Study On Preparation And Photocatalytic Activity Of AgBr/ZnO And AgCl/ZnO Nanocomposite Photocatalysts

In recent years, the ZnO nanomaterials have attracted considerable attention because of its advantages such as low prices, high photocatalytic activity and wide application prospect. Some researches show that the modification of ZnO nanomaterials could improve the photoinduced electron-hole pairs'separation efficiency and the sunlight utilization efficiency of ZnO. So the study of ZnO-based nanocomposite photocatalysts has become the hot research topic in fields of the chemistry, material science and environtology. In this dissertation, the AgBr/ZnO and AgCl/ZnO nanocoposite photocatalysts were prepared by simple two-step precipitation method and characterized by several analytical techniques. The preparation technicses of AgBr/ZnO and AgCl/ZnO nanocomposite photocatalysts were optimized. The photocatalytic activity and mechanism of AgBr/ZnO and AgCl/ZnO nanocoposite photocatalysts under sunlight or simulative sunlight irradiation were studied and discussed. In this dissertation, the main research contents as follows:(1) AgBr/ZnO nanocoposite photocatalysts have been synthesized by two-step precipitation method, in which NH₄HCO₃, Zn(NO₃)₂, AgNO₃and KBr were used as raw materials. They were systematically characterized by different techniques such as X-ray diffraction (XRD), transmission electron microscopy (TEM), high resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS) inductively coupled plasma optical emission spectrometry (ICP-OES) and ultraviolet-visible spectrophotometer (UV-vis). The preparation technicses of AgBr/ZnO nanocomposite photocatalysts were optimized by the orthogonal experiment, and the effect of pH value, reaction temperature and light intensity on the photocatalytic activity of AgBr/ZnO nanocomposite photocatalysts were examined. The photocatalytic mechanism of AgBr/ZnO was discussed carefully. The results show that the AgBr/ZnO nanocomposite is an efficient photocatalyst under simulative sunlight irradiation. The MO degradation efficiency for AgBr/ZnO is about 95% after 1.5 hour under 300W halogen tungsten lamp irradiation. The optimum preparation technicses of AgBr/ZnO nanocomposite photocatalysts are pH value of 6, KBr concentration of 0.04mol·L^-1, reaction temperature of 55℃and reaction time of 2.0 hours. The optimum condition of photocatalytic reaction is pH value of 6, reaction temperature of 45℃and light intensity of 300W.(2) The photocatalytic activity of AgBr/ZnO was studied under sunlight irradiation. The changes of the photocatalytic activity, component, morphology and photoluminescence properties for AgBr/ZnO in the cycle photocatalytic reaction were characterized by UV-vis, XRD, scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDXA) and Photoluminescence spectrophotometer (PL). The photocatalytic mechanism of AgBr/ZnO under sunlight irradiation was discussed carefully. The results show that the AgBr/ZnO possesses excellent photocatalytic activity under sunlight irradiation. The MO degradation efficiency for AgBr/ZnO is about 98% after 1.0 hour under the sunlight irradiation. The rhodamine B degradation efficiency for AgBr/ZnO is about 98% after 15 minutes under the sunlight irradiation. In the cycle photocatalytic reaction, the AgBr was photoreduced to Ag gradually. The photocatalyst composition were AgBr/ZnO, Ag/AgBr/ZnO and Ag/ZnO, after first, second, third and more cycle photocatalytic reacted,respectively. Though the compositions of photocatalyst have been changed in the cycle photocatalytic reaction, the photocatalytic activity for MO degradation under sunlight irradiation is not still reduced. The PL intensity of three different systems is lower than that of ZnO.(3) AgCl/ZnO nanocoposite photocatalysts have been synthesized by two-step precipitation method, in which NH₄HCO₃, Zn(NO₃)₂, AgNO₃and KBr were used as raw materials. They were systematically characterized by different techniques such as XRD, TEM, EDXA and UV-vis. The effect of pH value, reaction temperature, NH₄Cl concentration, the molar ratio of Ag:Cl and reaction time on photocatalytic activity of AgCl/ZnO nanocomposite photocatalysts were examined. The effect of AgCl mass percentage and ZnO morphology on the photocatalytic activity of AgCl/ZnO nanocomposite photocatalysts was studied. The photocatalytic mechanism of AgCl/ZnO was discussed carefully. The results show that optimum preparation technicses of AgCl/ZnO nanocomposite photocatalysts are pH value of 10, NH₄Cl concentration of 0.1 mol·L^-1, Ag:Cl molar ratio of 1:1.2, reaction temperature of 25℃and reaction time of 1.0 hour. When AgCl/ZnO nanocomposite is consists of ZnO nanoparticles and the 20% mass percentage of AgCl, it possesses the best photocatalytic activity. The MO degradation efficiency for AgCl/ZnO is about 97% after 1.5 hour under 350W xenon lamp irradiation. The effect of ZnO morphology on the UV-vis absorption spectra of AgCl/ZnO could be ignored. The mass percentage of AgCl will influence the UV-vis absorption spectra intensity of AgCl/ZnO in visible light region (400nm-650nm).