Bi2O2S-coated Ag2S composite photocatalyst for producing methane through photocatalytic reduction of CO2 and preparation method of Bi2O2S-coated Ag2S composite photocatalyst

Abstract

The invention belongs to the technical field of photocatalytic nano materials, and relates to a Bi2O2S and Ag2S composite photocatalyst for producing methane through photocatalytic reduction of CO2 and a preparation method of the Bi2O2S and Ag2S composite photocatalyst. Comprising the following steps: ultrasonically dispersing Bi2O2S nanosheets in deionized water, then adding AgNO3, vigorously stirring for at least 2 hours, repeatedly washing, centrifuging and drying to obtain a target product Bi2O2S-Ag2S, and the molar ratio of Bi to Ag is 1: (1.2-2.89). According to the preparation method disclosed by the invention, Bi2O2S-coated Ag2S is creatively prepared by the method, and Ag2S and Bi2O2S share a sulfur source and grow on the surface of a Bi2O2S nanosheet to form a nano-particle morphology. The problems of rapid compounding of Bi2O2S photo-induced electrons and poor stability of silver-based semiconductors are solved, and the prepared catalyst can efficiently catalyze carbon dioxide to obtain methane and has good catalytic stability.

Description

Technical Field

[0001] This invention belongs to the field of photocatalytic nanomaterials technology, and relates to a Bi2O2S@Ag2S composite photocatalyst for photocatalytic reduction of CO2 to methane and its preparation method. Background Technology

[0002] With the increasing severity of global climate change, CO2 emission reduction and conversion have become a hot topic in scientific research. Since Fujishima and Honda first demonstrated photoelectrocatalytic water splitting on a photoactive semiconductor catalyst in 1972, researchers have been dedicated to developing highly efficient photocatalysts capable of harvesting solar energy and converting it into chemical energy. Bismuth (Bi)-based catalysts, due to their abundant reserves, non-toxicity, and unique electronic structure, show promising application prospects in photocatalytic carbon dioxide reduction. Bismuth oxysulfate (Bi2O2S), as a layered material, possesses alternating [Bi2O2]... 2+ Layers and S 2- The open framework structure of photogenerated electrons creates an internal electrostatic field between layers, which is beneficial for the separation of photogenerated carriers. However, photogenerated electrons readily recombine, leading to a decrease in carrier separation efficiency and thus limiting the catalytic performance of Bi2O2S. Existing methods to improve the rapid recombination of photogenerated electrons in Bi2O2S include introducing oxygen vacancies and forming heterojunctions. For example, Chinese patent document (application number 202411624158.6) discloses a photocatalytic material based on Bi2O2S, its preparation method, and its application. The structure of this material includes Bi2O2S, oxygen vacancies introduced on Bi2O2S, and an S-type heterojunction constructed by introducing Bi4O5I2 onto Bi2O2S. The main problems are that the modification process of the composite material is cumbersome and it is not suitable for the production of methane from carbon dioxide. Summary of the Invention

[0003] The existing technology has the following problems: pure Bi2O2S photocatalysts have low carbon dioxide reduction performance and cannot produce methane as a high-calorific-value fuel. To address these problems, this invention provides a method for preparing a Bi2O2S@Ag2S composite photocatalyst for photocatalytic reduction of CO2 to methane. This method is simple to operate and easy to control. The prepared Bi2O2S@Ag2S composite photocatalyst exhibits good photocatalytic activity for carbon dioxide to methane production and has certain application prospects.

[0004] To achieve the objectives of this invention, the technical solution adopted is as follows:

[0005] A method for preparing a Bi2O2S@Ag2S composite photocatalyst for photocatalytic reduction of CO2 to methane includes the following steps: ultrasonically dispersing Bi2O2S nanosheets in deionized water, then adding AgNO3, stirring vigorously for at least 2 hours, repeatedly washing and centrifuging, and drying to obtain the target product Bi2O2S@Ag2S, wherein the molar ratio of Bi to Ag is 1:1.2~2.89.

