Hollow spherical CdS / Ag2S photocatalyst and preparation method and application thereof

Abstract

This invention discloses a hollow spherical CdS / Ag2S photocatalyst, its preparation method, and its applications, belonging to the field of photocatalytic material preparation technology. The preparation method includes the following steps: preparing SiO2 template nanospheres via hydrolysis-condensation; dispersing the SiO2 template nanospheres in water, adding sodium citrate, a cadmium source, ammonia, and a sulfur source for reflux reaction to obtain CdS / SiO2 composite nanospheres; dispersing the CdS / SiO2 composite nanospheres in an organic solvent, then adding a silver source for cation exchange reaction to obtain a CdS / Ag2S / SiO2 composite material; and removing SiO2 using etching to obtain the final product. This invention also discloses a hollow spherical CdS / Ag2S photocatalyst and its applications. This invention can solve the problems of high photogenerated carrier recombination rate, severe photocorrosion, small specific surface area, and low intrinsic activity of existing CdS photocatalysts, and has broad application prospects.

Description

Technical Field

[0001] This invention relates to the field of photocatalytic material preparation technology, specifically to a hollow spherical CdS / Ag2S photocatalyst, its preparation method, and its application. Background Technology

[0002] With the continuous depletion of fossil fuels globally, the energy crisis and environmental pollution problems are becoming increasingly prominent, making the development of clean and renewable alternative energy sources an urgent priority. Solar energy, due to its inexhaustible nature, has attracted much attention, and utilizing photocatalysis technology to convert solar energy into chemical energy, especially through photocatalytic water splitting to produce hydrogen, is considered one of the ideal ways to achieve a sustainable energy supply. In photocatalytic systems, the performance of the photocatalytic materials directly determines the conversion efficiency from solar energy to hydrogen energy.

[0003] Cadmium sulfide (CdS), as a typical visible-light-responsive semiconductor photocatalyst, possesses a suitable bandgap width and a conduction band bottom level that is more horizontal than H. + The reduction potential of O2 / H2O is more negative, and the top level of its valence band is more positive than that of O2 / H2O. Therefore, thermodynamically speaking, CdS possesses both the ability to reduce protons to produce hydrogen and the ability to oxidize water to produce oxygen. This unique band structure makes it a semiconductor material with great application potential in the field of photocatalytic water splitting.

[0004] However, pure-phase CdS photocatalysts still face several key defects in practical applications, severely limiting their photocatalytic efficiency and long-term stability. First, the rapid recombination rate of photogenerated carriers is the most prominent problem with CdS; under photoexcitation, electron-hole pairs generated in CdS readily recombine in the bulk phase or on the surface, significantly reducing the number of carriers effectively participating in surface redox reactions, resulting in generally low quantum efficiencies. Second, the S in CdS... 2- The ion has reducing properties and is easily oxidized to elemental sulfur or sulfate by photogenerated holes under light conditions. Meanwhile, Cd... 2+ The reduction to metallic cadmium leads to the collapse of the CdS crystal structure, loss of active components, and rapid decline in photocatalytic activity. Third, the particles are prone to agglomeration; CdS nanoparticles prepared by conventional methods have high surface energy and tend to spontaneously aggregate in the reaction system, forming large agglomerates. This results in a significant decrease in specific surface area and a reduction in surface active sites, while simultaneously weakening the adsorption capacity for reactants (such as water molecules and protons), further exacerbating the deterioration of photocatalytic performance.

[0005] In summary, pure CdS photocatalysts suffer from high carrier recombination rates, poor photochemical stability, and particle aggregation, making it difficult to meet the practical application requirements for efficient and stable hydrogen production. Therefore, there is an urgent need to develop effective modification strategies to prepare photocatalysts that can suppress charge recombination, improve resistance to photocorrosion, and enhance dispersibility, thereby fully realizing the photocatalytic potential of CdS-based materials. Summary of the Invention

[0006] The problem to be solved by this invention is to provide a hollow spherical CdS / Ag2S photocatalyst, its preparation method and application, so as to solve the problems of high photogenerated carrier recombination rate, severe photocorrosion, small specific surface area and low intrinsic activity of existing CdS photocatalysts, as well as complex photocatalyst preparation process, uneven morphology and uncontrollable loading of active material.

