Design And Synthesis Of Composite Photocatalysts And Their Structure-Activity Relationship Study

Semiconductor photocatalysis has received ever-increasing attention because it holds the potential to become a green technology to utilize solar energy to alleviate the environmental and energy issues.The development and modification of composite photocatalysts and the establishment of their structure-activity relationship have great scientific significance for promoting the application of semiconductor photocatalysis in solar energy conversion.This thesis is focused on the design and synthesis of core-shell structured and graphene-based composite photocatalysts,and the effects of component,interface and microscopic structure of the composite photocatalysts on their photocatalytic performance have also been studied.The noble metal(Au,Pd,Pt)@semiconductor TiO2 core-shell structured composite photocatalysts have been synthesized through a hydrothermal reaction.The effects of different noble metal core with dissimilar characteristics on the physicochemical properties and photocatalytic activity of the composites toward degradation of organic pollutants under UV and visible light irradiation have been studied to reveal the regulation law of the noble metal components on the performance of composite photocatalysts.New synthetic approaches have been developed by means of the synergistic effect of multiple mechanisms(including heterogeneous seeded growth,Ostwald ripening,etc.)to synthesize core-shell,yolk-shell and "plum-pudding" multi-core@shell structured noble metal(Pt,Pd)@semiconductor CeO2 composite photocatalysts.On this basis,the effects of interfacial interaction between noble metal and semiconductor on the visible-light-driven photocatalytic performance of composite photocatalysts toward selective organic transformations have been revealed.Pd@CeO2 hollow core-shell structured composites have been designed and synthesized through a template method.The multifunctional applications of the composites have been investigated by taking advantages of the merits of each component.The Pd@CeO2 composites have been applied for selective reduction of aromatic nitro compounds through thermocatalytic and photocatalytic processes.The evident advantages of the hollow core-shell structure over the supported counterpart during the process of high temperature calcination and liquid-phase reaction have been demonstrated.A systematic comparison between graphene and other carbon allotropes(carbon nanotube and fullerene)in improving the visible-light photocatalytic activity of semiconductor CdS for selective oxidation of alcohols has been carried out based on a reasonable benchmark framework in which the carbon-CdS composites feature analogous and close interfacial contact.The results reveal that graphene cannot manifest its unique advantage over its carbon allotropes in enhancing the photoactivity of semiconductor CdS,which highlights the importance of rationally focusing on how to make better use of remarkable properties of graphene in designing more efficient graphene-semiconductor composite photocatalysts.From the angle of the systems materials engineering concept,the interface domain between graphene and semiconductor CdS has been optimized with the intimate interfacial contact of graphene-CdS remained.The introduction of a small amount of metal ions(Ca2+,Cr3+,Mn2+,Fee+,Co2+,Ni2+,Cu2+,Zn2+)as generic interfacial mediator into the interfacial layer matrix of graphene-CdS aims to optimize the atomic charge carrier transfer pathway across the interface between graphene and CdS,and improve their lifetime and transfer efficiency.This strategy can not only significantly boost the visible-light photocatalytic activity of graphene-semiconductor composites for selective photoredox reaction,but also offset the "shielding effect" of graphene resulting from the high weight addition of graphene,thus improving the net efficiency of graphene to enhance the photoactivity of semiconductor.