A sulfide photocatalyst, its preparation method and application

Abstract

This invention provides an oxygen sulfide photocatalyst, its preparation method, and its uses. The chemical formula is Sr3In4O4S5, and it belongs to the orthorhombic crystal system. Pmmn The space group contains a one-dimensional chain structure, in which In is coordinated in the form of [InO2S3] distorted tetragonal pyramids, which are interconnected and extend along the c-axis. Sr ions are located between the one-dimensional chains. This oxysulfide has suitable band edge positions, which can simultaneously meet the conditions for photocatalytic water splitting to produce oxygen and hydrogen. Furthermore, the hybridization of the oxygen and sulfur anion orbitals at the valence band apex can effectively mitigate the oxidation of sulfur ions by photogenerated holes. The oxysulfide described in this invention exhibits excellent photocatalytic performance and is of great significance for the practical application of photocatalytic water splitting.

Description

Technical Field

[0001] This invention relates to the field of photocatalysts, and more particularly to a method for preparing an oxysulfide photocatalyst and its application. Background Technology

[0002] Solar energy is an inexhaustible, clean, and pollution-free green energy source, promising to alleviate the increasingly severe energy crisis, and has therefore become one of the future energy sources that countries around the world are vying to develop. Photocatalytic materials are an important medium for achieving efficient utilization of solar energy. The photocatalytic process can be described as follows: under illumination, electrons at the top of the valence band of a semiconductor with a certain band gap have a certain probability of being excited to jump to the conduction band, forming photogenerated electron-hole pairs. After the electron-hole pairs separate under a specific driving force and migrate to the semiconductor surface, they can undergo redox reactions with species in the environment, thereby realizing the conversion of solar energy into chemical energy. The photocatalytic process of semiconductors can be applied to the photocatalytic synthesis of various chemical substances (such as hydrogen, oxygen, and high-value-added organic matter), and can also catalytically degrade pollutants in the environment. Among them, the photocatalytic water splitting reaction can produce another clean, pollution-free, and easier-to-store chemical energy—hydrogen. Therefore, the exploration of photocatalysts for water splitting has important scientific significance and practical value.

[0003] In recent years, oxysulfide photocatalysts have attracted widespread attention from researchers. Oxysulfides refer to compounds in which oxygen ions and sulfide anions (such as S-oxides) coexist in the same crystal structure. 2- Se 2- Inorganic compounds such as Y₂Ti₂S₂O₅ (e.g., oxysulfides) exhibit unique advantages over single-anion photocatalysts. Compared to oxides, oxysulfides have a higher valence band top, thus enabling them to achieve photocatalytic water splitting while maintaining a narrow band gap. Compared to chalcogenides, the hybridized valence band composition of oxysulfides mitigates the auto-oxidation behavior of chalcogen anions by photogenerated holes. These characteristics make oxysulfides a highly promising photocatalyst system for water splitting. However, the number of known oxysulfide photocatalysts is currently very small, and oxysulfide photocatalysts with novel structures urgently need to be developed. Summary of the Invention

[0004] This invention proposes an oxygen sulfide photocatalyst, its preparation method, and its application.

[0005] In a first aspect, the present invention provides an oxysulfide with the chemical formula Sr3In4O4S5, belonging to the orthorhombic crystal system. Pmmn The space group is [InO2S3], where the coordination form of In is a distorted tetragonal pyramid. The tetragonal pyramids are interconnected and extend along the c-axis to form a one-dimensional chain structure. Sr ions are located between the one-dimensional chains. The valence of Sr is +2, the valence of In is +3, the valence of O is -2, and the valence of Se is -2.

[0006] In the oxysulfide, Sr in Sr3In4O4S5 may be partially replaced by Ca, Ba or Pb, and S in Sr3In4O4S5 may be partially replaced by Se or Te, including but not limited to Ca or Ba.

[0007] Secondly, the present invention provides a method for preparing the above-mentioned oxysulfide, comprising placing raw materials containing Sr, In, O, S and dopant elements under vacuum or inert atmosphere conditions, holding them at 650~800℃ for 24~72 hours, and then cooling them down.

