A stepwise photocatalytic water splitting method for hydrogen and oxygen production

Abstract

This invention discloses a stepwise photocatalytic water splitting method for hydrogen and oxygen production, comprising: dispersing an oxidant and a photocatalyst in a mixed solvent composed of water and a first organic solvent to obtain a water oxidation oxygen production reaction system; subjecting the system to visible light irradiation, causing water to undergo an oxidation reaction to produce oxygen; simultaneously, using water as a proton source, reducing the oxidant to a hydrogen-rich reductant; separating and recovering the reductant and photocatalyst, and dispersing them in a second organic solvent to obtain a hydrogen production reaction system; subjecting the system to visible light irradiation, causing the hydrogen-rich reductant to release hydrogen to produce hydrogen gas; and simultaneously, oxidizing the reductant back to an oxidant. This invention constructs a stable, regenerable, and easily separable and recyclable reversible redox cycle of an organic redox medium, coupling the water oxidation oxygen production reaction and the proton reduction hydrogen production reaction derived entirely from water, allowing the oxygen and hydrogen production reactions to proceed stepwise at different reaction stages, thereby achieving spatiotemporal decoupling and high quantum efficiency stepwise execution of the oxygen and hydrogen production processes.

Description

Technical Field

[0001] This invention belongs to the field of photocatalytic water splitting for hydrogen and oxygen production, specifically relating to a stepwise photocatalytic water splitting method for hydrogen and oxygen production. Background Technology

[0002] Hydrogen, as a clean energy source and an important chemical, is widely used in energy storage, petrochemicals, and fine chemicals. Currently, the main sources of hydrogen are gray hydrogen processes such as steam reforming and water-gas conversion, which consume large amounts of heat energy and generate significant carbon emissions. Water electrolysis is one of the more mature green hydrogen production technologies and has been applied in systems such as alkaline water electrolysis and proton exchange membrane water electrolysis. However, water electrolysis relies on external electrical energy input, resulting in high overall energy consumption. Therefore, further development of low-energy-consumption and high-efficiency hydrogen production technologies is still needed.

[0003] Photocatalysis enables the production of hydrogen and oxygen from water using sunlight under mild conditions, representing a low-carbon, clean, and energy-efficient technology. However, photocatalytic water splitting systems still face safety risks, including low reaction efficiency (the energy conversion efficiency of solar-powered hydrogen production is typically less than 1%) and the presence of a mixed gas of hydrogen and oxygen. Furthermore, the generated hydrogen and oxygen may undergo a reverse reaction on the catalyst surface to regenerate water, further impacting system efficiency. To address this, current research often employs sacrificial agents such as alcohols or amines as electron donors to consume photogenerated holes, promoting the participation of photogenerated electrons in the proton reduction reaction to produce hydrogen. However, these sacrificial agents are irreversibly consumed through oxidation during the reaction, making recycling impossible and limiting the system's sustainability and practical application value. Moreover, this system cannot achieve the oxygen production from water oxidation.

[0004] Currently, related studies have also achieved spatial separation of water oxidation and reduction reactions. This is achieved by introducing redox pairs (such as I3) into the system. - / I - Fe 3+ / Fe 2+ Electron transfer (e.g., oxidation-reduction) is a commonly used method. However, this method faces the following challenges: First, there is a reaction equilibrium between redox pairs, which may trigger side reactions and compete with the water splitting reaction; second, redox pairs have light absorption and scattering effects, leading to a decrease in the light absorption rate of the photocatalyst; in addition, special photocatalysts and membranes are required to match the redox pairs, resulting in additional catalyst synthesis costs, operating costs, and concerns about the long-term stability of the reaction system; finally, the two half-reactions of water oxidation and proton reduction based on redox pairs must be carried out simultaneously in a small space, making it impossible to achieve spatiotemporal separation of the two half-reactions, which is not conducive to the flexible production and use of hydrogen and oxygen. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of the prior art and provide a stepwise photocatalytic water splitting method for hydrogen and oxygen production. By constructing a reversible redox cycle of a stable, regenerable, and easily separable and recyclable organic redox medium, the oxygen production reaction of water oxidation and the hydrogen production reaction of proton reduction derived entirely from water are coupled separately, so that the oxygen production reaction and the hydrogen production reaction are carried out stepwise at different reaction stages, thereby achieving spatiotemporal decoupling of the oxygen production and hydrogen production processes and high quantum efficiency stepwise execution.

[0006] This invention provides the following technical solution:

[0007] A stepwise photocatalytic water splitting method for hydrogen and oxygen production includes the following steps:

[0008] An oxidant and a photocatalyst are dispersed in a mixed solvent consisting of water and a first organic solvent to obtain a water oxidation oxygen production reaction system.

[0009] Under an inert atmosphere, the water oxidation oxygen production reaction system is irradiated with visible light, and the water undergoes an oxidation reaction to produce oxygen. At the same time, water is used as a proton source to reduce the oxidant to a hydrogen-rich reducing agent, and the reducing agent and photocatalyst are separated and recovered.

