Modification Of ZnIn₂S₄ And Mechanism Of Photocatalytic Hydrogen Production

As an important method to directly utilize solar energy to produce clean energy,photocatalytic hydrogen evolution reaction（HER）has attracted extensive attention of researchers.As one of the representatives of ternary metal chalcogenides,ZnIn₂S₄（ZIS）is known for its low cost,stability and excellent catalytic performance.However,the narrow band gap and rapid recombination of photogenerated electron-hole pairs of pure ZIS result in poor photocatalytic hydrogen production activity.Due to its special layered structure,it can be easily modified and combined with other semiconductor catalysts to build photocatalytic systems with excellent performance.Therefore,efforts have been devoted to suppressing the recombination of charge carriers and promoting the separation of charge pairs,thereby enhancing the photocatalytic efficiency.In this paper,the ZIS photocatalyst is used as the modified substrate,and the modification methods such as ion doping or quantum dot deposition are carried out.Based on the improvement of photocatalytic performance,the following research contents are made:（1）Sn²⁺and Sn⁴⁺double-doped ZIS was prepared by one-step solvothermal method.Through the physicochemical characterization of the system,it is found that Sn²⁺combines with the edge S atoms of ZIS due to its large ionic radius,which adjusts the band gap structure and provides a special electron transport channel.Sn⁴⁺replaces the Zn ion,creating an additional energy state near the Fermi level.Sn²⁺/Sn⁴⁺ion double doping also acts as electron and hole acceptors to separate photogenerated carriers.Therefore,Sn²⁺/Sn⁴⁺-ZIS exhibits efficient photocatalytic hydrogen evolution activity under visible light irradiation.The photolysis rate of Sn²⁺/Sn⁴⁺-ZIS from water to hydrogen is 35.4 times higher than that of pure ZIS.In addition,the interconversion of Sn²⁺and Sn⁴⁺enhancs the stability of the photocatalyst.（2）I ion-doped ZIS was prepared by one-step solvothermal method.After a series of characterization results,I-ZIS has the best hydrogen release rate(4.39 mmol·g^-1·h^-1)and good cyclability under simulated sunlight irradiation.Meanwhile,the carrier transport mechanism and possible catalytic mechanism are further discussed.After doping with I ions,the synergistic effect of enhanced visible light absorption and efficient photo-activated carrier separation is achieved due to the reduction of the band gap,which is the main reason for the significantly improved hydrogen production behavior.（3）SnS₂ quantum dots（SnS₂ QDs）deposited ZIS composites were successfully prepared by hydrothermal method,and the morphology,structure and properties of the materials were tested by various technical means and theoretical analysis.The results show that SnS₂ QDs have tight interfacial contacts through self-growth on the ZIS surface.Furthermore,SnS₂ QDs have high electrical conductivity with metalloid behavior due to their own properties.Therefore,the photocatalytic hydrogen production activity of the optimized SnS2 QDs/ZIS composite under visible light irradiation is 13.2 times higher than that of pure ZIS.