Study Of Highly Efficient Photocatalysts Based On Modulation Of Oxygen Vacancies And Metal Vacancies

With the increasing concerns of energy and environmental crises,solar driven photocatalytic technology is attracting more and more attention in the field of energy and environmental chemistry.The key for the development of photocatalytic technology lies in promoting the charge transfer and separation efficiency of photocatalysts,whereas defect engineering plays a critical role in tuning the photocatalytic performance.Therefore,the study of defect modulation will lay solid theoretical foundation for the design and construction of highly efficient photocatalytic system.In this article,we mainly focus on the defect modulation in oxide photocatalysts such as TiO2 and ZnO,including oxygen vacancies and metal vacancies,and constructed p-n homojunction based on oxygen defected semiconductor and metal defected semiconductor.Then we systematically studied the structure-activity relationship between defect modulation and photocatalytic performance.Firstly,from the point view of oxygen vacancy modulation,oxygen deficient ZnO ball-in-ball hollow microspheres(BHMs)were synthesized through a simple solvothermal method in ethanol-ethylene glycol mixed solution.It is found that the content of ethylene glycol and solvothermal time played a critical role in the introduction of oxygen vacancies and the formation of the BHMs structure.Compared with ZnO nanoparticles,the oxygen vacancies and BHMs structure in ZnO can improve the light utilization,promote charge transfer and separation efficiency and mass transfer performance.Particularly,with optimized oxygen vacancy concentration and proper hollow structure,the ZnO BHMs will exhibit higher photocatalytic activity.These results indicate that intrinsic oxygen vacancy and complex hollow structure can effectively promote the performance of photocatalysts.Then,compared with the often studied oxygen vacancies,the research on the metal vacancy modification is seldom reported.Herein,undoped metal-defected Zn0.925 O and Ti0.905O2 were fabricated for the first time through a solvothermal-calcination approach.DFT theoretical calculations and experimental results indicate that the existence of metal vacancies will change the lattice constant,reduce the charge density of neighbouring atoms,lead to increased XPS binding energy and generate new EPR singals.Contary to normal n-type and nonferromagnetic ZnO and TiO2,metal-defected ZnO and TiO2 exhibit inherent p-type conductivity and strong room temperature ferromagnetism.Meanwhile,the introduction of metal vacancies raises the width of valence band,whose width intrinsically controls the mobility of holes,leading to improved charge transfer and separation efficiency,and thus higher photocatalytic activity.This work demonstrates that metal vacancy engineering can change the structural and physicochemical properties of semiconductors,which represents a kind of instructive design idea to construct highly efficient photocatalytic system.At last,p-n homojunctions were fabricated based on oxygen-defected semiconductor and metal-defected semiconductor to further promote the charge transfer and separation efficiency.The obtained product exhibits typical characteristics of p-n homojunction,such as the "V" type Mott-Schottky plots,anodic shift of onset potential and two-semi-cycle in the electrochemical impedance spectrum.The existence of p-n homojunction realize the spatial separation of photogenerated electrons and holes.Moreover,compared with single semiconductor and n-n type II homojunction,the asprepared TiO2 and ZnO p-n homojunctions are more effective in promoting charge transfer and separation due to the larger electric field at the interface.These results indicate that the fabrication of semiconductor p-n homojunction is an effective approach to promote charge transfer and separation and provides new opportunities to design and fabricate highly efficient photocatalytic materials.