[0010] The reducing agent and photocatalyst obtained from the separation and recovery are dispersed in a second organic solvent to obtain a hydrogen production reaction system;

[0011] Under an inert atmosphere, the hydrogen production reaction system is irradiated with visible light, causing the hydrogen-rich reducing agent to release hydrogen to produce hydrogen gas, while the reducing agent is oxidized into an oxidizing agent.

[0012] The reducing agent and oxidizing agent can undergo a reversible redox reaction under photocatalytic conditions.

[0013] Furthermore, the oxidant includes one or more of quinone compounds, quinoline compounds, indole compounds, disulfide compounds, aldehyde compounds, and ketone compounds.

[0014] In the above technical solution, the selected oxidant has the properties of being stable, renewable, and easy to separate and recover. It can also generate corresponding stable, renewable, and easy-to-separate and recoverable reducing agents through reduction reactions, such as hydroquinone compounds, 1,2,3,4-tetrahydroquinoline compounds, indoline compounds, thiophenol compounds, thiols, and alcohols.

[0015] Furthermore, the photocatalyst includes one or more of the following: metal oxides, metal sulfides, supported metal oxides, supported metal sulfides, and graphitic carbon nitride materials.

[0016] Furthermore, the concentration of the oxidant in the water oxidation oxygen production reaction system is 0.001~10 mol / L;

[0017] And / or, the concentration of the reducing agent in the hydrogen production reaction system is 0.001~10 mol / L.

[0018] In the above technical solution, by controlling the oxidant and reductant within a suitable range, it is beneficial to balance the reaction efficiency, light transmittance and mass transfer stability of the system. When the concentration of reductant and oxidant is too low, the number of substrate molecules that can participate in the reaction in the system is insufficient and the effective collision probability of intermediates is reduced, resulting in a decrease in reaction rate and product formation efficiency. When the concentration is too high, the viscosity of the system and light absorption are enhanced, and the active sites on the catalyst surface are covered by excessive substrate, which is not conducive to long-term high-efficiency and stable operation.

[0019] Furthermore, in preparing the water oxidation oxygen production reaction system, the mass ratio of oxidant, photocatalyst and water is 1:(0.01~100):(0.01~1800);

[0020] And / or, when preparing the hydrogen production reaction system, the mass ratio of reducing agent to photocatalyst is 1: (0.01~100).

[0021] In the above technical solution, by controlling the mass ratio of raw materials, on the one hand, it can ensure that the appropriate water content provides a sufficient source of protons and oxygen, and helps to use a small amount of organic solvent, thereby reducing costs and pollution; on the other hand, appropriate amounts of oxidant / reductant and photocatalyst are conducive to the effective conversion of substrates and the oxygen / hydrogen production reaction, so that the system can achieve a good balance in reaction efficiency, stability and mass transfer performance.

[0022] Furthermore, the water is H2O, D2O, or H2. 18 One of O.

[0023] In the above technical solution, deuterium water (D2O) or heavy oxygen water (H2O) is used. 18 O) can be used to synthesize high-purity deuterium and heavy oxygen. 18 O2).

[0024] Furthermore, when preparing the water oxidation oxygen production reaction system, an acidic or alkaline regulator is used to adjust the pH.

[0025] The acid regulator includes one or more of hydrochloric acid, sulfuric acid, nitric acid, phosphoric acid, and acetic acid;

[0026] The alkalinity regulator includes one or more of sodium hydroxide, potassium hydroxide, sodium carbonate, potassium carbonate, cesium carbonate, and sodium bicarbonate.

[0027] The water oxidation oxygen production reaction system can achieve photo-induced oxygen production under both acidic and alkaline conditions. The preferred pH range is 7-14. By controlling the pH value of the water oxidation oxygen production reaction system, the reaction system can achieve both high substrate conversion rate and catalyst stability. If the pH is too low, the overly acidic conditions may lead to problems such as photocorrosion of the catalyst, decreased stability, increased electron-hole recombination, and slower reaction rate.

[0028] Furthermore, the first organic solvent and the second organic solvent are each independently selected from one or more of acetonitrile, ethyl acetate, tetrahydrofuran, dioxane, cyclohexane, N,N-dimethylformamide, N,N-dimethylacetamide, and dimethyl sulfoxide.

[0029] Furthermore, the visible light irradiation uses one or more of the following: a xenon lamp, an LED, a halogen lamp, or a mercury lamp with a power of 0.01 to 100 W.

[0030] And / or, the reaction time under visible light irradiation is 0.5 to 24 hours.

[0031] Furthermore, the inert atmosphere may be composed of one or more of He, Ar, and N2.

[0032] Compared with the prior art, the beneficial effects of the present invention are:

[0033] (1) In this invention, when the water oxidation oxygen production reaction system is irradiated with visible light, the water undergoes an oxidation reaction to produce oxygen. At the same time, water is used as a proton source to reduce the oxidant to a hydrogen-rich reducing agent. When the hydrogen production reaction system is irradiated with visible light, the hydrogen-rich reducing agent releases hydrogen to produce hydrogen. In the process of oxygen production and hydrogen production, water is used as the only oxygen source and hydrogen source. The generated oxygen and hydrogen are both derived from the transformation process of water molecules. There is no need to introduce additional sacrificial agents or add hydrogen- or oxygen-containing reactants. This realizes the true process of water decomposition to produce hydrogen and oxygen. The raw materials are widely available and the cost is low.

