Preparation Of CdS-ZnS And CdS-Ag₂S And Photocatalytic Performance Of Toluene Oxidation

Benzaldehyde,an aromatic aldehyde,widely used in the fields of spices and plastic additive.However,most of the methods for preparing benzaldehyde have many shortcomings such as high cost,heavy pollution and low selectivity of target products.Photocatalytic technology has gradually attracted people’s attention due to its characteristics of green,economical and mild reaction conditions.Cadmium sulfide（CdS）is a common semiconductor materials whose band position can satisfy the thermodynamic requirements of the photocatalytic toluene selective oxidation.However,the application of cadmium sulfide（CdS）in photocatalysis is greatly hindered by its shortcomings,such as carrier recombination and the photocorrosion of CdS.In order to solve the above problems,CdS-based photocatalytic materials were prepared by means of controlling morphology and constructing heterogeneous junction,and the catalytic performance of the prepared CdS-based photocatalytic materials was investigated by taking the selective oxidation of toluene to benzaldehyde as the model reaction.By means of XPS,ESR,BET,etc.,the physical and chemical properties such as structure and optical properties of the prepared catalytic materials were analyzed and characterized.The main research contents and innovative results are as follows:1.The precursor Cd₃（C₃N₃S₃）₂was prepared by precipitation method,then the intermediate Cd_xZn_3-x（C₃N₃S₃）₂were prepared by ion exchange between Zn²⁺and Cd²⁺,and then C-S bond in the intermediate was broken by hydrothermal method,CO₂and NO_xgases are epoxided by triazine,and the S^2-released at the same time react with Cd²⁺and Zn²⁺to form three-dimensional CdS-ZnS nanostructures composite photocatalyst which was first prepared for preparing benzaldehyde with octahedron by selective toluene.Comparing with other catalysts used in photocatalytic oxidation of toluene,the CdS-ZnS nanostructures composite photocatalyst also has significant advantages.After five cycles,the photocatalytic performance of CdS-ZnS composite photocatalyst still maintained a high benzaldehyde generation rate and selectivity.Its strong stability is due to the effective separation of photogenerated carriers and the migration of photogenerated electrons from CdS to ZnS on the CdS-ZnS interface,as well as the rapid consumption of photogenerated holes to inhibit the photocorrosion of CdS.The results show that the formation of CdS-ZnS heterojunction can protect CdS from photoetching to some extent and increase the stability of photocatalytic activity.2.CdS nanorods were prepared by solvothermal method first,and then CdS-Ag₂S composite photocatalyst with nanorods structure was prepared by in-situ ion exchange.The CdS-Ag₂S composite photocatalyst for the preparation of benzaldehyde by selective toluene was prepared for the first time by controlling the amount of silver nitrate solution.CdS-Ag₂S composite photocatalyst showed the best photocatalytic activity when the content of silver nitrate was 5%.The main reason for the enhanced photocatalytic activity is that the heterojunction between Ag₂S and CdS enhances the visible light absorptivity of CdS composite material and inhibits its photocorrosivity.