Composite photocatalyst Ni3S2 / ZnIn2S4 as well as preparation method and application thereof

Abstract

The invention discloses a composite photocatalyst Ni3S2 / ZnIn2S4 as well as a preparation method and application thereof, and belongs to the technical field of photocatalysis. The preparation method comprises the following steps: dissolving zinc nitrate hexahydrate, indium nitrate tetrahydrate and L-cysteine in deionized water, uniformly stirring, transferring into a reaction kettle, and reacting at 180 DEG C to obtain a ZIS matrix material; then dissolving nickel nitrate and sodium citrate to form a solution, adding ZIS powder, uniformly dispersing, dropwise adding thioacetamide, carrying out hydrothermal reaction, cooling, and carrying out centrifugal washing to obtain the Ni3S2 / ZnIn2S4 composite photocatalyst. Under the irradiation of visible light, the catalyst can efficiently catalyze benzyl alcohol to be decomposed to generate hydrogen and benzaldehyde. Compared with a traditional catalyst, the photocatalytic activity is remarkably enhanced. Through the synergistic effect of Ni3S2 and ZIS, the photo-generated charge separation efficiency is improved, and efficient combination of photocatalytic hydrogen production and green synthesis of fine chemicals is achieved.

Description

Technical Field

[0001] The present invention belongs to the technical field of photocatalysts, and in particular relates to a composite photocatalyst Ni3S2 / ZnIn2S4 and a preparation method and application thereof. Background Art

[0002] As a pollution-free, high-energy-density energy carrier, hydrogen is a clean energy raw material with great development potential in future industry and human life. Photocatalytic hydrogen production has become an important research direction in the current energy field due to its advantages of being green, sustainable and utilizing solar energy. The development of efficient and highly stable photocatalysts is of great significance for the practical application of photocatalytic hydrogen production.

[0003] ZnIn2S4 (ZIS) is a widely studied ternary metal chalcogenide compound that has shown great potential in the field of photocatalysis due to its good photocatalytic performance, high chemical stability and unique layered structure. However, in practical applications, ZIS still has problems such as high recombination rate of photogenerated electrons and holes and insufficient active sites, which limits the further improvement of its photocatalytic efficiency.

[0004] In order to solve this problem, the present invention will improve its photocatalytic performance by introducing metal sulfide and ZIS to construct a composite catalyst, and construct a heterojunction with ZIS and the introduced material, which can effectively improve the efficiency of photogenerated charge separation and enhance the catalytic activity. Summary of the invention

[0005] Purpose of the invention: In order to improve the catalytic efficiency of the photocatalyst ZIS, the present invention provides a composite photocatalyst Ni3S2 / ZnIn2S4 and its preparation method and application, so as to improve the photocatalytic efficiency and realize the green and economical simultaneous production of hydrogen and benzaldehyde.

[0006] The Ni3S2 / ZIS composite photocatalyst proposed in the present invention is an efficient visible light photocatalyst prepared by loading Ni3S2 onto the surface of ZIS by a hydrothermal method. The composite catalyst has significant catalytic activity in the decomposition reaction of benzyl alcohol and can efficiently generate hydrogen and benzaldehyde. Compared with the pure ZIS catalyst, the Ni3S2 / ZIS composite photocatalyst significantly improves the separation efficiency of photogenerated electrons and holes through the synergistic effect of Ni3S2, reduces the recombination probability of photogenerated charges, and thus greatly improves the photocatalytic efficiency. The present invention verifies the rational construction of Ni3S2 and ZIS, which not only realizes the efficient generation of green energy hydrogen, but also provides a new way to prepare fine chemicals, opening up new possibilities for solar energy conversion and green chemical applications.

[0007] Technical solution: A method for preparing a composite photocatalyst Ni3S2 / ZnIn2S4, comprising dissolving nickel nitrate and sodium citrate to form a solution, adding ZnIn2S4 to disperse the solution evenly, then dropping thioacetamide to carry out a hydrothermal reaction, cooling, centrifuging and washing to obtain the composite photocatalyst Ni3S2 / ZnIn2S4.

[0008] Further, the preparation method of ZnIn2S4 is as follows:

[0009] Zinc nitrate hexahydrate, indium nitrate tetrahydrate and L-cysteine ​​are dissolved in water, ultrasonically dispersed to form a solution, and magnetically stirred at room temperature until it becomes clear; the solution is transferred to a reaction kettle, heated in an oven, and naturally cooled to room temperature. The generated precipitate is washed several times with water and ethanol, and then dried to obtain ZnIn2S4, which is ZIS nanosheets.