[0008] The molar ratio of Sr, In, O and S in the raw material is (2.8~3.5):4:4:(4.8~5.5).

[0009] The high-temperature reaction may include heating from room temperature to 650~800°C within 10 hours.

[0010] The high-temperature reaction may include heating to 700-800°C and holding at that temperature for 24-72 hours, then cooling to 500°C within 24-72 hours, and then naturally cooling to room temperature.

[0011] In the above preparation process, fluxes can be added to the reaction raw materials. Fluxes include, but are not limited to, alkali metal halides such as KCl, KI, RbCl, CsI, etc., to promote crystal growth.

[0012] Thirdly, the present invention provides a surface modification method for the above-mentioned oxysulfides, namely, dispersing Sr3In4O4S5 in a dilute acid solution, stirring at room temperature, filtering, washing with deionized water, and drying.

[0013] The hydrogen ion concentration of the dilute acid solution can be 0.01 ~ 0.1 mol / L, and the acid can be hydrochloric acid, sulfuric acid, nitric acid, etc.

[0014] The room temperature stirring process can last for 10 to 24 hours.

[0015] Fourthly, the present invention provides a use for the above-mentioned oxysulfide in the photocatalytic splitting of water to produce hydrogen and oxygen. Before surface modification, the maximum hydrogen production rate is 257.9 μmol × g. -1 ×h -1 The maximum oxygen production rate is 75.5 μmol × g. -1 ×h -1 After surface modification using the method described in the third aspect above, the maximum hydrogen production rate can reach 760.2 μmol × g. -1 ×h -1 The maximum oxygen production rate can reach 258.4 μmol × g. -1 ×h-1 .

[0016] When using the above-mentioned oxysulfide photocatalyst for photocatalytic hydrogen production, Na2S and Na2SO3 are used as sacrificial agents.

[0017] When using the above-mentioned oxysulfide photocatalyst for photocatalytic oxygen production, NaIO3 is used as a sacrificial agent.

[0018] In summary, this invention provides an oxygen sulfide photocatalyst with a novel crystal structure, which has the following beneficial effects:

[0019] 1. The oxysulfide photocatalyst obtained by this invention has suitable band edge positions, which can simultaneously meet the conditions for photocatalytic water splitting to produce oxygen and hydrogen, and has certain advantages. Practical value and application prospects.

[0020] 2. In the oxysulfide obtained by this invention, the hybridization of the oxygen-sulfur anion orbitals at the top of the valence band effectively stabilizes the sulfur ion, alleviates the oxidation effect of photogenerated holes, and achieves a relatively stable oxygen production capacity.

[0021] 3. This invention provides a simple and effective strategy for modifying the surface of oxysulfides, which significantly improves the rate of photocatalytic hydrogen and oxygen production. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of the Sr3In4O4S5 crystal structure of the present invention; Figure 2 This is the X-ray diffraction pattern of Sr3In4O4S5 powder in Example 1 of the present invention; Figure 3 The image shows a scanning electron microscope (SEM) image and an energy dispersive spectroscopy (EDS) analysis diagram of Embodiment 1 of the present invention; Figure 4 The ultraviolet-visible absorption spectra of Examples 1 and 4 of the present invention are shown; Figure 5 The photocatalytic hydrogen production graphs of Examples 1 and 4 of the present invention are shown; Figure 6 The diagrams show the photocatalytic oxygen production of Examples 1 and 4 of the present invention. Detailed Implementation

[0023] The present invention will be further illustrated by the following embodiments. It should be understood that the following embodiments are for illustrative purposes only and are not intended to limit the present invention.

[0024] The oxygen sulfide Sr3In4O4S5 in this embodiment belongs to the orthorhombic crystal system. PmmnThe space group is in which the coordination form of In is [InO2S3] distorted tetragonal pyramids, which are interconnected and extend along the c-axis to form a one-dimensional chain structure. Sr ions are located between the one-dimensional chains (see...). Figure 1 The oxidation states of Sr are +2, In are +3, O are -2, and Se are -2. Sr can be replaced by doping with elements such as Ca, Ba, or Pb, and S can be replaced by doping with elements such as Se or Te. The cell parameters of Sr3In4O4S5 are... a = 9.1558(8)Å, b = 17.8619(18) Å, c = 3.9038(3) Å, a = b = g = 90°, Z = 2, and its crystallographic data are shown in Table 1.

