缺陷可調控的氧化鋅之研究： 合成、性質與應用

Abstract

Defects play a very important role in photoactivity of ZnO for the applications of photocatalysis and cosmetic physical UV blocker. In this study, there are two strategies to synthesize the defect-tailored ZnO. First, as graphene oxide (GO) is used as an additive in a solvothermal reaction, paramagnetic VO+ and VZn- defects are formed in ZnO. Whereas, in the absence of GO, only paramagnetic VO+ defects are produced through oxygen desorption. Experimental results indicate that GO not only acts as a catalyst for the ionization reaction, but also changes the dominant defect formation pathway in ZnO lattice. Both GO and reduced graphene oxide (rGO) function as catalysts for further ionization to create paramagnetic zinc and oxygen vacancies, respectively. ZnO/rGO with many zinc and oxygen vacancies exhibits significant photocatalytic activity. Photoluminescence and electron paramagnetic resonance measurements indicate that the zinc vacancies and oxygen vacancies are generated on the ZnO surface, and are crucial to that photocatalytic behavior. The photodegradation of methylene orange is significantly reduced by the addition of scavengers with the ZnO/rGO by scavenges of h+ and •OH. Both zinc and oxygen vacancies cause effective charge separation in the photodegradation of methylene orange, which markedly inhibits the recombination of charges. Second, thermal decompose of amorphous/layered basic zinc salts (LBZ) spheres is used to prepare highly defected ZnO with Mie scattering properties as a cosmetic physical UV blocker material. Amorphous/layered basic zinc salts spheres are synthesized in a reflux reaction. The trisodium citrate is employed as the chelating agent. The sphere size is controlled by the nuclei number which depends on the competition between hydroxyl ion and citrate to complex with Zn2+. The formation pathway and morphology evolution are discussed. The wurtzite ZnO sphere obtained by thermal decomposition exhibits the visible absorption owing to the oxygen vacancies in ZnO lattice. In addition, excess oxygen vacancies in the ZnO spheres become a recombination center and reduced the radical formation during photocatalysis. The uniform microspheres exhibit Mie scattering in the visible range due to the interaction with specific incident electromagnetic radiation, and thus the full absorption spectrum is easily obtained by tuning the size of spheres. Such uniform ZnO spheres exhibit superior visible absorption and Mie scattering effects thus is expected for the material of cosmetic physical UV blocker.