Nickel cobalt phosphate@indium zinc sulfide@cobalt oxide composite photocatalyst, preparation method and application thereof

Abstract

The present invention discloses a nickel cobalt phosphate @ indium zinc sulfide @ cobalt oxide composite photocatalyst, its preparation method and application, belonging to the field of photocatalysis. The preparation process is: after the aqueous solution of nickel source and cobalt source and the aqueous solution of phosphine source are mixed and reacted; the solid is calcined to obtain Ni2CoPO x , Ni2CoPO x Add to the ZnIn2S4 precursor solution; after the reaction is completed, Ni2CoPO x @ZnIn2S4. Dissolve polyvinyl pyrrolidone in a mixed solvent of distilled water and methanol, then add Ni2CoPO x @ZnIn2S4, add tributylphosphine dropwise and stir; then add cobalt chloride solution dropwise and stir at room temperature until the reaction is complete; centrifuge, collect the solid, wash, and dry to obtain Ni2CoPO x @ZnIn2S4@CoO x Composite photocatalyst. Ni2CoPO x and CoO x It can serve as an active site for water oxidation to produce hydrogen peroxide. x and CoO x The introduction of clusters can effectively improve the separation efficiency of photogenerated carriers, enhance the light absorption capacity, and thus significantly improve the photocatalytic water splitting performance. x @ZnIn2S4@CoO x The hydrogen production rate of the composite photocatalyst was 1541.2 μmol·g ‑1 ·h ‑1 The hydrogen peroxide production rate reached 1381.1 μmol·g ‑1 ·h ‑1 .

Description

Technical Field

[0001] The present invention belongs to the field of photocatalysis, and specifically relates to a nickel cobalt phosphate@indium zinc sulfide@cobalt oxide composite photocatalyst, a preparation method and application thereof. Background Art

[0002] Using solar energy to decompose water to produce hydrogen can directly convert solar energy into chemical energy, and is one of the ideal methods to solve the energy crisis. ZnIn2S4 (ZIS) is one of the most common photocatalysts with the advantages of suitable band gap, large surface area and simple preparation method. However, the photogenerated electrons and holes of pure ZIS are easy to recombine, which seriously limits its photocatalytic reaction activity. The mass of the photogenerated holes of ZIS is much larger than that of the photogenerated electrons, resulting in the mobility of the holes being much lower than that of the electrons. At the same time, the surface oxidation reaction is a four-electron or two-electron reaction with slow kinetics. Therefore, the photocatalytic water splitting performance of ZIS is limited by the slow hole migration rate and slow surface oxidation kinetics. Therefore, the construction of Ni2CoPO x @ZnIn2S4@CoO x Composite photocatalyst, using Ni2CoPO x and CoO x By regulating the kinetics of photogenerated holes and surface oxidation reactions, it is expected to significantly improve the performance of ZIS for hydrogen production via complete water splitting. Summary of the Invention

[0003] The purpose of the present invention is to provide a nickel cobalt phosphate @ indium zinc sulfide @ cobalt oxide (Ni2CoPO x @ZnIn2S4@CoO x ) Composite photocatalyst, preparation method and application thereof.

[0004] Based on the above objectives, the present invention adopts the following technical solutions:

[0005] A Ni2CoPO x @ZnIn2S4@CoO x The preparation method of the composite photocatalyst comprises the following steps:

[0006] (1) dissolving a nickel source compound and a cobalt source compound in deionized water to form a solution A, dissolving a phosphine source compound in deionized water to form a solution B, and mixing the two solutions A and B;

[0007] (2) reacting the mixed solution obtained in step (1) at 80-200°C for 2-24 hours;

[0008] (3) The product obtained in step (2) is centrifuged, the solid is collected, washed, dried, and calcined to obtain Ni2CoPO x ;

[0009] (4) Ni2CoPO obtained in step (3) x adding it to the ZnIn2S4 precursor solution to obtain a mixed solution;

[0010] (5) reacting the mixed solution obtained in step (4) at 50°C to 200°C for 2 to 24 hours;

[0011] (6) The product obtained in step (5) is centrifuged, the solid is collected, washed, and dried to obtain Ni2CoPO x @ZnIn2S4 composite photocatalyst;

[0012] (7) Prepare Ni2CoPO in step (6) x Add the ZnIn2S4 composite photocatalyst to a mixed solution of polyvinyl pyrrolidone, deionized water, and methanol, stir to dissolve, then dropwise add tributylphosphine and cobalt source compound solution. Continue stirring for at least 1 hour after the addition is complete.

