Method for hydrogen production by photocatalytic decomposition of water

Abstract

This invention relates to the field of hydrogen energy technology, specifically to a photocatalytic water splitting method for hydrogen production. It addresses the problems of harsh reaction conditions, low hydrogen production efficiency, and poor catalyst cycle stability in existing photocatalytic hydrogen production methods. Specifically, it uses water as the reaction medium, adds a catalyst and an electron sacrificial agent, and achieves hydrogen production through water splitting under visible light irradiation. The catalyst is prepared from cobalt ferrite, indium zinc sulfide, and biochar, and the electron sacrificial agent is triethanolamine. This method enhances the separation and transport of photogenerated carriers through the synergistic effect of the catalyst and electron sacrificial agent, resulting in high hydrogen production efficiency, strong stability, simple process, and controllable cost. Furthermore, hydrogen energy, as a zero-carbon energy source, can replace fossil fuels, reducing pollution and carbon emissions at the source, contributing to the dual carbon goals, and providing an efficient solution for large-scale hydrogen production, possessing both industrial application and ecological environmental value.

Description

Technical Field

[0001] This invention relates to the field of hydrogen energy technology, specifically to a method for producing hydrogen by photocatalytic water splitting. Background Technology

[0002] With the global energy crisis and environmental pollution becoming increasingly severe, hydrogen energy, as a clean, efficient, and renewable secondary energy source, has become a research hotspot in the field of new energy. Photocatalytic water splitting technology can directly convert solar energy into chemical energy, achieving efficient conversion of water into hydrogen. It has advantages such as being green and low-carbon, having a wide range of raw material sources, and mild reaction conditions, and is considered one of the most promising hydrogen production methods.

[0003] The core of photocatalytic hydrogen production technology lies in the performance of the catalytic material. An ideal photocatalytic material must possess a wide spectral response range, high efficiency in separating photogenerated carriers, excellent chemical stability, and low preparation cost. Currently, commonly used photocatalytic materials include semiconductor materials such as metal oxides, sulfides, and nitrides. However, single-component catalysts generally suffer from narrow light absorption ranges, rapid recombination of photogenerated electron-hole pairs, and low catalytic activity. Constructing heterojunctions can improve the efficiency of photogenerated carrier separation to some extent, but heterojunction nanoparticles are prone to aggregation, leading to a reduction in specific surface area and active sites, thus limiting hydrogen production efficiency. Furthermore, existing photocatalytic hydrogen production methods also suffer from harsh reaction conditions, low hydrogen production efficiency, and poor catalyst cycle stability, making it difficult to meet the needs of industrial applications. Summary of the Invention

[0004] In view of the shortcomings of the existing technology, the purpose of this invention is to provide an efficient, stable and low-cost photocatalytic water splitting method for hydrogen production.

[0005] To achieve the above objectives, the present invention provides a method for hydrogen production by photocatalytic water splitting, using water as the reaction medium, adding a catalyst and an electron sacrificial agent, and achieving hydrogen production by water splitting under visible light irradiation; the catalyst (CoFe2O4-ZnIn2S4@BC) is prepared from cobalt ferrite (CoFe2O4), zinc indium sulfide (ZnIn2S4), and biochar (BC) as raw materials, and the electron sacrificial agent is triethanolamine.

[0006] The working principle of this technical solution is as follows: photocatalytic water splitting for hydrogen production, as a technology that converts solar energy and water resources into hydrogen energy, can provide a sustainable path to alleviate fossil fuel depletion, address environmental pollution, and build a green and healthy ecological system. This technology consumes only water and light energy during the reaction process, reducing air pollutant and greenhouse gas emissions at the source. Simultaneously, the composite photocatalyst using biochar as a carrier effectively realizes the high-value resource utilization of agricultural waste, aligning with the concepts of ecological recycling and pollution and carbon reduction. Therefore, developing efficient photocatalytic water splitting materials for hydrogen production has significant strategic importance and practical value for promoting the achievement of "dual carbon" goals and building a low-carbon ecosystem where humans and nature coexist harmoniously.

