Preparation And Photocatalytic Properties Of Nano-ZnO And Its Ag-loaded Composites

As a new type of wide gap multifunctional inorganic material, nano-ZnO has wideapplication prospect in many fields, especially in photocatalytic degradation of organicpollutants which is closely related to the survival and health of human beings. How toimprove the photocatalytic activity of ZnO semiconductor materials is one of the keytopics in the field of their photocatalytic applications. The morphology of ZnO and theadsorption of the noble metal on the surface of ZnO could change some intrinsicperformance of ZnO, such as internal electronic structures and lattice defects, which playan important role in imporoving the physical and chemical properties of ZnO at a certainextent. Based on this point, this paper aims to improve the photocatalytic performance ofnano-ZnO through changing the surface morphology of ZnO and adsorbing nobel metalon the surface of ZnO to form Ag/ZnO nanocomposites.Nano-ZnO powders were prepared by direct precipitation method at60oC usingammonia (NH3H2O) as precipitation agent and polyethylene glycol (PEG) as dispersingagent. The influence of calcination on the morphology and properties of the preparednano-ZnO was investigated. The experimental results showed that the ZnO powders werewurtzite hexagonal phase structure with good crystalline and assembled by nanorods withsmooth elongated side, which had lengths in the range600-800nm with diameters varyingfrom80±20nm. After calcination at300oC, it was found that the calcination induced nodrastic changes in the size and shape of the nano-ZnO, but resulted in significantlychanges on the surface of ZnO nanorods. The formation of this unique structure was dueto the ZnO(NH3)n complexes in ZnO crystals. The photocatalytic property of thenano-ZnO was evaluated by the degradation of methylene blue. The results demonstratedthat the calcination treatment could reduce the internal defects and increased the surfacedefects in the nano-ZnO. Moreover, the pitted structure increased the effective contact areabetween the photocatalyst and and MB molecules, and at the same time, the coated PEG on the surface of nano-ZnO was removed, resulting an enhancement of the photocatalyticactivity of nano-ZnO.In order to further improve photocatalytic activity of nano-ZnO, nano-Ag particleswhich were prepared by the PVP reduction method and interfacial method respectively,absorbed on the surface of the pitted nano-ZnO to form Ag/ZnO nanocomposites. Theresults indicated that the adsorbed nano-Ag particles had interaction with ZnO andaffected the surface charge distribution of nano-ZnO. The experiments of the degradationof methylene blue showed that the photocatalytic activity high pure Ag-loaded Ag/ZnOcomposite was much higher than that of coating agent containing Ag-loaded Ag/ZnOcomposite, due to the highly pure Ag particle with high catalytic activity, which had nocoating agents on the surface. Furthermore, the result of the photocatalytic performance ofthe Ag/ZnO composites with different concentrations of the loaded high pure Ag particlesshowed that the optimal value of the loaded Ag was8%.