[0034] (2) In the present invention, during the oxygen and hydrogen production process, the oxidant and the reductant can cycle between the oxidized and reduced states under photocatalytic conditions, and participate in the reaction only as electron and proton transfer carriers. They have no net consumption, are stable, recyclable and easy to separate and recover, thereby improving the separation and utilization efficiency of photogenerated carriers, significantly enhancing the reaction rate and reducing the operating cost of the reaction system.

[0035] (3) This invention introduces reversible oxidants and reductants. By constructing a reversible redox cycle of a stable, regenerable and easily separable organic redox medium, the oxygen production reaction of water oxidation and the hydrogen production reaction of proton reduction derived entirely from water are coupled respectively, thereby realizing the spatiotemporal decoupling of the oxygen production and hydrogen production processes and the stepwise execution with high quantum efficiency. Among them, when the oxygen production reaction is carried out in an alkaline aqueous environment, photogenerated holes preferentially participate in the H2O oxidation reaction to generate O2, while the reaction of alcohol dehydrogenation to generate aldehydes, ketones and hydrogen is inhibited both thermodynamically and kinetically. At the same time, different organic solvents can further affect the reverse reaction activity of alcohol dehydrogenation by controlling the polarity of the system, interfacial mass transfer and catalyst surface adsorption behavior, etc., avoiding problems such as hydrogen-oxygen mixing, severe reverse reaction and difficulty in gas separation in the system, and improving the safety of the system reaction and the purity of the product.

[0036] (4) The stepwise high-efficiency photocatalytic water splitting method for producing hydrogen and oxygen provided by the present invention can recycle the oxidant, catalyst, organic solvent, etc., which is low in cost and has the advantages of high quantum efficiency, safety and long-term stability. It is not limited to laboratory production, but is also suitable for large-scale industrial applications. Attached Figure Description

[0037] Figure 1 This is a schematic diagram of the stepwise photocatalytic water splitting method for hydrogen and oxygen production in this embodiment of the invention.

[0038] Figure 2 This is a diagram showing the catalyst cycle performance in Example 1 of the present invention;

[0039] Figure 3 This is a performance diagram of the stepwise photocatalytic water splitting reaction for hydrogen production in Example 21 of this invention;

[0040] Figure 4 This is a schematic diagram of the stepwise photocatalytic water splitting experimental scale-up device in Embodiment 21 of the present invention. Detailed Implementation

[0041] The present invention will be further described below with reference to the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solution of the present invention, and should not be used to limit the scope of protection of the present invention.

[0042] In the description of this invention, it should be understood that the terms "first," "second," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. In the description of this invention, unless otherwise stated, "multiple" means two or more.

[0043] Example 1

[0044] like Figure 1 As shown in the figure, this embodiment provides a stepwise photocatalytic water splitting method for hydrogen and oxygen production, the steps of which are as follows:

[0045] (1) 32 mg benzaldehyde and 50 mg ZnIn2S4 photocatalyst were dispersed in 2 ml of a mixture of dioxane and water (the volume ratio of dioxane to water was 1:4), and the pH was adjusted to 12 with sodium hydroxide as a pH adjuster to obtain a water oxidation oxygen production reaction system with a benzaldehyde concentration of 0.15 mol / L.

[0046] (2) The reaction was stirred for 3 h under N2 atmosphere and visible light irradiation, and the oxygen produced by the oxidation of water was collected, with a rate of 2.0 mmol·g. -1 ·h -1 Simultaneously, using water as a proton source, benzaldehyde undergoes a reduction reaction to produce benzyl alcohol, and benzyl alcohol and photocatalyst are separated and recovered; according to HPLC analysis, the yield of benzyl alcohol is 99% and the quantum efficiency is 45.1%.

[0047] (3) The benzyl alcohol and 20 mg ZnIn2S4 photocatalyst obtained in step (2) are dispersed in ethyl acetate to obtain a hydrogen production reaction system.

[0048] (4) The reaction was stirred for 3 h under N2 atmosphere and visible light irradiation. The hydrogen gas produced by the dehydrogenation reaction of benzyl alcohol was collected, and the rate reached 5.0 mmol·g. -1 ·h -1 Meanwhile, benzyl alcohol is oxidized to benzaldehyde; HPLC analysis showed that the benzaldehyde yield was 99% and the quantum efficiency reached 45.1%.

[0049] (5) Repeat steps (1) to (4) to achieve continuous photocatalytic water splitting for hydrogen and oxygen production.

[0050] Figure 2 The figure shows the cycle performance test results of the catalyst in this embodiment. As can be seen from the figure, after four consecutive cycles, no significant performance degradation of the catalyst's catalytic activity was observed, indicating that the catalyst has excellent cycle stability.

