Oxygen vacancies-enriched and porous hierarchical structures of ZnO microspheres with improved photocatalytic performance

Controlling the morphology and surface defects is an effective strategy for enhancing photocatalytic performance. In this paper, we have successfully prepared zinc oxide (ZnO) microspheres with oxygen vacancies enriched and porous hierarchical structures by hydrothermal annealing. The porous hierarchical structure of the ZnO microspheres was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and other analytical techniques, and their photocatalytic properties were studied by the decomposition of methylene blue, tetracycline and phenol in condition simulated sunlight. The porous hierarchical structure of ZnO-SO(4)(2-)microspheres showed higher photocatalytic activity compared to ZnO-Cl- and ZnO-NO3- (ZnO from different sources of zinc as ZnO-X, where X is SO42-, Cl- and NO3-, respectively.). Under sunlight, the photocatalytic removal rates of methylene blue, tetracycline and phenol by ZnO-SO(4)(2-)were 98%, 100% and 83%, respectively. Meanwhile, the photoelectrochemical tests showed that the porous hierarchical structures of ZnO-SO42- microspheres had the best photocurrent response and the lowest charge transfer resistance. After five cycles of photocatalytic degradation of phenol, the synthesized ZnO microspheres also showed good durability and stability. In addition, superoxide radicals (center dot O-2(-)) and hydroxyl radicals (center dot OH) were identified as the active species by the trapping experiments. This study showed that the improvement of photocatalytic performance of ZnO microspheres could be owing to abundant oxygen vacancies and the porous hierarchical structures.