[0025] Table 1 Crystallographic data of Sr3In4O4S5 molecular weight 946.44 Space Group a (Å) 9.1558(8) b (Å) 17.8619(18) c (Å) 3.9038(3) <![CDATA[Volume (Å 3 )]]> 638.43(10) <![CDATA[density (g×cm -3 )]]> 4.923 The following is an exemplary description of the preparation method of the oxysulfide Sr3In4O4S5 of the present invention.

[0026] The raw materials containing strontium, indium, oxygen, sulfur, and other doping elements can be placed under vacuum conditions and prepared by high-temperature reaction. The raw materials can be thoroughly ground and mixed uniformly in a mortar, with the molar ratio of Sr, In, O, and S in the raw materials being (2.8~3.5):4:4:(4.8~5.5). The Sr source can be elemental Sr, SrO, or SrS, and the In source can be elemental In, In₂O₃, or In₂S₃. Fluxes can be added to the raw materials to create a liquid-phase reaction environment; fluxes include, but are not limited to, alkali metal halides such as KCl, KI, or CsI.

[0027] The reaction vessel containing the reactants is placed in a muffle furnace, heated to 650–800°C, held at that temperature for 24–72 hours, and then cooled. In this high-temperature reaction method, it is preferable to raise the temperature to 650–800°C at a rate of 65–80°C / hour to achieve high-quality and pure crystal preparation. In some embodiments, the reaction vessel can be a quartz tube, which is evacuated to 0.1 Pa, melted and sealed, and then placed in a muffle furnace, heated to 650–800°C at a rate of 65–80°C / hour. Furthermore, it is preferable to raise the temperature to 650–800°C, hold for 24–72 hours, and then cool to 500°C at a rate of 3–8°C / hour, followed by natural cooling to room temperature. For samples with added flux, after the reaction, the sample is thoroughly washed with deionized water and dried to obtain the final product.

[0028] Implementation Form 2 This embodiment is a surface modification method for Sr3In4O4S5, which involves selectively etching Sr and O ions on the sample surface through acid treatment. By reconstructing the surface, the light absorption properties and carrier transport performance of the material are controlled, thereby significantly improving the photocatalytic hydrogen and oxygen production performance.

[0029] The following describes an exemplary method for surface modification of the oxysulfides of the present invention.

[0030] A certain mass of oxysulfide is dispersed in a dilute acid solution with a hydrogen ion concentration of 0.01 ~ 0.1 mol / L. The acid can be hydrochloric acid, sulfuric acid, nitric acid, etc. The solution is placed on a magnetic stirring table and stirred at room temperature for 10 ~ 24 hours. After filtration, it is washed with deionized water until the pH of the washing solution is close to neutral. Then it is washed with ethanol and acetone in turn and dried.

[0031] This invention provides a method for preparing and using an oxygen-sulfur photocatalyst with the chemical formula Sr3In4O4S5, representing a novel crystal structure. This photocatalyst possesses suitable band-edge positions, simultaneously satisfying the conditions for photocatalytic water splitting to produce oxygen and hydrogen. Furthermore, the hybridization of the oxygen-sulfur anion orbitals at the valence band apex effectively stabilizes the sulfur ion, mitigating the oxidation effect of photogenerated holes and thus enabling relatively stable oxygen production. In addition, simple surface modification through room-temperature acid treatment can effectively regulate the material's light absorption properties and carrier transport performance, significantly improving its photocatalytic hydrogen and oxygen production performance, demonstrating considerable practical value and application prospects.