[0051] Example 2

[0052] This embodiment provides a stepwise photocatalytic water splitting method for hydrogen and oxygen production, the steps of which are as follows:

[0053] (1) 11 mg benzaldehyde and 10 mg ZnIn2S4 catalyst were dispersed in 2 ml of a mixture of dioxane and water (the volume ratio of dioxane to water was 1:9), and the pH was adjusted to 10 with potassium hydroxide as a pH adjuster to obtain a water oxidation oxygen production reaction system with a benzaldehyde concentration of 0.05 mol / L.

[0054] (2) The reaction was stirred for 3 h under N2 atmosphere and visible light irradiation. The oxygen produced by the oxidation of water was collected, and the rate reached 3.3 mmol·g. -1 ·h -1 Simultaneously, using water as a proton source, benzaldehyde undergoes a reduction reaction to produce benzyl alcohol, and benzyl alcohol and photocatalyst are separated and recovered; according to HPLC analysis, the yield of benzyl alcohol is 99%, and the quantum efficiency reaches 15.0%.

[0055] (3) The benzyl alcohol and 10 mg ZnIn2S4 photocatalyst obtained in step (2) are dispersed in acetonitrile to obtain a hydrogen production reaction system.

[0056] (4) The reaction was stirred for 1 h under N2 atmosphere and visible light irradiation. The hydrogen gas produced by the dehydrogenation reaction of benzyl alcohol was collected, and the rate reached 10.0 mmol·g. -1 ·h -1 Meanwhile, benzyl alcohol is oxidized to benzaldehyde; HPLC analysis showed that the benzaldehyde yield was 99% and the quantum efficiency reached 45.1%.

[0057] (5) Repeat steps (1) to (4) to achieve continuous photocatalytic water splitting for hydrogen and oxygen production.

[0058] Example 3

[0059] This embodiment provides a stepwise photocatalytic water splitting method for hydrogen and oxygen production, the steps of which are as follows:

[0060] (1) 212 mg benzaldehyde and 200 mg ZnIn2S4 catalyst were dispersed in 2 ml of a mixture of dioxane and water (the volume ratio of dioxane and water was 1:1), and the pH was adjusted to 14 with sodium hydroxide as a pH adjuster to obtain a water oxidation oxygen production reaction system with a benzaldehyde concentration of 1 mol / L.

[0061] (2) The reaction was stirred for 12 h under N2 atmosphere and visible light irradiation, and the oxygen produced by the oxidation of water was collected at a rate of 0.8 mmol·g. -1 ·h -1 Simultaneously, using water as a proton source, benzaldehyde undergoes a reduction reaction to produce benzyl alcohol, and benzyl alcohol and photocatalyst are separated and recovered; HPLC analysis shows that the benzyl alcohol yield is 99% and the quantum efficiency reaches 75.2%;

[0062] (3) The benzyl alcohol obtained in step (2) and 100 mg of ZnIn2S4 photocatalyst are dispersed in ethyl acetate to obtain a hydrogen production reaction system.

[0063] (4) The reaction was stirred for 12 h under N2 atmosphere and visible light irradiation. The hydrogen gas produced by the dehydrogenation reaction of benzyl alcohol was collected, and the rate reached 1.7 mmol·g. -1 ·h-1 Meanwhile, benzyl alcohol is oxidized to benzaldehyde; HPLC analysis showed that the benzaldehyde yield was 99%, with a quantum efficiency of 75.2%.

[0064] (5) Repeat steps (1) to (4) to achieve continuous photocatalytic water splitting for hydrogen and oxygen production.

[0065] Example 4

[0066] This embodiment provides a stepwise photocatalytic water splitting method for hydrogen and oxygen production, which is basically the same as that in Example 1, except that: in step (1), the solvent used is a mixture of dioxane and deuterated water; in step (2), after 4 h of reaction, HPLC analysis showed that the yield of deuterated benzyl alcohol was 99%, and the oxygen generation rate reached 1.5 mmol·g. -1 ·h -1 The quantum efficiency was 33.8%; in step (4), the reaction conditions remained unchanged, and after 3.5 h of reaction, the benzaldehyde yield was 99%, and the deuterium generation rate reached 4.2 mmol·g. -1 ·h -1 The quantum efficiency reaches 38.7%.

[0067] Example 5

[0068] This embodiment provides a stepwise photocatalytic water splitting method for hydrogen and oxygen production, which is basically the same as that in Example 1, except that: in step (1), the solvent used is a mixture of dioxane and deoxygenated water; in step (2), after 4 hours of reaction, HPLC analysis showed that the yield of benzyl alcohol was 99%. 18 The O2 generation rate reached 1.5 mmol·g -1 ·h -1 The quantum efficiency was 33.8%; in step (4), the reaction conditions remained unchanged, the benzaldehyde yield was 99%, and the hydrogen production rate reached 5.0 mmol·g. -1 ·h -1 The quantum efficiency reaches 45.1%.

