Multifunctional ZnS / BiVO4 composite catalyst and preparation method and application of ZnS / BiVO4 / CC electrode

Abstract

The invention discloses a multifunctional ZnS / BiVO4 composite catalyst and a preparation method and application of a ZnS / BiVO4 / CC electrode. The preparation method comprises the following steps: firstly, preparing a ZnS photocatalyst; then preparing a BiVO4 photocatalyst; and finally, adding ZnS powder according to the molar ratio of ZnS: 1: 1, 1: 2 and 1: 3 to obtain ZS / BV-1, ZS / BV-2 and ZS / BV-3. The preparation process is simple and convenient, photo-induced electron-hole pair compounding can be effectively inhibited, the visible light response range is widened, and the multifunctional composite catalyst has the performance of photocatalytic degradation of pollutants, photocatalytic synthesis of H2O2 and electro-catalytic oxygen evolution. The method has important scientific significance and practical value for promoting practical application of a photocatalysis technology in treatment of refractory organic wastewater, synthesis of green chemicals and energy conversion.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of preparation of ZnS / BiVO4 composite catalyst, in particular to a multifunctional ZnS / BiVO4 composite catalyst and a preparation method and application of ZnS / BiVO4 / CC electrode. BACKGROUND

[0002] With the rapid development of chemical synthesis technology, synthetic dyes have gradually replaced natural dyes and become mainstream products. According to global literature data, up to 280,000 tons of synthetic dyes are discharged into the environment by industry every year. Such dyes are extremely stable and are usually difficult to biodegrade and decompose in water. They mainly come from the clothing, textile, plastic, leather, ink and papermaking industries. These synthetic dyes pose a serious threat to human health, can cause a variety of diseases, and also harm aquatic organisms; when they enter water bodies, they can hinder sunlight transmission, affect the photosynthesis process, and disrupt the balance of the aquatic ecosystem, and if wastewater containing such high concentrations of organic pollutants is discharged directly without proper treatment, it can cause lasting and far-reaching harm to the water environment.

[0003] Among the many synthetic dyes, methylene blue (MB) as a representative of aromatic heterocyclic dyes is widely used due to its excellent dyeing performance, and its usage accounts for more than 30% of the total amount of dyes. As a typical cationic thiazine dye, methylene blue (MB) contains stable aromatic rings and heteroatom structures in its molecular structure, making it highly chemically stable and resistant to biodegradation, and it can persist in the environment for a long time. More seriously, methylene blue (MB) has been proven to have a "three-effect" effect, and it can accumulate through the food chain in the natural environment, ultimately endangering human health. In addition, methylene blue (MB) also has significant toxicity to aquatic ecosystems, which can inhibit algal photosynthesis and disrupt the self-purification capacity of water bodies.

[0004] Currently, traditional methods such as adsorption, coagulation and biodegradation face significant technical bottlenecks in treating wastewater containing methylene blue (MB) dyes. Although the adsorption method is simple to operate and relatively low in cost, it can only achieve the transfer of pollutants from the liquid phase to the solid phase, cannot completely degrade methylene blue, and the regeneration of the adsorbent is difficult, which can easily lead to secondary pollution. The coagulation method has good effect on removing suspended dyes, but its removal ability for soluble dyes is limited, with a removal rate generally lower than 50%, and a large amount of high-water-content chemical sludge is generated, increasing the subsequent disposal cost. The biodegradation method has low operating cost, but due to the stable molecular structure and strong biological toxicity of methylene blue (MB), the degradation efficiency of microorganisms is not high, and the COD removal rate is usually difficult to exceed 60%, and the process is sensitive to conditions such as pH and temperature, and has weak resistance to water quality fluctuations. Limited by these inherent defects, traditional treatment methods are difficult to meet the current requirements of high-efficiency purification and strict standard discharge of printing and dyeing wastewater.

[0005] Among the various advanced oxidation technologies, photocatalysis is considered a promising approach for dye wastewater treatment due to its ability to harness solar energy, mild reaction conditions, complete degradation, and no secondary pollution. The core of this technology lies in the photocatalyst, which generates electron-hole pairs under light irradiation and degrades organic pollutants into harmless small molecules through a series of redox reactions. Compared with traditional treatment methods, photocatalysis can efficiently and completely degrade pollutants at room temperature and pressure without secondary pollution.

[0006] Meanwhile, hydrogen peroxide (H2O2) is an important green oxidant and potential energy carrier, showing broad application prospects in environmental remediation and clean energy. Traditional H2O2 industrial production mainly relies on the anthraquinone method, which has high energy consumption, complex steps, and uses noble metal catalysts and organic solvents, easily causing environmental pollution.

[0007] Therefore, it is of great significance to develop a green, safe, and sustainable new route for H2O2 synthesis.

[0008] Photocatalysis is a promising alternative that can directly synthesize H2O2 using solar energy, water, and oxygen, with a clean process and mild conditions. However, the core challenge of this technology lies in developing efficient and selective photocatalysts. Ideal photocatalysts need to effectively absorb visible light, promote efficient separation and migration of photo-generated carriers, and have the ability to selectively activate the two-electron oxygen reduction pathway to inhibit side reactions, thereby improving the yield and selectivity of H2O2.

[0009] In addition, electrocatalytic water splitting for hydrogen production is a promising clean energy technology, where the oxygen evolution reaction (OER) is the anodic reaction of water splitting. Due to its slow kinetics and high overpotential, it has become a bottleneck for water splitting. Currently, noble metal catalysts such as IrO2 and RuO2 are efficient OER catalysts, but their scarcity and high cost limit their large-scale application. Therefore, it is of great significance to develop non-noble metal, efficient, and stable OER catalysts. Among the various non-noble metal catalysts, bismuth vanadate (BiVO4) has shown good application potential in photocatalysis and photoelectrocatalysis due to its suitable energy band structure, good visible light response, and excellent chemical stability.

