Preparation And Performance Study Of Two Typical Visible Light Photocatalyzed Materials For Hydrogen Production

Hydrogen,with its high calorific value and lack of pollution,is considered one of the green fuels suitable for solving the world’s three major issues of energy crisis,environmental pollution and climate change.And photocatalytic technology is one of the ideal ways to produce hydrogen,because it cracks water into hydrogen by absorbing solar energy and undergoing catalytic reaction,a process that truly realizes the development of green and sustainable energy.However,photocatalysts are currently limited by poor light absorption,rapid recombination of photogenerated carriers and slow surface reaction,and the photocatalytic activity is not satisfactory.Therefore,developing efficient and stable photocatalytic materials has become the key and urgent difficulty to be solved for the application of photocatalytic technology.This article focuses on the limitations of photocatalytic materials and investigates the modification of two typical visible light responsive photocatalytic materials in sulfur compounds,ZnIn₂S₄ and CdS.A combination of improvements such as morphological construction,heterostructure building,doping engineering and co-catalyst loading synergistically improve their light absorption capacity,enhance the separation efficiency of photogenerated carriers,accelerate the surface reaction rate,and finally optimize their hydrogen production activity.These rational improvements broaden their applications.The research contents and results are as follows:（1）Hollow caged Zn_0.01Co_0.99Se₂/ZnIn₂S₄ Z-scheme heterojunction photocatalysts were prepared by combining morphological construction,heterostructure building and doping engineering.The hollow Zn-doped CoSe₂ is obtained in one step by hydrothermal selenization of bimetallic-based MOF materials,and the Z-scheme heterojunction is constructed with ZnIn₂S₄ nanosheets.The results show that the hollow structure not only prevents the self-aggregation tendency of ZnIn₂S₄,but also enhances the light absorption ability while providing a large number of reactive sites.The Z-scheme heterojunction is designed for efficient separation of photogenerated electron-hole pairs.By incorporating Zn doping,the band gap is reduced,and the conduction band becomes deeper,thereby improving light absorption capability.The DFT shows that Zn doping makes the heterojunction have faster surface charge transfer efficiency,which again enhances the photogenerated carrier separation efficiency and surface reaction rate.It is demonstrated that the heterojunction is further optimized by Zn element doping.Based on the synergy of the above three improvements,the hydrogen production efficiency of the Zn_0.01Co_0.99Se₂/ZnIn₂S₄ Z-scheme heterojunction photocatalyst reaches 2648μmol/g/h,which is 7.1 and 3.3 times higher than that of the original ZnIn₂S₄ and CoSe₂/ZnIn₂S₄,respectively.（2）The hollow spherical Pd/CdS/NiS photocatalysts were prepared by combining the morphological construction with the co-catalyst loading.The hollow spherical CdS photocatalysts are prepared by using SiO₂ as the template,and the Pd and NiS co-catalysts are loaded inside and outside the CdS shell layer,respectively.The results show that Pd,as a reduction co-catalyst,forms a Schottky junction with the inner interface of CdS to accelerate the electron migration.NiS,as an oxidation co-catalyst,forms a p-n junction with the outer surface of CdS to promote the hole transfer.And the thin shell layer of CdS can further reduce the migration distance of photogenerated carriers.Therefore,the dual co-catalysts promote the electron and hole migration respectively,and combined with the advantage of hollow spherical shape,different reactions are carried out inside and outside the shell layer,creating the effect of carrier spatial separation.With the synergistic effect of both,the hydrogen production efficiency of the Pd/CdS/NiS photocatalyst reached 3804μmol/g/h,which is 33.4 times higher than that of pristine CdS.