[0010] Furthermore, in the preparation method of ZnIn2S4, the molar ratio of zinc nitrate hexahydrate, indium nitrate tetrahydrate and L-cysteine ​​is 1:2:8; the heating temperature in the oven is 180°C and the heating time is 3-4h.

[0011] Furthermore, the preparation method of the composite photocatalyst Ni3S2 / ZnIn2S4 comprises the following steps:

[0012] Step 1: dissolving nickel nitrate hexahydrate and sodium citrate dihydrate in water and stirring, then adding ZIS to the solution and stirring to disperse; then, adding an aqueous solution of thioacetamide dropwise and stirring the mixture again;

[0013] Step 2: Transfer the solution to a reaction kettle, heat it in an oven for a period of time, and then cool it naturally to room temperature. Wash the generated precipitate several times by centrifugation with water and ethanol, and dry it to obtain Ni3S2 / ZnIn2S4, referred to as Ni3S2 / ZIS.

[0014] Furthermore, in step 1, the usage ratio of nickel nitrate hexahydrate, sodium citrate dihydrate and ZIS is 0.0698:0.5:(0.3-1); the molar ratio of nickel nitrate hexahydrate to thioacetamide is 3:4.

[0015] Furthermore, in step 1, ZIS is added to the solution, and the stirring and dispersion time is not less than 2 hours.

[0016] Furthermore, in step 2, the heating temperature in the oven is 160° C. and the heating time is 6-8 hours.

[0017] Compared with the prior art, the present invention has the following beneficial effects:

[0018] 1) The present invention constructs a composite catalyst by introducing metal sulfide and ZIS, and ZIS and the introduced material are constructed into a heterojunction catalyst, which effectively improves the efficiency of photogenerated charge separation and enhances the catalytic activity.

[0019] The present invention successfully prepared a composite photocatalyst in which Ni3S2 was loaded on the surface of ZnIn2S4 (ZIS) by hydrothermal in-situ synthesis technology. The catalyst prepared by the present invention utilizes the instantaneous charge transfer path provided by ZIS nanosheets, and at the same time significantly enhances the photocatalytic performance through the abundant active points of Ni3S2. The close interface contact between Ni3S2 and ZIS effectively improves the separation efficiency of photogenerated electrons and holes, broadens the light absorption range, accelerates the migration speed of carriers, thereby significantly improving the catalytic activity and reducing the overpotential of hydrogen reduction.

[0020] The catalyst prepared by the present invention exhibits excellent activity in the photocatalytic reaction of benzyl alcohol decomposition to produce hydrogen and benzaldehyde. The experimental results show that at the optimal loading ratio (Ni3S2 content is 3.2%), the catalyst exhibits excellent visible light catalytic performance. When used for the dehydrogenation reaction of benzyl alcohol to produce hydrogen and benzaldehyde, the generation rates reach 4.342mmol g - 1 h -1 and 4.213mmol g -1 h -1 , which are 1.79 times and 1.76 times higher than pure ZIS respectively.

[0021] The photocatalyst of the present invention exhibits good selectivity and stability in the dehydrogenation reaction of benzyl alcohol to produce hydrogen and benzaldehyde, and no other by-products are detected, which indicates that the Ni3S2 / ZIS composite material has broad application prospects in sustainable hydrogen production and green chemical synthesis.

[0022] 2) The present invention verifies the rational construction of precious metal-free composite photocatalytic materials, which not only realizes the efficient generation of green energy hydrogen, but also promotes the green and sustainable production of fine chemicals, providing a new path for the development of renewable energy and chemicals. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 SEM spectra, HRTEM spectra, HAADF-STEM images and elemental mapping diagrams of ZIS and 3.2% Ni3S2 / ZIS prepared in Example 1; wherein, a is the SEM spectrum of ZIS in Example 1, b is the SEM spectrum of 3.2% Ni3S2 / ZIS, c is the HRTEM spectrum of 3.2% Ni3S2 / ZIS, d is the HAADF-STEM image of 3.2% Ni3S2 / ZIS, and eh is the elemental mapping diagram of 3.2% Ni3S2 / ZIS.