[0007] The catalyst used in this technical solution uses porous biochar as a carrier, with spinel-structured cobalt ferrite nanoparticles and flake-like zinc indium sulfide nanoparticles loaded on the surface to form a pn heterojunction, thereby improving the separation efficiency of photogenerated carriers. The molar ratio of cobalt ferrite, zinc indium sulfide, and biochar is (1-4):(2-5):1, preferably 2:3:1. The cobalt ferrite is a p-type semiconductor with a band gap of 1.50 eV; the zinc indium sulfide is an n-type semiconductor with a band gap of 2.46 eV. Biochar, as a low-cost carrier derived from biomass pyrolysis, has advantages such as large specific surface area, abundant surface functional groups, and good conductivity, which can effectively inhibit nanoparticle aggregation and provide channels for photogenerated charge transport. Loading heterojunction materials onto biochar can achieve synergistic effects among the components, enhancing photocatalytic performance. In addition, triethanolamine, as an electron sacrificial agent in photocatalytic reactions, can effectively capture photogenerated holes, inhibit electron-hole pair recombination, and generate highly oxidizing active species under the activation of transition metal ions in the catalyst. This forms a synergistic effect with the photocatalytic hydrogen production reaction, further improving the efficiency of water splitting for hydrogen production.

[0008] Pure-phase ZnIn2S4 is a typical photocatalyst material, exhibiting a strong emission peak at approximately 575 nm with a peak intensity of about 1.20 au, indicating severe recombination of photogenerated carriers and a limited number of effective electrons for photocatalytic hydrogen production, resulting in low catalytic activity. After constructing a CoFe2O4-ZnIn2S4 heterojunction, the fluorescence intensity significantly decreased to 0.35 au, with a fluorescence quenching efficiency of 70%, indicating that the built-in electric field at the heterojunction interface effectively promoted the spatial separation of photogenerated charges and broadened the visible light absorption range. The fluorescence signal of this catalyst (CoFe2O4-ZnIn2S4@BC) was further quenched to near baseline levels, with a peak intensity of approximately 0.05 au, indicating a significant synergistic effect between biochar and the heterojunction. Biochar can act as a highly efficient electron acceptor and transport medium, rapidly transferring electrons separated from the heterojunction and significantly suppressing electron-hole recombination, thus maximizing the effective electron density participating in the reduction reaction from the source, which is key to achieving ultra-high hydrogen production rates.

[0009] The charge transfer resistance of the CoFe2O4-ZnIn2S4 heterojunction is higher than that of the pure-phase ZnIn2S4, indicating that although the heterojunction effectively improves the charge separation efficiency, interfacial transport still faces resistance, forming a kinetic bottleneck. This catalyst (CoFe2O4-ZnIn2S4@BC) exhibits a lower charge transfer resistance, demonstrating that biochar can construct highly efficient electron transport channels, significantly reducing the interfacial charge transfer energy barrier and enabling photogenerated electrons to rapidly migrate to the active sites on the catalyst surface to participate in the reaction. The efficient charge separation and rapid interfacial transport are synergistically coupled, forming a "highly efficient separation-rapid migration" synergistic mechanism, resulting in a significant improvement in hydrogen production performance from a kinetic perspective.

[0010] This catalyst exhibits excellent cycling stability, indicating that the introduction of biochar can effectively mitigate hole-induced photocorrosion by rapidly extracting electrons, significantly improving the catalyst's structural stability and cycle durability. This result is corroborated by the long-term operational stability of the material in actual hydrogen production tests.

[0011] This catalyst constructs a synergistic system of CoFe2O4-ZnIn2S4 heterojunction and biochar, which utilizes the heterojunction to achieve efficient charge separation and biochar to accelerate the rapid conduction and migration of separated charges, while significantly improving the photochemical stability of the material.

[0012] The aforementioned "separation-migration" synergistic mechanism systematically explains, from the perspective of microscopic charge dynamics, the fundamental reason why this catalyst has superior and stable photocatalytic hydrogen production performance.