[0007] The technical solution adopted to solve this technical problem is to provide a method for preparing hollow spherical CdS / Ag2S photocatalyst, including the following steps: (1) The silicon source is dissolved in an organic solvent and hydrolyzed and condensed under the action of an alkaline catalyst to obtain SiO2 template nanospheres; (2) Disperse SiO2 template nanospheres in water, add sodium citrate, cadmium source, ammonia and sulfur source for reflux reaction to obtain CdS / SiO2 composite nanospheres; (3) CdS / SiO2 composite nanospheres were dispersed in an organic solvent, and then a silver source was added to carry out a cation exchange reaction to obtain CdS / Ag2S / SiO2 composite material. (4) The SiO2 in the CdS / Ag2S / SiO2 composite material was removed by etching to obtain hollow spherical CdS / Ag2S photocatalyst.

[0008] The beneficial effects of the above-mentioned technical solution in this invention are as follows: This invention successfully constructs a CdS / Ag2S heterojunction photocatalyst with a hollow spherical structure by combining the template method and the cation exchange method. The hollow structure not only effectively reduces the apparent density of the material and increases the specific surface area, but also provides abundant internal cavities, which is beneficial for multiple reflections and absorption of light, thereby improving light energy utilization efficiency. Simultaneously, the hollow spherical shell structure facilitates the rapid diffusion of reactant molecules and product desorption, enhancing the surface catalytic reaction kinetics. The introduction of sodium citrate as a complexing and dispersing agent after the preparation of SiO2 template nanospheres helps to improve the CdS / Ag2S heterojunction photocatalyst. 2+ The CdS is uniformly adsorbed on the SiO2 template surface, and the nucleation and growth rates of CdS are controlled to obtain a uniform and dense CdS coating layer. The addition of ammonia not only adjusts the pH value but also reacts with CdS. 2+The formation of cadmium-ammonia complex ions further modulates the reaction rate, preventing spontaneous CdS aggregation and ensuring the integrity and uniformity of the coating layer, thus guaranteeing the morphological regularity of the composite nanospheres. Furthermore, a cation exchange reaction is used to transfer Ag... + Partial replacement of Cd in CdS 2+ Ag₂S nanoparticles were generated in situ on a CdS matrix, forming a tightly contacted CdS / Ag₂S heterojunction. Due to the narrow band gap of Ag₂S and its band structure matching that of CdS, this heterojunction effectively promotes the separation and migration of photogenerated electron-hole pairs and inhibits carrier recombination, thereby significantly improving the photocatalytic hydrogen production activity. Furthermore, the introduction of Ag₂S can alleviate the photocorrosion problem of CdS itself and enhance the stability of the catalyst. Finally, the SiO₂ template was selectively removed using an etching method, which is mild and does not damage the CdS / Ag₂S shell structure, enabling the efficient preparation of hollow spherical products.

[0009] Preferably, in step (1), the silicon source is tetraethyl orthosilicate or methyl orthosilicate; the organic solvent is anhydrous ethanol, methanol or isopropanol; the alkaline catalyst is ammonia water with a mass fraction of 25~30%; and the volume ratio of silicon source, organic solvent and alkaline catalyst is (10~14):(55~65):(110~130).

[0010] More preferably, in step (1), the silicon source is tetraethyl orthosilicate; the organic solvent is anhydrous ethanol; the alkaline catalyst is ammonia water with a mass fraction of 28%; and the volume ratio of the silicon source, organic solvent and alkaline catalyst is 12:60:120.

[0011] Preferably, the hydrolysis-condensation reaction in step (1) is carried out under ultrasonic conditions, with an ultrasonic frequency of 20~40kHz, a temperature of 35~45℃, and a time of 35~45min.

[0012] More preferably, the hydrolysis-condensation reaction in step (1) is carried out under ultrasonic conditions, with an ultrasonic frequency of 40 kHz, a temperature of 40 °C, and a time of 40 min.

[0013] More preferably, after the hydrolysis-condensation reaction is completed, the reaction solution is centrifuged at 8000~12000 r / min for 8~15 min to remove the supernatant. The precipitate obtained by centrifugation is washed alternately with deionized water and anhydrous ethanol 2~3 times. Each time, the precipitate is ultrasonically dispersed and centrifuged. The washed precipitate is placed in a vacuum drying oven and vacuum dried at 45~55℃ for 8~12 h to obtain SiO2 template nanospheres.

[0014] Preferably, in step (2), the cadmium source is cadmium acetate, cadmium nitrate, or cadmium chloride; the sulfur source is thiourea, thioacetamide, or sodium thiosulfate; and the ratio of SiO2 template nanospheres, sodium citrate, cadmium source, ammonia, and sulfur source is (0.05~0.15)g:(0.2~0.4)g:(0.1~0.2)g:(2~3)mL:(0.05~0.15)g.

