Study On Continuous Preparation And Photocatalytic Activity Of ZnO And ZnO/Ag Nanocomposite Photocatalysts By Microzone Impinging Stream Reactor

Based on the review and analysis of related literatures, a new type of microzone impinging streams reactor was designed and produced by ourselves and used in the preparation of ZnO and ZnO/Ag nanocomposites. The influences of the process conditions on the morphology, productivity, photocatalytic activity of ZnO nanophotocatalyst were investigated. The main contents are as follows:(1) A self-made microzone impinging stream reactor were successfully adopted to prepare ZnO nanophotocatalyst with Zn(NO3) as raw materials, Na2CO3as precipitant. The influences of the reaction temperature, flow rate, reactant concentration and aging time on the photocatalytic activity of ZnO nanophotocatalyst were investigated, and the phase and morphology of ZnO nanophotocatalyst prepared under the optimum process conditions was characterized by X ray diffraction(XRD) and scanning electronmicroscopy (SEM).The results indicated that the continuous high efficiency production of ZnO nanophotocatalyst can be achieved by the microzone impinging stream reactor, uniform ZnO nanoparticles with am ean size of about20.1nm were obtained when using the reaction temperature of80℃, the reactant concentration of0.2mol·L-1, the flow rates of Na2CO3and Zn(NO3)2solution of350mL·min-1and291mL·min-1, respectively. The ZnO nanophotocatalyst has excellent photocatalytic activity for degrading methyl orange(MO), the degradation efficiency is exceeded93.9%under100W mercury lamp for40min.(2) A self-made microzone impinging stream reactor was successfully adopted to prepare ZnO nanopholocatalyst using Zn(NO3)2as raw materials, NaOH as precipitant and C6H5Na3O7as surfactant, the effect of temperature, flow rate, flow ratio, reactant concentration and concentration of on the nature of ZnO nanopholocatalyst such as particle size, particle size distributions and dispersity was studied, and the phase and morphology of ZnO nanophotocatalyst prepared under the optimum process conditions was characterized by X ray diffraction(XRD) and scanning electronmicroscopy (SEM). The results showed that:when reactant concentration and flow rate was0.2mol-L-1and350ml·min-1respectively, the dispersity of ZnO nanopholocatalyst prepared at80℃is best, and the mean particle size is about365nm; The mean particle size of ZnO nanoparticles sharply decreased with increasing the flow rate and the reactant concentration, and the dispersity have a obvious improvement at the same time. The mean particle size of ZnO nanoparticles sharply decreased with reducing the flow ratio, and the dispersity have also obvious improvement at the same time. The morphology of ZnO nanoparticles was also strongly dependent on the concentration of C6H5Na3O7, and the mean particle size of ZnO nanoparticles first decreased and subsequently increased with increasing the concentration of C6H5Na3O7, The mean particle size of ZnO nanoparticles was least when the concentration of C6H5Na3O7was0.004mol-L-1. The optimum process conditions is as follows:the temperature is80℃, the flow rates of Na2CO3and Zn(NO3)2solution of350mL·min-1and291mL·min-1, respectively, the flow ratio is1:1, the reactant concentration is0.4mol·L-3and the concentration of C6H5Na3O7is0.004mol·L-1.(3) A self-made microzone impinging stream reactor was successfully adopted to ZnO/Ag composite nanopholocatalyst using Zn(NO3)2and AgNO3as raw materials, NaOH as precipitant and C6H5Na3O7as surfactant and reductant. The effect of reaction time and Ag content on the nature of ZnO/Ag composite nanopholocatalyst such as particle size, particle size distributions, dispersity and photocatalytic activity was studied. The phase and morphology of ZnO nanophotocatalyst prepared under the optimum process conditions was characterized by transmission electron microscopy (TEM), high resolution transmission electron microscopy(HRTEM), X-ray diffraction meter (XRD) was used to characterize the nature of the samples. The samples were composed of ZnO with wurtzite structure and Ag with cubic structure. Ag particles was evenly distributed on the surface of ZnO, the mean particle size of ZnO and Ag particles increased slightly with increasing the reaction time, and amount of Ag particles also improved at the same time.The photocatalytic activity of ZnO/Ag increased first and then decreased with the increasing Ag content, and the ZnO/Ag sample with Ag content7.5atom%has the best photocatalytic activity, the degradation efficiency is100%under100W mercury lamp for1h.