A selenium-doped sulfur-rich zinc-cadmium sulfur material with vacancy sites and its application in photocatalytic water splitting for hydrogen production.

Abstract

This invention relates to a selenium-doped sulfur-vacancy-rich zinc-cadmium-sulfur (ZnCdS) material and its application in photocatalytic water splitting for hydrogen production, belonging to the field of photocatalytic water splitting for hydrogen production. This invention employs a synergistic strategy of vacancies and doping, using zinc acetate dihydrate, cadmium acetate dihydrate, thioacetamide (TAA), and selenium powder (Se) as raw materials, and hydrazine hydrate as a reducing agent, to prepare uniformly Se-doped sulfur-vacancy-rich ZnCdS nanoparticles via a one-step hydrothermal method. Sulfur vacancy defects, acting as electron-trapping sites, facilitate the separation of photogenerated electrons and holes in bulk ZnCdS, while Se doping effectively increases the Fermi level of the material and activates more reactive sites. The synergistic effect of sulfur vacancies and Se doping optimizes the electronic structure of the material, significantly improving the efficiency and stability of ZnCdS water splitting for hydrogen production under visible light. This invention demonstrates the great potential of transition metal selenium sulfides in the field of photocatalytic water splitting for hydrogen production.

Description

Technical Field

[0001] This invention relates to a selenium-doped sulfur-rich vacancy zinc-cadmium sulfur material and its application in photocatalytic water splitting for hydrogen production, belonging to the field of photocatalytic water splitting for hydrogen production technology. Background Technology

[0002] Solar-driven photocatalytic water splitting for hydrogen production is a sustainable and cost-effective strategy for alleviating the current energy crisis and addressing environmental pollution. The key to achieving efficient hydrogen production lies in the development of highly efficient photocatalysts. Zinc cadmium sulfide (ZnCdS) is a transition metal sulfide semiconductor material with tunable bandgap, flexible band edge positions, simple synthesis process, strong visible light response, and high resistance to photocorrosion, and has been widely studied in the field of photocatalytic water splitting for hydrogen production. However, the photocatalytic activity and stability of bulk ZnCdS are still insufficient to meet the needs of practical applications. Therefore, developing ZnCdS photocatalysts with high activity and long-lasting stability is crucial.

[0003] Studies have shown that surface defects such as cation or anion vacancies can introduce defect energy levels into the band structure of semiconductors. The presence of these defect energy levels, acting as electron-trapping sites, can enhance the visible light capture capability of materials and accelerate charge transport of photogenerated carriers, ultimately improving photocatalytic hydrogen production activity. For example, using Li-EDA as a reducing agent, Hu et al. prepared a disordered ZnCdS solid solution containing Zn and S double vacancies. The presence of these double vacancies promoted the separation and migration of photogenerated charge carriers, significantly enhancing the photocatalytic activity of ZnCdS, reaching a maximum of 33.6 mmol·g⁻¹. -1 ·h -1 (E.Ha, S.Ruan, D.Li, Y.Zhu, Y.Chen, J.Qiu, Z.Chen, T.Xu, J.Su, L.Wang, J.Hu, Nano Research, 2022, 15:996-1002). Huang et al. prepared twinned Cd with abundant sulfur vacancies and wurtzite-zincblende phase junctions. 0.6 Zn 0.4 S catalyst. The combination of twinned structure and sulfur vacancies ultimately endows Cd with... 0.6 Zn 0.4 S showed significant photocatalytic hydrogen production activity from water splitting (42.66 mmol·g). -1 ·h -1 ) (H.-B. Huang, Z.-B. Fang, K. Yu, J. Lü, R. Cao, Journal of Materials Chemistry A, 2020, 8: 3882-3891).

