V-Ni.SUB.2.P/g-C.SUB.3.N.SUB.4 .photocatalyst and its preparation method and application thereof

Abstract

The invention relates to a V-Ni.sub.2P/g-C.sub.3N.sub.4 photocatalyst, a preparation method, and application thereof. The V-Ni.sub.2P/g-C.sub.3N.sub.4 photocatalyst is a composite material of V-Ni.sub.2P and g-C.sub.3N.sub.4, wherein V-Ni.sub.2P has the spherical structure formed by nanosheets; the mass ratio of the V-Ni.sub.2P and g-C.sub.3N.sub.4 is (0.01 to 0.2):1.

Claims

1. A method for preparing a V-Ni.sub.2P/g-C.sub.3N.sub.4 photocatalyst comprising a composite material of V-Ni.sub.2P and g-C.sub.3N.sub.4, wherein the V-Ni.sub.2P is Ni.sub.2P doped with V and the mass ratio of the V-Ni.sub.2P and the g-C.sub.3N.sub.4 is (0.01 to 0.2):1, the method comprising: (1) dissolving nickel chloride and vanadium chloride in water, adjusting the pH value to 3 to 5 with an acid solution, to obtain a first mixed solution, and filling the first mixed solution into a first chamber of a two-chamber reactor; (2) dissolving g-C.sub.3N.sub.4, urea, and ammonium fluoride in water, adding ethylene glycol to obtain a second mixed solution and loading the second mixed solution into a second chamber of the two-chamber reactor; (3) putting the two-chamber reactor into a homogeneous reactor, firstly heating at 50° C. to 100° C. for 15 to 30 minutes, then starting rotation to mix the first mixed solution and the second mixed solution, and then heating at 80° C. to 200° C. for 6 to 24 hours, and finally cooling, centrifuging, washing, and drying to obtain a precipitate; (4) respectively placing sodium hypophosphite and the precipitate on the left side and the right side of a dual-temperature zone tubular atmosphere furnace, heating the left side of the dual-temperature zone tubular atmosphere furnace to 280° C. to 320° C., simultaneously heating the right side to 300° C. to 600° C., and heating for 1 to 3 hours to obtain the V-Ni.sub.2P/g-C.sub.3N.sub.4 photocatalyst.

2. The preparation method of claim 1, wherein in step (1), the molar ratio of the nickel chloride to the vanadium chloride is (1 to 6):(1 to 3).

3. The preparation method of claim 1, wherein the acid solution is a hydrochloric acid solution.

4. The preparation method of claim 3, wherein the hydrochloric acid solution is 0.005 to 0.01 mol/L.

5. The preparation method of claim 1, wherein in step (2), the mass ratio of the g-C.sub.3N.sub.4, the urea, and the ammonium fluoride is (1 to 20):(1 to 8):(1 to 4).

6. The preparation method of claim 1, wherein in step (3), the ratio of the nickel chloride to the g-C.sub.3N.sub.4 is (0.001 to 0.07) mol:(1 to 5) g.

7. The preparation method of claim 1, wherein in step (4), the mass ratio of the precipitate and the sodium hypophosphite is (1 to 5):(1 to 10), and the temperature of each side is raised at a heating rate of 2 to 10° C./min.

8. The preparation method of claim 1, further comprising calcining wherein the melamine is calcined at 450° C. to 600° C. for 1 to 5 hours to obtain the g-C.sub.3N.sub.4.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 shows an X-ray diffraction analysis chart of the V-Ni.sub.2P/g-C.sub.3N.sub.4 photocatalyst prepared in Example 1, wherein the abscissa is the 2θ angle and the ordinate is the absorption intensity.

(2) FIG. 2 shows a scanning diagram of the V-Ni.sub.2P/g-C.sub.3N.sub.4 photocatalyst prepared in Example 1 under 1 μm.