[0010] However, single BiVO4 still faces problems such as poor conductivity, limited active sites, and low charge transfer efficiency in photo / electrocatalysis, which limits its performance in photocatalytic synthesis of H2O2 and OER reactions. In recent years, building heterojunction composite structures to regulate material electronic structure and enhance interface charge separation and transmission efficiency has become an effective strategy to improve the performance of photo / electrocatalysts. Zinc sulfide (ZnS) is a typical semiconductor material with good electron mobility and structural adjustability, and its combination with BiVO4 is expected to form a synergistic effect in photocatalytic synthesis of H2O2 and electrocatalysis.

[0011] The existing photocatalysts still face the following problems in practical application: (1) The recombination rate of photo-generated electron-hole pairs is too fast, and when the recombination is too fast, a large number of electron-hole pairs will recombine before participating in the catalytic reaction; (2) The utilization efficiency of sunlight by the photocatalyst is not high, and the response range of the sunlight spectrum is narrow, only a specific wavelength band in the sunlight spectrum can be effectively utilized, resulting in low light energy conversion efficiency, which greatly reduces the degradation efficiency of pollutants and the production efficiency of hydrogen peroxide. The present technology can solve the problems faced by photocatalysis.

[0012] The existing electrocatalysts still face the following problems in practical application: (1) The most optimal OER catalysts currently still rely on noble metal materials such as IrO2 and RuO2, which have high costs and limited natural reserves, severely restricting large-scale commercial application; (2) Most non-noble metal catalysts have lower costs, but their intrinsic catalytic activity is poor, and the charge transfer efficiency is low, resulting in a high reaction overpotential and high energy consumption.

[0013] Therefore, developing a multifunctional composite catalyst with a simple preparation process, which can effectively inhibit the recombination of photo-generated electron-hole pairs, broaden the visible light response range, and have the performance of photocatalytic degradation of pollutants, photocatalytic synthesis of H2O2, and electrocatalytic oxygen evolution, has important scientific significance and practical value for promoting the practical application of photocatalytic technology in the treatment of refractory organic wastewater, green chemical synthesis, and energy conversion.

[0014] The literature (Materials Letters, 2024, 360, 136039) used a two-step hydrothermal method to synthesize ZnS / Cu2SnS3 heterojunction composite materials, and conducted photocatalytic degradation of methylene blue under visible light irradiation. The degradation rate of methylene blue can reach 90.9% after 4h of light irradiation.

[0015] In comparison, the present application successfully constructs a ZnS / BiVO4 composite photocatalyst by a simple solvothermal method, and the degradation efficiency of methylene blue can be as high as 91.03% after 2h of light irradiation, and the degradation rate is further improved to 99.55% under the optimized conditions (pH=11, catalyst mass 30mg). Meanwhile, the composite catalyst of the present application also has a certain electrocatalytic oxygen evolution performance.

[0016] The comparative literature (Journal of Materials Science: Materials in Electronics, 2023, 34, 1627) also synthesizes ZnS-rGO (zinc sulfide-reduced graphene oxide) nanocomposites by a solvothermal method, and the highest degradation efficiency of methylene blue is 73.73% after 2h of light irradiation.

[0017] In comparison, the present application successfully constructs a ZnS / BiVO4 composite photocatalyst by a solvothermal method, and the degradation rate of methylene blue can be as high as 91.03% within the same light irradiation time (2h), and the performance of the composite material of the present application only decreases by 6.07% after 5 cycles, showing more excellent catalytic stability and industrial application potential.

[0018] At the same time, the ZnS / BiVO4 composite photocatalyst successfully constructed by the present application has a production rate of H2O2 of within the same light irradiation time (2h), and has good stability. The comparative literature (Chemistry Select, 2018, 3, 9422-9430) synthesizes ZnS-WO3 nanosheet hybrid materials by a wet impregnation method, and performs photocatalytic degradation of methylene blue under ultraviolet-visible light irradiation. The degradation rate of methylene blue reaches 92.40% after 4h of light irradiation.

[0019] In comparison, the present application successfully constructs a ZnS / BiVO4 composite photocatalyst by a solvothermal method, and the degradation rate of methylene blue can be as high as 91.03% within the same light irradiation time (2h). At the same time, the present application not only has significantly higher degradation efficiency and shorter reaction time, but also has a more simple and efficient solvothermal preparation process and low cost. More importantly, the composite system is first applied to the electrocatalytic oxygen evolution reaction (OER), and shows significantly enhanced catalytic activity and reaction kinetics, successfully realizing "one material for multiple uses", and showing a broader application prospect in the fields of environmental remediation and energy conversion. Therefore, the composite material prepared in the present work has better catalytic activity, and the preparation process is more simple and efficient, and has better industrial application prospect. SUMMARY

[0020] Therefore, the application provides a multifunctional ZnS / BiVO4 composite catalyst and a preparation method and application of a ZnS / BiVO4 / CC electrode.