[0069] Example 6

[0070] This embodiment provides a stepwise photocatalytic water splitting method for hydrogen and oxygen production, which is basically the same as that in Example 1, except that: in step (1), the pH adjuster is hydrochloric acid, and the pH is adjusted to 4; in step (2), HPLC analysis shows that the yield of benzyl alcohol is 62%, and the oxygen generation rate reaches 1.2 mmol·g -1 ·h -1 The quantum efficiency was 27.9%; in step (4), the reaction conditions remained unchanged, the benzaldehyde yield was 99%, and the hydrogen production rate reached 5.0 mmol·g. -1 ·h -1 The quantum efficiency reaches 27.7%.

[0071] Compared to Example 1, Example 6 only changed the acid-base conditions of the reaction system, changing it from alkaline to acidic, while keeping all other reaction parameters the same. However, the yield of the target product decreased from 99% to 62%, indicating that the water oxidation oxygen production reaction system can achieve photo-induced oxygen production under both acidic and alkaline conditions, but the reaction system has a higher substrate conversion rate under alkaline conditions.

[0072] Example 7

[0073] This embodiment provides a stepwise photocatalytic water splitting method for hydrogen and oxygen production, which is basically the same as that in Example 1, except that: in step (1), the catalyst is 50 mg CdSe; in step (2), HPLC analysis shows that the yield of benzyl alcohol is 72% and the oxygen generation rate reaches 1.4 mmol·g -1 ·h -1 The quantum efficiency was 32.4%; in step (3), the catalyst was 20 mg CdS; in step (4), the benzaldehyde yield was 89%, and the hydrogen generation rate reached 3.2 mmol·g. -1 ·h -1 The quantum efficiency reaches 28.9%.

[0074] Example 8

[0075] This embodiment provides a stepwise photocatalytic water splitting method for hydrogen and oxygen production, which is basically the same as that in Example 1, except that: in step (1), the catalyst is 50 mg Co-ZIS catalyst; in step (2), HPLC analysis shows that the yield of benzyl alcohol is 99% and the oxygen generation rate reaches 2.0 mmol·g -1 ·h -1 The quantum efficiency was 45.1%; in step (3), the catalyst was 20 mg Pt-ZIS catalyst; in step (4), the benzaldehyde yield was 99%, and the hydrogen generation rate reached 5.0 mmol·g. -1 ·h -1 The quantum efficiency reaches 45.1%.

[0076] Example 9

[0077] This embodiment provides a stepwise photocatalytic water splitting method for hydrogen and oxygen production, which is basically the same as that in Example 1, except that: in step (1), the catalyst is 50 mg of graphitic carbon nitride catalyst; in step (2), HPLC analysis shows that the yield of benzyl alcohol is 64%, and the oxygen generation rate reaches 1.3 mmol·g -1 ·h -1The quantum efficiency was 28.8%; in step (3), the catalyst was 20 mg CeO2 catalyst; in step (4), the benzaldehyde yield was 82%, and the hydrogen generation rate reached 2.6 mmol·g. -1 ·h -1 The quantum efficiency reaches 23.7%.

[0078] Example 10

[0079] This embodiment provides a stepwise photocatalytic water splitting method for hydrogen and oxygen production, which is basically the same as that in Example 1, except that: in step (1), the oxidant is 0.15 mol / L p-methylbenzaldehyde; in step (2), HPLC analysis shows that the yield of p-methylbenzaldehyde is 99%, and the oxygen generation rate reaches 2.0 mmol·g. -1 ·h -1 The quantum efficiency was 45.1%; in step (4), the yield of p-methylbenzaldehyde was 99%, and the hydrogen generation rate reached 5.0 mmol·g. -1 ·h -1 The quantum efficiency is 45.1%.

[0080] Example 11

[0081] This embodiment provides a stepwise photocatalytic water splitting method for hydrogen and oxygen production, which is basically the same as that in Example 1, except that: in step (1), the oxidant is 0.15 mol / L p-trifluoromethylbenzaldehyde; in step (2), HPLC analysis shows that the yield of p-trifluoromethylbenzaldehyde is 83%, and the oxygen generation rate reaches 1.7 mmol·g. -1 ·h -1 The quantum efficiency was 26.6%; in step (4), the reaction conditions remained unchanged, the yield of trifluoromethylbenzaldehyde was 99%, and the hydrogen production rate reached 4.1 mmol·g. -1 ·h -1 The quantum efficiency reaches 37.0%.

[0082] Example 12

[0083] This embodiment provides a stepwise photocatalytic water splitting method for hydrogen and oxygen production, which is basically the same as that in Example 1, except that: in step (1), the oxidant is 0.15 mol / L p-toluene disulfide; in step (2), HPLC analysis shows that the yield of p-toluene thiophenol is 99%, and the oxygen generation rate reaches 2.0 mmol·g. -1 ·h -1 The quantum efficiency was 45.1%; in step (4), the yield of p-toluene disulfide was 99%, and the hydrogen production rate reached 5.0 mmol·g. -1 ·h -1 The quantum efficiency is 45.1%.

[0084] Example 13

[0085] This embodiment provides a stepwise photocatalytic water splitting method for hydrogen and oxygen production, which is basically the same as that in Example 1, except that: in step (1), the oxidant is 0.15 mol / L 2-naphthaldehyde; in step (2), HPLC analysis shows that the yield of 2-naphthaldehyde is 88%, and the oxygen generation rate reaches 1.8 mmol·g. -1 ·h -1 The quantum efficiency was 40.0%; in step (4), the yield of 2-naphthaldehyde was 99%, and the hydrogen generation rate reached 4.4 mmol·g. -1 ·h -1 The quantum efficiency is 39.7%.