[0013] To better implement the method of the present invention, the method further includes the following steps: Step S1: Prepare a catalyst using cobalt ferrite, indium zinc sulfide, and biochar as raw materials; Step S2: Triethanolamine is added to deionized water to prepare a 15 vol% solution. Then, the prepared catalyst is dispersed in the prepared triethanolamine solution to form a catalyst suspension with a concentration of 0.02 g / L to 0.07 g / L, thus constructing a reaction system. The mass ratio of triethanolamine to catalyst is (0.8 to 11.2):1. Step S3: Place the constructed reaction system in a photocatalytic reactor, purge with high-purity argon for 0.2 h to 0.7 h to remove dissolved oxygen, stir the reaction under visible light at 20 °C to 30 °C for 2 h to 5 h, and collect the hydrogen produced by the reaction.

[0014] To better implement the method of the present invention, further, in step S1, the specific preparation process of the catalyst is as follows: the catalyst is prepared by hydrothermal-solvothermal method, with porous biochar as the carrier, and spinel structured cobalt ferrite nanoparticles and flake-shaped zinc indium sulfide nanoparticles loaded on the surface to form a pn heterojunction, wherein the molar ratio of cobalt ferrite, zinc indium sulfide and biochar is (1-4):(2-5):1.

[0015] To better implement the method of the present invention, the specific preparation process of the catalyst further includes the following steps: Step S11: Place the biomass raw material in an inert gas and pyrolyze and carbonize it at 160℃~650℃ for 2 h~4 h. After cooling, wash and dry to obtain porous biochar. Step S12: Dissolve the iron source and cobalt source in water at a molar ratio of (1-4):1, add the biochar and citric acid complexing agent prepared in step S11, mix evenly, and then perform a hydrothermal reaction at 100℃-250℃ for 12-24 h. After washing and drying, the product is obtained as biochar loaded with cobalt ferrite. Step S13: Dissolve the indium source, zinc source, and sulfur source in an organic solvent of N,N-dimethylformamide and glycerol, wherein the molar ratio of the indium source to the zinc source is (1-4):1. Then add the biochar loaded with cobalt ferrite obtained in step S12, disperse it evenly, and react it in a solvothermal manner at 100℃-260℃ for 8-12 h. The product is washed and dried to obtain the catalyst.

[0016] To better implement the method of the present invention, in step S11, the biomass raw material used is corn straw, the pyrolysis temperature is 450℃, and the heating rate is 3℃ / min.

[0017] To better implement the method of the present invention, the iron source used in step S12 is ferric nitrate nonahydrate, the cobalt source is cobalt nitrate hexahydrate, the hydrothermal reaction temperature is 180°C, and the reaction time is 20 h.

[0018] To better implement the method of the present invention, in step S13, the zinc source is zinc nitrate hexahydrate, the indium source is indium nitrate, the sulfur source is thioacetamide, the solvothermal reaction temperature is 180°C, and the reaction time is 10 h.

[0019] To better implement the method of the present invention, in step S2, the concentration of the catalyst suspension is 0.03 g / L, and the mass ratio of triethanolamine to catalyst is 5.6:1.

[0020] To better implement the method of the present invention, in step S3, the high-purity argon purging time is 0.5 h, the reaction temperature is 25 ± 2 °C, and the stirring rate is 200 r / min to 300 r / min.

[0021] To better implement the method of the present invention, in step S3, the visible light is provided by a 300 W xenon lamp equipped with a 420 nm cutoff filter, and the surface illumination intensity of the reaction system is 34.93 W / m². 2 The reaction time is 3 hours.

[0022] Compared with the prior art, the present invention has the following advantages and beneficial effects: (1) This invention provides a method for photocatalytic hydrogen production under visible light irradiation by adding a catalyst and an electron sacrificial agent using water as the reaction medium. This method benefits from the synergistic effect of the catalyst and the electron sacrificial agent. The system exhibits excellent photocatalytic hydrogen production activity and the hydrogen production efficiency is significantly improved. (2) In the continuous multi-round photocatalytic cycle test, the hydrogen production activity of the method provided by the present invention is reduced by a very small amount. The chemical state of the elements on the surface of the material and the crystal structure of the material remain basically unchanged before and after the reaction. The metal ion leaching amount meets the environmental protection standards and there is no risk of secondary pollution. (3) The catalyst used in this invention effectively inhibits the recombination of photogenerated carriers, improves the separation efficiency of photogenerated electrons, broadens the visible light absorption range, and increases the rapid conduction and migration of separated charges through the synergistic effect of pn heterojunction and biochar support, thus making full use of solar energy resources; (4) The hydrogen production process of this invention is carried out at room temperature and pressure, the reaction conditions are mild, and no high temperature and high pressure equipment is required; the catalyst used is prepared by hydrothermal-solvothermal method, which is simple, mild and easy to scale up; (5) The present invention uses water as the reaction medium and no secondary pollutants are generated during the reaction process; the catalyst is biochar prepared from biomass waste as a carrier, which realizes the efficient resource utilization of waste and conforms to the concept of green and sustainable development. Attached Figure Description