[0004] Selenium (Se), an element with semi-metallic properties, has low electronegativity (2.55) and a suitable size. It exhibits high polarizability and is environmentally friendly. Selenium doping of typical photocatalysts is also an effective method for modulating the electronic structure of semiconductors and improving the charge transport dynamics of materials. For example, patent CN109225307B discloses an Eu... 3+ This paper discusses Se-co-doped ZnO / g-C3N4 materials and their application in photocatalysis. The material catalyzes the oxidation of isopropanol to acetone under visible light with high acetone selectivity. Patent CN110841661A discloses a nitrogen-vacancy-rich Se-doped graphitic carbon nitride photocatalyst controllably prepared using Se-assisted chemical vapor deposition (CVD). This catalyst exhibits excellent visible-light water splitting hydrogen production performance (5418 μmol·g⁻¹). -1 ·h -1 Li et al. prepared quaternary CdIn2S using a one-step hydrothermal method. 4-x Se x Solid solution nanocrystalline photocatalysts demonstrate the superiority of transition metal selenium sulfides in photocatalytic hydrogen production (Z.Li,W.Zhong,D.Gao,F.Chen,H.Yu,Advanced Sustainable Systems,2023,7:2200030). Shi et al. synthesized a series of Se-doped CdS quantum dots using a solvothermal method. Se doping enhances the Fermi level of CdS, providing a basis for the effective capture of photogenerated electrons. Furthermore, Se doping increases the carrier density, thus improving the photocatalytic hydrogen production of CdS. 0.9 Se 0.1 It showed 29.12 mmol·g -1 ·h -1 Photocatalytic hydrogen evolution rate (J.-W.Shi,D.Sun,Y.Zou,D.Ma,C.He,X.Ji,C.Niu,Chemical Engineering Journal,2019,364:11-19).

[0005] Leveraging the advantages of vacancy regulation and elemental doping in improving charge separation and transfer efficiency and activating reactive sites in bulk materials, this invention employs a synergistic strategy of vacancy and doping. Using zinc acetate dihydrate, cadmium acetate dihydrate, thioacetamide (TAA), and selenium powder (Se) as raw materials and hydrazine hydrate as a reducing agent, a one-step hydrothermal method is used to prepare sulfur-vacancy-rich ZnCdS nanomaterials uniformly doped with Se. Sulfur vacancy defects, acting as electron-trapping sites, facilitate the separation of photogenerated electrons and holes in bulk ZnCdS. Se doping effectively increases the Fermi level and activates more reactive sites. The synergistic effect of sulfur vacancies and Se doping optimizes the electronic structure of the material, significantly improving the efficiency and stability of hydrogen production from ZnCdS via visible light-driven water splitting. This invention discloses the preparation method of this photocatalyst and its application in photocatalytic water splitting for hydrogen production, which is of great significance for developing highly efficient transition metal selenium sulfide photocatalysts. Summary of the Invention

[0006] The purpose of this invention is to provide a selenium-doped sulfur-rich vacancy zinc-cadmium sulfur material with high activity and stability and its application in photocatalytic hydrolysis for hydrogen production.

[0007] To achieve the above objectives, the present invention adopts the following technical solution:

[0008] A method for synthesizing selenium-doped sulfur-rich vacancy zinc-cadmium-sulfur materials is characterized by the following steps: Zinc acetate dihydrate (Zn(CH3COO)2·2H2O) (1.0976 g), cadmium acetate dihydrate (Cd(CH3COO)2·2H2O) (1.3326 g), and thioacetamide (TAA) (0.8981–0.8938 g) are dissolved in 43 mL of deionized water and ultrasonically dispersed to obtain solution A. Simultaneously, selenium powder (0.0036–0.0081 g) is dissolved in 7 mL of hydrazine hydrate, and the resulting solution B is placed in an 80°C water bath. Solution B is then added dropwise to solution A, stirred thoroughly, and transferred to a 100 mL high-pressure reactor. The mixture is then reacted at 160–190°C for 10–13 h. After naturally cooling to room temperature, the precipitate is collected by centrifugation, washed thoroughly with deionized water and ethanol in sequence, and then dried thoroughly to obtain selenium-doped sulfur-vacancy-rich ZnCdS, denoted as Se / Vs-ZCS; wherein the mass percentage of Se powder to (TAA+Se powder) is 0.4-0.9%, and the molar ratio of zinc source, cadmium source, and (TAA+Se powder) is 5:5:12.

[0009] The synthesized selenium-doped sulfur-vacancy-rich ZnCdS material was applied to a photocatalytic hydrolysis reaction for hydrogen production. The process included the following steps: 5 mg of sulfur-vacancy-rich selenium-doped ZnCdS material powder was weighed and ultrasonically dispersed in 100 mL of a 0.35 M Na₂S / 0.25 M Na₂SO₃ mixed aqueous solution, which was then added to a reactor. The reactor was then connected to a photocatalytic reaction system and evacuated. The reaction system was irradiated with a xenon lamp (λ≥420 nm) equipped with a 420 nm UV cutoff filter. The generated hydrogen gas was detected using a GC 7900 gas chromatograph.

