Photocatalytic Activity Of Zinc Oxide And Zinc Sulfide Based Visible-light Photocatalysts

Photocatalysis as an effective energy conversion technology has attracted wide attention of researchers.A number of photocatalytic materials have been widely studied and applied in photocatalytic hydrogen production from water,photoelectrochemical hydrogen evolution and photo-degradation of organic pollutants.ZnO and ZnS semiconductor photocatalysts with conduction band positions more negative than H+/H2 reduction potential are widely used in the photocatalytic field under light irradiation.However,ZnO and ZnS with wide bandgaps more than 3.2 eV only utilize ultraviolet light less than 5% in solar light spectra,which greatly restricts their application in the photocatalytic field.Therefore,it is necessary to modify the surface structure,crystal structure and electronic structure of ZnO and ZnS to achieve visible-light response.In the thesis,the ZnO and ZnS based photocatalytic materials with a wide range of visible-light absorption were obtained by metal ions doping,morphological modification,and heterostructure construction.Firstly,to prevent the agglomeration of zinc powders and imprve photoexcited carrier transport rate,zinc powders with strong reductive ability are loaded on the surface graphene oxide(GO)nanosheets with oxidative ability through a redox reaction in aqueous solution at room temperature.Co-doped ZnO/rGO nanoparticles were synthesized in aqueous solution via a novel Co-induced electrochemical method at room temperature.Compared with ZnO/rGO,Co-doped ZnO/rGO shows a wide visible-light absorption region from 400 nm to 700 nm.The Co-doped ZnO/rGo exhibits the enhanced photodegradation efficiency of methylene blue(MB)and photocurrent intensity under visible light(??420 nm)irradiation.Secondly,to shorten the migration distance of photogenerated carriers,reduce the recombination rate of photogexcited electrons and holes,and improve the visible photocatalytic activity of ZnS,the morphology and light absorption ability of ZnS are adjusted by the introduction of molybdenum(Mo)ions.In this study,Mo-doped ZnS sheets were synthesized by a hydrothermal method using Mo ions as precursors.During the growth process,Mo ions are adsorbed on the{111}facet of ZnS to restrict the growth of the crystal facet the ZnS.The light absorption range of Mo-doped ZnS sheets covers the whole visible light and even extends to near infrared light area.The p-type Mo-doped ZnS sheets were used in the applications of photo-electrochemicaland photodegradation and then exhibited the enhanced photocatalytic activity under visible-light irradiation.Finally,to improve visibe-light absorption and photoctalyitc hydrogen evolution of ZnS and ZnO,The ZnO sheets are prepared and used for synthesizing ZnO-ZnS-CdS heterostructural sheets through ion-exchange and light-assisted growrh methods.In the heterostructures,CdS and ZnS nanoparticles are embedded in ZnO sheets and then form stable interfaces among ZnS,CdS and ZnO,which is favorable for the migration of photogenerated carriers.ZnO-ZnS-CdS heterostructural sheets show higher photocatalytic hydrogen production rate under visible light irradation.The hydrogen production rate is furtherly improved by the loading of Pt nanoparticles.