Solid-state Preparation And Photocatalytic Hydrogen Evolution Activity Of CdS-Based Heterostructure Materials

The use of fossil fuels has greatly promoted the development of the society,meanwhile,it has also resulted in the serious issues such as environment pollution and the energy shortage.The solar photocatalysis technology is one of the most promising methods to resolve the currently environmental and energy problems.Since the discovery of the Honda-Fujishima effect in 1972,there has achieved delightful fruits in promoting photocatalytic H₂ evolution activity.However,the photocatalytic H₂ evolution efficiency is far from satisfactory.Presently,the research on the promotion of photocatalytic H₂ evolution efficiency can be devided into two research directions: discovering new photocatalysts with high photocatalytic H₂ evolution efficiency and promoting the photocatalytic H₂ evolution efficiency of the discovered photocatalysts.CdS is acknowledged as one of the ideal photocatalytic materials due to the proper bandgap structure,however,the high charge carrier recombination rate and the serious photocorrosion lead to the low photocatalytic H₂ evolution efficiency.When composite CdS with two-dimensional materials or semiconductor materials with proper bandgap structure,CdS-based composites with enhanced photocatalytic H₂ evolution efficiency may obtained.In addition,solid-state method is a facile,efficient and environmental friendly method for the preparation of photocatalytic nano-materials compared with conventional synthetic methods in solvent system.This study focused on the preparation of CdS-based composites synthesized by solid-state method;the impaction of the CdS-based heterostructure on photocatalytic activity and photocorrosion resistance,the mechanisms of charge carrier transfer/separation in the CdS-based composites.The main contents are summarized as follow:Firstly,CdS-based binary/ternary composites have enhanced photocatalytic H₂ evolution activity due to positive synergistic effect of the heterojunctions in promoting the charge carrier separation and transportation properties.A facile and efficient room-temperature solid-state method is used to synthesize the ternary CdS/g-C₃N₄/CuS.The ternary CdS/g-C₃N₄/CuS composite has enhanced photocatalytic H₂ evolutionactivity compared with any one of the component,it is ascribed to the following three aspects.On one hand,the two-dimensional structure of g-C₃N₄ and the n-n heterojunction between CdS and g-C₃N₄ facilitate the photo-generated carrier dispersion and separation.On the other hand,the p-n heterojunction between n-type CdS and p-type CuS further promote the separation of charge separation.In addition,the supplementary effect of different contents' bandgap in utilizing the different wavelengths of light.The study demonstrated that the room-temperature solid-state method is a facile and efficient synthesis for the preparation of CdS-based ternary photocatalysts with enhanced photocatalytic H₂ evolution activity.Secondly,the heterostructures between CdS and transition metal dichaldogenide?MS,such as ZnS,CuS?can enhance the photocatalytic H₂ evolution activity of the materials.The binary composites consist of CdS and ZnS or CdS were prepared through the solid-state method,and their visible-light photocatalytic H₂ evolution activity were studied.The prepared CdS and ZnS indicate the cubic phase,while the CuS indicate the hexagonal phase.CdS and ZnS formed cubic phase ZnxCd1-xS solid solution,while CdS and p-type CuS formed p-n heterojunction.The optimal visible-light photocatalytic H₂ evolution rate of ZnxCd1-xS is 411.08 umol·h-1when x=0.5???420 nm?,which should ascribed to the optimized bandgap structure and the resulting depressed charge recombination.The visible-light photocatalytic H₂ evolution rate of optimized CdS/CuSx is five-fold of CdS,which is due to that the p-n heterojunction in CdS/CuS composites.The study not only provides a one pot solid-state method for the preparation of CdS/MS composites,but also demonstrates the solid-solution structure and the p-n heterojunction play an important role in enhancing visible-light photocatalytic activity of CdS/MS composites.