[0006] Ag₂S exhibits excellent performance in photocatalytic applications. Its narrow bandgap structure (0.9-1.2 eV) is beneficial for the generation of photogenerated electron-hole pairs and the utilization of solar energy, making it a common photosensitive material in the preparation of composite photocatalytic materials. However, due to Ag₂S… + It can be reduced to Ag by high-energy photogenerated electrons. 0 Silver-based semiconductors suffer from poor stability, thus limiting their application in photocatalysis. This invention creatively prepares Bi₂O₂S@Ag₂S using the aforementioned method, where Ag₂S and Bi₂O₂S share a sulfur source and grow on the surface of Bi₂O₂S nanosheets, forming nanoparticles. This not only overcomes the problems of rapid recombination of photogenerated electrons in Bi₂O₂S and the poor stability of silver-based semiconductors, but also provides a catalyst that can efficiently catalyze the conversion of carbon dioxide to methane while exhibiting good catalytic stability.

[0007] There are various methods for preparing Bi2O2S nanosheets in this field. For example, Chinese patent document (application number 202310611934.8) discloses a low-temperature solid-phase chemical method for preparing Bi2O2S nanomaterials. This method involves a chemical reaction of bismuth nitrate pentahydrate, sodium hydroxide, and different sulfur source reactants during solid-phase grinding, followed by water bath heating, washing, and drying to finally obtain Bi2O2S nanomaterials. However, this method involves a low-temperature reaction after solid-phase grinding, resulting in uneven contact of reactants. This leads to poor crystallinity, purity, and regularity of the layered structure of the product, directly affecting its basic performance as a photocatalytic material and consequently impacting the effectiveness of subsequent modification. To further improve the catalytic activity of the above catalyst in the production of methane from carbon dioxide, this invention further incorporates the following method for preparing Bi2O2S nanosheets: bismuth nitrate pentahydrate and thiourea in a molar ratio of 1.9~2.1:1 are mixed in water (distilled water or deionized water) (preferably using magnetic stirring for at least 60 minutes) until the reagents are completely dispersed in the water. Next, excess lithium hydroxide monohydrate was added, and stirring continued. Once all reagents were uniformly dispersed in the water, the mixture was transferred to an autoclave and maintained at 200°C for 72 hours. The product was then collected by centrifugation and vacuum dried overnight to obtain pure Bi₂O₂S crystals.

[0008] Furthermore, the mass ratio of bismuth nitrate pentahydrate to thiourea is 10:1.

[0009] Furthermore, the mass ratio of lithium hydroxide monohydrate to bismuth nitrate pentahydrate after conversion exceeds 8:1.

[0010] Furthermore, the preparation of the Bi2O2S@Ag2S composite photocatalyst also includes the following steps: First, the pre-prepared Bi2O2S nanosheets are ultrasonically dispersed in 60 mL of deionized water, then AgNO3 is added, the mixture is vigorously stirred until homogeneous, repeatedly washed and centrifuged, and dried at 60 °C to obtain the target product Bi2O2S@Ag2S.

[0011] The beneficial effects of this invention are: the preparation method is simple and easy to implement, and the preparation conditions are easy to control. The prepared Bi2O2S@Ag2S composite photocatalyst has good photocatalytic methane production activity and has certain application prospects. Attached Figure Description

[0012] Figure 1 These are X-ray diffraction comparison images of Bi2O2S and Bi2O2S@Ag2S composite photocatalysts prepared in Examples 1-3 of this invention;

[0013] Figure 2 This is a transmission electron microscope image of the Bi2O2S@Ag2S composite photocatalyst prepared in Example 3 of this invention;

[0014] Figure 3 The graphs show the photocatalytic carbon dioxide reduction performance of the Bi2O2S and Bi2O2S@Ag2S composite photocatalysts prepared in Examples 1-3 of this invention.

