Design,Synthesis And Photocatalytic Performance Of Cadmium Chalcogenides/Titanium Dioxide Heterojunction Photocatalysts

Due to its inexpensivenss,nontoxcity and high stability,TiO₂ is considered as a promising photocatalyst.However,its widely practical application faces two main challenges of 1)poor utilization of solar energy??<387 nm?,2)high recombination rate ofphotogenerated electrons and holes.Aimed to extended the optical response range and facilitate charge carrier seperation,we fabricated cadmium chalcogenides/titanium dioxide heterojunction photocatalysts and evaluated its photocatalytic performance by degradation of TC-HCl and RhB under visible-light irradiation.The structure,morphology,optical and electrochemical properties are characterized by combing TEM,XRD,Raman,BET,DRS,XPS and EIS measurments.In addition,we also explore the effect of cadmium chalcogenide alloying on the photocatalytic activity.This thesis include three parts:?1?CdTe/TiO₂ composite photocatalystes were prepared by hydrothermal method under different temperature,duration time,and pH.Based on the results of decomposition TC-HCl under visible-light irradiation,it is found that CdTe/TiO₂heterojunction and effectively improve the photocatalytic performance,and among all the samples CdTe/TiO₂ synthesized at 120?for 6h and the sample prepared at 140?for 4h had the highest degradation efficiency of 78%after 40 min.Then enhancement of photocatalytic activity can be attributed to the improved optical absorption in visible?even infrared?region and the reduced charge carrier recombinnation.?2?A series of CdSe/TiO₂ composite photocatalystes were synthesized by a hydrothermal method under different temperature.It is found that CdSe sensitization can also effectively enhance the photocatalytic activity,and among all the samples the CdSe/TiO₂ prepared at 120oC has the highest efficiency of 78%.Similar to the case of CdTe/TiO₂,the result of EIS measurements indicate the fabrication of heterojunction structure is benificcial for reducing the recombination of electron-hole pairs.The enhancement of optical absorption of CdSe/TiO₂ is not as prounanced as that of CdTe/TiO₂ whereas the conduction band?valence band?of CdSe is more negative?positive?than that of CdTe and thus CdSe has stronger redox ability.?3?We explore the chemical composition of alloys on photocatalytic performance.?i?Alloys with different anions.Considering that CdTe has narrower band gap while CdSe has higher redox potential,we fabricated CdTe_xSe_1-xalloys/TiO₂ with different x.However,it is found that the photocatalytic performance of CdTe_xSe_1-x/TiO₂ is deteriorate compared to CdTe/TiO₂ and CdSe/TiO₂,which might be due to different growth rate of CdTe and CdSe and high density of defects.?ii?Alloys with different cations.Zn_xCd_1-xS with different compositions were prepared by a co-precipitation method,and the photocatalytic activity was evaluated by degradation of RhB and hydrogen production by water splitting.It is found that wen x=0.25,the sample has optimal photocatalytic performance,which can be attributed to its reasonable visible-light absorption,relatively high redox potential and reduced charge carrier recombination.