[0023] Other features, objects, and advantages of the invention will become more apparent from the following detailed description of non-limiting embodiments with reference to the accompanying drawings: Figure 1 The present invention provides a test result diagram of the method for cyclically stable hydrogen production; Figure 2 XRD patterns of the catalyst before and after reaction are provided for the present invention. Detailed Implementation

[0024] Embodiments of the present invention are described in detail below, examples of which are shown in the accompanying drawings, wherein the same or similar reference numerals denote elements with the same or similar functions throughout. The embodiments described with reference to the accompanying drawings are illustrative and are only used to explain the present invention, and should not be construed as limiting the present invention.

[0025] To make the objectives, process conditions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the following embodiments. However, the embodiments of this invention are not limited thereto. Various substitutions and modifications made based on ordinary technical knowledge and conventional methods in the art without departing from the above-described technical concept of this invention should be included within the scope of this invention. The specific embodiments described herein are only used to explain this invention and are not intended to limit this invention.

[0026] Example 1: This embodiment provides a method for producing hydrogen through photocatalytic water splitting, the specific process of which is as follows: (1) Construction of reaction system: Take 15 mL of triethanolamine, add deionized water to make up to 100 mL, and prepare a 15 vol% triethanolamine solution. Take 3 mg of catalyst and disperse it in the prepared triethanolamine solution, stir magnetically until uniform, and form a suspension with a concentration of 0.03 g / L, which is the constructed reaction system; The catalyst preparation process is as follows: (1.1) Preparation of biochar Corn stalks were placed in a sealed crucible and pyrolyzed at 450°C for 2 h under oxygen-limited conditions in a muffle furnace at a heating rate of 3°C / min. After cooling to room temperature, the stalks were washed three times with distilled water, dried at 80°C, and then ground uniformly to obtain porous biochar.

[0027] (1.2) Preparation of biochar loaded with cobalt ferrite Weigh 50 mg Co(NO3)2•6H2O and 140 mg Fe(NO3)3•9H2O (the molar ratio of iron to cobalt is approximately 2:1) into a container, add 50 mL of deionized water, and stir vigorously until completely dissolved. Then, add 2.0 g of biochar and 100 mg of citric acid to the above solution, sonicate for 0.5 h, and continue stirring for 1 h. Transfer the resulting mixed solution to a 100 mL polytetrafluoroethylene-lined high-pressure reactor and react at 180 °C for 20 h. After the reaction is complete, allow it to cool naturally to room temperature. Wash the reaction product three times by centrifugation with deionized water and ethanol, respectively, and finally dry it at 90 °C to constant weight to obtain biochar loaded with cobalt ferrite. (1.3) Preparation of catalyst Weigh 0.6 g Zn(NO3)2•6H2O, 1.5 g In(NO3)3•4.5H2O, and thioacetamide, dissolve them in 50 mL N,N-dimethylformamide organic solvent, add 20 mL glycerol, and sonicate for 1 h. Add 0.5 g of cobalt ferrite-loaded biochar prepared in step (1.2), and sonicate again for 1 h. Transfer the solution to a polytetrafluoroethylene-lined high-pressure reactor and react at 180 °C for 10 h. After cooling to room temperature, wash three times each with deionized water and ethanol, and dry at 55 °C to obtain the catalyst, which has a pn heterojunction. (2) Deoxygenation treatment: The reaction system was placed in a photocatalytic reactor and continuously purged with high-purity argon for 0.5 h to remove dissolved oxygen from the system; (3) Photocatalytic reaction: A 300 W xenon lamp (equipped with a 420 nm cutoff filter) was used as the visible light source, the reaction temperature was controlled at 25℃, the magnetic stirring rate was 250 r / min, and the reaction was continuously irradiated for 3 h. (4) Hydrogen detection: 0.5 mL of top gas was extracted every 0.5 h using an airtight syringe, and the hydrogen production was quantitatively analyzed by a gas chromatograph equipped with a thermal conductivity detector (TCD).