(3) FIG. 3 shows a hydrogen production performance diagram of the V-Ni.sub.2P/g-C.sub.3N.sub.4 photocatalyst prepared in Example 1, wherein the abscissa is the number of samples and the ordinate is the hydrogen production;

(4) FIG. 4 shows an X-ray diffraction analysis chart of pure phase g-C.sub.3N.sub.4, wherein the abscissa is the 2θ angle, and the ordinate is the absorption intensity;

(5) FIG. 5 shows a scanning image of V-Ni.sub.2P prepared in Comparative Example 2 at 1 μm;

(6) FIG. 6 shows an X-ray diffraction analysis chart of Ni.sub.2P/g-C.sub.3N.sub.4 prepared in Comparative Example 3, wherein the abscissa is the 2θ angle, and the ordinate is the absorption intensity;

(7) FIG. 7 shows a scanning image of Ni.sub.2P/g-C.sub.3N.sub.4 prepared in Comparative Example 3 at 1 μm;

(8) FIG. 8 shows a graph of the hydrogen production performance of Ni.sub.2P/g-C.sub.3N.sub.4 prepared in Comparative Example 3, wherein the abscissa is the number of samples and the ordinate is the hydrogen production.

DETAILED DESCRIPTION

(9) The present disclosure will be further described below through the following embodiments. It should be understood that the following embodiments are only used to illustrate the present disclosure, not to limit the present disclosure.

(10) In the present disclosure, the V-Ni.sub.2P/g-C.sub.3N.sub.4 photocatalyst comprises V-Ni.sub.2P and g-C.sub.3N.sub.4, wherein V-Ni.sub.2P has a spherical structure formed by nanosheets, and the doping form of V is lattice doping. The mass ratio of V-Ni.sub.2P and g-C.sub.3N.sub.4 can be (0.05 to 0.3):1. Among them, when V-Ni.sub.2P is used as an electrocatalyst, the introduction of V can regulate the electronic structure of Ni.sub.2P and increase its catalytic active sites of the Ni.sub.2P, and defects are made to increase the catalytic active sites of the Ni.sub.2P. Moreover, in the V-Ni.sub.2P/g-C.sub.3N.sub.4 photocatalyst, due to the excellent electron transport ability of V-Ni.sub.2P, V-Ni.sub.2P can effectively promote the transport and separation of photogenerated-electron-hole pairs of g-C.sub.3N.sub.4, but V-Ni.sub.2P does not have the performance of photocatalytic hydrogen production, and the active sites for photocatalytic hydrogen production are provided by g-C.sub.3N.sub.4.

(11) In one embodiment of the present disclosure, the V-Ni.sub.2P/g-C.sub.3N.sub.4 photocatalyst is formed by growing V-Ni.sub.2P nanoflowers on a g-C.sub.3N.sub.4 matrix through a hydrothermal and solid phase sintering method to form a nano-level photocatalytic phase. The preparation process is simple, and the obtained product has high-efficiency photocatalytic hydrogen production energy.

(12) The preparation method of the V-Ni.sub.2P/g-C.sub.3N.sub.4 photocatalyst is illustrated below.

(13) Preparation of g-C.sub.3N.sub.4 matrix.

(14) For example, g-C.sub.3N.sub.4 can be obtained from muffle furnace calcination. Firstly, 10 g to 15 g of melamine is put into a porcelain boat, the calcination temperature is 450° C. to 600° C., the heat preservation time is 1 hour to 5 hours, the heating rate is 2 to 10° C./min, so that the blocky g-C.sub.3N.sub.4 is obtained. Then taking out the sample and grinding for 30 minutes to 60 minutes, taking 1 g to 5 g of block g-C.sub.3N.sub.4, adding 100 to 200 mL of ethanol and carrying out ultrasonic treatment for 5 hours to 10 hours, then carrying out centrifugal washing with deionized water for three times, drying at 60° C. to 80° C. for 6 hours to 12 hours, taking out and grinding for later use.