[0021] To solve the above technical problems, the application adopts the following technical solutions:

[0022] A preparation method of a multifunctional ZnS / BiVO4 composite catalyst, comprising the following steps:

[0023] Step 1: preparation of ZnS

[0024] Anhydrous zinc acetate C4H6O4Zn and thiourea CH4N2S are added to deionized water, and magnetic stirring is carried out at room temperature until complete dissolution;

[0025] The mixed solution is then transferred to a polytetrafluoroethylene-lined stainless steel reaction kettle for reaction;

[0026] After the reaction is completed, the precipitate is collected by centrifugation, washed and dried;

[0027] After grinding treatment, the ZnS photocatalyst is obtained;

[0028] Step 2: preparation of BiVO4

[0029] Bismuth nitrate pentahydrate and ammonium metavanadate NH4VO3 are added to a mixed solvent composed of ethylene glycol and deionized water, and magnetic stirring and ultrasonic treatment are carried out at room temperature until complete dissolution;

[0030] The mixed solution is then transferred to a polytetrafluoroethylene-lined stainless steel reaction kettle for reaction;

[0031] After the reaction is completed, the precipitate is collected by centrifugation, washed and dried;

[0032] After grinding treatment, the BiVO4 photocatalyst is obtained;

[0033] Step 3: preparation of ZnS / BiVO4

[0034] Bismuth nitrate pentahydrate and ammonium metavanadate NH4VO3 are added to a mixed solvent composed of ethylene glycol and deionized water, and magnetic stirring and ultrasonic treatment are carried out at room temperature until complete dissolution;

[0035] ZnS powder is added in a molar ratio of 1:1, 1:2 and 1:3, respectively, magnetic stirring and ultrasonic treatment are continued; The mixed system is then transferred to a polytetrafluoroethylene-lined stainless steel reaction kettle for reaction;

[0036]

[0037] ​After the reaction, the precipitate was collected by centrifugation, washed, and dried.

[0038] After grinding, three different ZnS / BiVO4 molar ratio composites were obtained, marked as ZS / BV-1, ZS / BV-2 and ZS / BV-3 respectively; wherein ZS / BV-1, ZS / BV-2 and ZS / BV-3 are ZnS:BiVO4=1:1, ZnS:BiVO4=1:2 and ZnS:BiVO4=1:3 respectively.

[0039] Preferably, in step 1, the amount of zinc acetate C4H6O4Zn added is 1.16 g, the amount of thiourea CH4N2S added is 0.48 g, and the amount of deionized water added is 35 mL.

[0040] Preferably, in step 1, the magnetic stirring is continued at room temperature at a speed of 600 rpm for 4 hours until complete dissolution, and then the mixed solution is transferred to a 50 mL polytetrafluoroethylene lined stainless steel reaction kettle, and reacted at 180°C for 20 hours.

[0041] Preferably, in step 1, the precipitate is collected by centrifugation at 8000 rpm, and washed with deionized water and anhydrous ethanol five times respectively, and dried at 60°C for 12 hours.

[0042] Preferably, in steps 2 and 3, the amount of bismuth nitrate pentahydrate Bi(NO3)3·5H2O is 2 mmol, the amount of ammonium metavanadate NH4VO3 is 2 mmol, the amount of ethylene glycol is 40 mL, and the amount of deionized water is 20 mL.

[0043] Preferably, in steps 2 and 3, the magnetic stirring is continued at room temperature at a speed of 600 rpm for 1 hour, and ultrasonic treatment is performed for 45 minutes until complete dissolution.

[0044] Then the mixed solution is transferred to a 100 mL polytetrafluoroethylene lined stainless steel reaction kettle, and reacted at 160°C for 6 hours, and the precipitate is collected by centrifugation at 8000 rpm, and washed with deionized water and anhydrous ethanol five times respectively, and dried at 60°C for 12 hours.

[0045] A method for preparing a ZnS / BiVO4 / CC electrode, comprising the following steps:

[0046] a. Weigh the ZnS / BiVO4 composite powder and disperse it in N-methyl-2-pyrrolidone (NMP) solvent;

[0047] b. Intermittent ultrasonic treatment is performed on the mixed system to form a uniform and stable suspension;

[0048] ​c. Take a piece of carbon cloth CC which is pre-treated by acid and cleaned and dried by deionized water as an electrode substrate, use forceps to clamp the carbon cloth, and immerse the carbon cloth in the prepared catalyst suspension completely;

[0049] d. After the immersion is completed, the carbon cloth loaded with the catalyst is transferred to a blast drying oven for drying, and a self-supported composite working electrode, denoted as a ZnS / BiVO4 / CC electrode, is obtained.

[0050] Preferably, in the step a, the added amount of the ZnS / BiVO4 composite powder is 80.0 mg, and the added amount of the N-methyl-2-pyrrolidone NMP solvent is 2.4 mL;

[0051] In the step b, the ultrasonic treatment is performed once every 5 minutes, and the cumulative ultrasonic treatment is 5 times;

[0052] In the step c, the immersion time is 30 seconds;

[0053] In the step d, the drying is performed at 60 DEG C for 4 hours.

[0054] Application of a multifunctional ZnS / BiVO4 composite catalyst in photocatalytic degradation of dyes, synthesis of hydrogen peroxide and electrocatalytic oxygen evolution.