[0015] More preferably, the cadmium source is cadmium acetate; the sulfur source is thiourea; and the ratio of SiO2 template nanospheres, sodium citrate, cadmium source, ammonia water and sulfur source is 0.1g:0.3g:0.19g:2.5mL:0.1g.

[0016] More preferably, the mass fraction of ammonia is 25-28%.

[0017] More preferably, the ammonia water mass fraction is 28%.

[0018] Preferably, the reflux reaction temperature in step (2) is 55~65℃ and the time is 2.5~3.5h.

[0019] More preferably, the reflux reaction temperature in step (2) is 60°C and the time is 3h.

[0020] Preferably, in step (3), the organic solvent is diethylene glycol; the silver source is silver nitrate or silver sulfate; and the mass ratio of CdS / SiO2 composite nanospheres to silver source is 0.2:(0.03~0.13).

[0021] More preferably, the silver source is silver nitrate; the mass ratio of CdS / SiO2 composite nanospheres to silver source is 0.2:(0.0318 ~0.1272).

[0022] More preferably, the mass ratio of CdS / SiO2 composite nanospheres to silver source is 0.2:0.0954.

[0023] More preferably, the method of adding the silver source is as follows: after dissolving the silver source in deionized water to form a silver source solution, it is then added dropwise to the suspension formed by CdS / SiO2 composite nanospheres under stirring conditions.

[0024] Preferably, the cation exchange reaction temperature in step (3) is 65~75℃ and the time is 2.5~3.5h.

[0025] More preferably, the cation exchange reaction in step (3) is carried out at a temperature of 70°C for 3 hours.

[0026] Preferably, step (4) includes the following steps: adding the CdS / Ag2S / SiO2 composite material to a sodium hydroxide solution and refluxing at 85~95℃ for 3.5~4.5h to remove SiO2 from the CdS / Ag2S / SiO2 composite material, centrifuging and washing until neutral, and vacuum drying to obtain hollow spherical CdS / Ag2S photocatalyst.

[0027] More preferably, step (4) includes the following steps: adding the CdS / Ag2S / SiO2 composite material to a sodium hydroxide solution and refluxing at 90°C for 4 hours to remove SiO2 from the CdS / Ag2S / SiO2 composite material, centrifuging and washing until neutral, and vacuum drying to obtain hollow spherical CdS / Ag2S photocatalyst.

[0028] More preferably, the concentration of the sodium hydroxide solution is 2.0 mol / L.

[0029] More preferably, the ratio of CdS / Ag2S / SiO2 composite material to sodium hydroxide solution is 100mg:200mL.

[0030] The present invention also provides a hollow spherical CdS / Ag2S photocatalyst prepared by the above preparation method.

[0031] This invention also provides the application of the above-mentioned hollow spherical CdS / Ag2S photocatalyst in photocatalytic water splitting for hydrogen production.

[0032] The present invention has the following beneficial effects: This invention utilizes an integrated template-cation exchange-template etching process to prepare hollow spherical CdS / Ag2S photocatalysts with uniform morphology and high purity. This hollow structure significantly increases the specific surface area, providing more catalytic active sites and facilitating multiple light reflection absorption and rapid diffusion of reactant molecules. Simultaneously, the cation exchange reaction allows for precise control of the Ag2S loading, achieving atomic-level uniform dispersion of Ag2S on the CdS matrix and effectively avoiding agglomeration phenomena common in traditional loading methods. Furthermore, the constructed CdS / Ag2S heterojunction, together with in-situ generated Ag nanoparticles, forms a ternary composite structure. Combined with the unique spatial advantages of the hollow structure, this significantly improves the separation efficiency of photogenerated carriers and effectively suppresses the photocorrosion problem of CdS, resulting in catalytic activity and long-term stability far exceeding existing technologies. This makes it suitable for visible light-driven photocatalytic water splitting for hydrogen production and other photocatalytic applications. In addition, the preparation process of this invention is simplified, the reaction conditions are mild, and it is easy to scale up for production, laying a solid foundation for the industrial application of hollow structure photocatalysts. Attached Figure Description