(15) The nickel chloride and vanadium chloride are dissolved in water, and the pH value is adjusted to 3 to 5 with an acid solution to obtain a mixed solution A. Among them, nickel chloride (nickel chloride hexahydrate) and vanadium chloride are mixed according to the following molar ratio: nickel chloride hexahydrate:vanadium chloride=(1 to 6):(1 to 3). Nickel chloride and vanadium chloride can also be prepared into solutions with different concentrations and then used as a source of nickel and vanadium, for example, 0.1 mol/L to 0.5 mol/L nickel chloride hexahydrate solution and 0.01 mol/L to 0.2 mol/L vanadium chloride solution. The acid solution used can be 0.005 mol/L to 0.01 mol/L hydrochloric acid solution. As an example, 5 to 20 mL of 0.1 mol/L to 0.5 mol/L hexahydrate nickel chloride solution and 5 to 20 mL of 0.01 mol/L to 0.2 mol/L vanadium chloride solution are added into a 50 mL beaker, and then 0.005 mol/L to 0.01 mol/L of hydrochloric acid solution is added to adjust the pH value to 3 to 5, and the mixture is magnetically stirred for 30 minutes to 80 minutes to obtain a mixed solution A.

(16) G-C.sub.3N.sub.4, urea, and ammonium fluoride are dissolved in water, and ethylene glycol is added to obtain a mixed solution B. Among them, the mass ratio of g-C.sub.3N.sub.4:urea:ammonium fluoride=(1 to 20):(1 to 8):(1 to 4), the mass ratio of g-C.sub.3N.sub.4:ethylene glycol=(1 to 10) g:(5 to 25) mL. As an example, 10 mL to 80 mL of deionized water and 5 mL to 15 mL of ethylene glycol are added into a 100 mL beaker, and then ingredients of g-C.sub.3N.sub.4, urea, ammonium fluoride are added, and the mass of g-C.sub.3N.sub.4, urea, and ammonium fluoride can be (1 to 5) g, (0.5 to 2) g, (0.1 to 0.6) g respectively, and the mixture is magnetically stirred for 30 minutes to 80 minutes to obtain a mixed liquid B.

(17) The solution A is poured into one side of a two-chamber hydrothermal kettle. Finally, the mixed solution B is poured into the other side of the two-chamber hydrothermal kettle. Among them, the ratio of nickel chloride in the mixed solution A to g-C.sub.3N.sub.4 in the mixed solution B can be (0.001 to 0.07) mol:(1 to 5) g.

(18) The two-chamber hydrothermal kettle is loaded into a homogeneous reactor, and the temperature is raised to 50° C. to 100° C. after the reactor is started, and the continuous heating time is 15 minutes to 30 minutes. At this time, the mixed solution A and the mixed solution B are still not mixed. The purpose of the pre-reaction at 50° C. to 100° C. is to fully dissolve the nickel chloride and vanadium chloride to form an ionic form.

(19) Heating the hydrothermal temperature of the two-chamber hydrothermal kettle to 80° C. to 200° C., starting to rotate to mix the mixed solution A and the mixed solution B, and maintaining the temperature for 6 hours to 24 hours to obtain a precipitate C, taking out the reaction kettle for cooling after lowering the temperature. The cooled reaction solution is taken out and centrifuged, and washed with deionized water and ethanol for three times respectively to obtain the precipitate C, which is then placed in a vacuum drying oven to dry for 10 hours to 24 hours. In the hydrothermal process, a precursor of V-Ni.sub.2P grows on a g-C.sub.3N.sub.4 matrix or is wrapped by g-C.sub.3N.sub.4, the precursor is tightly combined with g-C.sub.3N.sub.4, and a V-Ni.sub.2P/g-C.sub.3N.sub.4 compound is formed through phosphorization, and the V-Ni.sub.2P tightly combined with g-C.sub.3N.sub.4 is favorable for transmission and separation of photo-generated electron-hole pairs, so that the photocatalytic performance is promoted.

(20) The precipitate C is ground to obtain a powder D, and the grinding time is controlled to be 30 minutes to 80 minutes. The powder D and sodium hypophosphite are mixed in the following mass ratio: powder:sodium hypophosphite=(1 to 5):(1 to 10). The porcelain boat filled with sodium hypophosphite is placed on the left side of the dual temperature zone tubular atmosphere furnace. The porcelain boat filled with the powder D is placed on the right side of the dual temperature zone tubular atmosphere furnace. Finally, the dual temperature zone tube furnace is evacuated to vacuum, and argon gas is introduced, and the operation is repeated for three times until all the oxygen in the tube furnace is discharged.