[0055] The present application has the following technical effects relative to the prior art:

[0056] (1) In the present application, the BiVO4 with a unique spindle shape is loaded on the surface of the spherical ZnS by a solvothermal method, and a novel ZnS / BiVO4 composite catalyst system is successfully constructed, and a compact composite structure is formed, which not only promotes the efficient transfer of photo-generated electrons, effectively inhibits the recombination of carriers, but also widens the utilization range of sunlight and improves the utilization rate, and the novel ZnS / BiVO4 composite catalyst system exhibits excellent comprehensive performance in photocatalytic degradation of pollutants, photocatalytic synthesis of hydrogen peroxide and electrocatalytic oxygen evolution reaction;

[0057] (2) The ZnS / BiVO4 composite photocatalyst in the present application is prepared by a simple solvothermal method, and has the advantages of simple preparation process, low cost and easy reuse, and the degradation effect is excellent, and under the optimized conditions (pH=11, catalyst mass 30 mg), the degradation rate of 10 mg / L methylene blue solution is as high as 99.55% within 120 min, and the performance only decreases by 6.07% after 5 cycles, and the ZnS / BiVO4 composite photocatalyst exhibits excellent stability and practical application potential;

[0058] (3) In the aspect of photocatalytic synthesis of hydrogen peroxide (H2O2), the ZnS / BiVO4 composite material exhibits excellent H2O2 production activity;

[0059] (4) Under visible light irradiation, the H2O2 production rate of ZS / BV-2 reached 0. 16 mmol / g / h, which was 2.29 times and 20.35 times of that of pure ZnS and pure BiVO4, respectively, which reflected the key role of heterojunction structure in promoting electron transfer and inhibiting carrier recombination;

[0060] (5) After 3 cycles of experiments, the H2O2 production rate of ZS / BV-2 still maintained 80.4% of the initial value, which showed good structural stability and sustained catalytic capacity;

[0061] (6) At the same time, it also had certain performance in electrocatalytic oxygen evolution, and compared with carbon cloth and single-component electrodes, the composite material showed significantly enhanced catalytic activity, especially the ZS / BV-2 / CC electrode showed the lowest overpotential and Tafel slope, which effectively overcame the problems of traditional catalysts, such as dependence on noble metals, insufficient intrinsic activity and single function. BRIEF DESCRIPTION OF DRAWINGS

[0062] Figure 1 X-ray diffraction (XRD) of the ZnS / BiVO4 composite material of the application;

[0063] Figure 2 (a) SEM image of ZnS; (b) SEM image of BiVO4; (c) SEM image of ZS / BV-2;

[0064] Figure 3 (a) curves of degradation of methylene blue at different proportions; (b) first-order kinetics; (c) kinetic constant; (d) cycle experiment of degradation of methylene blue;

[0065] Figure 4 (a) curves of degradation of methylene blue at different masses; (b) first-order kinetics; (c) kinetic constant;

[0066] Figure 5 (a) curves of degradation of methylene blue at different solution pH values; (b) first-order kinetics; (c) kinetic constant;

[0067] Figure 6 (a) LSV curves of composite materials at different molar ratios; (b) Tafel curves of composite materials at different molar ratios

[0068] Figure 7 (a) curves of H2O2 production of different catalysts; (b) performance comparison of H2O2 production of different catalysts; (c) cycle stability test of ZS / BV-2. DETAILED DESCRIPTION

[0069] ​The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0070] Example 1: Structural and morphological characterization of ZnS / BiVO4 composite material

[0071] First, the crystal structure of the ZnS / BiVO4 composite material was analyzed by X-ray diffraction (XRD).

[0072] like Figure 1 As shown, the diffraction peaks of pure ZnS match the standard card (PDF#05-0566) for hexagonal ZnS, while the diffraction peaks of pure BiVO4 match the standard card (PDF#14-0688) for monoclinic BiVO4. In the XRD pattern of the ZnS / BiVO4 composite material, characteristic diffraction peaks of both hexagonal ZnS and monoclinic BiVO4 phases appear simultaneously, and both match the standard cards for ZnS (PDF#05-0566) and BiVO4 (PDF#14-0688), respectively, indicating the successful synthesis of the ZnS / BiVO4 composite material.

[0073] Among them, the characteristic diffraction peaks of the hexagonal ZnS are at 2θ=29.0°, 48.2° and 57.2°, corresponding to crystal planes (111), (220) and (311), respectively; the characteristic diffraction peaks of the monoclinic BiVO4 are at 2θ=19.1°, 29.1°, 30.7°, 34.7°, 35.2°, 40.1°, 42.6°, 46.7°, 47.3°, 50.3°, 53.4°, 58.6° and 59.3°, corresponding to crystal planes (011), (121), (040), (200), (002), (211), (051), (240), (042), (202), (161), (321) and (123), respectively.

[0074] The XRD results show that the ZnS / BiVO4 composite photocatalyst was successfully synthesized.

[0075] The morphology and structure of pure ZnS, BiVO4 and ZS / BV-2 composites were systematically characterized using scanning electron microscopy (SEM).

[0076] like Figure 2 As shown in (a), pure ZnS exhibits a regular spherical morphology with a uniform particle size distribution, an average diameter of about 4-5 μm, and a certain degree of surface roughness.

[0077] As Figure 2 As shown in (b), pure BiVO4 presents a uniform unique spindle morphology, with an average diameter of about 1.5 μm, and the surface is constructed by accumulation of fine particles.

[0078] As Figure 2 As shown in (c), in the ZS / BV-2 composite material, the spindle-shaped BiVO4 is successfully and closely loaded on the surface of the ZnS sphere, both the spherical morphology of ZnS and the spindle-shaped characteristics of BiVO4 are completely retained, and a unique composite structure is presented due to the combination of the two, which directly proves the successful preparation of the composite material.

[0079] Example 2: Performance of ZnS / BiVO4 composite material in degrading methylene blue

[0080] The performance of the ZnS / BiVO4 composite photocatalyst was evaluated by degrading methylene blue using a 300 W xenon lamp with a cutoff filter (λ≥420 nm) as a visible light source.