[0010] This invention employs a one-step hydrothermal method to simultaneously introduce S vacancies and Se doping into the ZnCdS lattice, overcoming the complex defects of traditional transition metal selenium sulfide synthesis processes. It effectively regulates the electronic structure of the material, activates its inert active sites, promotes photogenerated carrier transport, and significantly improves the efficiency and stability of hydrogen production from water splitting in ZnCdS.

[0011] The beneficial effects of the selenium-doped sulfur-rich ZnCdS material of the present invention and its application in photocatalytic water splitting for hydrogen production are as follows:

[0012] (1) The material of the present invention can be synthesized by a one-step hydrothermal method. The process is simple, controllable, and reproducible, providing a good technical foundation for the practical application of efficient transition metal sulfide photocatalysts.

[0013] (2) The selenium-doped sulfur-rich vacancy ZnCdS material prepared by the present invention further enhances the photogenerated electron migration capability of the material by introducing S vacancy and Se doping, effectively suppresses the recombination of photogenerated electrons and holes, and activates the surface inert active sites, thereby realizing the efficient utilization of photogenerated carriers and the efficient hydrogen production of photocatalytic reaction.

[0014] (3) The selenium-doped sulfur-rich ZnCdS material prepared in this invention exhibits significantly better photocatalytic hydrogen production performance than pristine ZnCdS under the synergistic effect of S vacancies and Se doping. Specifically, 0.6% Se / V S -ZCS exhibits the highest photocatalytic activity, with a hydrogen production rate reaching ~85.3 mmol·g. -1 ·h -1 After six cycles over 12 hours, the photocatalytic activity of the catalyst decreased by only 4.9%. This demonstrates that the selenium-doped sulfur-rich ZnCdS visible light catalyst prepared in this invention possesses excellent photocatalytic activity and stability. Attached Figure Description

[0015] Figure 1 X-ray powder diffraction (XRD) patterns of zinc cadmium sulfur prepared as a control example and selenium-doped sulfur-rich vacancy zinc cadmium sulfur (Se / Vs-ZCS-1) prepared in Example 1.

[0016] Figure 2 Transmission electron microscopy (TEM) images of zinc cadmium sulfur prepared as a control example and selenium-doped sulfur-rich vacancy zinc cadmium sulfur (Se / Vs-ZCS-1) prepared in Example 1.

[0017] Figure 3 High-resolution transmission electron microscopy (HRTEM) images of zinc cadmium sulfur prepared as a control example and selenium-doped sulfur-rich vacancy zinc cadmium sulfur (Se / Vs-ZCS-1) prepared in Example 1.

[0018] Figure 4 In-situ electron paramagnetic resonance (EPR) images of zinc cadmium sulfur prepared as a control example and selenium-doped sulfur-rich vacancy zinc cadmium sulfur (Se / Vs-ZCS-1) prepared in Example 1.

[0019] Figure 5 Photocatalytic hydrogen production performance of zinc-cadmium sulfur prepared as a control example and selenium-doped sulfur-rich vacancy zinc-cadmium sulfur prepared in Examples 1-2;

[0020] Figure 6 Photocatalytic hydrogen production cycle stability test diagrams of zinc-cadmium sulfur prepared as a control example and selenium-doped sulfur-rich vacancy zinc-cadmium sulfur prepared in Examples 1-2.

[0021] Figure 7 Energy level structure diagrams of zinc-cadmium-sulfur prepared as a control example and selenium-doped sulfur-rich vacancy zinc-cadmium-sulfur prepared as a control example.