[0086] Example 14

[0087] This embodiment provides a stepwise photocatalytic water splitting method for hydrogen and oxygen production, which is basically the same as that in Example 1, except that: in step (1), the oxidant is 0.15 mol / L p-methoxybenzaldehyde; in step (2), HPLC analysis shows that the yield of p-methoxybenzaldehyde is 99%, and the oxygen generation rate reaches 2.0 mmol·g. -1 ·h -1 The quantum efficiency was 45.1%; in step (4), the yield of p-methoxybenzaldehyde was 97%, and the hydrogen generation rate reached 4.85 mmol·g. -1 ·h -1 The quantum efficiency is 43.7%.

[0088] Example 15

[0089] This embodiment provides a stepwise photocatalytic water splitting method for hydrogen and oxygen production, which is basically the same as that in Example 1, except that: in step (1), the oxidant is 0.15 mol / L quinoline; in step (2), HPLC analysis shows that the yield of tetrahydroquinoline is 72%, and the oxygen generation rate reaches 1.4 mmol·g. -1 ·h -1 The quantum efficiency was 32.4%; in step (4), the quinoline yield was 87%, and the hydrogen production rate reached 3.1 mmol·g. -1 ·h -1 The quantum efficiency reaches 28.2%.

[0090] Example 16

[0091] This embodiment provides a stepwise photocatalytic water splitting method for hydrogen and oxygen production, which is basically the same as that in Example 1, except that: in step (1), the oxidant is 0.15 mol / L p-fluorobenzaldehyde; in step (2), HPLC analysis shows that the yield of p-fluorobenzaldehyde is 88%, and the oxygen generation rate reaches 1.8 mmol·g. -1 ·h -1 The quantum efficiency was 40.0%; in step (4), the yield of p-fluorobenzaldehyde was 87%, and the hydrogen generation rate reached 3.8 mmol·g. -1 ·h -1 The quantum efficiency reaches 34.5%.

[0092] Example 17

[0093] This embodiment provides a stepwise photocatalytic water splitting method for hydrogen and oxygen production, which is basically the same as that in Example 1, except that: in step (1), the oxidant is 0.15 mol / L cyclohexanedione; in step (2), HPLC analysis shows that the cyclohexanediol yield is 86% and the oxygen generation rate reaches 1.7 mmol·g. -1 ·h -1 The quantum efficiency was 38.8%; in step (4), the yield of cyclohexanedione was 99%, and the hydrogen generation rate reached 4.3 mmol·g. -1 ·h -1 The quantum efficiency is 38.8%.

[0094] Example 18

[0095] This embodiment provides a stepwise photocatalytic water splitting method for hydrogen and oxygen production, which is basically the same as that in Example 1, except that: in step (1), the oxidant is 0.15 mol / L benzophenone; in step (2), HPLC analysis shows that the yield of benzyl alcohol is 84%, and the oxygen generation rate reaches 1.7 mmol·g. -1 ·h -1 The quantum efficiency was 37.8%; in step (4), the yield of benzophenone was 92%, and the hydrogen production rate reached 3.7 mmol·g. -1 ·h -1 The quantum efficiency is 34.8%.

[0096] Example 19

[0097] This embodiment provides a stepwise photocatalytic water splitting method for hydrogen and oxygen production, and verifies it using a scale-up device.

[0098] (1) Preparation of catalyst film: Weigh 200 mg ZnIn2S4, add 200 μL Nafion solution, and disperse in 2 mL ethanol. After ultrasonic treatment, obtain a uniformly dispersed catalyst suspension. Then, uniformly coat the obtained suspension onto the surface of a glass substrate and dry it at room temperature to obtain the catalyst film.

[0099] (2) Dissolve 1.6 g of benzaldehyde in a mixture of 50 mL of dioxane and aqueous solution (the volume ratio of dioxane to water is 1:9), adjust the pH to 12 with sodium hydroxide as a pH adjuster, and obtain a reaction solution with a benzaldehyde concentration of 0.3 mol / L. Place the catalyst film and reaction solution from step (1) in a plate reaction apparatus.

[0100] (3) Under an inert atmosphere and visible light irradiation, the reaction was carried out for 5 h. HPLC analysis showed that the yield of benzyl alcohol was 99%, and oxygen was also detected to be generated at a rate of 15.0 mmol·g. -1 ·h -1 The quantum efficiency is 18.0%.

[0101] (4) The benzyl alcohol recovered from step (3) was dissolved in 50 mL of ethyl acetate and subjected to a photocatalytic reaction for 4.5 h under the same reaction conditions. HPLC analysis showed that the yield of benzaldehyde was 99%, and hydrogen gas was generated at a rate of 16.7 mmol·g. -1 ·h -1 The quantum efficiency is 20.0%.