[0081] A 10 mg / L methylene blue simulated dye wastewater with a pH of 7.0 was prepared, 100 mL of the simulated wastewater was added to a 200 mL reactor, 30 mg of photocatalyst was used to degrade the methylene blue at room temperature, the solution was stirred in the dark for 40 min to balance adsorption, and then the photocatalytic reaction was carried out under a 300 W xenon lamp and a 420 nm cutoff filter for 2 h, the absorbance was measured every 20 min. The remaining pollutants in the filtered methylene blue degradation solution were analyzed by ultraviolet-visible spectrophotometer (λ= 663 nm). (Before measuring the absorbance, the sample was filtered with a 0.45 μm syringe filter).

[0082] The degradation rate of methylene blue was calculated according to the following formula:

[0083] ;

[0084] Wherein, C0 is the initial concentration of methylene blue, C t is the concentration of methylene blue after degradation.

[0085] First, in order to evaluate the photocatalytic activity of the ZnS / BiVO4 composite material, we added 30 mg of catalyst to 100 mL of 10 mg / L methylene blue solution;

[0086] As Figure 3As shown in (a), after 40 min of adsorption equilibrium, the methylene blue adsorption removal rates of ZnS, BiVO4, ZS / BV-1, ZS / BV-2, and ZS / BV-3 were 2.25%, 4.17%, 9.50%, 12.06%, and 8.64%, respectively. After 120 min of visible light irradiation, the degradation rates of methylene blue by ZnS, BiVO4, ZS / BV-1, ZS / BV-2, and ZS / BV-3 were 63.89%, 75.43%, 73.16%, 91.03%, and 87.55%, respectively.

[0087] The results showed that the degradation of methylene blue mainly depended on photocatalysis rather than physical adsorption. When the molar ratio of ZnS to BiVO4 increased from 1:1 to 1:2, the degradation rate significantly improved. This was because the addition of an appropriate amount of BiVO4 led to the formation of a more suitable heterojunction structure between ZnS and BiVO4, promoting the effective separation of photogenerated carriers and broadening the absorption range of visible light, thereby significantly enhancing the photocatalytic activity.

[0088] However, when the molar ratio was further increased from 1:2 to 1:3, the degradation rate decreased. This is because excess BiVO4 covers some active sites, hindering the adsorption of reactants on the catalyst surface and subsequent catalytic processes. Among them, ZS / BV-2 exhibited the best photocatalytic degradation performance, with a degradation rate (91.03%) that was 1.42 times and 1.21 times that of pure ZnS (63.89%) and pure BiVO4 (75.43%), respectively.

[0089] Next, the degradation kinetics were studied, and the first-order degradation kinetics linear curve was obtained, as shown below. Figure 3 As shown in (b), ZS / BV-2 has the largest slope of the first-order kinetic line, indicating that ZS / BV-2 has the best photocatalytic degradation efficiency among all samples.

[0090] To more intuitively compare the differences in reaction rates, a bar chart of the first-order kinetic constant (k) for each catalyst was plotted, and the results are as follows: Figure 3 As shown in (c).

[0091] The kinetic constants for ZnS, BiVO4, ZS / BV-1, ZS / BV-2, and ZS / BV-3 are 0.00847 min. -1 0.01154min -1 0.01016min -1 0.01862min -1 and 0.01647min -1 The kinetic constant of ZS / BV-2 is 0.01862 min. -1 The values ​​are pure ZnS (0.00847 min).-1 ) and pure BiVO4 (0.01154 min -1 ) were 2.20 and 1.61 times, respectively.

[0092] In summary, by introducing an appropriate amount of BiVO4 to compound with ZnS and constructing a heterojunction structure, the separation of photo-generated carriers was effectively promoted, and the absorption range of the material in the visible light region was widened, thereby significantly improving its photocatalytic degradation efficiency of methylene blue.

[0093] In addition, the stability of the composite ZS / BV-2 was also tested, as shown in Figure 3 (d), it can be seen that after 5 cycles, the degradation rate of ZS / BV-2 composite only decreased by 6.07%, indicating that ZS / BV-2 has good stability and reusability.

[0094] Next, the effect of the mass of ZS / BV-2 composite catalyst on the degradation performance of methylene blue solution with an initial concentration of 10 mg / L was studied.

[0095] As shown in Figure 4 (a), when the mass of the catalyst was 10 mg, 20 mg, 30 mg, 40 mg and 50 mg, the photocatalytic degradation efficiency of ZS / BV-2 on methylene blue was 79.13%, 82.53%, 91.03%, 84.49% and 60.67%, respectively. Among them, when the mass of the catalyst was 30 mg, the degradation rate of 10 mg / L methylene blue solution reached the highest (91.03%). As the mass of the catalyst increased from 10 mg to 30 mg, the degradation efficiency gradually increased, which was mainly due to more catalysts dispersed in the solution, exposing more active sites, thereby improving the photocatalytic reaction efficiency. However, when the mass of the catalyst continued to increase to 40 mg and 50 mg, the degradation efficiency decreased, which was attributed to the agglomeration of excess catalyst particles, resulting in a decrease in effective active sites, and too many particles enhanced the scattering of incident light, causing the light to be unable to penetrate the deep layer of the solution, reducing the light energy utilization efficiency. Therefore, 30 mg was the optimal catalyst dosage, at which the best balance between active site exposure and light utilization efficiency was achieved.