[0013] (8) The product obtained in step (7) is centrifuged, the solid is collected, washed, and dried to obtain Ni2CoPO x @ZnIn2S4@CoO x Composite photocatalyst.

[0014] Furthermore, in step (1), the molar ratio of the nickel source compound, the cobalt source compound and the phosphine source compound is (4-8): (1-2): (1-2); and in step (3), the calcination temperature is 250-350°C.

[0015] Furthermore, in step (1), the nickel source compound is selected from one or a mixture of any two or more of nickel acetate tetrahydrate, nickel oxide, nickel sulfate, nickel hydroxide, nickel chloride, and nickel bromide, and the concentration of the nickel source compound in deionized water is 0.1 mmol / L to 5 mol / L; the cobalt source compound is selected from one or a mixture of any two or more of cobalt acetate tetrahydrate, cobalt nitrate hexahydrate, cobalt chloride, cobalt sulfate, cobalt oxalate, and cobalt carbonate, and the concentration of the cobalt source compound in deionized water is 0.1 mmol / L to 5 mol / L; the phosphine source compound is selected from one or a mixture of any two or more of ammonium dihydrogen phosphate, diammonium hydrogen phosphate, and phosphoric acid, and the concentration of the phosphine source compound in deionized water is 0.1 mmol / L to 5 mol / L.

[0016] Preferably, in step (1), the nickel source compound is selected from nickel acetate tetrahydrate, and the concentration of nickel acetate tetrahydrate in deionized water is 0.01 mol / L to 0.1 mol / L, specifically, the concentration of nickel acetate tetrahydrate in deionized water is 66.7 mmol / L; the cobalt source compound is selected from cobalt acetate tetrahydrate, and the concentration of cobalt acetate tetrahydrate in deionized water is 0.01 mol / L to 0.05 mol / L, specifically, the concentration of cobalt acetate tetrahydrate in deionized water is 33.3 mmol / L; the phosphine source compound is selected from ammonium dihydrogen phosphate, and the concentration of the phosphine source compound in deionized water is 0.01 mol / L to 0.05 mol / L; specifically, the concentration of ammonium dihydrogen phosphate in deionized water is 33.3 mmol / L.

[0017] Furthermore, the drying in step (3) refers to drying at 60°C.

[0018] Furthermore, in step (4), Ni2CoPO x The mass ratio of ZnIn2S4 is (0.5%~3.0%):1.

[0019] Furthermore, in step (4), the ZnIn2S4 precursor solution is prepared as follows: deionized water is taken, the pH is adjusted to 2-3 with hydrochloric acid, and the zinc source compound, the indium source compound, and the sulfur source compound are dissolved in deionized water in a molar ratio of (1-2):(2-4):(4-8), and glycerol is added. The concentration of hydrochloric acid is 1-5 mol / L, and the volume ratio of deionized water to glycerol is 4:1.

[0020] Furthermore, the zinc source compound is selected from one or a mixture of any proportion of zinc chloride, zinc nitrate, zinc acetate, zinc carbonate, zinc sulfate, zinc hydroxide and zinc oxalate, and the concentration of the zinc source compound in the mixed solvent of deionized water and glycerol is 0.001 mol / L to 10 mol / L, preferably zinc chloride, and the concentration of zinc chloride in the mixed solvent of deionized water and glycerol is 0.01 mol / L to 0.05 mol / L.

[0021] Furthermore, the indium source compound is selected from one or a mixture of any proportion of indium nitrate, indium chloride, indium sulfate, indium acetate and indium oxide, and the concentration of the indium source compound in the deionized water and glycerol mixed solvent is 0.001 mol / L to 10 mol / L; indium nitrate is preferred, and the concentration of indium nitrate in the deionized water and glycerol mixed solvent is 0.02 mol / L to 0.10 mol / L.

[0022] Furthermore, the sulfur source compound is selected from one or a mixture of two or more of thioacetamide, sulfur powder, thiourea, and ammonium sulfide in any proportion, and the concentration of the sulfur source compound in the deionized water and glycerol mixed solvent is 0.001 mol / L to 10 mol / L. Thioacetamide is preferred, and its concentration in the deionized water and glycerol mixed solvent is 0.04 mol / L to 0.20 mol / L.

[0023] Furthermore, the drying in step (6) refers to drying at 60° C. for 12 hours.