[0102] Example 20

[0103] This embodiment provides a stepwise photocatalytic water splitting method for hydrogen and oxygen production, and verifies it using a scale-up device.

[0104] (1) Preparation of catalyst membrane: Weigh 200 mg ZnIn2S4, add 200 μL Nafion solution, and disperse in 2 mL ethanol. After ultrasonic treatment, obtain a uniformly dispersed catalyst suspension. Then, uniformly coat the obtained suspension onto aluminum foil and dry it in an oven to obtain the catalyst membrane. The obtained catalyst membrane is wound onto 5 glass rods, and the 5 glass rods are connected and assembled in a quartz tube reactor to construct a scale-up reaction device.

[0105] (2) Dissolve 1.6 g of benzaldehyde in a mixture of 50 mL of dioxane and water (the volume ratio of dioxane to water is 1:9), adjust the pH to 12 with sodium hydroxide as a pH adjuster, and form a reaction solution with a benzaldehyde concentration of 0.3 mol / L. Then, transfer the reaction solution to the quartz tube reactor in step (1) to maintain the flow state.

[0106] (3) Under an inert atmosphere and visible light irradiation, the reaction was carried out for 9 h. HPLC analysis showed that the yield of benzyl alcohol was 99%, and oxygen was also detected to be generated at a rate of 8.3 mmol·g. -1 ·h -1 The quantum efficiency is 17.2%.

[0107] (4) The benzyl alcohol recovered from step (3) was dissolved in 50 mL of ethyl acetate and subjected to photocatalytic reaction for 8 h under the same reaction conditions. HPLC analysis showed that the yield of benzaldehyde was 99%, and hydrogen gas was generated at a rate of 9.4 mmol·g. -1 ·h -1 The quantum efficiency is 19.4%.

[0108] Example 21

[0109] This embodiment provides a stepwise photocatalytic water splitting method for hydrogen and oxygen production, and verifies it using a batch reactor scale-up apparatus.

[0110] Weigh 200 mg of ZnIn2S4 photocatalyst and disperse it in a mixture of 80 mL of dioxane and water containing 4.2 g benzaldehyde (the volume ratio of dioxane to water is 1:9). Adjust the pH to 12 using sodium hydroxide as a pH adjuster to form a large-volume suspension reaction system with a benzaldehyde concentration of 0.5 mol / L.

[0111] Under an inert atmosphere and visible light irradiation, the reaction was stirred for 14 h. HPLC analysis showed that the yield of benzyl alcohol was 99%, and oxygen was also detected, with a formation rate of 14.3 mmol·g⁻¹. -1 ·h -1 The quantum efficiency is 23.2%.

[0112] The benzyl alcohol recovered from the above reaction was dissolved in 80 mL of ethyl acetate, and a photocatalytic reaction was carried out under the same reaction conditions for 12.5 h. HPLC analysis showed that the yield of benzaldehyde was 99%, and hydrogen gas was produced simultaneously at a rate of 8.0 mmol·g⁻¹. -1 ·h -1 The quantum efficiency is 25.8%.

[0113] Figure 3 This is a performance diagram of the stepwise photocatalytic water splitting reaction for hydrogen production in this embodiment. From... Figure 3 It can be seen that after 5 hours of reaction, the system produced a total of about 350 mL of hydrogen, with an apparent quantum efficiency of 25%. The hydrogen production curve showed a basically linear growth trend, indicating that the catalytic system maintained a relatively stable and high hydrogen production rate during the long reaction process. This shows that the system of the present invention not only has good laboratory-scale performance, but also has certain potential for scale-up applications.

[0114] Figure 4 This is a schematic diagram of the scaled-up stepwise photocatalytic water splitting experimental setup for this embodiment. The setup mainly includes a light source system, a circulating reaction system, a gas collection system, and a reactor body, used to achieve continuous photocatalytic water splitting under large-volume conditions.

[0115] Comparative Example 1

[0116] This comparative example is essentially the same as Example 1, except that no benzaldehyde / benzyl alcohol redox medium was added, and photocatalytic water dissociation was performed directly, with almost no hydrogen or oxygen produced. This demonstrates that without a stable, regenerable, and easily separable organic redox pair, the catalyst cannot achieve efficient complete water splitting.

[0117] Comparative Example 2

[0118] This comparative example is basically the same as Example 1, except that: a classic sacrificial agent system is used, in which 10 mg of ZnIn2S4 catalyst is dispersed in an aqueous solution containing 10 vol% triethanolamine to carry out photocatalytic reaction. The initial hydrogen production rate is high, but as the reaction proceeds, the triethanolamine is continuously consumed and cannot be regenerated, and the reaction rate decreases by more than 70% within 3 hours.

[0119] Comparative Example 3

[0120] This comparative example is basically the same as Example 1, except that the organic solvent used in step (1) is replaced with ethyl acetate instead of dioxane, and the ethyl acetate used in step (3) is replaced with dioxane. All other experimental conditions are the same as in Example 1. The photocatalytic water splitting reaction was carried out, and it was found by HPLC that the yield of benzyl alcohol was 15% and the oxygen generation rate reached 0.3 mmol·g. -1 ·h -1 The quantum efficiency reached 6.8%; in step (4), the yield of benzophenone was 33%, and the hydrogen production rate reached 1.65 mmol·g. -1 ·h -1 The quantum efficiency reaches 14.9%.

