Synthesis And Properties Of Easily Recyclabe Zinc Oxide And Bismuth Oxide Based Composite Photocatalysts

Photocatalysts are chemical substances that play a catalytic role in the photon excitation. Oxide and sulfide semiconductors,such as titanium dioxide, zinc oxide, tin oxide, zirconium dioxide or cadmium sulfide, are common photocatalysts.With the rise of nanotechnology, a lot of work has focused on the preparation of the photocatalyst with nanosized photocatalysts, their pergormance has been significantly improved. However, the practical application of photocatalytic technology has been hampered due to the recovery difficulty of photocatalyst nanocrystals in liquid phase.In this paper, using natural porous diatomite and magnetic SiO2/Fe3O4as carriers, the easy recovery of composite photocatalysts of ZnO/diatomite, Bi2O3/diatomite, ZnO/LDHs/SiO2/Fe3O4and ZnO/MMO/SiO2/Fe3O4(LDHs is layered double hydroxides and MMO is mixed metal oxides which is formed after the calcination of LDHs) have been prepared through different methods. These catalysts were recycled by natural subsidence or applied magnetic field.In this study, some works have been done:(1) The zinc oxide (ZnO) nanocrystals with crystallite size of15nm were layer-by-layer self-assembled onto the surface of diatomite to prepare ZnO/diatomaite composite photocatalysts. XRD, FE-SEM, and BET were used to characterize the structure and morphology of ZnO/diatomite. The results showed that ZnO nanoparticles uniformly loaded on the diatomite surface and its porous structure had been kept. Methylene blue (MB) was used as the model pollutant to evaluate the photocatalytic properties of ZnO/diatomite composite photocatalysts. The results indicated that the photocatalytic properties of the composite materials were improved with increasing the self-assembled layers. When the number of layers was5, MB solution with initial concentration of20mg/L was degraded during30min under UV light irradiation. (2) Bi2O3/diatomite composite photocatalysts with mass ratio of Bi2O3to diatomite ranged from0.1:1to0.6:1were prepared via freeze-drying method and the subsequent calcination in air. The as-prepared Bi2O3/diatomite composite photocatalysts were characterized by XRD, FE-SEM and N2adsorption-desorption measurement. The photocatalytic properties of the samples were investigated through the photocatalytic degradation of methylene blue (MB) under visible light irradiation using a500W Xe lamp. The results showed that the Bi2O3nanoparticles with particle size of32nm had a good dispersibility on the diatomite surface. Combining the porous structure of diatomite and the photocalalytic properties of Bi2O3, the Bi2O3/diatomite composite photocatalysts gave a better photocalalytic property under visible light irradiation, and the degradation rate of methylene blue (20mg/L) reached more than90%after2h visible light irradiation over the composite Bi2O3/diatomite of0.4:1.(3) The homemade SiOO2/FeO4composite particles as magnetic core were coated with LDHs to obtain LDHs/SiO2/Fe3O4by co-precipitation method. Then ZnO nanoparticals were deposited onto the surface of LDHs/SiO2/Fe3O4to obtain ZnO/LDHs/SiO2/Fe3O4composite photocatalyst by impregnation method. The ZnO/MMO/SiO2/Fe3O4composite photocatalyst was obtained by calcining ZnO/LDHs/SiO2/Fe3O4at500℃for4h. The structure and morphology were characterized by XRD, FE-SEM, TG and BET. The methylene blue (MB) and dichromate ions (Cr2O72-) were used as model pollutants to evaluate the adsorption and photocatalytic abilities of composite photocatalysts. The results indicate that ZnO/LDHs/SiO2/Fe3O4and ZnO/MMO/SiO2/Fe3O4samples have higher degradation capacity for MB and Cr2O72-solution, and these photocatalysts were almost recoveried through the applied magnetic field.