[0096] Then, further kinetic analysis of the degradation process was carried out, as shown in Figure 4 (b-c), the results showed that the degradation process under different catalyst masses all conformed to the first-order reaction kinetic model. Among them, 30 mg catalyst mass showed the highest kinetic constant (k = 0.01862 min -1 ), which was 1.47, 1.37 and 1.30 times of 10 mg (0.01262 min -1 ), 20 mg (0.01381 min -1 ) and 40 mg (0.01414 min-1 ) and 50 mg (0.00668 min -1 ) under the condition of 1.48 times, 1.35 times, 1.32 times and 2.79 times of the mass, further indicating that the catalyst has the optimal photocatalytic performance under the condition of 30 mg mass.

[0097] The pH value of the solution can significantly affect the adsorption behavior and photocatalytic degradation performance of the ZS / BV-2 catalyst on methylene blue (MB) by adjusting the surface charge state of the ZS / BV-2 catalyst.

[0098] As shown in Figure 5 (a), when 30 mg of the ZS / BV-2 catalyst is added to 100 mL of a methylene blue (MB) solution with a concentration of 10 mg / L for photocatalytic testing, it can be seen that when the initial pH value of the solution is 3, 5, 7, 9 and 11, the corresponding photocatalytic degradation efficiencies are 23.67%, 35.87%, 91.03%, 98.79% and 99.55%, respectively.

[0099] The experimental results show that alkaline conditions are more conducive to the degradation of methylene blue (MB). Among them, under the strong alkaline condition of pH=11, the degradation efficiency of the catalyst on the methylene blue solution reaches the highest. The change of the degradation efficiency of ZS / BV-2 under different pH values is mainly due to the electrostatic interaction mechanism between the surface charge state of the catalyst and the morphology of the MB molecules. Since the MB molecules exist in the form of cations in the solution, when in acidic conditions, the catalyst surface will adsorb H + + in water, which carries positive charges, and at this time, it will produce electrostatic repulsion with MB cations. Due to the electrostatic repulsion, it is not conducive to the adsorption of the catalyst on the pollutants, thereby leading to a decrease in the degradation efficiency; when the solution is in alkaline conditions, the catalyst surface carries negative charges, and electrostatic adsorption occurs with MB cations. Due to the electrostatic adsorption, the enrichment of pollutants on the catalyst surface is enhanced, thereby significantly improving the photocatalytic degradation efficiency. Then, the degradation process under different pH conditions is analyzed kinetically.

[0100] As shown in Figure 5 (b-c), when pH=11, not only is the degradation efficiency the highest (99.55%), but also the reaction kinetic constant reaches the maximum value ( ), which is 18.70 times, 12.61 times, 1.77 times and 1.18 times of the values under the conditions of pH=3 ( ), pH=5 ( ), pH=7 ( ) and pH=9 ( ), respectively. This kinetic result is highly consistent with the change trend of the degradation efficiency, and the degradation efficiency under alkaline environment is more than 98.5%, which further proves that the alkaline environment has a significant promoting effect on the photocatalytic degradation of methylene blue (MB).

[0101] Example 3: Performance of ZnS / BiVO4 / CC for electrocatalytic oxygen evolution

[0102] To evaluate the application potential of ZnS / BiVO4 composite in the field of energy conversion, the ZnS / BiVO4 / CC working electrode was prepared and its electrocatalytic oxygen evolution reaction (OER) performance was tested in a standard three-electrode system. The electrochemical test was carried out in 1.0 M KOH electrolyte, with a mercury-mercury oxide (Hg / HgO) electrode as the reference electrode, a platinum plate as the counter electrode, and the prepared ZnS / BiVO4 / CC electrode as the working electrode.

[0103] The intrinsic catalytic activity of the material was evaluated by linear sweep voltammetry (LSV) test, and the results are shown in Figure 6 (a).

[0104] At a current density of 10 mA cm⁻², the overpotential of the bare carbon cloth (Bare CC) and the pure BiVO4 electrode is high, while all the ZnS / BiVO4 composite electrodes show significantly enhanced OER activity. Among them, the ZS / BV-2 / CC electrode shows the best catalytic activity, with the lowest overpotential, which is significantly lower than that of ZS / BV-1, ZS / BV-3 and single-component electrodes. This indicates that when the molar ratio of ZnS to BiVO4 is 1:2, the most suitable heterojunction interface is formed between them, and the catalytic activity is maximized through synergistic effect.

[0105] To further explore the reaction kinetics of the electrode, the corresponding Tafel slope was obtained by fitting the LSV curve, and the results are shown in Figure 6 (b). The Tafel slope value of the ZS / BV-2 / CC electrode is the smallest, lower than that of ZS / BV-1, ZS / BV-3 and single-component electrodes. The smallest Tafel slope indicates that ZS / BV-2 / CC has a faster charge transfer rate and superior intrinsic catalytic reaction kinetics.

[0106] The above-mentioned improvement of electrochemical performance is mainly attributed to the following mechanisms: first, the tight heterojunction structure formed between ZnS and BiVO4 effectively regulates the interface electron distribution and optimizes the adsorption / desorption energy barrier of reaction intermediates on the active sites; second, the composite structure significantly improves the electrical conductivity of the electrode material, accelerating the electron transfer in the OER process; finally, the special combination of spherical ZnS and spindle-shaped BiVO4 provides a wealth of high-activity sites. The comprehensive results show that the ZnS / BiVO4 composite material prepared by the present application is not only a highly efficient photocatalyst, but also has certain oxygen evolution reaction performance under alkaline conditions.

[0107] Example 4: Performance of ZnS / BiVO4 for producing hydrogen peroxide (H2O2)

[0108] To evaluate the application potential of ZnS / BiVO4 composites in photocatalytic synthesis of green chemicals, we tested their photocatalytic performance in the production of hydrogen peroxide (H2O2) under visible light irradiation (λ ≥ 420 nm). By monitoring the accumulated concentration of H2O2 in the reaction system, we systematically evaluated the H2O2 production activity, selectivity and stability of different catalysts. The photocatalytic hydrogen peroxide production experiment was carried out at room temperature and atmospheric pressure, 60 mg of catalyst was added to 60 mL of water solution containing 10% isopropanol, and the concentration of hydrogen peroxide contained was measured by iodometric method.