[0022] Figure 8 The hydrogen evolution reaction polarization curves of zinc-cadmium sulfur prepared as a control example and selenium-doped sulfur-rich vacancy zinc-cadmium sulfur are shown. Detailed Implementation

[0023] The present invention will be described in more detail below with reference to specific embodiments. The accompanying drawings and specific embodiments are merely exemplary, but the scope of protection of the present invention is not limited to the following embodiments:

[0024] Example 1:

[0025] 1.0976 g of zinc acetate dihydrate (Zn(CH3COO)2·2H2O), 1.3326 g of cadmium acetate dihydrate (Cd(CH3COO)2·2H2O), and 0.8964 g of thioacetamide (TAA) were dissolved in 43 mL of deionized water and stirred for 0.5 h to obtain solution A. 0.0054 g of Se powder was weighed and dispersed in 7 mL of hydrazine hydrate. After stirring in an 80 °C water bath for 0.5 h, a brown solution B was obtained. Solution B was added dropwise to solution A using a dropper, and the mixture was stirred for 0.5 h. The resulting mixture was transferred to a 100 mL high-pressure reactor and reacted at 180 °C for 12 h. After the reactor cooled to room temperature, the mixture was centrifuged and the orange-yellow precipitate was collected. The precipitate was washed with deionized water and ethanol, respectively, and then vacuum dried at 60 °C for 12 h to obtain 0.6% selenium-doped sulfur-rich zinc-cadmium-sulfur nanomaterials, denoted as Se / Vs-ZCS-1.

[0026] Example 2:

[0027] 1.0976 g of zinc acetate dihydrate (Zn(CH3COO)2·2H2O), 1.3326 g of cadmium acetate dihydrate (Cd(CH3COO)2·2H2O), and 0.8946 g of thioacetamide (TAA) were added to 43 mL of deionized water and stirred for 0.5 h to obtain solution A. 0.0072 g of Se powder was dissolved in 7 mL of hydrazine hydrate under an 80 °C water bath and stirred for 0.5 h to obtain a brown solution B. Solution B was added dropwise to solution A, and after stirring for 0.5 h, the mixture was transferred to a 100 mL high-pressure reactor and hydrothermally reacted at 170 °C for 11 h. After the reactor cooled to room temperature, the precipitate was centrifuged and collected. The precipitate was washed with deionized water and ethanol, respectively, and then dried in a 60 °C oven for 12 h to obtain 0.8% selenium-doped sulfur-rich vacancy zinc-cadmium-sulfur nanomaterials, denoted as Se / Vs-ZCS-2.

[0028] Example 3 (Control Example):

[0029] 1.0976 g of zinc acetate dihydrate (Zn(CH3COO)2·2H2O), 1.3326 g of cadmium acetate dihydrate (Cd(CH3COO)2·2H2O), and 0.9016 g of thioacetamide (TAA) were weighed and dissolved in 50 mL of deionized water. After stirring for 0.5 h, the mixture was transferred to a 100 mL high-pressure reactor and reacted at 180 °C for 12 h. After the reactor cooled to room temperature, the precipitate was centrifuged and collected. The precipitate was washed with deionized water and ethanol, respectively, and then vacuum dried at 60 °C for 12 h to obtain zinc-cadmium-sulfur nanomaterials, denoted as ZCS.

[0030] from Figure 1The X-ray powder diffraction pattern shows that the characteristic diffraction peaks of Se / Vs-ZCS-1 prepared in Example 1 at 26.026°, 27.769°, and 29.564° correspond to the (100), (002), and (101) crystal planes of the ZnCdS solid solution, respectively. Compared with the control example ZCS, after sulfur vacancies and Se doping, the above three diffraction peaks of Se / Vs-ZCS-1 show a significant blue shift, proving the successful doping of Se element in the ZnCdS lattice. Figure 2 Transmission electron microscopy (TEM) images of Se / Vs-ZCS-1 were prepared for comparison with ZCS and Example 1. The images show that both Se / Vs-ZCS-1 and ZCS exhibit uniform nanoparticle morphology, indicating that selenium doping and the introduction of sulfur vacancies do not alter the overall morphology of zinc-cadmium-sulfur. Compared to ZCS, the larger particle size of Se / Vs-ZCS-1 indicates successful selenium doping. Furthermore, high-resolution transmission electron microscopy... Figure 3 As can be seen, some lattice fringes are missing on the (101) plane of Se / Vs-ZCS-1, indicating the presence of defects in Se / Vs-ZCS-1. Figure 4 The strong Lorentz signal at g = 2.003 in the in-situ electron paramagnetic resonance (EPR) image of Se / Vs-ZCS-1 indicates the presence of S vacancies in Se / Vs-ZCS-1.

