Construction Of ZnIn₂S₄-based Heterojunction Photocatalytic Water Splitting Syste

In recent years,due to the excessive consumption of fossil energy and environmental pollution,the development of renewable and clean energy is considered as a technological support to achieve"carbon neutrality and carbon peaking".As a clean energy source,hydrogen has received close attention from researchers because of its high calorific value and energy density.Among all hydrogen production technologies,the use of solar energy,one of the renewable energy sources,to drive hydrogen production from water decomposition is considered an effective way to convert solar energy into hydrogen energy and thus achieve energy conversion.Unfortunately,the low efficiency of photogenerated carrier separation and slow kinetic migration lead to the extremely easy compounding of photogenerated electron-hole pairs generated by single-component semiconductor catalysts.Therefore,constructing heterojunction systems between semiconductor catalysts of different components is a direct way to improve photocatalytic performance.ZnIn₂S₄,as a typical ternary sulfur semiconductor with unique crystal structure and suitable band gap as well as excellent visible light response,is widely used for photocatalytic decomposition of water.However,its photogenerated electron-hole pairs are highly complexable,resulting in low carrier transfer efficiency,which limits the photocatalytic hydrogen production activity.To solve the above problems,ZnIn₂S₄was modified by constructing a double heterostructure and introducing piezoelectric catalysis,and the conformational relationships of its structure,morphology and catalytic performance and the thermodynamic mechanism of photocatalytic decomposition of water were investigated.The study and conclusions of this paper are as follows:（1）Black phosphorus crystals were prepared by chemical vapor deposition and exfoliated into black phosphorus nanosheets using N-Methylpyrrolidone（NMP）solution.ZnIn₂S₄nanosheets（ZIS）were grown in situ on two-dimensional black phosphorus nanosheets（BPNSs）using a solvothermal method.Subsequently,a novel hierarchical structure of Au/BPNSs/ZIS type II heterojunction photocatalyst was synthesized by depositing gold nanoparticles on the outer surface of ZIS using photodeposition method.The Au/BPNSs/ZIS composite catalyst was tested for photocatalytic hydrogen production activity,and the catalyst with the optimal composite ratio reached a hydrogen production rate of 1674μmol·h^-1·g^-1,which was 5 and 17times higher than that of pure ZIS and BPNSs,respectively.x-ray photoelectron spectroscopy（XPS）demonstrated that the photocatalyst of BPNSs/ZIS stabilizes the connection of BPNSs and ZIS heterojunction mainly by forming Zn-P bond between BPNSs/ZIS.Meanwhile,the work function calculations show that the interfacial electric field formed from ZIS to BPNSs is the driving force for interfacial charge transfer,which causes photoexcited electrons to migrate directionally to the interface under visible light irradiation to improve the hydrogen production efficiency.In addition,the Au nanoparticles were photo-deposited on the ZIS surface to form Schottky junctions,which further improved the photocatalytic performance.（2）BiFeO₃（BFO）with large size polyhedra was synthesized by the solvothermal method,and ZIS nanosheets were grown in situ on the BFO surface by the solvothermal method.Then an Au/BFO/ZIS Z-scheme type heterojunction photocatalyst with three-dimensional hierarchical structure was synthesized by loading Au nanoparticles on the ZIS surface using photodeposition.The composite catalysts were tested for photocatalytic,piezoelectric and photo-piezoelectric catalytic hydrogen production activities,and the results showed that the hydrogen production rate of the Au/BFO/ZIS catalyst with the optimal composite ratio was increased to 1433μmol·h^-1·g^-1with the synergistic effect of photo-piezoelectric catalysis,which was nearly 6 times and 86times higher compared with pure ZIS and BFO nearly 6-fold and 86-fold higher than that of pure ZIS and BFO,respectively.It was demonstrated by the characterization analysis and work function calculation and combined with the basic theoretical knowledge that under the synergistic effect of light and ultrasound,the conduction band of the piezoelectric material BFO tilted downward driven by the built-in piezoelectric field,so that the photogenerated electrons of BFO conduction band（CB）combined with the photogenerated holes of ZIS valence band（VB）at the interface,while the photogenerated electrons of ZIS migrated to the surface to participate in the redox reaction and improve the hydrogen production activity.The combination of chemical potential difference and piezoelectric potential difference promotes the directional migration of carriers.In addition,deposition of Au nanoparticles on the ZIS surface to form Schottky junctions further improved the efficiency of electron migration to the catalyst surface to participate in the reduction reaction.In this paper,ZIS nanosheets were used to construct Au/BPNSs/ZIS type II heterojunction photocatalyst and Au/BFO/ZIS Z-scheme type heterojunction photocatalyst by solvothermal method and photodeposition method,respectively,and Schottky junctions were combined with The heterojunction system was formed by combining the Schottky junction with the two heterojunctions,which improved the separation rate and directional migration efficiency of photogenerated carriers,solved the problems of extremely easy compounding of photogenerated electron-hole pairs and low electron transfer efficiency of ZIS,and provided a new method for constructing heterojunction composite photocatalysts of black phosphorus and piezoelectric material bismuth ferrate.