[0028] The test results are shown in the table below: Table 1 Hydrogen production at different reaction times

[0029] As can be seen from Table 1, the method provided in this embodiment has high and stable hydrogen production efficiency.

[0030] The key process parameters of the method of this invention are as follows: Catalyst concentration: 0.03 g / L is the optimal concentration. Too low a concentration will result in insufficient active sites, while too high a concentration will easily produce a light-shielding effect.

[0031] Triethanolamine addition: 15 mL of triethanolamine is added to deionized water and brought to a final volume of 100 mL to form a 15 vol% solution. The mass ratio of triethanolamine to the catalyst is 5.6:1, which yields the best synergistic effect.

[0032] Illumination conditions: Visible light provided by a 300 W xenon lamp (with a 420 nm cutoff filter) ensures sufficient light intensity while matching the photoresponse range of the catalyst.

[0033] Reaction temperature: 25±2℃ is the suitable temperature. Avoid excessively high or low temperatures that may affect reaction kinetics.

[0034] Example 2: In this embodiment, to verify the hydrogen production performance of the hydrogen production method provided by the present invention, different reaction systems were set up for comparative testing.

[0035] The experiments with different reaction systems were divided into four groups. Experimental group 1 added a catalyst, an electron sacrificial agent, and light; experimental group 2 added a catalyst and light; experimental group 3 added an electron sacrificial agent and light; and experimental group 4 added a catalyst and an electron sacrificial agent. Each group conducted a systematic photocatalytic experiment under controlled conditions.

[0036] The specific method for Experiment 1 is as follows: 15 mL of triethanolamine was taken and diluted to 100 mL with deionized water to obtain a 15 vol% triethanolamine solution; 3 mg of catalyst was dispersed in the prepared triethanolamine solution and magnetically stirred until homogeneous, resulting in a suspension with a concentration of 0.03 g / L, which was then transferred to the photocatalytic reactor. The reaction system was thoroughly purged with high-purity argon to remove dissolved oxygen, ensuring the reaction proceeded in an anaerobic environment. A 300 W xenon lamp (equipped with a 420 nm cutoff filter) was used as the visible light source. The photocatalytic reaction was continued for 3 h, with gas extracted from the top of the reactor every 0.5 h. Hydrogen production was quantitatively analyzed using a gas chromatograph equipped with a thermal conductivity detector (TCD) via external standard method. Each experiment was repeated three times, and the average value was taken.

[0037] While maintaining the same core parameters as Experiment 1, such as catalyst dosage, sacrificial agent type, reaction volume, illumination conditions, purging process, and detection methods, other experimental groups adjusted the reaction system according to preset variables and simultaneously carried out photocatalytic hydrogen production experiments and quantitative analysis of hydrogen production.

[0038] The hydrogen production test results at each time point are shown in the table below.

[0039] Table 2 Hydrogen yield per unit time for each group

[0040] According to Table 2: (1) Significant differences in activity: Experimental group 1 and experimental group 2 both showed visible light photocatalytic hydrogen production activity, while experimental groups 3 and 4 did not show obvious hydrogen gas within a 3-h reaction period, indicating that their reaction systems do not have the ability to produce hydrogen through photocatalysis. (2) Optimal system confirmation: Throughout the entire reaction cycle, the unit hydrogen yield of experimental group 1 was consistently higher than that of experimental group 2. After 0.5 h of reaction, the yield of experimental group 1 (0.73 mmol / g) was approximately 1.74 times that of experimental group 2 (0.42 mmol / g); after 3 h of reaction, the cumulative yield of experimental group 1 (8.38 mmol / g) was approximately 64.3% higher than that of experimental group 2 (5.10 mmol / g). The hydrogen production method provided by this invention has significant advantages in both hydrogen production rate and cumulative yield, and its reaction system exhibits optimal hydrogen production performance. (3) Trend characteristics: The hydrogen production of both active systems continued to increase with the extension of reaction time, and no obvious plateau period was observed, indicating that the catalyst maintained stable catalytic activity within 3 h.