[0024] Furthermore, in step (7), the cobalt source compound is selected from one or a mixture of two or more of cobalt acetate tetrahydrate, cobalt nitrate hexahydrate, cobalt chloride hexahydrate, cobalt sulfate, cobalt oxalate, and cobalt carbonate in any proportion, and the concentration of the cobalt source compound solution is 0.001 mol / L to 10 mol / L. Cobalt chloride hexahydrate is preferred, and the concentration of the cobalt chloride hexahydrate solution is 0.001 mol / L to 10 mol / L.

[0025] Furthermore, in step (7), polyvinyl pyrrolidone, Ni2CoPO x The ratio of @ZnIn2S4 photocatalyst, tributyl phosphine and cobalt source compound is (1~3) g:0.2 g:(1~2) mL:(0.002~0.005) mmol. In step (7), the volume ratio of deionized water and methanol is 1:1, Ni2CoPO x The concentration of @ZnIn2S4 photocatalyst in deionized water and methanol is 0.1~0.5mg / mL.

[0026] Ni2CoPO prepared by the above preparation method x @ZnIn2S4@CoO x Composite photocatalyst.

[0027] The above Ni2CoPO x @ZnIn2S4@CoO x Application of composite photocatalysts in photocatalytic water splitting.

[0028] Preferably, when photocatalytically splitting water, a 300 W xenon lamp (λ>400 nm) is used as the light source, Ni2CoPO x @ZnIn2S4@CoO x The concentration of the composite photocatalyst in water is 0.01 mg / mL ~1 mg / mL.

[0029] Beneficial effects of the present invention: Ni2CoPO x and CoO x The clusters can serve as active sites for water oxidation to produce hydrogen peroxide.x and CoO x The introduction of clusters can effectively improve the separation efficiency of photogenerated carriers, enhance the light absorption capacity, and thus significantly improve the photocatalytic water splitting performance. x @ZnIn2S4@CoO x The hydrogen production rate of the composite photocatalyst was 1541.2 μmol·g -1 ·h -1 The hydrogen peroxide production rate reached 1381.1 μmol·g -1 ·h -1 In addition, the Ni2CoPO x @ZnIn2S4@CoO x Composite photocatalysts have the advantages of simple preparation methods and easy control of preparation conditions, and have certain research and application value. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 1 is an X-ray diffraction pattern of the photocatalysts prepared in Example 1, Example 2, Example 3 and Example 4 of the present invention;

[0031] Figure 2 (a) ZnIn2S4, (b) CoO prepared in Example 1, Example 2, Example 3 and Example 4 of the present invention x @ZnIn2S4、(c) Ni2CoPO x @ZnIn2S4 and (d) Ni2CoPO x @ZnIn2S4@CoO x SEM images, scale bars are 1 μm;

[0032] Figure 3 are the ultraviolet-visible light absorption spectra of the photocatalysts prepared in Examples 1, 2, 3 and 4 of the present invention;

[0033] Figure 4 1 is a graph of steady-state fluorescence spectra of the photocatalysts prepared in Example 1, Example 2, Example 3 and Example 4 of the present invention;

[0034] Figure 5 Graphs showing the photocatalytic water splitting rates of the photocatalysts prepared in Examples 1, 2, 3, and 4 of the present invention. DETAILED DESCRIPTION

[0035] In order to facilitate understanding of the present invention, the present invention will be described in more detail below with reference to the accompanying drawings, which illustrate preferred embodiments of the present invention, but are not limited to the embodiments described herein.

[0036] Example 1

[0037] Preparation of ZnIn2S4 photocatalyst:

[0038] Take 96 mL of deionized water and adjust its pH to approximately 2.5 with 3 mol / L dilute hydrochloric acid. After mixing thoroughly, zinc chloride (ZnCl₂, 545 mg, 4 mmol), indium trichloride tetrahydrate (InCl₃·4H₂O, 1173 mg, 4 mmol), and thioacetamide (TAA, 601 mg, 8 mmol) are added sequentially. Finally, 24 mL of glycerol is added and stirred until the chemicals are completely dissolved. The reaction is allowed to proceed at 80°C for 2 h. After cooling and precipitation, the solid is centrifuged and collected. Washed sequentially with deionized water and anhydrous ethanol, the solid is then dried in a vacuum oven at 60°C for 12 h. The resulting powder sample is the ZnIn₂S₄ photocatalyst.