[0033] Figure 1The following are the preparation process and corresponding SEM and diameter distribution histograms of the products in Example 1: (a) is a flowchart of the preparation process in Example 1; (b) is an SEM image of the obtained SiO2 template nanospheres; (c) is a diameter distribution histogram of the obtained SiO2 template nanospheres; (d) is an SEM image of the obtained CdS / SiO2 composite nanospheres; (e) is a diameter distribution histogram of the obtained CdS / SiO2 composite nanospheres; (f) is an SEM image of the obtained CdS / Ag2S / SiO2 composite material; (g) is a diameter distribution histogram of the obtained CdS / Ag2S / SiO2 composite material; (h) is an SEM image of the obtained CdS / Ag2S-15%-HSP; and (i) is a diameter distribution histogram of the obtained CdS / Ag2S-15%-HSP. Figure 2 The images show the TEM and HRTEM images of CdS / Ag2S-15%-HSP prepared in Example 1; where (a) is the TEM image of CdS / Ag2S-15%-HSP; (b) is the HRTEM image of CdS / Ag2S-15%-HSP; and (c) is a magnified view of region A in (b). Figure 3 The images are spectral analysis diagrams; (a) are the light absorption spectra of the photocatalysts prepared in Examples 1-4 and Comparative Example 2; (b) is a comparison diagram of the band gap values ​​of the photocatalysts prepared in Example 1 and Comparative Example 2. Detailed Implementation

[0034] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are only for explaining the invention and are not intended to limit the invention; that is, the described embodiments are only a part of the embodiments of this invention, and not all of them.

[0035] Therefore, the following detailed description of the embodiments of the present invention is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0036] The features and performance of the present invention will be further described in detail below with reference to embodiments.

[0037] Example 1 A method for preparing a hollow spherical CdS / Ag2S photocatalyst includes the following steps: (1) Dissolve 12 mL of tetraethyl orthosilicate in 60 mL of anhydrous ethanol, then add 120 mL of 28% ammonia water and mix well. Place the mixture in a constant temperature ultrasonic cleaner, set the ultrasonic frequency to 40 kHz, and perform hydrolysis and condensation at 40 °C for 40 min. After the reaction, centrifuge the resulting milky white mixture at 10000 r / min for 10 min, remove the supernatant, and wash the precipitate obtained by centrifugation three times alternately with deionized water and anhydrous ethanol. Each time, ultrasonic dispersion and centrifugation are performed. Place the washed precipitate in a vacuum drying oven and vacuum dry at 50 °C for 10 h to obtain SiO2 template nanospheres with regular morphology, good dispersibility and monodispersity. (2) Weigh 0.1g of SiO2 template nanospheres and disperse them in 150mL of water. Add 0.3g of sodium citrate, 0.19g of cadmium acetate, 2.5mL of ammonia water with a mass fraction of 28% and 0.1g of thiourea and mix well. Reflux the mixture at 60℃ for 3h. Centrifuge and wash to obtain CdS / SiO2 composite nanospheres. (3) Weigh 0.2g of CdS / SiO2 composite nanospheres and disperse them in 50mL of diethylene glycol. Stir at room temperature until the powder is uniformly dispersed to obtain a CdS / SiO2 composite nanosphere suspension. Dissolve 0.0954g of silver nitrate in deionized water and add it dropwise to the CdS / SiO2 composite nanosphere suspension under stirring. After the addition is complete, heat to 70℃ for cation exchange reaction for 3h. After the reaction is completed, centrifuge the reaction solution and wash the solid precipitate repeatedly with deionized water and anhydrous ethanol 3 times to obtain CdS / Ag2S / SiO2 composite material. (4) 100 mg of CdS / Ag2S / SiO2 composite material was added to 200 mL of 2.0 mol / L sodium hydroxide solution and refluxed at 90 °C for 4 h to remove SiO2 from the CdS / Ag2S / SiO2 composite material. After centrifugation and washing until neutral, the mixture was vacuum dried at 50 °C for 6 h to obtain hollow spherical CdS / Ag2S photocatalyst, denoted as CdS / Ag2S-15%-HSP.

[0038] Example 2 A method for preparing a hollow spherical CdS / Ag2S photocatalyst differs from Example 1 only in that the mass of silver nitrate in step (3) is 0.0318 g, ultimately yielding a hollow spherical CdS / Ag2S photocatalyst, denoted as CdS / Ag2S-5%-HSP. The remaining steps and parameters are the same as in Example 1.