[0041] Example 3: In this embodiment, to verify the hydrogen production performance of the hydrogen production method of the present invention, different materials were used as catalysts under completely identical experimental conditions to conduct photocatalytic hydrogen production performance tests.

[0042] The catalyst system includes: the catalyst (CoFe2O4-ZnIn2S4@BC) prepared in this invention, biochar supported on zinc indium sulfide (ZnIn2S4@BC), zinc indium sulfide (ZnIn2S4), biochar supported on cobalt ferrite (CoFe2O4@BC), cobalt ferrite (CoFe2O4), and cobalt ferrite-zinc indium sulfide (CoFe2O4-ZnIn2S4) as the research objects.

[0043] 15 vol% triethanolamine was used as the electron sacrificial agent, with a catalyst concentration controlled at 0.03 g / L and a total solution volume of 100 mL. The reaction system was thoroughly purged with high-purity argon before illumination to establish an anaerobic environment. A 300 W xenon lamp (equipped with a 420 nm cutoff filter) was used as the visible light source. The reaction lasted for 3 h, and the gas from the top of the reactor was extracted every 0.5 h. Hydrogen production was quantitatively analyzed using a gas chromatograph equipped with a thermal conductivity detector (TCD) via the external standard method. Each experiment was repeated three times, and the average value was taken. The test results are shown in the table below: Table 3. Hydrogen yield per unit volume for different catalysts

[0044] According to Table 3: (1) Significant differences in activity: No hydrogen was detected in either the cobalt ferrite-loaded biochar or pure cobalt ferrite within the 3-hour reaction period, indicating that they had no visible light photocatalytic hydrogen production activity under the experimental conditions. The other four materials all exhibited visible light photocatalytic hydrogen production activity, and the hydrogen yield per unit area continued to increase with the extension of reaction time without significant decay; (2) The catalyst of the present invention has the best performance: at 3 h, the hydrogen production per unit of the catalyst of the present invention reaches 8.38 mmol / g. In the entire time period from 0.5 h to 3 h, its hydrogen production rate and cumulative production are significantly better than other comparative materials. (3) Synergistic effect mechanism: In the catalyst of this invention, cobalt ferrite, zinc indium sulfide and biochar form a synergistic effect at this ratio, which effectively promotes the separation and transport of photogenerated carriers and improves the efficiency of surface catalytic reaction, thereby achieving the optimal hydrogen production performance.

[0045] Example 4: In this embodiment, to verify the effect of different mass concentrations of the sacrificial agent triethanolamine on the photocatalytic hydrogen production performance of the catalyst of the present invention, performance tests were carried out under completely consistent experimental conditions.

[0046] Triethanolamine solutions of 0%, 5%, 10%, 15%, and 20 vol% were prepared, and 3 mg of the catalyst prepared in this invention was added to each solution. The mixture was magnetically stirred until homogeneous, with a catalyst concentration of 0.03 g / L. A 300 W xenon lamp (equipped with a 420 nm cutoff filter) was used as the visible light source. The reaction was carried out for 3 h, and the gas from the top of the reactor was extracted every 0.5 h. The hydrogen production was quantitatively analyzed using a gas chromatograph equipped with a thermal conductivity detector (TCD) by external standard method. Each group was repeated three times, and the average value was taken. The test results are shown in the table below.

[0047] Table 4. Hydrogen yield per unit volume of reaction systems prepared with triethanolamine solutions of different volume percentages.

[0048] According to Table 4: (1) Only a very small amount of hydrogen was produced in the 0 vol% group, proving that the electron sacrificial agent (triethanolamine) is a necessary condition for photocatalytic hydrogen production; (2) As the volume fraction of triethanolamine increased from 0 to 15 vol%, the unit hydrogen production continued to increase significantly; at 15 vol%, the cumulative production over 3 hours reached 8.38 mmol / g, which was the highest among all groups and represented the best hydrogen production performance of the catalyst of this invention. (3) The yield of the 20 vol% group (8.15 mmol / g) was slightly lower than that of the 15 vol% group, indicating that the high concentration may lead to a decrease in the consumption efficiency of photogenerated carriers due to increased viscosity or steric hindrance effect.