(21) Heating the left tube furnace to 280° C. to 320° C. at a heating rate of 2 to 10° C./min. At the same time, the temperature of the right tube furnace is raised to 300° C. to 600° C. at a heating rate of 2 to 10° C./min. Among them, the separated calcination avoids sodium impurities introduced after calcination with sodium hypophosphite, and at the same time can ensure that a sufficient phosphorus source exists in the tubular furnace. Finally, preserving the heat for 1 hour to 3 hours to obtain the V-Ni.sub.2P/g-C.sub.3N.sub.4 photocatalyst. Cooling the product, taking out and grinding for 30 minutes to 60 minutes.

(22) Using LabSolar 6A model equipment to test the photocatalytic effect of V-Ni.sub.2P/g-C.sub.3N.sub.4. The specific test process comprises the steps of weighing 10 mg to 50 mg photocatalyst and 5 mL to 20 mL triethanolamine, putting into a glass reaction vessel containing 50 mL to 100 mL deionized water, and irradiating for 2 hours to 6 hours.

(23) Hereinafter, the present disclosure will be further described with the following examples. It should be understood that the following examples are used to explain this invention and do not mean to limit the scope of this invention. Any non-essential improvements and modifications made by a person skilled in the art based on this invention all fall into the protection scope of this invention. The specific process parameters below are only exemplary, and a person skilled in the art can choose proper values within an appropriate range according to the description, and are not restricted to the specific values shown below.

Example 1

(24) (1) First, putting 15 g of melamine into a porcelain boat, calcining at 550° C., maintaining the temperature for 4 hours, and raising the temperature at 2° C./min to obtain blocky g-C.sub.3N.sub.4, taking out the sample and grinding for 60 minutes. Taking 1 g of block g-C.sub.3N.sub.4, adding 100 mL of ethanol, performing ultrasonic treatment for 6 hours, then performing centrifugal washing for three times by using deionized water, drying at 60° C. for 10 hours, taking out and grinding for later use;

(25) (2) in a 50 mL beaker was added 10 mL of 0.2 mol/L nickel chloride hexahydrate solution and 10 mL of 0.04 mol/L vanadium chloride solution. The nickel chloride hexahydrate and vanadium chloride were mixed according to the following molar ratio: hexahydrate nickel chloride:vanadium chloride=5:1. Then 0.005 mol/L hydrochloric acid solution was added to adjust the pH value to 4, and the mixture was magnetically stirred for 15 minutes to obtain a mixed solution A. Then pouring the mixed solution A into one side of the two-chamber hydrothermal kettle;

(26) (3) adding 20 mL of deionized water and 10 mL of ethylene glycol into a 100 mL beaker, and then adding ingredients of g-C.sub.3N.sub.4, urea, ammonium fluoride, etc., according to the following mass ratio: g-C.sub.3N.sub.4:urea:ammonium fluoride=2.5 g:0.8 g:0.2 g, and magnetically stirred for 30 minutes to obtain a mixed solution B. Finally, pouring the mixed solution B into the other side of the two-chamber hydrothermal kettle;

(27) (4) loading the two-chamber hydrothermal kettle into a homogeneous reactor, starting the reactor, raising the temperature to 50° C., and maintaining the temperature for 15 minutes. Then raising the temperature to 120° C., starting to rotate, and maintaining the temperature for 12 hours. Taking out the reaction kettle for cooling after lowering the temperature;

(28) (5) taking out the cooled solution, centrifugal, washing with deionized water and ethanol for three times respectively, and drying in a vacuum drying oven for 12 hours to obtain a precipitate C;