[0039] Example 3 A method for preparing a hollow spherical CdS / Ag2S photocatalyst differs from Example 1 only in that the mass of silver nitrate in step (3) is 0.0636 g, ultimately yielding a hollow spherical CdS / Ag2S photocatalyst, denoted as CdS / Ag2S-10%-HSP. The remaining steps and parameters are the same as in Example 1.

[0040] Example 4 A method for preparing a hollow spherical CdS / Ag2S photocatalyst differs from Example 1 only in that the mass of silver nitrate in step (3) is 0.1272 g, ultimately yielding a hollow spherical CdS / Ag2S photocatalyst, denoted as CdS / Ag2S-20%-HSP. The remaining steps and parameters are the same as in Example 1.

[0041] Example 5 A method for preparing a hollow spherical CdS / Ag2S photocatalyst includes the following steps: (1) Dissolve 10 mL of tetraethyl orthosilicate in 55 mL of methanol, then add 110 mL of 25% ammonia water and mix well. Place the mixture in a constant temperature ultrasonic cleaner, set the ultrasonic frequency to 40 kHz, and perform hydrolysis and condensation at 35 °C for 45 min. After the reaction, centrifuge the resulting milky white mixture at 8000 r / min for 15 min, remove the supernatant, and wash the precipitate obtained by centrifugation three times alternately with deionized water and anhydrous ethanol. Each time, ultrasonic dispersion and centrifugation are performed. Place the washed precipitate in a vacuum drying oven and vacuum dry at 45 °C for 12 h to obtain SiO2 template nanospheres with regular morphology, good dispersibility and monodispersity. (2) Weigh 0.05g of SiO2 template nanospheres and disperse them in 150mL of water. Add 0.2g of sodium citrate, 0.1g of cadmium acetate, 2mL of ammonia water with a mass fraction of 28% and 0.05g of thiourea and mix well. Reflux the mixture at 55℃ for 3.5h. Centrifuge and wash to obtain CdS / SiO2 composite nanospheres. (3) Weigh 0.2g of CdS / SiO2 composite nanospheres and disperse them in 50mL of diethylene glycol. Stir at room temperature until the powder is uniformly dispersed to obtain a CdS / SiO2 composite nanosphere suspension. Dissolve 0.0954g of silver nitrate in deionized water and add it dropwise to the CdS / SiO2 composite nanosphere suspension under stirring. After the addition is complete, heat to 65℃ for cation exchange reaction for 3.5h. After the reaction is completed, centrifuge the reaction solution and wash the solid precipitate repeatedly with deionized water and anhydrous ethanol 3 times to obtain CdS / Ag2S / SiO2 composite material. (4) 100 mg of CdS / Ag2S / SiO2 composite material was added to 200 mL of 2.0 mol / L sodium hydroxide solution and refluxed at 85 °C for 4.5 h to remove SiO2 from the CdS / Ag2S / SiO2 composite material. After centrifugation and washing until neutral, the composite material was vacuum dried at 50 °C for 6 h to obtain hollow spherical CdS / Ag2S photocatalyst.

[0042] Example 6 A method for preparing a hollow spherical CdS / Ag2S photocatalyst includes the following steps: (1) Dissolve 14 mL of tetraethyl orthosilicate in 65 mL of isopropanol, then add 130 mL of 30% ammonia water and mix well. Place the mixture in a constant temperature ultrasonic cleaner, set the ultrasonic frequency to 20 kHz, and perform hydrolysis and condensation at 45 °C for 35 min. After the reaction, centrifuge the resulting milky white mixture at 12000 r / min for 8 min, remove the supernatant, and wash the precipitate obtained by centrifugation three times alternately with deionized water and anhydrous ethanol. Each time, ultrasonic dispersion and centrifugation are performed. Place the washed precipitate in a vacuum drying oven and vacuum dry at 55 °C for 8 h to obtain SiO2 template nanospheres with regular morphology, good dispersibility and monodispersity. (2) Weigh 0.15g of SiO2 template nanospheres and disperse them in 150mL of water. Add 0.4g of sodium citrate, 0.2g of cadmium acetate, 3mL of ammonia water with a mass fraction of 28% and 0.15g of thiourea and mix well. Reflux the mixture at 65℃ for 2.5h. Centrifuge and wash to obtain CdS / SiO2 composite nanospheres. (3) Weigh 0.2g of CdS / SiO2 composite nanospheres and disperse them in 50mL of diethylene glycol. Stir at room temperature until the powder is uniformly dispersed to obtain a CdS / SiO2 composite nanosphere suspension. Dissolve 0.0954g of silver nitrate in deionized water and add it dropwise to the CdS / SiO2 composite nanosphere suspension under stirring. After the addition is complete, heat to 75℃ for cation exchange reaction for 2.5h. After the reaction is completed, centrifuge the reaction solution and wash the solid precipitate repeatedly with deionized water and anhydrous ethanol 3 times to obtain CdS / Ag2S / SiO2 composite material. (4) 100 mg of CdS / Ag2S / SiO2 composite material was added to 200 mL of 2.0 mol / L sodium hydroxide solution and refluxed at 95 °C for 3.5 h to remove SiO2 from the CdS / Ag2S / SiO2 composite material. After centrifugation and washing until neutral, the composite material was vacuum dried at 50 °C for 6 h to obtain hollow spherical CdS / Ag2S photocatalyst.