[0024] Figure 2 are the XRD spectra of ZIS, Ni3S2 and Ni3S2 / ZIS in Examples 1-4; wherein, a is the XRD spectra of ZIS, 3.2% Ni3S2 / ZIS and Ni3S2 in Example 1, and b is the XRD spectra of 1.9% Ni3S2 / ZIS, 3.2% Ni3S2 / ZIS, 4.8% Ni3S2 / ZIS and 6.4% Ni3S2 / ZIS in Examples 1-4.

[0025] Figure 3 The nitrogen adsorption-desorption isotherms and pore size distribution of ZIS and 3.2% Ni3S2 / ZIS in Example 1. Wherein, a is the nitrogen adsorption-desorption isotherms of ZIS and 3.2% Ni3S2 / ZIS composite material in Example 1, and b is the pore size distribution of ZIS and 3.2% Ni3S2 / ZIS in Example 1.

[0026] Figure 4 These are the Zn 2p XPS spectrum, In 3d XPS spectrum, S2pXPS spectrum and Ni 2p XPS spectrum of the ZIS and 3.2% Ni3S2 / ZIS in Example 1; wherein, a is the Zn2p XPS spectrum of the ZIS and 3.2% Ni3S2 / ZIS in Example 1 of the present invention, b is the In 3d XPS spectrum of the ZIS and 3.2% Ni3S2 / ZIS, c is the S2p XPS spectrum of the ZIS and 3.2% Ni3S2 / ZIS, and d is the Ni 2p XPS spectrum of Ni3S2 and 3.2% Ni3S2 / ZIS.

[0027] Figure 5 The electrochemical impedance Nyquist diagram and instantaneous photocurrent response diagram of ZIS and 3.2% Ni3S2 / ZIS in Example 1; wherein a is the electrochemical impedance Nyquist diagram of ZIS and 3.2% Ni3S2 / ZIS in Example 1, and b is the instantaneous photocurrent response diagram of ZIS and 3.2% Ni3S2 / ZIS.

[0028] Figure 6 Schematic diagram of the results of optical absorption test on ZIS and 3.2% Ni3S2 / ZIS catalyst of Example 1; wherein, a is the UV-visible diffuse reflectance spectrum of ZIS and 3.2% Ni3S2 / ZIS of Example 1, b is the relationship curve between Kubelka-Munk function and light energy of ZIS and 3.2% Ni3S2 / ZIS, c is the Mott-Schottky curve of ZIS and 3.2% Ni3S2 / ZIS, and d is the band gap diagram of ZIS and 3.2% Ni3S2 / ZIS.

[0029] Figure 7 1 and 2 are steady-state photoluminescence spectra of the ZIS of Example 1 and 3.2% Ni3S2 / ZIS.

[0030] Figure 8 It is a schematic diagram of the results of the hydrogen production rate of benzyl alcohol catalyzed by Ni3S2 / ZIS under visible light irradiation; wherein, a is the trend of H2 evolution over time, b is the H2 precipitation rate of Ni3S2, ZIS and x Ni3S2 / ZIS (x is the mass percentage of Ni3S2 in ZIS), c is the evolution rate of benzyl alcohol of Ni3S2, ZIS and x Ni3S2 / ZIS, and d is a schematic diagram of the cyclic test results of the photocatalytic hydrogen production performance of 3.2% Ni3S2 / ZIS sample.

[0031] Fig. 9 This is a schematic diagram of the XRD test results of the 3.2% Ni3S2 / ZIS sample before and after cycling in Example 1.

[0032] Fig.10 The electron spin paramagnetic resonance spectra of ZIS of Example 1 and 3.2% Ni3S2 / ZIS under visible light irradiation and no light conditions; wherein, a is the electron spin paramagnetic resonance spectrum of ZIS of Example 1 under visible light irradiation and no light conditions, and b is the electron spin paramagnetic resonance spectrum of 3.2% Ni3S2 / ZIS under visible light irradiation and no light conditions.

[0033] Fig.11 It is a schematic diagram of the redox reaction in the Ni3S2 / ZIS photocatalytic process and a schematic diagram of the mechanism of catalyzing the dehydrogenation of benzyl alcohol to generate benzaldehyde and hydrogen; wherein, a is a schematic diagram of the redox reaction in the photocatalytic process of Example 1, and b is a schematic diagram of the mechanism of catalyzing the dehydrogenation of benzyl alcohol to generate benzaldehyde and hydrogen by the Ni3S2 / ZIS composite photocatalyst. DETAILED DESCRIPTION

[0034] The technical solution of the present invention is described in detail below through embodiments and drawings, but the protection scope of the present invention is not limited to the embodiments.