[0109] First, to evaluate the photocatalytic H2O2 production activity of ZnS / BiVO4 composites, we tested pure ZnS, pure BiVO4, and different molar ratio of ZS / BV-1, ZS / BV-2 and ZS / BV-3 composites under the same reaction conditions.

[0110] The results are shown in Figure 7 (a-b), after visible light irradiation for a period of time, the H2O2 production rates of pure ZnS, pure BiVO4, ZS / BV-1, ZS / BV-2 and ZS / BV-3 are , , , and , respectively.

[0111] The results show that pure ZnS has limited production rate due to the serious photo-generated carrier recombination and narrow visible light absorption range. Pure BiVO4 has certain visible light response, but its charge separation efficiency is not high, resulting in very low production rate activity. When ZnS and BiVO4 are combined, the H2O2 production rate of all composites is significantly higher than that of single component, which directly proves the key role of heterojunction structure in improving photocatalytic performance. When the molar ratio of ZnS to BiVO4 increases from 1:1 to 1:2, the H2O2 production rate increases significantly, because the more suitable heterojunction interface is formed, which greatly promotes the effective separation of photo-generated electron-hole pairs, and provides more optimal electron transfer path and more surface active sites for the two-electron reduction reaction of oxygen molecules. However, when the molar ratio is further increased to 1:3, the excess BiVO4 may cover part of the active sites on the surface of ZnS, resulting in a decrease in H2O2 production rate. Among them, ZS / BV-2 shows the best photocatalytic H2O2 production performance, its production rate is 2.29 times and 20.35 times that of pure ZnS and pure BiVO4, respectively, highlighting its excellent catalytic activity and structural advantages.

[0112] The stability of the catalyst is an important indicator for its practical application. We performed three consecutive cycles of the most efficient ZS / BV-2 composite to evaluate its stability in photocatalytic H2O2 production, and the results are shown in Figure 7 (c) are shown.

[0113] After three cycles, the H2O2 production rate of ZS / BV-2 was maintained at , and , and respectively. The calculated production rate of the third cycle was still 80.4% of the initial value, indicating that the ZS / BV-2 composite had good reusability and structural stability in the photocatalytic synthesis of H2O2 reaction. The slow decline in production rate may be due to the loss of a small amount of catalyst in each cycle or the temporary occupation of some active sites during the reaction, but the overall performance decay rate is low, which proves that the composite has reliable long-term application potential in continuous operation.

[0114] In summary, the ZnS / BiVO4 composite catalyst was prepared by the solvothermal method. In this composite system, ZnS has strong redox ability, but its visible light absorption range is narrow, and it can only respond to part of the short-wavelength visible light, and the utilization rate of sunlight is low, and the photo-generated electron-hole pairs are prone to rapid recombination, which limits its photocatalytic efficiency. Although BiVO4 is a visible light responsive semiconductor with a wide spectral absorption range, it can utilize more visible light, but its carrier mobility is low, and the photocharge separation efficiency is not high, and the photocatalytic performance of single BiVO4 is also difficult to meet the demand of efficient degradation of pollutants and synthesis of hydrogen peroxide (H2O2). By loading BiVO4 with unique spindle morphology on the surface of spherical ZnS, a new ZnS / BiVO4 composite catalyst system was constructed, forming a tight composite structure, which not only promotes the efficient transfer of photo-generated electrons and effectively inhibits the recombination of carriers, but also widens the utilization range of sunlight and improves the utilization rate, thereby simultaneously improving the degradation efficiency of methylene blue and the production rate of photocatalytic synthesis of H2O2.

[0115] The composite catalyst improves the photocatalytic performance through the following key mechanisms: first, the close combination of ZnS and BiVO4 forms an efficient charge transport channel, greatly promotes the separation efficiency of photo-generated electron-hole pairs, and effectively inhibits the recombination of carriers; second, the unique spindle morphology of BiVO4 significantly enhances the light trapping capacity of the composite material, and the band structure of the two is matched, realizing the complementation of the spectral absorption range, widening the response range to visible light, especially improving the utilization efficiency of long-wavelength light, thereby improving the utilization rate of sunlight; finally, the special combination of spherical ZnS and spindle-shaped BiVO4 exposes more surface active sites, not only provides sufficient adsorption and reaction sites for methylene blue molecules, but also creates favorable conditions for the adsorption of oxygen molecules and the two-electron reduction reaction to generate H2O2.

[0116] In addition, in terms of electrocatalysis, the prepared ZnS / BiVO4 composite material is loaded on a pretreated carbon cloth substrate to construct a self-supported composite electrode. The electrode exhibits significantly enhanced OER catalytic activity relative to single components under alkaline conditions (1.0 M KOH electrolyte). The composite structure is superior to single components through the interface electron coupling effect, and provides abundant active sites, thereby synergistically improving the electrocatalytic oxygen evolution performance. The performance improvement is mainly due to the close heterojunction structure formed between ZnS and BiVO4, which effectively regulates the electronic structure of the material through the interface electron coupling effect, promotes the rapid migration of electric charges between the interfaces, and significantly enhances the electrical conductivity of the material. At the same time, the special combination of spherical ZnS and spindle-shaped BiVO4 not only provides a large specific surface area, but also exposes a large number of high-activity sites, which is beneficial to the adsorption of reactants and the conversion of intermediates.