[0032] The following examples further illustrate the present invention in detail. It should also be understood that the following examples are only for further explanation of the present invention and should not be construed as limiting the scope of protection of the present invention. Any non-essential improvements and adjustments made by those skilled in the art based on the above description of the present invention are within the scope of protection of the present invention. The specific process parameters, etc., in the following examples are merely examples within a suitable range; that is, those skilled in the art can make appropriate selections within the appropriate range based on the description herein, and are not intended to be limited to the specific values ​​in the examples below.

[0033] In the following embodiments, unless otherwise specified, the reagents, materials and instruments used are all conventional reagents, materials and instruments, and are commercially available. The reagents involved can also be synthesized by conventional synthesis methods.

[0034] Example 1 Preparation of Sr3In4O4S5 by High-Temperature Solid-State Method: 0.7000 g SrO, 0.1850 g In2O3, and 1.086 g In2S3 were weighed and thoroughly ground and mixed in a mortar. The mixture was then transferred to a quartz tube with an inner diameter of 1 cm and vacuum-sealed. The vacuum was then evacuated to 0.1... Pa. A sealed quartz tube was placed in a muffle furnace, and the following holding program was set: the temperature was raised to 700 °C in 10 hours, held at 700 °C for 48 hours, and then cooled to 500 °C at a rate of 3 °C per hour, followed by natural cooling to room temperature. The product was removed from the quartz tube, yielding Sr3In4O4S5 polycrystalline powder.

[0035] Example 2 Preparation of Sr3In4O4S5 by flux method: Weigh 0.7000 g SrO, 0.1850 g In2O3, 1.086 g In2S3 and 7.5 g KI, grind and mix thoroughly in a mortar, then transfer to a quartz tube with an inner diameter of 1 cm and vacuum seal. Evacuate to 0.1 Pa. A sealed quartz tube was placed in a muffle furnace, and the following holding program was set: the temperature was raised to 700 °C over 10 hours, held at 700 °C for 48 hours, then cooled to 500 °C at a rate of 3 °C per hour, and finally allowed to cool naturally to room temperature. The product was removed from the quartz tube, thoroughly washed with deionized water to remove the flux, then washed sequentially with ethanol and acetone, and finally dried to obtain Sr3In4O4S5 polycrystalline powder.

[0036] Example 3 Preparation of Se-doped Sr3In4O4S5: Weigh 0.7000 g SrO, 0.1850 g In2O3, 0.825 g In2S3, 0.372 g In2Se3 and 7.5 g KI, grind and mix thoroughly in a mortar, then transfer to a quartz tube with an inner diameter of 1 cm and vacuum seal. Evacuate to 0.1 Pa. Place the sealed quartz tube in a muffle furnace and set the following holding program: heat to 700 °C for 10 hours, hold at 700 °C for 48 hours, then cool to 500 °C at a rate of 3 °C per hour, and then allow to cool naturally to room temperature. Remove the product from the quartz tube, wash thoroughly with deionized water to remove flux, wash successively with ethanol and acetone, and then dry to obtain Se-doped Sr3In4O4S5 polycrystalline powder.

[0037] Example 4 Sr3In4O4S5 surface modification: Weigh 1 g of Sr3In4O4S5 sample and disperse it in 100 ml of 0.06 mol / L dilute hydrochloric acid solution. Place the mixture on a magnetic stirrer and stir at room temperature for 24 hours. Filter and wash with deionized water until the pH of the washing solution is close to neutral. Then wash with ethanol and acetone in sequence and dry.

[0038] Example 5 Physical property characterization: 1) The obtained Sr3In4O4S5 crystals were ground and then subjected to powder X-ray diffraction testing. The results are as follows: Figure 2 As shown, the obtained powder X-ray diffraction pattern is consistent with the theoretical X-ray diffraction pattern of the crystal obtained from single-crystal structure analysis, proving that the obtained crystal has high purity.

[0039] 2) The obtained Sr3In4O4S5 crystal was observed using a scanning electron microscope, such as... Figure 3 As shown, the crystal exhibits a rod-like shape. Energy dispersive spectroscopy analysis indicates that the four elements are evenly distributed in the crystal, and the elemental ratios are consistent with the results obtained from the single crystal structure analysis.