[0035] Example 1

[0036] A method for preparing a composite photocatalyst Ni3S2 / ZIS comprises the following steps:

[0037] (1) Synthesis of pure ZIS

[0038] To synthesize pure ZIS, 3.5 mmol zinc nitrate hexahydrate, 7 mmol indium nitrate tetrahydrate, and 28 mmol L-cysteine ​​were dissolved in 40 mL deionized water. The solution was sonicated and magnetically stirred at room temperature for 30 min until it became clear. The resulting solution was then transferred to a 100 mL Teflon-lined stainless steel autoclave and heated at 180 °C for 3 h. After the autoclave was cooled to room temperature, the product was collected by centrifugation, washed several times with deionized water and ethanol, and dried in an oven at 60 °C for 12 h to obtain a sample ZIS composite catalyst.

[0039] (2) Preparation steps of Ni3S2 / ZIS composite catalyst

[0040] To prepare the Ni3S2 / ZIS composite catalyst, 0.24mmol nickel nitrate hexahydrate and 500mg sodium citrate dihydrate were first dissolved in 35mL deionized water and stirred for 30min. Subsequently, 0.6g of the synthesized ZIS was added to the solution and stirred for 2 hours. After that, 5mL of an aqueous solution containing 0.32mmol thioacetamide was gradually added, and the mixture was stirred for another hour. The resulting solution was transferred to a 100mL Teflon-lined stainless steel autoclave and heated at 160°C for 6 hours. After cooling to room temperature, the product was collected by centrifugation, washed several times with deionized water and ethanol, and dried at 60°C for 12 hours to obtain a sample of 3.2% Ni3S2 / ZIS catalyst.

[0041] Example 2

[0042] A method for preparing a composite photocatalyst Ni3S2 / ZIS comprises the following steps:

[0043] (1) Synthesis of pure ZIS

[0044] To synthesize pure ZIS, 3.5 mmol zinc nitrate hexahydrate, 7 mmol indium nitrate tetrahydrate, and 28 mmol L-cysteine ​​were dissolved in 40 mL deionized water. The solution was sonicated and magnetically stirred at room temperature for 30 min until it became clear. The resulting solution was then transferred to a 100 mL Teflon-lined stainless steel autoclave and heated at 180 °C for 3 h. After the autoclave was cooled to room temperature, the product was collected by centrifugation, washed several times with deionized water and ethanol, and dried in an oven at 60 °C for 12 h to obtain a sample ZIS composite catalyst.

[0045] (2) Preparation steps of Ni3S2 / ZIS composite catalyst

[0046] To prepare the Ni3S2 / ZIS composite material, 0.24mmol nickel nitrate hexahydrate and 500mg sodium citrate dihydrate were first dissolved in 35mL deionized water and stirred for 30min. Subsequently, 1g of the synthesized ZIS was added to the solution and stirred for 2 hours. After that, 5mL of an aqueous solution containing 0.32mmol thioacetamide was gradually added, and the mixture was stirred for another hour. The resulting solution was transferred to a 100mL Teflon-lined stainless steel autoclave and heated at 160°C for 6 hours. After cooling to room temperature, the product was collected by centrifugation, washed with deionized water and ethanol several times, and dried at 60°C for 12 hours to obtain a sample of 1.9% Ni3S2 / ZIS catalyst.

[0047] Example 3

[0048] A method for preparing a composite photocatalyst Ni3S2 / ZIS comprises the following steps:

[0049] (1) Synthesis of pure ZIS

[0050] To synthesize pure ZIS, 3.5 mmol zinc nitrate hexahydrate, 7 mmol indium nitrate tetrahydrate, and 28 mmol L-cysteine ​​were dissolved in 40 mL deionized water. The solution was sonicated and magnetically stirred at room temperature for 30 min until it became clear. The resulting solution was then transferred to a 100 mL Teflon-lined stainless steel autoclave and heated at 180 °C for 3 h. After the autoclave was cooled to room temperature, the product was collected by centrifugation, washed several times with deionized water and ethanol, and dried in an oven at 60 °C for 12 h to obtain a sample ZIS composite catalyst.

