Preparation, Characterization And Photocatalytic Properties Of A Novel Nano-ZnO

Nano-ZnO is a kind of novel photocatalyst, which can utilize UV-Vis light and has a potential application in persistent organic wastewater treatment. In this paper, three kinds of morphology of nano-ZnO photocatalyst dumbbell-shaped ZnO, ZnO hollow sphere and ZnO powder were successfully synthesized by hydrothermal, microwave heating and glucose-assisted synthesis methods, respectively. The prepared nano-ZnO were systematically characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), thermogravimetric analysis (TG-DTA), UV-Vis absorption spectrum (UV-Vis) and photoluminescence spectrum (PL), in order to investigate the particle size, crystallization, morphology, optical properties and the relationship between the characters and photocatalytic activity, the results were also compared with the commercial ZnO or P-25 TiO2. The photocatalytic activity of three as-prepared photocatalysts was investigated under UV (visible or solar) irradiation, which was evaluated by the decolorization, COD and TOC removal. This study may provide the theory reference for the preparation of ZnO photocatalyst and persistent organic wastewater treatment. All the experimental results were demonstrated as follows:1. Preparation, characterization and UV photocatalytic property of dumbbell-shaped ZnO photocatalyst: Unique dumbbell-shaped ZnO microcrystal photocatalyst was successfully synthesized by hydrothermal method, which is simple, rapid and easy operation. The characterization results show that the prepared ZnO microcrystal photocatalyst is pure and belongs to the hexagonal wurtzite family, the diameter is about 5μm and the length is about 10μm, with good properties of thermal stability and optical properties. The photocatalytic activity test results indicate that the prepared dumbbell-shaped ZnO microcrystal photocatalyst has good photocatalytic activity. After 75 min of photocatalytic degradation, the decolourization efficiency of CV, MV and MB dyes wastewater achieved 68.0%, 99.0% and 98.5%, the TOC removal efficiencies achieved 43.2%, 59.4% and 70.6%, respectively. Compared to commercial ZnO, 16-22% higher TOC removal efficiency was obtained by the dumbbell-shaped ZnO.2. Preparation, characterization and photocatalytic degradation of MB by ZnO hollow sphere: ZnO hollow sphere was successfully synthesized by microwave heating with a diameter of about 300 nm. The results show that the prepared ZnO with a hollow structure and rough surface structure, hexagonal wurtzite and the potential capacity of the visible light photocatalytic degradation. Methylene Blue dye as a model compound was degraded by nano-ZnO hollow spheres, after 90 min illumination, the decolorization of MB was 100% both under ultraviolet or visible irradiation. But the TOC removal rate of MB under visible irradiation was about 5% higher than that under UV irradiation. ZnO hollow spheres are still showing a high capacity of photocatalytic degradation even after five times reuse, decolorization and TOC removal of MB were 99% and 78% respectively, which indicate that the catalyst has a good ability of reuse.3. Preparation and characterization of ZnO powder and its photocatalytic degradation of MB under solar light: Nano-ZnO powder which could effectively utilize visible light was prepared through the decomposition of Zinc acetate by employing glucose as curing agent, with a hexagonal wurtzite structure and a mean diameter of 60 nm. Methylene Blue dye as a model compound was degraded under solar light irradiation to evaluate the photocatalytic activity of the prepared ZnO. After 10 h solar irradiation, both the decolorization and mineralization efficiency of MB wastewater by the prepared ZnO achieved 100%, about 18-22% higher than that by P25 for the similar system. The study of stability and reusability of the prepared ZnO also showed that the prepared ZnO was an effective solar photocatalyst. The feeding model of wastewater was also investigated to enhance the efficiency of photocatalytic degradation for the first time.