[0015] Figure 4 This is a cyclic diagram of the photocatalytic carbon dioxide reduction experiment of the Bi2O2S@Ag2S composite photocatalyst prepared in Example 3 of the present invention. Detailed Implementation

[0016] To further understand the purpose, content, and advantages of this invention, specific embodiments of the invention are described in detail below. However, these embodiments are not limited to the examples described below and should be freely combined according to actual circumstances. The endpoints and values ​​of the ranges disclosed herein are not limited to the precise ranges and values. For numerical ranges, endpoint values ​​of various ranges, endpoint values ​​of various ranges and individual point values, and individual point values ​​can be combined to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0017] The present invention will be further described in detail below with reference to the embodiments:

[0018] This invention provides a method for preparing a Bi2O2S@Ag2S composite photocatalyst for photocatalytic reduction of CO2 to methane, comprising the following steps: ultrasonically dispersing Bi2O2S nanosheets in deionized water, then adding AgNO3, stirring vigorously for at least 2 hours, repeatedly washing and centrifuging, and drying to obtain the target product Bi2O2S@Ag2S, wherein the molar ratio of Bi to Ag is 1:1.2~2.89.

[0019] The above-described method yields a Bi₂O₂S@Ag₂S catalyst, in which Ag₂S and Bi₂O₂S share a sulfur source and grow on the surface of Bi₂O₂S nanosheets, forming nanoparticles. This not only overcomes the problems of rapid recombination of photogenerated electrons in Bi₂O₂S and the poor stability of silver-based semiconductors, but also enables the catalyst to efficiently catalyze the conversion of carbon dioxide to methane, while exhibiting good catalytic stability.

[0020] In some preferred embodiments, the method for preparing Bi₂O₂S nanosheets includes the following steps: Bismuth nitrate pentahydrate and thiourea in a molar ratio of 1.9–2.1:1 are mixed in water (distilled or deionized water) (preferably using magnetic stirring for at least 60 minutes) until the reagents are completely dispersed in the water. Next, excess lithium hydroxide monohydrate is added, and stirring continues. After all reagents are uniformly dispersed in the water, the mixture is transferred to an autoclave and kept at 200°C for 72 hours. The product is then collected by centrifugation and vacuum dried overnight to obtain pure Bi₂O₂S crystals.

[0021] The present invention will be further described in detail below with reference to more specific embodiments: Example 1

[0022] (1) Preparation of Bi2O2S powder: Weigh 2.0 g of bismuth nitrate pentahydrate and 0.16 g of thiourea, add distilled water, and stir magnetically for more than 60 minutes until the reagents are completely dispersed in the solution. Add 12 g of excess lithium hydroxide monohydrate and continue stirring until uniformly dispersed, then transfer to a reaction vessel. Keep at 200℃ for 72 h. Wash and centrifuge the product three times, and place it in a vacuum drying oven overnight to obtain pure Bi2O2S powder.

[0023] (2) Preparation of Ag2S: First, 0.1 g of silver nitrate was ultrasonically dispersed in deionized water. Then, under magnetic stirring, an appropriate amount of 1 M Na2S aqueous solution was slowly added dropwise to the above solution. After stirring for 2 h, the solution was repeatedly washed, centrifuged, and dried to obtain the target product Ag2S.

[0024] (3) Preparation of Bi2O2S@Ag2S composite photocatalyst: First, 0.1 g of Bi2O2S nanosheets prepared in step (1) were dispersed in 60 mL of deionized water and sonicated for 20 min. Then, 0.1 g of AgNO3 was added, and the mixture was stirred vigorously for 2 h. After repeated washing and centrifugation, the product Bi2O2S@Ag2S was dried at 60 °C and labeled as BOS-AS(100). Example 2

[0025] (1) Preparation of Bi2O2S powder, same as step (1) in Example 1: Weigh 2.0 g of bismuth nitrate pentahydrate and 0.16 g of thiourea, add distilled water, and stir magnetically for more than 60 minutes until the reagents are completely dispersed in the solution. Add 12 g of excess lithium hydroxide monohydrate and continue stirring until uniformly dispersed, then transfer to a reaction vessel. Keep at 200°C for 72 h. Wash and centrifuge the product three times, and place it in a vacuum drying oven overnight to obtain pure Bi2O2S powder.