[0051] (2) Preparation steps of Ni3S2 / ZIS composite catalyst

[0052] In order to prepare the Ni3S2 / ZIS composite material, 0.24mmol (0.0698g) of nickel nitrate hexahydrate and 500mg of sodium citrate dihydrate were first dissolved in 35mL of deionized water and stirred for 30min. Subsequently, 0.4g of the synthesized ZIS was added to the solution and stirred for 2 hours. After that, 5mL of an aqueous solution containing 0.32mmol of thioacetamide was gradually added, and the mixture was stirred for another hour. The resulting solution was transferred to a 100mL Teflon-lined stainless steel autoclave and heated at 160°C for 6 hours. After cooling to room temperature, the product was collected by centrifugation, washed several times with deionized water and ethanol, and dried at 60°C for 12 hours to obtain a sample of 4.8% Ni3S2 / ZIS catalyst.

[0053] Example 4

[0054] A method for preparing a composite photocatalyst Ni3S2 / ZIS comprises the following steps:

[0055] (1) Synthesis of pure ZIS

[0056] To synthesize pure ZIS, 3.5 mmol zinc nitrate hexahydrate, 7 mmol indium nitrate tetrahydrate, and 28 mmol L-cysteine ​​were dissolved in 40 mL deionized water. The solution was sonicated and magnetically stirred at room temperature for 30 min until it became clear. The resulting solution was then transferred to a 100 mL Teflon-lined stainless steel autoclave and heated at 180 °C for 3 h. After the autoclave was cooled to room temperature, the product was collected by centrifugation, washed several times with deionized water and ethanol, and dried in an oven at 60 °C for 12 h to obtain a sample ZIS composite catalyst.

[0057] (2) Preparation steps of Ni3S2 / ZIS composite catalyst

[0058] To prepare the Ni3S2 / ZIS composite material, 0.24mmol nickel nitrate hexahydrate and 500mg sodium citrate dihydrate were first dissolved in 35mL deionized water and stirred for 30min. Subsequently, 0.3g of the synthesized ZIS was added to the solution and stirred for 2 hours. After that, 5mL of an aqueous solution containing 0.32mmol thioacetamide was gradually added, and the mixture was stirred for another hour. The resulting solution was transferred to a 100mL Teflon-lined stainless steel autoclave and heated at 160°C for 6 hours. After cooling to room temperature, the product was collected by centrifugation, washed with deionized water and ethanol several times, and dried at 60°C for 12 hours to obtain a sample of 6.4% Ni3S2 / ZIS catalyst.

[0059] The characterization results of Ni3S2 / ZIS prepared in Examples 1 to 4 are as follows:

[0060] Figure 1 SEM spectra, HRTEM spectra, HAADF-STEM images and elemental mapping diagrams of ZIS and 3.2% Ni3S2 / ZIS prepared in Example 1; wherein, a is the SEM spectrum of ZIS in Example 1, b is the SEM spectrum of 3.2% Ni3S2 / ZIS, c is the HRTEM spectrum of 3.2% Ni3S2 / ZIS, d is the HAADF-STEM image of 3.2% Ni3S2 / ZIS, and eh is the elemental mapping diagram of 3.2% Ni3S2 / ZIS. Figure 1 A and B confirm that Ni3S2 has been successfully deposited on ZIS, and eh shows that Zn, In, S, and Ni elements are uniformly distributed throughout the composite without obvious phase separation.

[0061] Figure 2The XRD spectra of ZIS, Ni3S2 and Ni3S2 / ZIS in Examples 1-4 are shown in Table 1. A is the XRD spectra of ZIS, 3.2% Ni3S2 / ZIS and Ni3S2 in Example 1, and B is the XRD spectra of 1.9% Ni3S2 / ZIS, 3.2% Ni3S2 / ZIS, 4.8% Ni3S2 / ZIS and 6.4% Ni3S2 / ZIS in Examples 1-4. Figure 2 It can be seen that after doping with a small amount of Ni3S2, the crystal structure of ZIS has not changed significantly.

[0062] Figure 3 The nitrogen adsorption-desorption isotherms and pore size distribution of ZIS and 3.2% Ni3S2 / ZIS in Example 1. Wherein, a is the nitrogen adsorption-desorption isotherms of ZIS and 3.2% Ni3S2 / ZIS composite material in Example 1 of the present invention, and b is the pore size distribution of ZIS and 3.2% Ni3S2 / ZIS in Example 1. Figure 3 It can be seen that the introduction of Ni3S2 increases the specific surface area by more than 20%, and the introduction of Ni3S2 provides more adsorption reaction sites to improve the photocatalytic efficiency.