[0043] Comparative Example 1 A method for preparing a solid CdS / Ag2S photocatalyst includes the following steps: (1) Weigh 1 mmol of cadmium acetate dihydrate into 10 mL of deionized water and stir continuously to dissolve it. Then add 0.176 mmol of silver acetate and stir continuously to obtain a uniform and transparent mixture A. (2) Add 1 mmol of urea and 12 mmol of L-cysteine ​​to 22 mL of deionized water and stir until completely dissolved to obtain a uniform and transparent mixture B. (3) Under stirring conditions, mixture A is injected into mixture B and stirred continuously for 1 hour to obtain a milky white mixed suspension. (4) The mixed suspension was transferred to a 50 mL polytetrafluoroethylene-lined hydrothermal reactor and reacted at a constant temperature of 145℃ for 10 h. After the reaction was completed, the mixture was naturally cooled to room temperature, centrifuged to collect the precipitate, and washed three times with deionized water and ethanol to remove residual ions and organic impurities. The precipitate was then dried in an oven at 60℃ for 12 h to obtain a solid CdS / Ag2S photocatalyst, denoted as CdS / Ag2S-15%-1.

[0044] Comparative Example 2 A method for preparing hollow spherical CdS photocatalyst includes the following steps: (1) Dissolve 12 mL of tetraethyl orthosilicate in 60 mL of anhydrous ethanol, then add 120 mL of 28% ammonia water and mix well. Place the mixture in a constant temperature ultrasonic cleaner, set the ultrasonic frequency to 40 kHz, and perform hydrolysis and condensation at 40 °C for 30 min. After the reaction, centrifuge the resulting milky white mixture at 10000 r / min for 10 min, remove the supernatant, and wash the precipitate obtained by centrifugation three times alternately with deionized water and anhydrous ethanol. Each time, ultrasonic dispersion and centrifugation are performed. Place the washed precipitate in a vacuum drying oven and vacuum dry at 50 °C for 10 h to obtain SiO2 template nanospheres with regular morphology, good dispersibility and monodispersity. (2) Weigh 0.1g of SiO2 template nanospheres and disperse them in 150mL of water. Add 0.3g of sodium citrate, 0.19g of cadmium acetate, 2.5mL of ammonia water with a mass fraction of 28% and 0.1g of thiourea and mix well. Reflux the mixture at 60℃ for 3h. Centrifuge and wash to obtain CdS / SiO2 composite nanospheres. (3) 100 mg of CdS / SiO2 composite nanospheres were added to 200 mL of 2.0 mol / L sodium hydroxide solution and refluxed at 90 °C for 4 h to remove SiO2 from the CdS / SiO2 composite nanospheres. After centrifugation and washing until neutral, the nanospheres were dried under vacuum at 50 °C for 6 h to obtain hollow spherical CdS photocatalyst, denoted as CdS-HSP.

[0045] Comparative Example 3 A method for preparing a CdS / Ag2S photocatalyst includes the following steps: (1) Add 0.002 mol of cadmium sulfate powder and 10 mL of saturated thiourea solution at 30 °C to a conical flask. Place the conical flask under normal temperature and pressure conditions and let it stand for 30 days. After the reaction is completed, collect the product, wash it thoroughly with distilled water, and dry it under vacuum at 35 °C for 4 h to obtain pure CdS powder. (2) Weigh 0.1 g of the pure CdS powder obtained above and disperse it in 100 mL of silver nitrate solution with a mass concentration of 0.0025 mol / L. Place it in an H66025 ultrasonic cleaner (power 20 W, frequency 13.5 kHz) for continuous ultrasonic treatment for 20 h. After the reaction is completed, filter the product and wash it with distilled water several times to remove residual ionic impurities on the surface. Dry it in a vacuum environment at 35 °C for 4 h to obtain CdS / Ag2S photocatalyst, denoted as CdS / Ag2S-15%-2.