[0049] Example 5: In this embodiment, to verify the effect of different catalyst dosages on the photocatalytic hydrogen production performance of the catalyst of the present invention, performance tests were conducted under completely consistent experimental conditions.

[0050] A 15 vol% triethanolamine solution was prepared, and 2, 3, 4, 5, 6, and 7 mg of catalyst were weighed out and dispersed in the solution. The mixture was magnetically stirred until homogeneous, yielding suspensions with concentrations of 0.02, 0.03, 0.04, 0.05, 0.06, and 0.07 g / L, respectively. A 300 W xenon lamp (equipped with a 420 nm cutoff filter) was used as the visible light source. The reaction was continued for 3 h, and the gas from the top of the reactor was extracted every 0.5 h. The hydrogen production was quantitatively analyzed using a gas chromatograph equipped with a thermal conductivity detector (TCD) via the external standard method. Each experiment was repeated three times, and the average value was taken. The test results are shown in the table below.

[0051] Table 5. Hydrogen yield per unit volume of reaction systems prepared with different catalyst concentrations

[0052] According to Table 5: (1) As the catalyst dosage increased from 2 mg to 3 mg, the hydrogen production per unit increased significantly. At 3 mg, the cumulative production over 3 hours reached 8.38 mmol / g, which was the best hydrogen production performance among all groups. (2) After the dosage exceeds 3 mg, the unit hydrogen production gradually decreases, and the 7 mg group is only 6.50 mmol / g. Excess catalyst will produce light shading effect, reduce photon utilization, and particle agglomeration will lead to insufficient exposure of active sites.

[0053] Example 6: To verify the stability of the hydrogen production method provided by this invention, the following experiment was conducted in this embodiment: The used catalyst was recovered, washed three times with deionized water and ethanol respectively, dried at 55°C, and then the photocatalytic hydrogen production experiment was repeated under the same conditions for five consecutive cycles (3 hours per cycle, with a cumulative irradiation of 15 hours).

[0054] Test results are as follows Figure 1 As shown, the hydrogen production in the five cycles was 8.38 mmol / g, 8.25 mmol / g, 8.10 mmol / g, 7.95 mmol / g, and 7.65 mmol / g, respectively, with an activity retention rate of 91.3%, indicating that the catalyst has good cycle stability and can be reused.

[0055] To verify the long-term stability of the catalyst of this invention, X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD) were used to compare and analyze the catalyst before and after five cycles of photocatalytic hydrogen production, examining the changes in the chemical state of the catalyst surface elements and the crystal structure of the material. The results are as follows: Figure 2 As shown in Table 6, the relative contents of the main elements (Co, Fe, O, C, Zn, In, S) in the catalyst did not change significantly before and after the reaction, with very small fluctuations. The structure still contains three components: CoFe2O4, ZnIn2S4, and BC, indicating that the overall chemical composition of the material remains highly stable during the photocatalytic hydrogen production process, and there is no obvious element dissolution or crystal structure destruction.

[0056] Based on the photocatalytic cyclic hydrogen production performance test results, the catalyst not only maintained stable hydrogen production activity in multiple consecutive reactions, but also kept its surface elemental ratio essentially unchanged. This indicates that the catalyst significantly improved the separation and transport efficiency of photogenerated carriers by constructing a synergistic system of "pn heterojunction" and "conductive biochar support." Simultaneously, the cyclic effect of the Co / Fe redox pair and the electronic regulation of the support surface provided abundant and stable active sites, jointly contributing to its excellent photocatalytic hydrogen production performance. This also demonstrates that the hydrogen production method of this invention has a low hydrogen production cost.

[0057] Table 6 Comparison of elemental contents before and after reaction in XPS full spectrum.

[0058] Although embodiments of the invention have been shown and described, those skilled in the art will understand that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the claims and their equivalents.

Claims

1. A method for producing hydrogen through photocatalytic water splitting, characterized in that, Using water as the reaction medium, a catalyst and an electron sacrificial agent are added to decompose water to produce hydrogen under visible light irradiation; the catalyst is prepared from cobalt ferrite, zinc indium sulfide, and biochar, and the electron sacrificial agent is triethanolamine.