[0063] Figure 4 The figures are the Zn 2p XPS spectra, In 3d XPS spectra, S2p XPS spectra and Ni 2p XPS spectra of ZIS and 3.2% Ni3S2 / ZIS of Example 1; wherein a is the Zn2p XPS spectra of ZIS and 3.2% Ni3S2 / ZIS of Example 1 of the present invention, b is the In 3d XPS spectra of ZIS and 3.2% Ni3S2 / ZIS, c is the S2p XPS spectra of ZIS and 3.2% Ni3S2 / ZIS, and d is the Ni 2p XPS spectra of Ni3S2 and 3.2% Ni3S2 / ZIS. The figures show that Ni3S2 effectively regulates the surface electronic structure of ZIS, enhances the interfacial electron transfer, and inhibits the recombination of photogenerated electrons and holes, thereby possibly improving the photocatalytic performance.

[0064] Figure 5 The electrochemical impedance Nyquist diagram and instantaneous photocurrent response diagram of ZIS and 3.2% Ni3S2 / ZIS in Example 1, wherein a is the electrochemical impedance Nyquist diagram of ZIS and 3.2% Ni3S2 / ZIS in Example 1, and b is the instantaneous photocurrent response diagram of ZIS and 3.2% Ni3S2 / ZIS. It can be seen from the figure that the Ni3S2 bimetallic cocatalyst can significantly accelerate charge separation and transport.

[0065] Test Example 1

[0066] 1. Optical absorption test: The ZIS of Example 1 and 3.2% Ni3S2 / ZIS catalyst were subjected to optical absorption test. The test results are shown in Figure 6 As shown, from Figure 6 As shown in Figure a, the absorption intensity of the 3.2% Ni3S2 / ZIS photocatalyst is significantly enhanced compared with that of ZIS, indicating that the addition of Ni3S2 can improve the optical response and expand the spectral range. Figure 6 b is the band gap energy value calculated using the Kubelka-Munk function. The calculated band gap values ​​of ZIS and 3.2% Ni3S2 / ZIS are 2.35eV and 2.15eV, respectively. The narrower band gap of 3.2% Ni3S2 / ZIS further verifies that its absorption capacity for visible light is improved, which is beneficial for photocatalytic applications. In addition, Figure 6 c is the conduction band position of ZIS and 3.2% Ni3S2 / ZIS determined using the Mott-Schottky plot. The flat band potentials of ZIS and 3.2% Ni3S2 / ZIS were measured to be -1.69 V and -0.81 V (relative to Ag / AgCl), respectively. By adjusting the flat band potential to 0.88 V, the conduction band position relative to NHE was calculated. Figure 6 As shown in Figure d, the introduction of Ni3S2 reduces the band gap of ZIS, thereby shifting the conduction and valence band positions to more favorable levels. This modification enhances the photocatalytic conversion of adsorbed H + The ability to be reduced to H2 significantly improves its photocatalytic performance.

[0067] 2. Steady-state photoluminescence spectrum test: Figure 7 is the steady-state photoluminescence spectra of ZIS of Example 1 of the present invention and 3.2% Ni3S2 / ZIS, such as Figure 7 As shown, the emission peaks of all samples are around 560nm, and the emission intensity of pure ZIS is the highest, indicating strong carrier recombination. In contrast, the reduced fluorescence intensity in 3.2% Ni3S2 / ZIS indicates that Ni3S2 loading effectively suppresses electron-hole recombination. This improvement can enable more photogenerated electrons to participate in the photocatalytic reaction, thereby improving the overall photocatalytic performance.

[0068] 3. Photocatalytic performance test: The photocatalytic performance of the prepared Ni3S2 / ZIS composite material was evaluated by measuring the hydrogen production rate of benzyl alcohol under visible light irradiation.

