Preparation And Photocatalytic Performance Of Ag-based Nanostructure Materials

Environmental pollution and energy shortage are the two major challenges that the current world faced with. Photocatalysis can not only degrade pollutants in the water and air directly by using sunlight, but can also convert solar energy with low density into electric energy with high density through dye-sensitized solar cells. Photocatalysis is an important approach to solve the two problems:energycrisis and environmental pollution. However, most traditional photocatalysts (such as TiO2) are not suitable for large-scal practical applications in the social life and industrial production, due to their limited visible-light absorption and low quantum efficiency. Recently, It was found that many Ag-based photocatalysts (such as AgX (X=Cl,Br, I),Ag3PO4,Ag2O,Ag-semiconductor) showed obviously higher photocatalytic under visible-light irradiation than the traditional photocatalysts, thus Ag-based photocatalysts have recived extensive attentions and applications in various fields. It is necessary to improve the photocatalytic activity of Ag-based photocatalysts to achieve the needs of practical applications. In this dissertation, valuable explorations have been carried out as follows:(1) construction of Ag8W4O16/Ag2S composite photocatalyst;(2) construction of Ag/ZnO photocatalyst with large specific surface area;(3) construction of Ag2O photocatalyst with unique structures. The main points could be summarized as follows:1. Ag8W4O16/Ag2S core-shell nanorods were formed on the surface of Ag8W4O16nanorods by a simple in situ anion-exchange route. The effect of concentrations of Na2S on the morphology and micro-structures of Ag8W4O16/Ag2S core-shell heterostructures were explored. It was found that the anion exchange reaction between S2-and WO42-was preferable to occur on the surface of Ag8W4O16,/Ag2S nanords rather than in the bulk solution, resulting in the formation of core-shell nanorods. The Ag2S nanoparticles coated on the surface of Ag8W4O16nanorods uniformLy, and it could be easily controlled by adjusting the concentration of Na2S solution. According to the results of photocatalytic activity experiments under visible-light irradiation, when the Na2S solution concentration is0.5mM, the core-shell nanorods exhibited the highest photocatalytic activity with the reaction rate constant k value of2.08×10-2min-1, which is41.5and4.5times more than Ag2S nanoparticles and Ag8W4O16nanorods, respectively.2. Ag modified ZnO (Ag/ZnO) nanocrystals were prepared by a facile and low temperature wet chemical method. The phase structures, morphologies, and optical properties of the as-prepared samples were characterized by XRD, FESEM, HRTEM, BET, UV-vis and PL, respectively. The photocatalytic performance of Ag/ZnO with diffent Ag contents was measured with the degradation of methyl orange (MO) at room temperature under UV light irradiation. The results indicated that the well-crystalline ZnO nanocrystals with a size of ca.5nm exhibited a high photocatalytic activity for the degradation of MO with the apparent rate constant (k) of1.57×10-2min-1, and the photocatalytic activities of ZnO were further enhanced by modification with silver. When the Ag loading was3at%, Ag/ZnO showed the highest photocatalytic acitivity with a k value of5.45X10-2min-1, which is3.5and2.5time more than that of ZnO and commercial P25, respectively.3. Ag2O nanocrystals with systematic shape evolution from cubic to edge-and corner-truncated octahedral and octahedral were prepared by a facile and room temperature precipitation method. The as-prepared Ag2O nanocrystals were characteriaed by XRD, SEM, TEM, BET, UV-vis and XPS. Our results demonstrated that cubic Ag2O nanocrystals are bounded by the {100} facets and octahedral Ag2O nanocrystals are bounded by the {111} facets, respectively. According to the results of photocatalytic activity experiments under visible-light irradiation, Ag2O nanocrystals with {111} facet exhibited higher photocatalytic activity than {100} facet. Because {111} facets contain positively Ag+which are not matched with O2-at the sufaces, wheras the {100} facets are electrically neutral. So {111} facets could accept more photogenerated electrons and easier to form metal Ag than {100} facets, resulting in the higher separation efficiency of photogenerated electron-hole and better photocatalytic activity. However, Ag2O nanocrystals stop to decompose after formation of partial Ag on the surface of Ag2O, the Ag2O/Ag composite can work as a stable visible-light photocatalyst.