[0121] Compared with Example 1, this comparative example only interchanged the organic solvents in steps (1) and (3), while keeping the other reaction conditions the same. However, the yield of benzyl alcohol decreased from 99% to 15%, and the yield of benzophenone decreased from 99% to 33%. The results show that the solvent environment in different steps has a significant impact on the reaction process. The solvent combination used in Example 1 can more effectively promote substrate conversion and intermediate stability, thereby significantly improving the yield of the target product and preventing the reverse reaction from occurring. This indicates that the selection of the solvent system plays a crucial role in the present invention.

[0122] As can be seen from the above examples and comparative examples, the stable, renewable, and easily separable organic redox couple used in this invention is the core medium driving the entire water splitting process; without it, the reaction cannot proceed effectively. Optimizing the reaction system for each of the two half-reactions—oxygen production and hydrogen production—is key to achieving high efficiency. Compared to traditional sacrificial agent systems, this invention achieves medium recycling and complete water splitting, exhibiting significant advantages in integrity and sustainability. It also features mild reaction conditions, high-efficiency mass production, and broad applicability, making it suitable for applications in industrial gases, organic synthesis, and laboratory analysis.

[0123] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the technical principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for stepwise photocatalytic water splitting to produce hydrogen and oxygen, characterized in that, Includes the following steps: An oxidant and a photocatalyst are dispersed in a mixed solvent consisting of water and a first organic solvent to obtain a water oxidation oxygen production reaction system. Under an inert atmosphere, the water oxidation oxygen production reaction system is irradiated with visible light, and the water undergoes an oxidation reaction to produce oxygen. At the same time, water is used as a proton source to reduce the oxidant to a hydrogen-rich reducing agent, and the reducing agent and photocatalyst are separated and recovered. The reducing agent and photocatalyst obtained from the separation and recovery are dispersed in a second organic solvent to obtain a hydrogen production reaction system; Under an inert atmosphere, the hydrogen production reaction system is irradiated with visible light, causing the hydrogen-rich reducing agent to release hydrogen to produce hydrogen gas, while the reducing agent is oxidized into an oxidizing agent. The reducing agent and oxidizing agent can undergo a reversible redox reaction under photocatalytic conditions.

2. The method for stepwise photocatalytic water splitting to produce hydrogen and oxygen according to claim 1, characterized in that, The oxidizing agent includes one or more of the following: quinones, quinolines, indoles, disulfides, aldehydes, and ketones.

3. The method for stepwise photocatalytic water splitting to produce hydrogen and oxygen according to claim 1, characterized in that, The photocatalyst includes one or more of the following: metal oxides, metal sulfides, supported metal oxides, supported metal sulfides, and graphitic carbon nitride materials.

4. The method for stepwise photocatalytic water splitting to produce hydrogen and oxygen according to claim 1, characterized in that, The concentration of the oxidant in the water oxidation oxygen production reaction system is 0.001~10 mol / L; And / or, the concentration of the reducing agent in the hydrogen production reaction system is 0.001~10 mol / L.

5. The method for stepwise photocatalytic water splitting to produce hydrogen and oxygen according to claim 1, characterized in that, When preparing the water oxidation oxygen production reaction system, the mass ratio of oxidant, photocatalyst and water is 1: (0.01~100): (0.01~1800); And / or, when preparing the hydrogen production reaction system, the mass ratio of reducing agent to photocatalyst is 1: (0.01~100).

6. The method for stepwise photocatalytic water splitting to produce hydrogen and oxygen according to claim 1, characterized in that, The water is H2O, D2O, and H2. 18 One of O.

7. The method for stepwise photocatalytic water splitting to produce hydrogen and oxygen according to claim 1, characterized in that, When preparing a water oxidation oxygen production reaction system, an acidic or alkaline regulator is used to adjust the pH. The acid regulator includes one or more of hydrochloric acid, sulfuric acid, nitric acid, phosphoric acid, and acetic acid; The alkalinity regulator includes one or more of sodium hydroxide, potassium hydroxide, sodium carbonate, potassium carbonate, cesium carbonate, and sodium bicarbonate.

8. The method for stepwise photocatalytic water splitting to produce hydrogen and oxygen according to claim 1, characterized in that, The first organic solvent and the second organic solvent are each independently selected from one or more of acetonitrile, ethyl acetate, tetrahydrofuran, dioxane, cyclohexane, N,N-dimethylformamide, N,N-dimethylacetamide, and dimethyl sulfoxide.

9. The method for stepwise photocatalytic water splitting to produce hydrogen and oxygen according to claim 1, characterized in that, The visible light irradiation uses one or more of the following: a xenon lamp, an LED, a halogen lamp, or a mercury lamp with a power of 0.01 to 100 W.

10. The method for stepwise photocatalytic water splitting to produce hydrogen and oxygen according to claim 1, characterized in that, The inert atmosphere uses one or more of the following gases: He, Ar, and N2.

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