[0069] The results are as follows Figure 8 As shown, Figure 8 As shown in Figures a and b, pure ZIS exhibits a relatively low hydrogen production rate of 2.422 mmol g -1 h -1, which is mainly due to the rapid recombination of photogenerated electron-hole pairs. The control experiment using only Ni3S2 showed no hydrogen production, confirming that Ni3S2 alone lacks intrinsic photocatalytic activity for hydrogen production. Figure 8 The volcano-like trend observed in (c) demonstrates that the incorporation of Ni3S2 into ZIS can significantly enhance the photocatalytic performance. The hydrogen production rate increases with the increase of Ni3S2 loading and reaches a peak of 4.342 mmol g at an optimal Ni3S2 content of 3.2%. -1 h -1 A similar trend was observed for the benzyl alcohol conversion, which reached a maximum of 4.213 mmol g at the same Ni3S2 loading. -1 h -1 . These results are 1.79-fold and 1.76-fold improvements, respectively, compared to pristine ZIS, highlighting the synergistic effect of Ni3S2 in enhancing the photocatalytic activity. However, beyond the optimal loading of 3.2% Ni3S2, the hydrogen evolution rate decreased, which may be due to excessive Ni3S2 coverage on the ZIS surface, blocking the active sites and hindering light absorption. Product analysis confirmed that benzaldehyde was the only reaction product with no detectable by-products, indicating that the system has excellent selectivity. The strong correlation between hydrogen yield and benzyl alcohol conversion indicates that the dehydrogenation of benzyl alcohol to benzaldehyde is highly efficient, with a conversion of 69% achieved after 24 h using the 3.2% Ni3S2 / ZIS composite. In addition, stability and reusability tests demonstrated the practical feasibility of the photocatalyst, such as Figure 8 As shown in (d), the 3.2%Ni3S2 / ZIS composite maintained its hydrogen production efficiency with minimal loss during four consecutive days of reaction cycles, indicating its excellent stability and reusability. Fig. 9 The XRD spectra of the composite catalyst 3.2% Ni3S2 / ZIS before and after the cycling experiment are depicted. It is noteworthy that there is no obvious difference between the two spectra. These findings, coupled with the high performance, selectivity and durability of the composite material, statistically demonstrate the potential of the 3.2% Ni3S2 / ZIS composite material as a sustainable and efficient photocatalyst for hydrogen production and green chemical synthesis under visible light. Table 1 below shows the conversion rate and selectivity of ZIS and Ni3S2 / ZIS prepared in Examples 1 to 4. The conversion rate and selectivity are calculated as follows:

[0070] Conversion rate = (C0–C1) / C0×100% (1)

[0071] Selectivity = C2 / (C0–C1)×100% (2)

[0072] Wherein, C0 represents the initial concentration of benzyl alcohol, C1 represents the remaining concentration of benzyl alcohol after the reaction, and C2 represents the concentration of benzaldehyde after the reaction.

[0073] Table 1

[0074] catalyst Conversion Rate Selectivity ZIS (Example 1) 55％ 99％ <![CDATA[1.9%Ni3S2 / ZIS]]> 63％ 99％ <![CDATA[3.2%Ni3S2 / ZIS]]> 69％ 99％ <![CDATA[4.8%Ni3S2 / ZIS]]> 67％ 99％ <![CDATA[6.4%Ni3S2 / ZIS]]> 61％ 99％

[0075] 4. Exploration of the mechanism of catalytic reaction Test: The 3.2% Ni3S2 / ZIS catalyst of Example 1 was subjected to quenching experiment and electron spin paramagnetic resonance spectroscopy analysis experiment in turn. The test results are shown in Table 2 and Table 3, respectively. Fig.10 As shown:

[0076] Table 2

[0077]

[0078]

[0079] In order to clarify the mechanism of photocatalytic decomposition of benzoic acid, the present invention conducted a quencher control experiment to determine the active substances in the photocatalytic system. As shown in Table 2, the introduction of the hole scavenger triethanolamine (TEOA) increased the benzaldehyde yield from 16.906 mmol g -1 Significantly reduced to 7.936mmol g -1 , while the hydrogen production remained almost unchanged. This indicates that the photogenerated holes mainly participate in the oxidation of benzoic acid during the photocatalytic process. In contrast, the addition of electron scavenger AgNO3 (0.1 mmol) leads to a complete cessation of hydrogen production, indicating that the photogenerated electrons are mainly responsible for the oxidation of H in the system. + These findings confirm that the role of photogenerated holes in benzoic acid oxidation and photogenerated electrons in hydrogen evolution are different in the photocatalytic reaction, emphasizing their synergistic contributions to the overall photocatalytic mechanism.