[0039] Example 2

[0040] CoO x Preparation of @ZnIn2S4 composite photocatalyst:

[0041] Polyvinyl pyrrolidone (PVP, 2g), 50mL deionized water and 50mL methanol solution were mixed evenly, and then 200mg of photocatalyst ZnIn2S4 was added and stirred at room temperature for 1 hour. 1mL of tributylphosphine (TBP) was added and stirred for 5 minutes. After that, 3.5mL of CoCl2 solution (concentration of 2mM) was added dropwise and stirred for another 1 hour. After centrifugation, the precipitate was washed twice with anhydrous ethanol and deionized water respectively, and dried in a vacuum at 60℃ for 12 hours to obtain CoO x @ZnIn2S4 composite photocatalyst.

[0042] Example 3

[0043] Ni2CoPO x Preparation of @ZnIn2S4 composite photocatalyst:

[0044] Solution A was prepared by dissolving 4 mmol of Ni(CH3COO)2·4H2O and 2 mmol of Co(CH3COO)2·4H2O in 30 mL of deionized water. Solution B was prepared by dissolving 2 mmol of NH4H2PO4 in 30 mL of deionized water. Solution A was added dropwise to solution B with stirring and stirred for a predetermined period. The mixture was heated at 120°C for 4 h. After cooling, the mixture was centrifuged and the solid was collected. The solid was washed twice with deionized water and twice with anhydrous ethanol, then dried in vacuum at 60°C for 12 h. The sample was then annealed in air at 300°C for 3 h to obtain Ni2CoPO4. xTake 96 mL of deionized water and adjust its pH to about 2.5 with 3 mol / L dilute hydrochloric acid. After the solution is mixed evenly, add 17 mg of the previously prepared Ni2CoPO x The mixture was ultrasonically dispersed and zinc chloride (ZnCl2, 545 mg, 4 mmol), indium chloride tetrahydrate (InCl3·4H2O, 1173 mg, 4 mmol), and thioacetamide (TAA, 601 mg, 8 mmol) were added in sequence. Finally, 24 mL of glycerol was added and stirred until the drugs were completely dissolved. The mixture was reacted at 80°C for 2 h. After cooling and precipitation, the solid was centrifuged and washed with deionized water and anhydrous ethanol in sequence. The solid was then dried in a vacuum at 60°C for 12 h. The resulting powder sample was Ni2CoPO4. x @ZnIn2S4 photocatalyst.

[0045] Example 4

[0046] Ni2CoPO x @ZnIn2S4@CoO x Preparation of composite photocatalyst:

[0047] Polyvinylpyrrolidone (PVP, 2 g), 50 mL of deionized water and 50 mL of methanol solution were mixed evenly, and 200 mg of Ni2CoPO4 was added. x @ZnIn2S4 and stir evenly, add 1 mL of tributylphosphine (TBP) solution, stir for 5 minutes, then add 3.5 mL of CoCl2 solution (concentration 2 mM) dropwise, and continue stirring for 1 hour. After centrifugation, the precipitate was washed twice with anhydrous ethanol and deionized water respectively, and dried in a vacuum at 60 ° C for 12 hours. The sample obtained after drying was collected and is Ni2CoPO x @ZnIn2S4@CoO x Composite photocatalyst.

[0048] The photocatalysts obtained from Examples 1 to 4 were characterized in various ways. Figures 1 to 5 It is the characterization result of the structure and performance of the photocatalyst. Figure 1 It can be seen that ZnIn2S4 was prepared in Example 1. Compared with single ZnIn2S4, CoO x The XRD spectrum of ZnIn2S4 composite photocatalysis is almost the same as that of single ZnIn2S4, Ni2CoPO x @ZnIn2S4 and Ni2CoPO x @ZnIn2S4@CoO x The XRD spectrum of the composite photocatalyst is almost the same as that of the single ZnIn2S4, which indicates that CoO x Clusters and Ni2CoPOx The introduction of does not change the crystal structure and phase composition of ZnIn2S4. Figure 2 (a) It can be seen that the morphology of ZnIn2S4 prepared in Example 1 is a flower-like microsphere structure composed of nanosheets. Figure 2 (b) It was observed that the CoO prepared in Example 2 x @ZnIn2S4 is still a flower-like microsphere structure, CoO x The introduction of clusters does not affect the morphology and structure of ZnIn2S4. Figure 2 (c) shows Example 3, introducing Ni2CoPO x Afterwards, the morphology of the composite sample changed significantly, Ni2CoPO x The morphology of the ZnIn2S4 composite photocatalyst is mainly composed of two types: one is a large flake structure and the other is a flower-like microsphere structure. Figure 2 (d) shows Example 4, in Ni2CoPO x @ZnIn2S4 further loaded with CoO x After clustering, its morphology did not change further, and it still maintained a large flake structure and a flower-like microsphere structure. Figure 3 It can be seen that the absorption band edge of ZnIn2S4 is around 500 nm. x The introduction of clusters improves the light absorption ability at 560-800 nm, and Ni2CoPO x The introduction of Ni2CoPO x @ZnIn2S4 and Ni2CoPO x @ZnIn2S4@CoO x The light absorption capacity in the ultraviolet region is significantly enhanced and the light absorption band edge is blue-shifted. Figure 4 It can be seen that ZnIn2S4 exhibits a strong fluorescence peak, indicating that the photogenerated carriers of ZnIn2S4 are seriously recombinated. X Clusters and Ni2CoPO x The fluorescence intensity is effectively reduced by the introduction of CoO, which proves that the efficiency of photogenerated carrier separation is improved. X Clusters and Ni2CoPO x The fluorescence intensity of the composite material is lower, which further indicates that CoO X Clusters and Ni2CoPO x Both can effectively separate photogenerated carriers.

