Performance And Mechanism Study Of ZnO-graphene Hybrid Material

X-ray absorption fine structure (XAFS:including EXAFS and XANES), in combination with transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), superconducting quantum inference device (SQUID) and other kinds of experimental techniques, was mainly used to study on tailoring the magnetic and photocatalytic performance of ZnO-based semiconductor nano material via the introduction of graphene in the dissertation. A sol-gel-like method was used to prepared Co doped ZnO quantum dots (Zn0.98Co0.02O QDs) and graphene composite Zn0.98Co0.02O/RGO and ZnO nanocrystals and graphene composite ZnO/RGO. Detailed theoretical and experimental results indicated that the Cozn+Vo complex induced by the interaction between Zn0.98Co0.02O and graphene was the key factor resulting in the room-temperature ferromagnetic coupling among Co2+; The effective and synergetic electron-capture by RGO and Vo improved the photocatalytic efficiency of ZnO/RGO by-10times, compared with that of ZnO.1. Manipulating the magnetic property of Co doped ZnO-based dilute magnetic semiconductor via grapheneDensity functional theory and XAFS were mainly adopted to study the electronic structure, magnetic properties and local structure of different Zn0.98Co0.02O and graphene composites. EXAFS results suggested that Co2+in all samples prepared occupied the Zn sites. UV-Vis, Raman and EPR results explained that strong electronic interaction existed between graphene and Zn0.98Co0.02O which resulted in the formation of abundant oxygen vacancies (Vo). The calculated results by VASP and XANES results demonstrated that Vo coexisted with the nearest Co2+(Co2+-Vo pairs), the Co2+empty t2g↓minority state broadens and forms a hybrid level (t2g↓-Vo) right at the CBM, favoring the strong ferromagnetic interaction among Co2+ions.2. Tailoring the photocatalytic performance of ZnO-based semiconductor photocatalyst via grapheneThe ZnO/RGO quasi-core-shell composite photocatalyst where ZnO NPs were wrapped by graphene nanoshells was prepared via a one-step method. ZnO nanocrystals with the particle size～6nm wrapped by RGO nanosheets could be observed in transmission electron microscopy (TEM) images. XRD results demonstrated that the structure of ZnO in all samples was hexagonal wurtzite. Raman and XPS results manifested that there was interaction between graphene and ZnO which introduced～3%interfacial stress and quantity of oxygen vacancies(Vo). Photoluminescence (PL) further evidenced the～80% decrease of band-gap emission intensity in ZnO/RGO compared with that in ZnO and the presence of interfacial Vo. At last, the mechanism of the enhanced photocatalytic activity in ZnO/RGO was proposed. The effective synergetic capture of graphene nanoshells and Vo as a result of interfacial strain interaction improved the photocatalytic activities of ZnO based semiconductor photocatalysts.