Studies Of Preparation And Photocatalytic Activity Of ZnO Composite Oxides

In recent years, zinc oxide (ZnO) has been a popular photocatalyst for the treatment of organic pollutants in water and air. However, ZnO photocatalysts have an inherent and obvious drawback, that is, the photogenerated charge carriers (hole-electron pairs) can recombine easy. Therefore, improvement of ZnO photocatalytic activity is important to decrease the recombination of photogenerated charge carriers. Coupling ZnO with other semiconductors can provide a beneficial solution in this aspect. The energy gaps of these two semi-conductors are match, which can prevent the recombination of photogenerated charge carriers, and show efficient photoactivity of ZnO. This dissertation consists of following contents:1. The direct precipition method has been used to prepare pure nano-ZnO with Na₂CO₃,ZnSO₄ as raw materials. Determined through experiments with the best photocatalytic activities of the preparation conditions: the Na₂CO₃ solution was added into the ZnSO₄ solution at the ratio of 1.5, at 80℃, reaction for 0.5h, intermediate products were washed three times with ethanol, then calcined at 600℃for 1h. The ZnO nanoparticles showed was produced at this method had the best photocatalytic activity on above mentioned conditions.2. The photocatalysts of Zr-doped ZnO can be synthesized by using the direct-precipition method. Primary optimum content of Zr doping in the samples and calcining temperature for the photocatalytic degradation of methylene blue were 1.0 Zr atom% and 700℃, respectively. X-ray diffraction was used to characterize the grain size of the pure ZnO and Zr-dped ZnO. The size of ZnO nanoparticles increased as calcining temperature. Doping Zr could retard growth of the grain size. Activity energy of the Zr-doped ZnO (1% molar ratio) growth as calcining temperature was 16.6 KJ/mol, bigger than pure ZnO nanoparticles(12.5 KJ/mol). 3. The photocatalysts of Sn-doped ZnO also can be synthesized by using the direct-precipition method. Primary optimum content of Sn doping in the samples and calcining temperature for the photocatalytic degradation of methylene blue were 5 atom% and 600℃, respectively, which was different from that of Zr-doped ZnO nanoparticles. X-ray diffraction (XRD), was also used to characterize the grain size of the pure ZnO and Sn-doped ZnO. Size of ZnO particles increased as calcining temperature. Results showed that doping Sn could play a role in reducing the grain size. The activation energy of the 5%Sn-doped ZnO particle size growth with the calcination temperature had been found 6.592 KJ/mol, almost half that of pure ZnO nanoparticles(12.5 KJ/mol), showing that the effect of calcinations temperature on the grain size was smaller compared to Zr-doping ZnO particles.