[0049] The complete water splitting experiment was carried out in a closed quartz reactor. A 300 W xenon lamp (λ>400 nm) was used as the light source, and 275 mL of distilled water was used as the reaction solution. The photocatalysts prepared in Examples 1 to 4 were added, and the amount of photocatalyst used was 10 mg. Before the experiment, the closed reactor was vacuumed for about 30 minutes to remove the air. After the reaction was completed, 5 mL of the supernatant was taken from the centrifugal reaction solution, 5 mL of 1.2 mM H2SO4 solution and 5 mL of 0.1 mM KMnO4 solution were added, and after mixing for 5 to 10 minutes, the light absorption test of the solution was performed using a UV-visible spectrophotometer (UV-2600, Shimadzu, Japan). The molar amount of H2O2 was calculated according to the fitting formula. The chemical equation is as follows:

[0050] 2MnO 4- + 5H2O2+ 6H + → 2Mn 2+ + 5O2↑+8H2O

[0051] The results of water splitting performance are as follows Figure 5 As shown. Figure 5 It can be seen that the rate of hydrogen and hydrogen peroxide production of pure ZnIn2S4 is low, mainly due to the low efficiency of photogenerated carrier separation and the lack of effective oxidation active sites. X Clusters and Ni2CoPO x The introduction of can significantly improve the photocatalytic water splitting performance. x @ZnIn2S4@CoO x The composite photocatalyst has the highest performance, with a hydrogen production rate of 1541.2 μmol / g / h and a H2O2 production rate of 1381.1 μmol / g / h, with the ratio of the two close to 1:1. The performance improvement comes from the improved separation and migration efficiency of photogenerated carriers and the CoO x Clusters and Ni2CoPO x can serve as active oxidation sites.

[0052] Based on the above-described ideal implementation of the present invention, and in accordance with the above description, relevant personnel can make various changes and modifications without departing from the technical scope of this invention. The technical scope of this invention is not limited to the contents of the specification, but must be determined according to the scope of the claims.

Claims

1. A Ni2CoPO x @ZnIn2S4@CoO x The preparation method of the composite photocatalyst is characterized in that: The following steps are involved: (1) dissolving a nickel source compound and a cobalt source compound in deionized water to form a solution A, dissolving a phosphorus source compound in deionized water to form a solution B, and mixing the two solutions A and B; (2) reacting the mixed solution obtained in step (1) at 80-200°C for 2-24 hours; (3) The product obtained in step (2) is centrifuged, the solid is collected, washed, dried, and calcined to obtain Ni2CoPO x ; (4) Ni2CoPO obtained in step (3) x adding it to the ZnIn2S4 precursor solution to obtain a mixed solution; (5) reacting the mixed solution obtained in step (4) at 50°C to 200°C for 2 to 24 hours; (6) The product obtained in step (5) is centrifuged, the solid is collected, washed, and dried to obtain Ni2CoPO x @ZnIn2S4 composite photocatalyst; (7) Prepare Ni2CoPO in step (6) x Add the ZnIn2S4 composite photocatalyst to a mixed solution of polyvinyl pyrrolidone, deionized water, and methanol, stir to dissolve, then dropwise add tributylphosphine and cobalt source compound solution. Continue stirring for at least 1 hour after the addition is complete. (8) The product obtained in step (7) is centrifuged, the solid is collected, washed, and dried to obtain Ni2CoPO x @ZnIn2S4@CoO x Composite photocatalyst.

