| Currently, there is an increasing interest in the photocatalytic degradation of organic pollutants technology, which stands out as an effective way for purifying environment. ZnO, as one of the several semiconductors which could realize quantum size effect, has been widely used as photocatalysts for its high photosensitivity, environmental sustainability, and large bandgap (3.3eV). But pure ZnO shows some disadvantages which lead to its lower photocatalytic efficiency and thus largely limit the wider applications, such as spectral response range is narrow, the photo-generated electrons and holes easily get combined. Photocatalytic efficiency of ZnO can be improved by compounding semiconductors or depositing noble-metal, which, therefore, has become an attractive and challenging field in the efforts to enhance the photocatalytic properties of pure ZnO.In this paper, the characterization, photocatalytic properties, and function-properties’ relationship of ultrafine Ag-ZnO and Sn-Zn-0composite photocatalyst were discussed, respectively.Part1, The synthesis, characterization, and photocatalytic performance of ultrafine Ag-Zn-O composite photocatalyst.The composite photocatalyst Ag-ZnO has been prepared by citric acid sol-gel method and characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), N2adsorption-desorption, UV-visible diffuse reflectance spectra (UV-vis) and photoluminescence spectra (PL). The photocatalytic activity of Ag-ZnO composite catalyst was evaluated with the photocatalytic degradation of2-propanol in aqueous solution, The results showed:(1) Ultrafine Ag-ZnO composite photocatalysts were synthesized by a citric acid sol-gel method. Ag-doping could reduce the crystal size of ZnO, and with the increase of Ag loading, the crystal size of ZnO increased and its specific surface area decreased. Surface Plasmon Resonance (SPR) related phenomena was observed, correlated to the optical properties of Ag-ZnO photocatalyst.(2) When the content of Ag was5at.%, the photocatalytic property of the Ag-ZnO sample calcined at500℃was excellent. The degradation rate of2-propanol could reach83%in4h at room temperature when the concentration of catalyst was1g/L, slightly better than that of Degussa P25TiO2.(3) The reaction for photodegradating2-propanol with pure ZnO and5%Ag-ZnO composites was both in accordance with the first order kinetic model. And the apparent reaction rate constant of5%Ag-ZnO was0.199mmol/L·min-1, which was10times better than that of the pure ZnO. Conclusively,5%Ag-ZnO possessed better photocatalytic property than pure ZnO.Part2, The synthesis, characterization, and photocatalytic performance of nanosized Sn-Zn-O composite photocatalyst.In order to further perfect the study on the improvement of the photocatalytic performance of ZnO, the other photocatalyst based on ZnO was also investigated. The nanosized Sn-Zn-0composite photocatalyst was prepared via a coprecipitation-method with the aid of ultrasonic treatment and characterized by XRD, SEM, N2adsorption-desorption, FT-IR and UV-vis. The photocatalytic activity of nanosized Sn-Zn-O composite photocatalyst was evaluated for the photocatalytic degradation of formaldehyde in aqueous solution. The results showed:(1) The nano Sn-Zn-O composite photocatalyst was synthesized via a coprecipitation method with the assitance of ultrasonic treatment. It was amorphousness and the specific surface was greater than that of pure ZnO. When the molar ratio of Sn/Zn was1:1, the nano Sn-Zn-O sample exhibited higher optical band. The as-prepared Sn-Zn-O photocatalyst exhibited better photocatalytic performance than the pure ZnO and the degradation rate of formaldehyde by SnpZn1-O sample could reach72%in4h, obviously better than that of Degussa P25TiO2(ca.40%).(2) The influence of different reaction conditions was also discussed. The results showed that the most efficient degradation of formaldehyde was achieved in a highly alkaline region, when the concentration of catalyst was1g/L. The reaction of pure ZnO and Sn1-Zn1-O composite photodegradating formaldehyde were both in accordance with the first order kinetic model. And the apparent reaction rate constant of pure ZnO and Sn1-Zn1-O composite was0.2227mg/L·min-1and1.138mg/L·min-1, respectively, indicating that Sn1-Zn1-O possessed better photocatalytic property than pure ZnO. |
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