℃ at a rate of 5℃ / min under the protection of an inert atmosphere. Hold the temperature for 4 hours. After the product cools down, take it out and grind it for 30 minutes to obtain the Ni-Fe2P / CoP3 / g-C3N4 photocatalyst.

[0055] The photocatalytic effect of Ni-Fe2P / CoP3 / g-C3N4 was tested using a LabSolar 6A instrument. The specific test procedure included weighing 60 mg of photocatalyst and 10 mL of isopropanol, and then placing them into a glass reaction vessel containing 90 mL of ultrapure water, followed by irradiation for 4 hours.

[0056] Example 5:

[0057] Step 1: First, place 10g of melamine in a white porcelain boat, set the calcination temperature to 600℃, hold for 2 hours, and raise the temperature at a rate of 10℃ / min. After calcination, allow the sample to cool naturally, grind it for 60 minutes, and then place it back into the porcelain boat for a second calcination. Set the calcination temperature to 250℃, hold for 3 hours, and raise the temperature at a rate of 5℃ / min. After the second calcination, allow the sample to cool naturally in the furnace and grind it for 60 minutes to obtain light yellow powder A, i.e., flaky nano-g-C3N4.

[0058] Step 2: Mix nickel acetate, cobalt chloride hexahydrate, ferric chloride hexahydrate, cetyltrimethylammonium bromide, urea, and powder A in a mass ratio of 2:4:3:3:5:8, with 0.8g of flake nano-g-C3N4, to obtain mixed powder B. Then add 15mL of deionized water and 45mL of methanol, sonicate for 125min, then add 0.008g of pyrrole, and stir on a magnetic stirrer for 360min. Then quickly pour the mixture into the lining of a 100mL reaction vessel.

[0059] Step 3: Set the working temperature of the vacuum drying oven to 100℃. After the temperature inside the drying oven reaches the set temperature, place the sealed reaction vessel into the oven and keep it at that temperature for 20 hours. After the temperature inside the oven drops to room temperature, remove the reaction vessel and cool it. Pour out the cooled reaction solution and centrifuge it. Wash it four times with deionized water and anhydrous ethanol respectively to obtain a precipitate. Then place it in the vacuum drying oven at 80℃ for 24 hours to obtain solid C, i.e., the precursor.

[0060] Step 4: Place the solid C precursor and sodium hypophosphite in a white porcelain boat at a mass ratio of 1:20, put it in a tube furnace, and raise the temperature to 550℃ at a rate of 5℃ / min under the protection of an inert atmosphere. Hold the temperature for 2 hours. After the product cools down, take it out and grind it for 90 minutes to obtain the Ni-Fe2P / CoP3 / g-C3N4 photocatalyst.

[0061] The photocatalytic effect of Ni-Fe2P / CoP3 / g-C3N4 was tested using a LabSolar 6A instrument. The specific test procedure included weighing 60 mg of photocatalyst and 10 mL of isopropanol, and then placing them into a glass reaction vessel containing 90 mL of ultrapure water, followed by irradiation for 4 hours.

[0062] The above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the specific implementation of the present invention. Any modifications or equivalent substitutions that do not depart from the spirit and scope of the present invention should be covered within the scope of the claims.

Claims

1. A method for preparing a Ni-Fe2P / CoP3 / g-C3N4 composite photocatalyst, characterized in that, Includes the following steps: Step 1: Preparation of sheet-like nano-g-C3N4; Step 2: Nickel acetate, cobalt chloride hexahydrate, ferric chloride hexahydrate, hexadecyltrimethylammonium bromide, urea, and g-C3N4 prepared in Step 1 are mixed in a mass ratio of (0.1-2):(0.5-4):(0.2-3):(1-3):(1-5):(3-8) and placed in a beaker. Deionized water is added at a mass ratio of g-C3N4 to deionized water of 1:10, and methanol is added at a volume ratio of deionized water to methanol of 1:

3. After ultrasonication until uniform dispersion, pyrrole at 1% of the mass of g-C3N4 is added. After stirring until uniform dispersion, the mixed solution is quickly poured into the lining of the reaction vessel. Step 3: Seal the reaction vessel and place it in a vacuum drying oven. Keep it at 100-180℃ for 10-20 hours. After the temperature inside the oven drops to room temperature, remove the reaction vessel and cool it. Then pour out the reaction solution and centrifuge to separate it. Wash the precipitate and dry it to obtain the reaction precursor C. Step 4: Place the reaction precursor C and sodium hypophosphite in a white porcelain boat at a mass ratio of 1:(1-20), put it into a tube furnace, and raise the temperature to 300-550℃ at a rate of 5-20℃ / min under the protection of an inert atmosphere. Hold the temperature for 2-4 hours. After the product cools down, take it out and grind it to obtain the Ni-Fe2P / CoP3 / g-C3N4 composite photocatalyst.

2. The preparation method of the Ni-Fe2P / CoP3 / g-C3N4 composite photocatalyst as described in claim 1, characterized in that, The preparation of g-C3N4 in step one includes the following steps: S1. Melamine is placed in a white porcelain boat, the heating rate is set to 2-10℃ / min, the temperature is 450-650℃, the holding time is 2-5h, and calcination is carried out. After calcination, the sample is allowed to cool naturally and then ground. S2. The sample obtained in step S1 is placed in a porcelain boat for secondary calcination. The heating rate is set to 5-10℃ / min, the calcination temperature is 150-450℃, and the holding time is 0.5-3h. After secondary calcination, the sample is naturally cooled in the furnace and ground to obtain light yellow powder A, i.e., flake g-C3N4.

3. The preparation method of the Ni-Fe2P / CoP3 / g-C3N4 composite photocatalyst as described in claim 2, characterized in that, The grinding described in steps S1 and S2 is grinding with a mortar and pestle for 30 to 60 minutes.

4. The preparation method of the Ni-Fe2P / CoP3 / g-C3N4 composite photocatalyst as described in claim 1, characterized in that, The ultrasound time mentioned in step two is 45 to 125 minutes.

5. The preparation method of the Ni-Fe2P / CoP3 / g-C3N4 composite photocatalyst as described in claim 1, characterized in that, The stirring time mentioned in step two is 120 to 720 minutes.

6. The preparation method of the Ni-Fe2P / CoP3 / g-C3N4 composite photocatalyst as described in claim 1, characterized in that, The washing described in step three involves washing with deionized water and anhydrous ethanol 3 to 5 times respectively.

7. The preparation method of the Ni-Fe2P / CoP3 / g-C3N4 composite photocatalyst as described in claim 1, characterized in that, The drying process described in step three involves drying at 80°C in a vacuum drying oven for 8–24 hours.

8. The preparation method of the Ni-Fe2P / CoP3 / g-C3N4 composite photocatalyst as described in claim 1, characterized in that, The grinding described in step four involves grinding in a mortar and pestle for 30 to 90 minutes.

9. A Ni-Fe2P / CoP3 / g-C3N4 composite photocatalyst prepared by the method described in any one of claims 1 to 8.

10. The application of the Ni-Fe2P / CoP3 / g-C3N4 composite photocatalyst as described in claim 9 in photocatalytic hydrogen evolution.

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