[0040] 3) The obtained Sr3In4O4S5 crystal and the surface-modified sample were subjected to UV-Vis diffuse reflectance spectroscopy. The test results were converted into UV-Vis absorption spectra, and the results are as follows: Figure 4 As shown, the optical bandgap of Sr3In4O4S5 before modification was 3.2 eV, and the optical bandgap after modification became 2.47 eV.

[0041] Example 6 Performance testing: 1) Weigh 10 mg of Sr3In4O4S5 samples (before and after modification) and disperse them in 10 ml of an aqueous solution containing 0.06 mol / L Na2S and Na2SO3. Irradiate the solution with a 300 W xenon lamp, and analyze the amount of hydrogen gas produced using gas chromatography. Figure 5 It can be seen that the hydrogen production rate of the modified oxysulfide is significantly higher than that before modification, with a maximum hydrogen production rate of 760.2 μmol × g. -1 ×h -1 This is three times the hydrogen production rate before modification (257.9 μmol × g). -1 ×h -1 ).

[0042] 2) Weigh 10 mg of both the unmodified and modified Sr3In4O4S5 samples, disperse them in 10 ml of an aqueous solution containing 0.01 mol / L NaIO3, irradiate the solution with a 300 W xenon lamp, and analyze the amount of oxygen obtained using gas chromatography. Figure 6 It can be seen that the oxygen production rate of the modified oxysulfide is significantly higher than that before modification, with a maximum oxygen production rate of 258.4 μmol × g. -1 ×h -1 This is three times the oxygen production rate before modification (75.5 μmol × g). -1 ×h -1 ).

Claims

1. A sulfide oxide, characterized in that: (1) Its chemical formula is Sr3In4O4S5, which belongs to the orthorhombic crystal system. Pmmn Space group; (2) The coordination form of In is [InO2S3] distorted tetragonal pyramids, which are interconnected and extend along the c-axis to form a one-dimensional chain structure. Sr ions are located between the one-dimensional chains. (3) Sr valence is +2, In valence is +3, O valence is -2, S valence is -2.

2. The oxysulfide according to claim 1, characterized in that, The Sr can be partially replaced by one or more elements selected from Ca, Ba, or Pb.

3. The oxysulfide according to claim 1, characterized in that, The S can be partially replaced by one or more elements selected from Se or Te.

4. A method for preparing the oxysulfide according to any one of claims 1-3, characterized in that, Synthesized using high-temperature solid-state reaction, including the following steps: (1) The raw materials containing Sr, In, O, S and doped elements are mixed and ground evenly, wherein the molar ratio of Sr / In / O / S elements is (2.8~3.5):4:4:(4.8~5.5); (2) Heat the sample obtained in step (1) from room temperature to 650~800 ℃ in a vacuum or inert atmosphere, keep it at that temperature for 24~72 hours, then cool it down to 500 ℃ within 24~72 hours, and then let it cool naturally to room temperature.

5. A method for preparing the oxysulfide according to any one of claims 1-3, characterized in that, Adding a flux to the reactants includes the following steps: (1) The raw materials containing Sr, In, O, S and doped elements are mixed with flux and then ground evenly, wherein the molar ratio of Sr / In / O / S elements is (2.8~3.5):4:4:(4.8~5.5), and the flux is selected from at least one of alkali metal halides; (2) Heat the reactants from room temperature to 700-800 °C in a vacuum or inert atmosphere, keep them at that temperature for 24-72 hours, then cool them down to 500 °C within 24-72 hours, and then let them cool naturally to room temperature. Wash the flux with deionized water and then dry them.

6. A method for surface modification of the oxysulfide according to any one of claims 1-3, characterized in that, The process includes dispersing the oxysulfide in a dilute acid solution with a hydrogen ion concentration of 0.01 to 0.1 mol / L, stirring at room temperature for 10 to 24 hours, filtering, washing with deionized water, and then drying.

7. The use of an oxysulfide according to any one of claims 1-3 or an oxysulfide prepared by any one of claims 4-6 in the photocatalytic splitting of water to produce hydrogen and / or oxygen.

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