2. The method for producing hydrogen by photocatalytic water splitting according to claim 1, characterized in that, Specifically, the following steps are included: Step S1: Prepare a catalyst using cobalt ferrite, indium zinc sulfide, and biochar as raw materials; Step S2: Triethanolamine is added to deionized water to prepare a 15 vol% solution. Then, the prepared catalyst is dispersed in the prepared triethanolamine solution to form a catalyst suspension with a concentration of 0.02 g / L to 0.07 g / L, thus constructing a reaction system. The mass ratio of triethanolamine to catalyst is (0.8 to 11.2):

1. Step S3: Place the constructed reaction system in a photocatalytic reactor, purge with high-purity argon for 0.2 h to 0.7 h to remove dissolved oxygen, stir the reaction under visible light at 20 °C to 30 °C for 2 h to 5 h, and collect the hydrogen produced by the reaction.

3. A method for producing hydrogen through photocatalytic water splitting according to claim 1 or 2, characterized in that, In step S1, the specific preparation process of the catalyst is as follows: the catalyst is prepared by hydrothermal-solvothermal method, with porous biochar as the carrier, and spinel-structured cobalt ferrite nanoparticles and flake-shaped zinc indium sulfide nanoparticles loaded on the surface to form a pn heterojunction, wherein the molar ratio of cobalt ferrite, zinc indium sulfide and biochar is (1-4):(2-5):

1.

4. The method for producing hydrogen through photocatalytic water splitting according to claim 3, characterized in that, The specific preparation process of the catalyst includes the following steps: Step S11: Place the biomass raw material in an inert gas and pyrolyze and carbonize it at 160℃~650℃ for 2 h~4 h. After cooling, wash and dry to obtain porous biochar. Step S12: Dissolve the iron source and cobalt source in water at a molar ratio of (1-4):1, add the biochar and citric acid complexing agent prepared in step S11, mix evenly, and then perform a hydrothermal reaction at 100℃-250℃ for 12-24 h. After washing and drying, the product is obtained as biochar loaded with cobalt ferrite. Step S13: Dissolve the indium source, zinc source, and sulfur source in a mixed organic solvent of N,N-dimethylformamide and glycerol, wherein the molar ratio of the indium source to the zinc source is (1-4):

1. Then add the biochar loaded with cobalt ferrite obtained in step S12, disperse it evenly, and react it in a solvothermal manner at 100℃-260℃ for 8-12 h. The product is washed and dried to obtain the catalyst.

5. The method for producing hydrogen by photocatalytic water splitting according to claim 4, characterized in that, In step S11, the biomass raw material used is corn straw, the pyrolysis temperature is 450℃, and the heating rate is 3℃ / min.

6. A method for producing hydrogen through photocatalytic water splitting according to claim 4 or 5, characterized in that, The iron source used in step S12 is ferric nitrate nonahydrate, the cobalt source is cobalt nitrate hexahydrate, the hydrothermal reaction temperature is 180℃, and the reaction time is 20 h.

7. A method for producing hydrogen through photocatalytic water splitting according to claim 4 or 5, characterized in that, In step S13, the zinc source is zinc nitrate hexahydrate, the indium source is indium nitrate, the sulfur source is thioacetamide, the solvothermal reaction temperature is 180℃, and the reaction time is 10 h.

8. A method for producing hydrogen through photocatalytic water splitting according to claim 1 or 2, characterized in that, In step S2, the concentration of the catalyst suspension is 0.03 g / L, and the mass ratio of triethanolamine to catalyst is 5.6:

1.

9. A method for producing hydrogen through photocatalytic water splitting according to claim 1 or 2, characterized in that, In step S3, the high-purity argon purging time is 0.5 h, the reaction temperature is 25±2℃, and the stirring rate is 200 r / min~300 r / min.

10. A method for producing hydrogen through photocatalytic water splitting according to claim 1 or 2, characterized in that, In step S3, visible light is provided by a 300 W xenon lamp equipped with a 420 nm cutoff filter, and the surface irradiance of the reaction system is 34.93 W / m². 2 The reaction time is 3 hours.

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