Nanosized Tetrapod Zinc Oxide: Nucleation Mechanism, Controllable Synthesis And Propery Investigation

Nanosized tetrapod zinc oxide materials (T-ZnO) hold great potential applications for short-wavelength optoelectronic devices, chemical/biological sensors, catalysts, et al., due to their unique physical/chemical properties, three-dimentional morphology. However, the nucleation mechanism and controllable synthesis of T-ZnO still need to be explored, which limits the further understanding, research as well as applications of them. We herein investigated the nucleation mechanism, controllable fabrication, and the application in photocatalysis of the nanosized T-ZnO.The nuclei of T-ZnO were synthesized at high temperature via quick Zn vapor oxidization. The theory analysis and experimental data (phenomena) showed that the T-ZnO nanocrystals were grown from"octa-twin"nuclei. The X-ray diffraction, selected area electronic diffraction and high-resolution transmission microscopy indicated that T-ZnO and their nuclei were all hexagonal wurtzite crystal structure. The in situ observations of T-ZnO via scanning electronic microscopy and transmission electronic microscopy showed that the as-synthesized nuclei do server as the original growth center for the residual topology structures in certain T-ZnO. As a result, a two-dimentional monolayer growth model was proposed to explain the relationship of nuclei formation and legs morphology transformation. From our observation, the branch morphologies of T-ZnO are triangular and hexagonal geometries. With flow rate of oxygen high enough, there always emerged extra plane oriented form negative plane at the center of T-ZnO, and then cracked into three parts equally induced by thermal stress. The Energy Dispersive Spectrometer showed that the ratio of zinc and oxygen concentration in the nuclei was larger than 1, and the zinc concentration decreased in legs along growth direction. The T-ZnO with controlled sizes and morphologies were prepared by varying react vapor oxidization conditions, including temperature, flow rate of oxygen and the composition of the flow gas (for instance, the concentration of nitrogen). We demonstrated that the as-prepared T-ZnO nanocrystals show good photocatalytic behavior to the decomposistion of methyl orange.