Surface/Interface Structure Design And Photocatalytic Performance On TiO₂-Based Heterojunctions

The energy and environment crisis has motivated extensive research towards clean and sustainable energy resources.Photocatalytic technology can convert solar energy to stable chemical energy,thus showing great significance in reality and research field.As the most well-known photocatalyst TiO2,its practical applications are greatly hindered by insufficient light harvest and fast carrier recombination.Constructing TiO2-based heterojunctions is an effective modification strategy to solve these issues.However,the TiO2-based heterojunctions reported by literatures generally encounter a complex preparation process,poor photo-stability,and ambiguous surface/interface structure,which significantly limit our understanding of the structure-activity relationship in heterojunction catalysts.Enlightened by above analysis,my research topic focused on further study of Ti02-based heterojunctions towards specific photocatalytic reaction.On the one hand,facile preparation methods were proposed for constructing more energetic and stable TiO2-based materials in photocatalytic hydrogen evolution.On the other hand,Au-Pd alloy/TiO2 heterojunctions with well-defined interfacial structures were specially constructed on electron-enriched facets TiO2{101} by utilizing facet-induced effect and were studied as a model photocatalyst for revealing the structure-activity relationship in CO2 photoreduction.The main content of this thesis are listed as follows:1.The highly dispersed ZnO quantum dots(QDs)modified TiO2 nanowires(NWs)photocatalysts were prepared via a facile calcination method by using titanate NWs and ZnCl2 as precursors.In this synthetic pocess,the size of ZnO QDs could be adjusted by varying the dosage of ZnCl2,thereby directly regulating their band structure via the quantum size effect.Using this method,the driving force and mobility of electrons from conductiuon band of ZnO QDs to that of TiO2 NWs could be enhanced,thereby significantly improving photocatalytic activity in water splitting.Our results revealed that the rate of hydrogen evolution on the optimal sample TZ-0.6%was double and four times that obtained on TiO2 NWs and P25,respectively.Based on systematical photoelectric characterizations,it can be concluded that the excellent photocatalytic performance of this photocatalyst with ZnO QDs decorated TiO2 NWs was attributed to the synergism of heterojunction induced effective interfacial carrier migration and the size dependent quantum confinement effect.2.We constructed Au-Pd alloy catalytic sites on TiO2 {101} facets for robust CO2 conversion to hydrocarbons through photo-induced alloying strategy.The Au-Pd alloy provided abundant sites for CO2 adsorption and activation,in which the uniformly dispersed Pd atoms could synchronously act as hydrogenation centers.The synergistic effect of Au and Pd,in combination with the electrons-rich nature of TiO2 {101} facets,were proposed to account for the highly efficient CO2 reduction.Remarkably,the optimal sample PD-Au6Pd1 had achieved the highest selectivity of 85%(71%:CH4,14%:C2H4 and C2H6)for hydrocarbons with an evolution rate of 14.3 ?mol g-1 h-1.This work provided new insights into the design of active sites for CO2 photoreduction,and highlighted the significance of surface structure engineering in improving selectivity towards high grade carbon products.