2. Ni2CoPO according to claim 1 x @ZnIn2S4@CoO x The preparation method of the composite photocatalyst is characterized in that: In step (1), the molar ratio of the nickel source compound, the cobalt source compound and the phosphorus source compound is (4-8): (1-2): (1-2); in step (3), the calcination temperature is 250-350°C.

3. Ni2CoPO according to claim 1 x @ZnIn2S4@CoO x The preparation method of the composite photocatalyst is characterized in that: In step (1), the nickel source compound is selected from one or a mixture of any two or more of nickel acetate tetrahydrate, nickel oxide, nickel sulfate, nickel hydroxide, nickel chloride, and nickel bromide, and the concentration of the nickel source compound in distilled water is 0.1 mmol / L to 5 mol / L; the cobalt source compound is selected from one or a mixture of any two or more of cobalt acetate tetrahydrate, cobalt nitrate hexahydrate, cobalt chloride, cobalt sulfate, cobalt oxalate, and cobalt carbonate, and the concentration of the cobalt source compound in distilled water is 0.1 mmol / L to 5 mol / L; the phosphorus source compound is selected from one or a mixture of any two or more of ammonium dihydrogen phosphate, diammonium hydrogen phosphate, and phosphoric acid, and the concentration of the phosphorus source compound in distilled water is 0.1 mmol / L to 5 mol / L.

4. Ni2CoPO according to claim 1 x @ZnIn2S4@CoO x The preparation method of the composite photocatalyst is characterized in that: In step (4), Ni2CoPO x The mass ratio of ZnIn2S4 is (0.5%~3.0%):

1.

5. Ni2CoPO according to claim 1 x @ZnIn2S4@CoO x The preparation method of the composite photocatalyst is characterized in that: In step (4), the preparation process of the ZnIn2S4 precursor solution is as follows: take deionized water, adjust the pH to 2~3 with hydrochloric acid, dissolve the zinc source compound, indium source compound and sulfur source compound in the deionized water in a molar ratio of (1~2):(2~4):(4~8), and then add glycerol.

6. Ni2CoPO according to claim 5 x @ZnIn2S4@CoO x The preparation method of the composite photocatalyst is characterized in that: The zinc source compound is selected from one or a mixture of two or more of zinc chloride, zinc nitrate, zinc acetate, zinc carbonate, zinc sulfate, zinc hydroxide and zinc oxalate in any proportion, and the concentration of the zinc source compound in a mixed solvent of deionized water and glycerol is 0.001 mol / L to 10 mol / L; the indium source compound is selected from one or a mixture of two or more of indium nitrate, indium chloride, indium sulfate, indium acetate and indium oxide in any proportion, and the concentration of the indium source compound in a mixed solvent of deionized water and glycerol is 0.001 mol / L to 10 mol / L; the sulfur source compound is selected from one or a mixture of two or more of thioacetamide, sulfur powder, thiourea and ammonium sulfide in any proportion, and the concentration of the sulfur source compound in a mixed solvent of deionized water and glycerol is 0.001 mol / L to 10 mol / L.

7. Ni2CoPO according to claim 1 x @ZnIn2S4@CoO x The preparation method of the composite photocatalyst is characterized in that: In step (7), the cobalt source compound is selected from one or a mixture of two or more of cobalt acetate tetrahydrate, cobalt nitrate hexahydrate, cobalt chloride hexahydrate, cobalt sulfate, cobalt oxalate, and cobalt carbonate in any proportion, and the concentration of the cobalt source compound solution is 0.001 mol / L to 10 mol / L.

8. Ni2CoPO according to claim 1 x @ZnIn2S4@CoO x The preparation method of the composite photocatalyst is characterized in that: In step (7), polyvinyl pyrrolidone, Ni2CoPO x The ratio of @ZnIn2S4 photocatalyst, tributyl phosphine and cobalt source compound is (1~3) g:0.2 g:(1~2) mL:(0.002~0.005) mmol.

9. Ni2CoPO prepared by the preparation method according to any one of claims 1 to 8 x @ZnIn2S4@CoO x Composite photocatalyst.

10. Ni2CoPO according to claim 9 x @ZnIn2S4@CoO x Application of composite photocatalysts in photocatalytic water splitting.

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