[0031] Example 4:

[0032] Weigh 5 mg of the Se / Vs-ZCS powder prepared in Examples 1-2, ultrasonically disperse it in 100 mL of a 0.35 M Na₂S / 0.25 M Na₂SO₃ mixed aqueous solution, and add it to the reactor. Connect the reactor to the photocatalytic reaction system and evacuate. Irradiate the reaction system with a xenon lamp equipped with a 420 nm UV cutoff filter (λ ≥ 420 nm). Detect the generated hydrogen gas using a GC 7900 gas chromatograph. The results are as follows: Figure 5 As shown, after 2 hours of visible light irradiation, the photocatalytic hydrogen production rate of Se / Vs-ZCS-1 reached as high as 85.3 mmol·g. -1 ·h -1 The hydrogen production rate of Se / Vs-ZCS-2 can reach up to 74.3 mmol·g. -1 ·h -1 ZCS only showed 43.2 mmol·g -1 ·h -1 The hydrogen production performance is excellent. Therefore, the selenium-doped sulfur-rich ZnCdS material prepared in this invention exhibits good photocatalytic hydrogen production activity.

[0033] The Se / Vs-ZCS powders prepared in Examples 1-2 were subjected to photocatalytic hydrolysis six times to examine the cyclic stability of Se / Vs-ZCS-1 and Se / Vs-ZCS-2. Tests showed that the products obtained in Examples 1-2 maintained photocatalytic activity above 95% after a 12-hour cycle (2 hours per cycle), while the stability of the control ZCS after cycling was 93.36%. Figure 6 This indicates that selenium doping and sulfur vacancies are beneficial to improving the photochemical stability of the material. Further research shows that the excellent photocatalytic activity and stability of the selenium-doped, sulfur-vacancy-rich ZnCdS visible light catalyst prepared in this invention are mainly attributed to its elevated Fermi level (…). Figure 7 ) and more reactive sites ( Figure 8 ).

[0034] The results above show that the selenium-doped sulfur-rich vacancy zinc-cadmium-sulfur nanomaterials of the present invention have a simple synthesis process, good photocatalytic hydrolysis hydrogen production effect and stability, and are suitable for promotion.

[0035] The above description is only a preferred embodiment of the present invention. All equivalent changes and modifications made within the scope of the claims of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a selenium-doped sulfur-rich vacancy zinc-cadmium sulfur material, characterized in that, Using zinc acetate dihydrate, cadmium acetate dihydrate, thioacetamide (TAA), and selenium powder (Se) as raw materials, and hydrazine hydrate as a reducing agent, a one-step hydrothermal method was used to prepare sulfur-rich zinc cadmium sulfide (ZnCdS) nanoparticles uniformly doped with sulfur vacancies. The specific steps included: (1) Dissolve 1.0976 g Zn(CH3COO)2·2H2O, 1.3326 g Cd(CH3COO)2·2H2O and 0.8981 ~ 0.8938 g TAA in 43 mL of deionized water to obtain solution A; (2) Dissolve 0.0036 ~ 0.0081 g Se powder in 7 mL of hydrazine hydrate and dissolve in a water bath at 80 °C to form a brown solution B; (3) Add solution B dropwise to solution A, and transfer the resulting mixed solution to a 100 mL reaction vessel. React hydrothermally at 160 ~ 190 ℃ for 10 ~ 13 h. (4) After the reaction vessel is cooled to room temperature, centrifuge and collect the precipitate. After washing and drying, the selenium-doped sulfur-rich zinc-cadmium-sulfur nanoparticles are obtained.

2. The preparation method according to claim 1, characterized in that, The mass percentage of Se powder to TAA+Se powder is 0.4~0.9%, and the molar ratio of Zn(CH3COO)2·2H2O, Cd(CH3COO)2·2H2O, and TAA+Se powder is 5:5:

12.

3. A selenium-doped sulfur-rich vacancy zinc-cadmium sulfur material prepared by the preparation method according to claim 1 or 2, characterized in that, Sulfur vacancy defects, acting as electron trapping sites, facilitate the separation of photogenerated electrons and holes in bulk ZnCdS. Se doping effectively increases the Fermi level of the material and activates more reactive sites.

4. The application of a selenium-doped sulfur-rich vacancy zinc-cadmium sulfur material as described in claim 3 in photocatalytic water splitting for hydrogen production, characterized in that, The selenium-doped sulfur-rich vacancy zinc-cadmium sulfur material exhibits significantly improved efficiency and stability in hydrogen production via visible light-driven hydrolysis.

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