Preparation, Modification And Photocatalytic Activity Of ZnO

Recently, metal-oxide photocatalysts have become a focus of attention due to their possible application to degradation of environmental organic pollutants. ZnO has higher photocatalytic efficiencies, but the photocatalytic decolorization can only proceed under UV irradiation. Because of its wide band gap (3.3 ev), ZnO can only absorb UV light ofλ<380 nm. Solar spectrum consists only 5-7% of UV light, the other 46% and 47% of the spectrum are visible light and infrared radiation, respectively. In order to make use of solar spectrum, shift the optical absorption of ZnO into the visible region, the ZnO powders were improved by ions doping and semiconductor coupling.ZnO powders with different Co2+ ions doping concentrations (0,0.5,1,3 and 5 mol%) were prepared by the hydrothermal method at different temperature and characterized by X-ray diffraction (XRD), Scanning electron microscopy (SEM), UV-vis diffuse reflectance spectrometer, and photochemical reaction instrument. The results showed that the ZnO powders were hexagonal wurtzite structures and their crystallization decreased with the increase of Co2+ ions doping concentration. Their morphology and size had also changed from spherical(100-200 nm) to ellipsoidal(200 nm), sheet(300 nm) and then to hexagonal prism(10μm) with the increase of hydrothermal temperature. Whatever under low temperature or high temperature, the absorption edge of Co-doped ZnO shifted to longer wavelength with the increase of the Co2+ ions concentration. The photocatalytic activities of the powders were evaluated using a basic organic dye, methyl orange (MO). Compared with undoped ZnO, it was found that the photocatalytic properties under visible light of the Co-doped ZnO had been improved greatly. When the hydrothermal temperature was 60℃, the doping concentration was 3 mol%, the degradation ratio of MO can reach 78% after reacting for 180 min.ZnO/Cu2O compound photocatalysts were prepared by "soak-deoxidize-air oxidation" with different concentrations of Cu2+(0.125,0.25,0.5,1,1.5 and 2 mol/L). The results showed that ZnO was hexagonal wurtzite structures and the crystallinity had no change with the increase of Cu2+ concentration. Cu2O belonged to cubic structure and the crystallinity increased with the increase of Cu2+ concentration. ZnO were rods and bulks which had diameter of about 300-400 nm, some small round Cu2O particles which had a diameter of about 50 nm adhered to these rods and bulks. In the compounds the mole ratio of Cu2O to ZnO was 0.017,0.025,0.076,0.137, 0.138, and 0.136, respectively. An absorbance in the visible light region between 400 nm and 610 nm was seen and the reflection rate became less with the mole ratio of Cu2O to ZnO increasing. By degradating of MO, it was found that, compared with pure ZnO, the photocatalytic properties under visible light of ZnO/Cu2O compound were improved greatly and some compounds were better than pure Cu2O.