[0026] (2) Preparation of Ag2S is the same as step (2) in Example 1: First, 0.1 g of silver nitrate is ultrasonically dispersed in deionized water. Then, under magnetic stirring, an appropriate amount of 1 M Na2S aqueous solution is slowly added dropwise to the above solution. After stirring for 2 hours, the solution is repeatedly washed, centrifuged, and dried to obtain the target product Ag2S.

[0027] (3) Preparation of Bi2O2S@Ag2S composite photocatalyst: First, 0.1 g of Bi2O2S nanosheets prepared in step (1) were dispersed in 60 mL of deionized water and sonicated for 20 min. Then, 0.15 g of AgNO3 was added, and the mixture was stirred vigorously for 2 h. After repeated washing and centrifugation, the product Bi2O2S@Ag2S was dried at 60 °C and labeled as BOS-AS(150). Example 3

[0028] (1) Preparation of Bi2O2S powder, same as step (1) in Example 1: Weigh 2.0 g of bismuth nitrate pentahydrate and 0.16 g of thiourea, add distilled water, and stir magnetically for more than 60 minutes until the reagents are completely dispersed in the solution. Add 12 g of excess lithium hydroxide monohydrate and continue stirring until uniformly dispersed, then transfer to a reaction vessel. Keep at 200°C for 72 h. Wash and centrifuge the product three times, and place it in a vacuum drying oven overnight to obtain pure Bi2O2S powder.

[0029] (2) Preparation of Ag2S is the same as step (2) in Example 1: First, 0.1 g of silver nitrate is ultrasonically dispersed in deionized water. Then, under magnetic stirring, an appropriate amount of 1 M Na2S aqueous solution is slowly added dropwise to the above solution. After stirring for 2 hours, the solution is repeatedly washed, centrifuged, and dried to obtain the target product Ag2S.

[0030] (3) Preparation of Bi2O2S@Ag2S composite photocatalyst: First, 0.1 g of Bi2O2S nanosheets prepared in step (1) were dispersed in 60 mL of deionized water and sonicated for 20 min. Then, 0.2 g of AgNO3 was added, and the mixture was stirred vigorously for 2 h. After repeated washing and centrifugation, the product Bi2O2S@Ag2S was dried at 60 °C and labeled as BOS-AS(200).

[0031] The crystal phase structures of the Bi₂O₂S, Ag₂S, and Bi₂O₂S@Ag₂S composite photocatalysts prepared in Examples 1-3 were analyzed using a Rigaku D / max2500PC rotating X-ray diffractometer (Japan). The X-rays were applied using a Cu target Kα (λ = 1.54056 Å), with a voltage of 40 kV, a current of 100 mA, a step size of 0.02°, and a scanning range of 5°–80°. Figure 1 As shown, the diffraction peaks of the Bi2O2S phase in the composite sample are completely consistent with the standard card (JCPDS 34-1493), and its characteristic peak positions (such as 14.88°, 24.23°, 27.42°, etc.) correspond to a series of crystal planes such as (020), (110), and (120), respectively. In addition, the diffraction signal of Ag2S is clearly visible in the spectrum. Since Ag2S and Bi2O2S share the sulfur source and grow on the surface of Bi2O2S nanosheets, the diffraction intensity of some crystal planes is relatively weak. The morphology of the Bi2O2S@Ag2S composite photocatalyst (BOS-AS(150)) with an Ag2S addition of 150 mg prepared in Example 2 was observed using a JEM-2100 transmission electron microscope from Nippon Electronics Corporation. Figure 2 Transmission electron microscopy images show that Ag2S is distributed in nanoparticle form on the surface of Bi2O2S sheets.