[0046] Experimental Example 1: Product Morphology 1.1 SEM and diameter distribution characterization The morphology of the SiO2 template nanospheres, CdS / SiO2 composite nanospheres, CdS / Ag2S / SiO2 composite materials, and CdS / Ag2S-15%-HSP prepared in Example 1 was characterized, and the diameter distribution of the corresponding nanospheres was analyzed. The results are as follows: Figure 1 As shown.

[0047] from Figure 1 As can be seen, the prepared SiO2 nanospheres have very smooth surfaces and are of very uniform size. A diameter distribution histogram shows that the diameter of the prepared SiO2 nanospheres is approximately 450 nm. After CdS is deposited on the SiO2 nanospheres via deposition, the surface of the SiO2 nanospheres becomes rougher due to the formation and deposition of CdS, proving the successful deposition of CdS nanoparticles on the surface of the SiO2 nanospheres. The diameter distribution of the CdS / SiO2 composite nanospheres shows that the diameter is approximately 550 nm. The solubility product constants (Ksp) of CdS and Ag2S are significantly different, with Ksp = 1.4 × 10⁻⁶. -29 (CdS) and Ksp = 6.6 × 10 -50(Ag2S) shows a significant difference in their solubility product constants. This difference allows the cation exchange reaction between CdS and Ag ions to occur easily. Therefore, the morphology and diameter results of the CdS / Ag2S / SiO2 composite material obtained by cation exchange in diethylene glycol show that when Ag2S is loaded onto CdS / SiO2 composite nanospheres through ion exchange, the morphology of the CdS / Ag2S / SiO2 composite material remains consistent with that of the CdS / SiO2 composite nanospheres, which are also nanospheres with a diameter of approximately 550 nm. This is because the amount of Ag2S introduced is very small and the cation exchange occurs on the surface. After the SiO2 nanosphere template was etched away using a strong alkaline solution of NaOH, the SEM results of the obtained CdS / Ag2S-15%-HSP showed that the morphology of CdS / Ag2S-15%-HSP still maintained the shape of nanospheres with a diameter distribution of 550 nm after the SiO2 nanosphere template was removed.

[0048] 1.2 TEM and HRTEM characterization The CdS / Ag2S-15%-HSP prepared in Example 1 was characterized by TEM and HRTEM, and the results are as follows: Figure 2 As shown.

[0049] from Figure 2 As can be seen from the results, the CdS / Ag2S-15%-HSP prepared in Example 1 has a hollow spherical structure with a diameter of about 550 nm and a shell thickness of 25~30 nm. It contains only hexagonal CdS and monoclinic Ag2S and has no impurities.

[0050] 1.3 Spectral Analysis The light absorption spectra of the photocatalysts prepared in Examples 1-4 and Comparative Example 2 were analyzed, and the results are as follows: Figure 3 As shown.

[0051] from Figure 3 As can be seen, the photocatalyst prepared by this invention exhibits hollow scattering accompanied by Ag2S redshift. Under the condition of Ag2S presence, its band gap decreases from 2.28 eV to 2.1 eV, and the visible light utilization efficiency is greatly improved.

[0052] Experimental Example 2: Analysis of the Photocatalytic Performance of the Product The photocatalytic performance of the photocatalysts prepared in Example 1 and Comparative Examples 1-3 was analyzed. The photocatalytic hydrogen production performance of the samples was tested using an automated gas circulation system (model CEL-SPH2N-D9) from Zhongjiao Jinyuan, with Na2S-Na2SO3 aqueous solution as the sacrificial agent. In a typical photocatalytic hydrogen production reaction, 25 mg of photocatalyst powder was ultrasonically dispersed in 50 mL of 0.1 M Na2S-0.1 M Na2SO3 aqueous solution. The entire gas circulation system, including the reaction unit, was evacuated to completely remove air, and the reaction unit was maintained at 6°C using a cooling device. Then, the reaction unit was irradiated with light of different wavelengths for 4 hours. Nitrogen was used as the carrier gas in this system, and the H2 production was measured online using a thermal conductivity detector (TCD), from which the hydrogen production rate was calculated. The results are shown in Table 1.