(29) (6) the dried precipitate C was taken out and ground for 30 minutes to obtain a powder D. The powder D and sodium hypophosphite were blended in the following mass ratio: Powder D:Sodium hypophosphite=1:5. Putting the porcelain boat containing sodium hypophosphite on the left side of the dual temperature zone tubular atmosphere furnace, and placing the porcelain boat containing sample powder on the right side, and then pumping the tube furnace to be vacuum, introducing argon gas, and repeating the operation for three times, until all the oxygen in the tube furnace was discharged;

(30) (7) heating the left tube furnace to 300° C. at a heating rate of 10° C./min, and at the same time heating the right tube furnace to 500° C. at a heating rate of 10° C./min, and continuous heating for 2 hours;

(31) (8) cooling the product, taking out, and grinding for 30 minutes to obtain the V-Ni.sub.2P/g-C.sub.3N.sub.4 photocatalyst. The mass ratio of V-Ni.sub.2P and g-C.sub.3N.sub.4 in the obtained photocatalyst was 0.08:1. V in V-Ni.sub.2P was lattice doped with a doping content of 20 wt %.

(32) FIG. 1 is an X-ray diffraction analysis chart of V-Ni.sub.2P/g-C.sub.3N.sub.4 prepared in Example 1, wherein the abscissa is the 2θ angle, and the ordinate is the absorption intensity. The (100) crystal plane and (002) crystal plane of g-C.sub.3N.sub.4 are respectively corresponding to the positions of 13° and 27°, and V-Ni.sub.2P/g-C.sub.3N.sub.4 can accurately correspond to Ni.sub.2P PDF #03-0953, which indicates that V-Ni.sub.2P/g-C.sub.3N.sub.4 photocatalyst is successfully prepared.

(33) FIG. 2 is a scan diagram of V-Ni.sub.2P/g-C.sub.3N.sub.4 prepared in Example 1 at 1 μm. Among them, it can be clearly seen that the flower ball composed of V-Ni.sub.2P nanosheets, and the irregular block structure is the amorphous state of g-C.sub.3N.sub.4.

(34) FIG. 3 is a graph of the hydrogen production performance of V-Ni.sub.2P/g-C.sub.3N.sub.4 prepared in Example 1, wherein the abscissa is the number of samples and the ordinate is the hydrogen production. Among them, the hydrogen production performance of pure phase g-C.sub.3N.sub.4 is 0.21 μmol, while the pure phase V-Ni.sub.2P does not detect the trace of hydrogen, but the successfully compounded V-Ni.sub.2P/g-C.sub.3N.sub.4 hydrogen production performance is 25.18 μmol. The hydrogen performance has been significantly improved.

Example 2

(35) (1) Firstly, putting 10 g of melamine into a porcelain boat, the calcination temperature was 550° C., the heat preservation time was 3 hours, the heating rate was 5° C./min, to obtain blocky g-C.sub.3N.sub.4, taking out the sample and grinding for 60 minutes. Taking 2 g of block g-C.sub.3N.sub.4, adding 200 mL of ethanol and carrying out ultrasonic treatment for 10 hours, then carrying out centrifugal washing for three times by using deionized water, drying at 80° C. for 12 hours, taking out and grinding for later use;

(36) (2) 5 mL of 0.4 mol/L nickel chloride hexahydrate solution and 15 mL of 0.034 mol/L vanadium chloride solution were added into a 50 mL beaker, the nickel chloride hexahydrate and vanadium chloride were mixed according to the following molar ratio: hexahydrate nickel chloride:vanadium chloride=4:1. Then 0.008 mol/L hydrochloric acid solution was added to adjust the pH value to 5, and the mixture was magnetically stirred for 20 minutes to obtain a mixed solution A. Then pouring the mixed solution A into one side of the two-chamber hydrothermal kettle;

(37) (3) adding 30 mL of deionized water and 20 mL of ethylene glycol into a 100 mL beaker, and then adding ingredients of g-C.sub.3N.sub.4, urea, ammonium fluoride for batching, according to the following mass ratio: g-C.sub.3N.sub.4:urea:ammonium fluoride=2 g:0.5 g:0.1 g, and magnetically stirred for 30 minutes to obtain a mixed solution B. Finally, pouring the mixed solution B into the other side of the two-chamber hydrothermal kettle;