[0032] The Bi₂O₂S, Ag₂S, and Bi₂O₂S@Ag₂S composite materials prepared in Examples 1-3 were used as photocatalytic carbon dioxide reduction. 5 mg of the Bi₂O₂S@Ag₂S composite material was weighed and added to a mixed solution of 30 mL ethyl acetate and 10 μL deionized water. The solution was sonicated for 20 min until completely dispersed and then transferred to a reaction vessel. Under magnetic stirring, the air inside the vessel was purged with high-purity CO₂ gas, and the vessel was irradiated with a 300 W xenon lamp fitted with a 420 nm filter. Continuous stirring was performed during the irradiation to achieve photocatalytic reduction. Air was collected from the vessel every 30 min, and the gas composition was analyzed using gas chromatography. The experimental results are as follows: Figure 3As shown, the CO production rate of pure Bi₂O₂S is 2.74 μmol / g / h, and the CH₄ production rate is 3.75 μmol / g / h. The CO and CH₄ production rates of the BOS-AS(150) composite photocatalyst are 8.87 and 16.26 μmol / g / h, respectively. The comparison shows that the combination of Bi₂O₂S and Ag₂S can effectively improve the methane yield during photocatalysis, and the prepared Bi₂O₂S@Ag₂S composite photocatalyst exhibits higher photocatalytic activity.

[0033] To verify the stability of the Bi2O2S@Ag2S composite photocatalyst prepared in this invention, a photocatalytic carbon dioxide reduction cycle experiment was conducted on the BOS-AS(150) composite catalyst prepared in Example 2. The results are as follows: Figure 4 As shown, after four photocatalytic carbon dioxide reduction cycles, the photocatalytic yield of the Bi2O2S@Ag2S composite catalyst did not decrease significantly, indicating that the prepared Bi2O2S@Ag2S composite photocatalyst has good stability.

[0034] The above description is merely a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the technical scope disclosed in the present invention, based on the technical solution and concept of the present invention, should be covered within the scope of protection of the present invention. It should be noted that, in the absence of conflict, the embodiments and features in the embodiments of the present invention can be combined with each other.

Claims

1. A method for preparing a Bi2O2S@Ag2S composite photocatalyst for photocatalytic reduction of CO2 to methane, characterized in that, The process includes the following steps: Bi2O2S nanosheets are ultrasonically dispersed in deionized water, then AgNO3 is added, the mixture is stirred vigorously for at least 2 hours, and the product is repeatedly washed, centrifuged, and dried to obtain the target product Bi2O2S@Ag2S, wherein the molar ratio of Bi to Ag is 1:1.2~2.

89.

2. The method for preparing the Bi2O2S@Ag2S composite photocatalyst for photocatalytic reduction of CO2 to methane according to claim 1, characterized in that, The preparation method of Bi2O2S nanosheets includes the following steps: Bismuth nitrate pentahydrate and thiourea in water at a molar ratio of 1.9~2.1:1 are mixed until the reagents are completely dispersed in water; next, excess lithium hydroxide monohydrate is added and stirring is continued until all reagents are uniformly dispersed in water, then the mixture is transferred to an autoclave and kept at 200℃ for 72h.

3. The method for preparing the Bi2O2S@Ag2S composite photocatalyst for photocatalytic reduction of CO2 to methane according to claim 2, characterized in that, The method for mixing bismuth nitrate pentahydrate with thiourea includes stirring magnetically for more than 60 minutes.

4. The method for preparing the Bi2O2S@Ag2S composite photocatalyst for photocatalytic reduction of CO2 to methane according to claim 2, characterized in that, The mass ratio of bismuth nitrate pentahydrate to thiourea is 10:

1.

5. The method for preparing the Bi2O2S@Ag2S composite photocatalyst for photocatalytic reduction of CO2 to methane according to claim 2, characterized in that, The mass ratio of lithium hydroxide monohydrate to bismuth nitrate pentahydrate after conversion exceeds 8:

1.

6. The method for preparing the Bi2O2S@Ag2S composite photocatalyst for photocatalytic reduction of CO2 to methane according to claim 1, characterized in that, The preparation of the Bi2O2S@Ag2S composite photocatalyst also includes the following steps: First, the pre-prepared Bi2O2S nanosheets are ultrasonically dispersed in 60mL of deionized water, then AgNO3 is added, the mixture is vigorously stirred until homogeneous, and the mixture is repeatedly washed and centrifuged. The product Bi2O2S@Ag2S is then dried at 60℃ to obtain the target product.

7. A Bi2O2S@Ag2S composite photocatalyst for the photocatalytic reduction of CO2 to methane, characterized in that, Prepared by the method described in any one of claims 1 to 6.

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