[0080] To further confirm the generation of free radicals during the photocatalytic process, electron spin resonance (EPR) spectroscopy was performed using 5,5-dimethyl-1-pyrrolidine N-oxide (DMPO) as a free radical scavenger. Fig.10 As shown, no free radical signals were observed for both photocatalysts under dark conditions. However, under visible light irradiation, six characteristic signals corresponding to carbon-centered free radicals (especially α-hydroxybenzyl radicals) were detected for both ZIS and 3.2% Ni3S2 / ZIS photocatalysts, indicating that visible light activated the CH bonds in benzyl alcohol, thereby inducing the formation of free radicals. Importantly, the DMPO-Cα radical signal intensity of the 3.2% Ni3S2 / ZIS composite was significantly higher than that of ZIS alone, revealing the key role of the Ni3S2 cocatalyst in accelerating CH activation and dehydrogenation, thereby improving the performance of the composite photocatalytic system.

[0081] Based on the above findings, the present invention proposes a reasonable photocatalytic mechanism of Ni3S2 / ZIS composite materials, such as Fig.11 As shown. First, the photocatalyst absorbs incident light energy to generate photogenerated electron-hole pairs, and this effective separation of charge carriers prevents them from recombination. Subsequently, the photogenerated holes interact with benzyl alcohol molecules adsorbed on the catalyst surface, oxidizing them to benzaldehyde and releasing hydrogen ions. At the same time, the photogenerated electrons participate in the reduction of protons to produce hydrogen. The addition of Ni3S2 significantly improves the charge separation efficiency and promotes the migration of electrons through conductive channels while confining photogenerated holes to the catalyst surface. This improved charge carrier dynamics is the basis for the superior photocatalytic activity of Ni3S2 / ZIS over pristine ZIS.

[0082] As described above, although the present invention has been shown and described with reference to specific preferred embodiments, it should not be construed as limiting the present invention itself. Various changes may be made to the form and details without departing from the spirit and scope of the present invention.

Claims

1. A method for preparing a composite photocatalyst Ni3S2 / ZnIn2S4, characterized in that: Nickel nitrate and sodium citrate were dissolved to form a solution, ZnIn2S4 was added and dispersed evenly, and then thioacetamide was added dropwise to carry out a hydrothermal reaction. After cooling and centrifugal washing, a composite photocatalyst Ni3S2 / ZnIn2S4 was obtained.

2. The preparation method according to claim 1, characterized in that: The preparation method of ZnIn2S4 is as follows: Zinc nitrate hexahydrate, indium nitrate tetrahydrate and L-cysteine ​​are dissolved in water, ultrasonically dispersed to form a solution, and magnetically stirred at room temperature until it becomes clear; the solution is transferred to a reaction kettle, heated in an oven, and naturally cooled to room temperature. The generated precipitate is washed several times with water and ethanol, and then dried to obtain ZnIn2S4.

3. The preparation method according to claim 2, characterized in that: In the preparation method of ZnIn2S4, the molar ratio of zinc nitrate hexahydrate, indium nitrate tetrahydrate and L-cysteine ​​is 1:2:8; the heating temperature in the oven is 180°C and the heating time is 3-4h.

4. The preparation method according to claim 1, characterized in that: The steps include: Step 1: dissolving nickel nitrate hexahydrate and sodium citrate dihydrate in water and stirring, then adding ZnIn2S4 to the solution and stirring to disperse; then, adding an aqueous solution of thioacetamide dropwise and stirring the mixture again; Step 2: Transfer the solution to a reaction kettle, heat it in an oven for a period of time, and then cool it naturally to room temperature. Wash the generated precipitate several times by centrifugation with water and ethanol, and then dry it to obtain Ni3S2 / ZnIn2S4.

5. The preparation method according to claim 4, characterized in that: In step 1, the usage ratio of nickel nitrate hexahydrate, sodium citrate dihydrate and ZnIn2S4 is 0.0698:0.5:(0.3-1); the molar ratio of nickel nitrate hexahydrate to thioacetamide is 3:

4.

6. The preparation method according to claim 4, characterized in that: In step 1, ZnIn2S4 is added to the solution and the stirring and dispersion time is not less than 2 hours.

7. The preparation method according to claim 4, characterized in that: In step 2, the heating temperature in the oven is 160° C. and the heating time is 6-8 hours.

8. The composite photocatalyst Ni3S2 / ZnIn2S4 prepared by the preparation method described in any one of claims 1-7.

9. Use of the composite photocatalyst Ni3S2 / ZnIn2S4 prepared by the preparation method according to any one of claims 1 to 7 in catalyzing the decomposition of benzyl alcohol to produce hydrogen and benzaldehyde.

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