(38) (4) putting the two-chamber hydrothermal kettle into a homogeneous reactor, starting the reactor, raising the temperature to 60° C., maintaining the temperature for 20 minutes. Then raising the temperature to 140° C., starting rotation, maintaining the temperature for 6 hours. Taking out the reaction kettle for cooling after lowering the temperature;

(39) (5) taking out the cooled solution, carrying out centrifugal washing with deionized water and ethanol for three times respectively, and drying in a vacuum drying oven to dry for 12 hours to obtain a precipitate C;

(40) (6) taking out the dried precipitate C and grinding for 30 minutes to obtain a powder D. The powder D and sodium hypophosphite were blended in the following mass ratio: Powder D:Sodium hypophosphite=1:6. Placing the porcelain boat containing sodium hypophosphite on the left side of the dual temperature zone tubular atmosphere furnace, and placing the porcelain boat containing sample powder on the right side, and then pumping the tube furnace to be vacuum, introducing argon gas, and repeating the operation for three times, until all the oxygen in the tube furnace was discharged;

(41) (7) heating the left tube furnace to 300° C. at a heating rate of 5° C./min, and at the same time heating the right tube furnace to 450° C. at a heating rate of 5° C./min, and continuous heating for 2 hours;

(42) (8) cooling the product, taking out, and grinding for 30 minutes to obtain the V-Ni.sub.2P/g-C.sub.3N.sub.4 photocatalyst. The mass ratio of V-Ni.sub.2P and g-C.sub.3N.sub.4 in the obtained photocatalyst was 0.1:1. V in V-Ni.sub.2P was lattice doping with the doping content of 25 wt %.

Example 3

(43) (1) First, putting 13 g of melamine into a porcelain boat, calcining at 600° C., maintaining the temperature for 2 hours, raising the temperature at 5° C./min to obtain blocky g-C.sub.3N.sub.4, taking out the sample and grinding for 60 minutes, taking 2 g of block g-C.sub.3N.sub.4, adding 200 mL ethanol, carrying out ultrasound for 10 hours, then carrying out centrifugal washing for three times by using deionized water, drying at 80° C. for 12 hours, taking out and grinding for later use;

(44) (2) 15 mL of 0.134 mol/L nickel chloride hexahydrate solution and 5 mL of 0.134 mol/L vanadium chloride solution were added into a 50 mL beaker. The nickel chloride hexahydrate and vanadium chloride were mixed according to the following molar ratio: hexahydrate nickel chloride:vanadium chloride=3:1. Then 0.008 mol/L hydrochloric acid solution was added to adjust the pH value to 4.5, and the mixture was magnetically stirred for 25 minutes to obtain a mixed solution A. Then pouring the mixed solution A into one side of the two-chamber hydrothermal kettle;

(45) (3) adding 15 mL of deionized water and 15 mL of ethylene glycol into a 100 mL beaker, and then adding ingredients of g-C.sub.3N.sub.4, urea, ammonium fluoride, etc., according to the following mass ratio: g-C.sub.3N.sub.4:urea:ammonium fluoride=1.6 g:0.6 g:0.15 g, magnetically stirred for 30 minutes to obtain a mixed solution B. Finally, pouring the mixed solution B into the other side of the two-chamber hydrothermal kettle, and finally introducing nitrogen into the hydrothermal kettle to discharge air;

(46) (4) putting the two-chamber hydrothermal kettle into a homogeneous reactor, starting the reactor, raising the temperature to 60° C., maintaining the temperature for 15 minutes. Then raising the temperature to 120° C., starting rotation, maintaining the temperature for 8 hours, and taking out the reaction kettle for cooling after lowering the temperature;

(47) (5) taking out the cooled solution, carrying out centrifugal, washing with deionized water and ethanol for three times respectively, and drying in a vacuum drying oven to dry for 14 hours to obtain a precipitate C;

