| ZnO semiconductor has good photoelectric effect,thermal stability and quantum effect,which has become the focus of research in the field of photocatalysts.However,the large band gap(3.2 e V)of ZnO makes it only available in the UV light range(200-400 nm),and cannot effectively absorb in the visible light range(400-800 nm).In this paper,ZnO was modified by doping and heterojunction.In this paper,two hexagonal crystalline ZnO with different morphologies(microspheres and nanorods)were synthesized,and the absorption of ZnO in visible light region was changed in two different forms to improve the photocatalytic performance.Then,the recombination rate of photogenerated electrons and holes was reduced by using the characteristics of heterojunction and polyvalent metal respectively.Finally,methylene blue solution(MB)and 2-mercaptobenzothiazole solution(MBT)as traget waste water were used to evaluate the photocatalytic performance and infer the possible mechanism.(1)In this work,flower-like CdS microspheres were prepared via the hydrothermal method before ZnO nanorods growing on their surface to form uniform ZnO/CdS composites.Finally,Ag nanoparticles were loaded on ZnO nanorods via the photoreduction method to successfully prepare the ZnO/CdS/Ag ternary semiconductor photocatalyst.The crystalline phase,chemical state of each element,structure and morphology of the ZnO/CdS/Ag composite photocatalysts were characterized by X-ray diffraction(XRD),X-ray photoelectron spectroscopy(XPS),scanning electron microscopy(SEM)and transmission electron microscopy(TEM).The optical and electric performance of these photocatalysts were tested by a threeelectrode system.The photocatalytic degradation of methylene blue(MB)and the photocatalytic antibacterial performance towards gram-negative bacteria(E.coli)and gram-positive bacteria(Staphylococcus aureus)were also investigated.Results showed that more than 90% of MB molecules were decomposed by ZnO/CdS/Ag photocatalyst within 30 minutes under light irradiation.Besides,the prepared ZnO/CdS/Ag photocatalyst possessed good antibacterial property towards gramnegative bacteria(E.coli)and gram-positive bacteria(Staphylococcus aureus).(2)As a typical semiconductor,ZnO is considered to be a favorable photocatalyst due to its excellent photoelectrochemical properties.However,low response of visible light and the recombination of photoinduced carriers limits its application in photocatalysis.Herein,a novel,robust and recyclable heterogeneous photocatalyst based on flower-like Co doped ZnO microspheres was presented.Due to the transformation of Co2+ to Co3+,more oxygen vacancies were produced,with more photoinduced electrons transferring to Co3+ which would greatly inhibit the recombination of photoinduced electrons and holes and improve photocatalytic activity.As a result,the 7% Co-ZnO photocatalyst exhibited excellent photocatalytic activity for the degradation of 2-Mercaptobenzothiazole(MBT)with the rate constant of 0.1498 min-1 and removing ratio of 97.3 % in 50 min.The formation of excess oxygen vacancies and the conversion between Co2+ to Co3+ were further identified by XPS analysis.This work provides new sights for doping transition metal with different chemical valence in semiconductors for producing oxygen vacancy and improving the photocatalytic efficiency. |