[0117] The above is only a preferred embodiment of the present application, and does not limit the technical scope of the present application in any way. Therefore, any minor modification, equivalent change and modification made according to the technical essence of the present application to the above embodiment are still within the scope of the technical solution of the present application.

Claims

1. A method for preparing a multifunctional ZnS / BiVO4 composite catalyst, characterized in that, The method comprises the following steps: Step 1: Preparation of ZnS Anhydrous zinc acetate C4H6O4Zn and thiourea CH4N2S are added to deionized water, and magnetic stirring is carried out at room temperature until complete dissolution; The mixed solution is then transferred to a polytetrafluoroethylene-lined stainless steel reaction kettle for reaction; After the reaction is completed, the precipitate is collected by centrifugation, washed and dried; After grinding treatment, ZnS photocatalyst is obtained; Step 2: Preparation of BiVO4 Bismuth nitrate pentahydrate and ammonium metavanadate NH4VO3 were added to a mixed solvent consisting of ethylene glycol and deionized water, magnetically stirred at room temperature, and ultrasonically treated until completely dissolved; The mixed solution is then transferred to a polytetrafluoroethylene-lined stainless steel reaction kettle for reaction; After the reaction is completed, the precipitate is collected by centrifugation, washed and dried; After grinding treatment, BiVO4 photocatalyst is obtained; Step 3: Preparation of ZnS / BiVO4 Bismuth nitrate pentahydrate and ammonium metavanadate NH4VO3 were added to a mixed solvent consisting of ethylene glycol and deionized water, magnetically stirred at room temperature, and ultrasonically treated until completely dissolved; ZnS and ZnS powder was added in the molar ratio of 1 : 1, 1 :2 and 1 :3, respectively, and the magnetic stirring and ultrasonic treatment were continued; The mixed system is then transferred to a polytetrafluoroethylene-lined stainless steel reaction kettle for reaction; After the reaction is completed, the precipitate is collected by centrifugation, washed and dried; After grinding treatment, three kinds of composite materials with different molar ratios of ZnS / BiVO4 are obtained, which are marked as ZS / BV-1, ZS / BV-2 and ZS / BV-3 respectively; wherein ZS / BV-1, ZS / BV-2 and ZS / BV-3 are ZnS:BiVO4 = 1:1, ZnS:BiVO4 = 1:2 and ZnS:BiVO4 = 1:3 respectively.

2. The method according to claim 1, wherein the method is characterized by, In the step 1, the amount of anhydrous zinc acetate C4H6O4Zn added is 1.16 g, the amount of thiourea CH4N2S added is 0.48 g, and the amount of deionized water added is 35 mL.

3. The method according to claim 1, wherein the method is characterized by, In the step 1, magnetic stirring is carried out at a speed of 600 rpm for 4 hours at room temperature until complete dissolution, and then the mixed solution is transferred to a 50 mL polytetrafluoroethylene-lined stainless steel reaction kettle for reaction at 180℃ for 20 hours.

4. The method according to claim 1, wherein the method is characterized by, In the step 1, the precipitate is collected by centrifugation at 8000 rpm, washed with deionized water and anhydrous ethanol respectively for five times, and dried at 60℃ for 12 hours.

5. The method according to claim 1, wherein the method is characterized by, In the step 2 and step 3, the bismuth nitrate pentahydrate The amount of substance of the substance is 2 mmol, the amount of substance of the ammonium metavanadate NH4VO3 is 2 mmol, the added amount of ethylene glycol is 40 mL, and the added amount of deionized water is 20 mL.

6. The method according to claim 1, wherein the method is characterized by, In the step 2 and step 3, magnetic stirring is carried out at a speed of 600 rpm for 1 hour at room temperature, and ultrasonic treatment is carried out for 45 minutes until complete dissolution; The mixed solution is then transferred to a 100 mL polytetrafluoroethylene-lined stainless steel reaction kettle for reaction at 160℃ for 6 hours, and the precipitate is collected by centrifugation at 8000 rpm, washed with deionized water and anhydrous ethanol respectively for five times, and dried at 60℃ for 12 hours.

7. A method for preparing a ZnS / BiVO4 / CC electrode, characterized in that, The method comprises the following steps: a. ZnS / BiVO4 composite powder is weighed and dispersed in N-methyl-2-pyrrolidone (NMP) solvent; b. The mixed system is subjected to intermittent ultrasonic treatment to form a uniform and stable suspension; c. A piece of carbon cloth CC which has been acid-treated, washed with deionized water and dried is taken as an electrode substrate, the carbon cloth is clamped with tweezers and completely immersed in the prepared catalyst suspension for impregnation; d. After impregnation, the carbon cloth loaded with the catalyst is transferred to a forced air drying oven for drying, and a self-supported composite working electrode is obtained, which is marked as ZnS / BiVO4 / CC electrode.

8. The method for preparing ZnS / BiVO4 / CC electrode according to claim 7, characterized in that, In the step a, the adding amount of ZnS / BiVO4 composite powder is 80.0 mg, and the adding amount of N-methyl-2-pyrrolidone (NMP) solvent is 2.4 mL; In the step b, the ultrasonic is performed once every 5 minutes, and the cumulative times are 5 times; In the step c, the immersion time is kept for 30 seconds; In the step d, the drying is performed at 60 ℃ for 4 hours.

9. Application of a multifunctional ZnS / BiVO4 composite catalyst in photocatalytic degradation of dyes, synthesis of hydrogen peroxide and electrocatalytic oxygen evolution.

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