(48) (6) taking out the dried precipitate C and grinding for 30 minutes to obtain a powder D. And mixing the powder D and sodium hypophosphite in the following mass ratio: Powder D:Sodium hypophosphite=1:8. Placing the porcelain boat containing sodium hypophosphite on the left side of the dual temperature zone tubular atmosphere furnace, placing the porcelain boat containing sample powder on the right side, and then pumping the tube furnace to be vacuum, introducing argon gas, and repeating the operation for three times, until all the oxygen in the tube furnace was discharged;

(49) (7) heating the left tube furnace to 290° C. at a heating rate of 10° C./min, and at the same time heating the right tube furnace to 400° C. at a heating rate of 10° C./min, and preserving heat for 2 hours;

(50) (8) cooling the product, taking out and grinding for 30 minutes to obtain the V-Ni.sub.2P/g-C.sub.3N.sub.4 photocatalyst. The mass ratio of V-Ni.sub.2P and g-C.sub.3N.sub.4 in the obtained photocatalyst was 0.15:1. V in V-Ni.sub.2P was lattice doping with the doping content of 33 wt %.

Comparative Example 1

(51) Putting 13 g of melamine into a porcelain boat, calcining at 600° C., maintaining the temperature for 2 hours, and raising the temperature at 5° C./min to obtain blocky g-C.sub.3N.sub.4. The sample was taken out and ground for 60 minutes. Taking 2 g of block g-C.sub.3N.sub.4, adding 200 mL ethanol, carrying out ultrasonic treatment for 10 hours, then carrying out centrifugal washing for three times by using deionized water, drying at 80° C. for 12 hours, taking out and grinding for later use. FIG. 4 is an X-ray diffraction analysis chart of pure phase g-C.sub.3N.sub.4, wherein the abscissa is the 2θ angle and the ordinate is the absorption intensity. The (100) crystal plane and (002) crystal plane of g-C.sub.3N.sub.4 are respectively corresponding to the positions of 13° and 27°, which indicates that g-C.sub.3N.sub.4 is successfully prepared.

Comparative Example 2

(52) (1) adding 25 mL of 0.08 mol/L nickel chloride hexahydrate solution and 5 mL of 0.08 mol/L vanadium chloride solution into a 50 mL beaker, mixing the nickel chloride hexahydrate and vanadium chloride according to the following molar ratio: hexahydrate nickel chloride:vanadium chloride=5:1. Then adding 1 mL of dimethylformamide, and finally adding 0.005 mol/L hydrochloric acid solution to adjust the pH to 4, and the mixture was magnetically stirred for 15 minutes to obtain a mixed solution A. Then pouring the mixed solution A into one side of the two-chamber hydrothermal kettle;

(53) (2) adding 30 mL of deionized water into a 50 mL beaker, and then adding ingredients of urea, and ammonium fluoride, according to the following mass ratio: urea:ammonium fluoride=1.25 g:0.36 g, and the mixture was magnetically stirred for 30 minutes to obtain a mixed solution B. Finally, pouring the mixed solution B into the other side of the two-chamber hydrothermal kettle;

(54) (3) putting the two-chamber hydrothermal kettle into a homogeneous reactor, and starting the reactor, raising the temperature to 50° C., maintaining the temperature for 15 minutes. Then raising the temperature to 120° C., starting rotation, maintaining the temperature for 12 hours, and taking out the reaction kettle for cooling after lowering the temperature;

(55) (4) taking out the cooled solution, centrifuging, and washing with deionized water and ethanol for three times respectively, and drying in a vacuum drying oven to dry for 12 hours to obtain a precipitate C;

(56) (5) taking out the dried precipitate C and grinding for 30 minutes to obtain a powder D. And mixing the powder D and sodium hypophosphite in the following mass ratio: Powder D:Sodium hypophosphite=1:5. Placing the porcelain boat containing sodium hypophosphite on the left side of the dual temperature zone tubular atmosphere furnace, placing the porcelain boat containing sample powder on the right side, and then pumping the tube furnace to be vacuum, introducing argon gas, and repeating the operation for three times, until all the oxygen in the tube furnace was discharged;

(57) (6) heating the left tube furnace to 300° C. at a heating rate of 10° C./min, and at the same time heating the right tube furnace to 500° C. at a heating rate of 10° C./min, and continuous heating for 2 hours;

(58) (7) cooling the product, taking out and grinding for 30 minutes to obtain the V-Ni.sub.2P/g-C.sub.3N.sub.4 photocatalyst. FIG. 5 is a scanning image of V-Ni.sub.2P prepared in Comparative Example 2 at 1 μm. Among them, the flower ball composed of V-Ni.sub.2P nanosheets can be clearly seen.