[0053] Table 1. Photocatalytic performance analysis of the photocatalysts prepared in Example 1 and Comparative Examples 1-3

[0054] As can be seen from Table 1, the optimal hydrogen production rate of the hollow spherical CdS / Ag2S photocatalyst prepared in this invention is 275.3 μmol / L. g -1 h -1 The activity of the hollow spherical CdS / Ag2S photocatalyst prepared in this invention is 2.3 times that of the solid CdS / Ag2S photocatalyst in Comparative Example 1, 10.8 times that of the hollow spherical CdS photocatalyst in Comparative Example 2, and 1.48 times that of the hollow CdS / Ag2S photocatalyst prepared by the ordinary precipitation method in Comparative Example 3. Furthermore, the hollow spherical CdS / Ag2S photocatalyst prepared in this invention retains 95% of its activity after 4 cycles, has an intact hollow morphology, stable Ag2S phase, and significantly inhibits photocorrosion, demonstrating excellent performance in all aspects.

[0055] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a hollow spherical CdS / Ag2S photocatalyst, characterized in that, Includes the following steps: (1) The silicon source is dissolved in an organic solvent and hydrolyzed and condensed under the action of an alkaline catalyst to obtain SiO2 template nanospheres; (2) Disperse SiO2 template nanospheres in water, add sodium citrate, cadmium source, ammonia and sulfur source for reflux reaction to obtain CdS / SiO2 composite nanospheres; (3) CdS / SiO2 composite nanospheres were dispersed in an organic solvent, and then a silver source was added to carry out a cation exchange reaction to obtain CdS / Ag2S / SiO2 composite material. (4) The SiO2 in the CdS / Ag2S / SiO2 composite material was removed by etching to obtain hollow spherical CdS / Ag2S photocatalyst.

2. The method for preparing the hollow spherical CdS / Ag2S photocatalyst as described in claim 1, characterized in that, In step (1), the silicon source is tetraethyl orthosilicate or methyl orthosilicate; the organic solvent is anhydrous ethanol, methanol or isopropanol; the alkaline catalyst is ammonia water with a mass fraction of 25-30%; and the volume ratio of the silicon source, organic solvent and alkaline catalyst is (10-14):(55-65):(110-130).

3. The method for preparing the hollow spherical CdS / Ag2S photocatalyst as described in claim 1, characterized in that, In step (1), the hydrolysis-condensation reaction is carried out under ultrasonic conditions, with an ultrasonic frequency of 20-40 kHz, a temperature of 35-45 °C, and a time of 35-45 min.

4. The method for preparing the hollow spherical CdS / Ag2S photocatalyst as described in claim 1, characterized in that, In step (2), the cadmium source is cadmium acetate, cadmium nitrate, or cadmium chloride; the sulfur source is thiourea, thioacetamide, or sodium thiosulfate; the ratio of SiO2 template nanospheres, sodium citrate, cadmium source, ammonia, and sulfur source is (0.05~0.15)g:(0.2~0.4)g:(0.1~0.2)g:(2~3)mL:(0.05~0.15)g.

5. The method for preparing the hollow spherical CdS / Ag2S photocatalyst as described in claim 1, characterized in that, In step (2), the reflux reaction temperature is 55~65℃ and the time is 2.5~3.5h.

6. The method for preparing the hollow spherical CdS / Ag2S photocatalyst as described in claim 1, characterized in that, In step (3), the organic solvent is diethylene glycol; the silver source is silver nitrate or silver sulfate; and the mass ratio of the CdS / SiO2 composite nanospheres to the silver source is 0.2:(0.03~0.13).

7. The method for preparing the hollow spherical CdS / Ag2S photocatalyst as described in claim 1, characterized in that, In step (3), the cation exchange reaction temperature is 65~75℃ and the time is 2.5~3.5h.

8. The method for preparing the hollow spherical CdS / Ag2S photocatalyst as described in claim 1, characterized in that, Step (4) includes the following steps: adding the CdS / Ag2S / SiO2 composite material to a sodium hydroxide solution and refluxing at 85~95℃ for 3.5~4.5h to remove SiO2 from the CdS / Ag2S / SiO2 composite material. After centrifugation and washing until neutral, the material is vacuum dried to obtain hollow spherical CdS / Ag2S photocatalyst.

9. Hollow spherical CdS / Ag2S photocatalyst prepared by the preparation method according to any one of claims 1 to 8.

10. The application of the hollow spherical CdS / Ag2S photocatalyst according to claim 9 in photocatalytic water splitting for hydrogen production.

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