Comparative Example 3

(59) (1) First, putting 15 g of melamine into a porcelain boat, calcining at 550° C., maintaining the temperature for 4 hours, raising the temperature at 2° C./min, to obtain blocky g-C.sub.3N.sub.4, taking out the sample and grinding for 60 minutes, taking 1 g of block g-C.sub.3N.sub.4, adding 100 mL ethanol, carrying out ultrasound for 6 hours, then carrying out centrifugal washing for three times by using deionized water, drying at 60° C. for 10 hours, taking out and grinding for later use;

(60) (2) adding 0.29 g of nickel nitrate hexahydrate and 0.1 g of urea into a hydrothermal kettle containing 40 mL of deionized water and 20 mL of ethylene glycol, then adding 1.6 g of g-C.sub.3N.sub.4 powder and stirring for 30 minutes to form a uniform solution;

(61) (3) putting the hydrothermal kettle into the oven, starting the oven and raising the temperature to 120° C., maintaining the temperature for 10 hours, and taking out the reaction kettle for cooling after lowering the temperature;

(62) (4) taking out the cooled solution and carrying out centrifugal washing for three times by using deionized water and ethanol, and then putting in a vacuum drying oven to dry for 12 hours to obtain a precipitate E;

(63) (5) taking out the dried precipitate E and grinding to obtain a powder F, putting the powder F and sodium hypophosphite into a porcelain boat and mixing according to the following mass ratio: Powder F:Sodium hypophosphite=1:5. The sodium hypophosphite was placed upstream of the porcelain boat, the powder F was placed downstream of the porcelain boat, and the porcelain boat was placed in the tube furnace, and then pumping the tube furnace to be vacuum, and introducing argon gas, repeating the operation for three times, until all the oxygen in the tube furnace was discharged;

(64) (6) raising the tube furnace to 500° C. at a heating rate of 10° C./min, and continuous heating for 2 hours;

(65) (7) cooling the product, taking out, and grinding for 30 minutes to obtain the V-Ni.sub.2P/g-C.sub.3N.sub.4 photocatalyst.

(66) FIG. 6 is an X-ray diffraction analysis chart of Ni.sub.2P/g-C.sub.3N.sub.4 prepared in Comparative Example 3, where the abscissa is the 2θ angle, and the ordinate is the absorption intensity. The positions of 13° and 27° correspond to the (100) crystal plane and (002) crystal plane of g-C.sub.3N.sub.4 respectively. Ni.sub.2P in Ni.sub.2P/g-C.sub.3N.sub.4 corresponds to PDF #03-0953, indicating the successful preparation of Ni.sub.2P/g-C.sub.3N.sub.4 photocatalyst.

(67) FIG. 7 is a scan diagram of Ni.sub.2P/g-C.sub.3N.sub.4 prepared in Comparative Example 3 at 1 μm. Among them, it can be clearly seen that Ni.sub.2P nanosheets grow on bulk g-C.sub.3N.sub.4.

(68) FIG. 8 is a graph of the hydrogen production performance of Ni.sub.2P/g-C.sub.3N.sub.4 prepared in Comparative Example 3, where the abscissa is the number of samples and the ordinate is the hydrogen production. Among them, the hydrogen production performance of pure phase g-C.sub.3N.sub.4 is 0.21 μmol, while the pure phase Ni.sub.2P does not detect hydrogen production, and the hydrogen production performance of composite Ni.sub.2P/g-C.sub.3N.sub.4 is 13.06 μmol.