Preparation Of Zinc Oxide Composites Via Freeze-drying Process And Its Photocatalytic Performance Study

At present,the traditional dye wastewater treatment method has the problems of high cost and incomplete degradation,and the new photocatalytic technology has attracted much attention because of its green non-polluting and thoroughly degradation.The low cost and strong photocatalytic activity of zinc oxide semiconductor have great potential in the study of degradation of dye wastewater.However,during the preparation of zinc oxide,the powders are easy to agglomerate,and the rapid recombination of electron-hole pairs are the key factors that affect the photocatalytic process and the activity of the catalyst.Therefore,in this paper,the nano-zinc oxide(ZnO)powders was prepared by polymer assisted freeze-drying process,and composite reduced graphene oxide(rGO)to optimize the process conditions during the preparation.The effects of photocatalytic degradation process and degradation mechanism were investigated by the prepared zinc oxide-reduced graphene oxide(ZnO-rGO)composites which were used to degrade triphenylmethane-based rhodamine B and azo-type methyl orange in simulated dye wastewater.The main work of this paper includes:(1)The preparation of ZnO-rGO composites:nano-zinc oxide powder was prepared by polymer assisted freeze-drying process,graphene oxide was prepared by modified Hummers method and then ZnO-rGO composite photocatalyst was prepared by hydrothermal method.Control variable method was used to optimize the process conditions of preparation,the optimum technological conditions were as follows:the water-soluble polymer was polyvinyl alcohol(PVA),the content of graphene oxide was 10%,the hydrothermal temperature was 120 ?,and the hydrothermal time was 5 h.Under the optimal conditions,the degradation rate of rhodamine B reached over 95%after the photocatalytic reaction of ZnO-rGO composites for 40 min.(2)Characterization and analysis of ZnO-rGO composites:The chemical composition,morphology and optical properties of graphite oxide(GO),zinc oxide(ZnO)and ZnO-rGO were characterized and analyzed by a series of characterization methods.The relationship between structure and performance is clarified.(3)Photocatalytic degradation of dye wastewater:The preparation of ZnO-rGO composites were used to degrade rhodamine B and methyl orange simulated dye wastewater and investigated the effect of single variable such as initial concentration,solvent ratio and pH.The optimal degradation conditions of two dyes were obtained by orthogonal experiment.The kinetics of photocatalytic degradation was studied,and the fitting results were in accordance with the first order reaction kinetics equation that the correlation coefficient was greater than 0.96.The degradation mechanism of two dyes in different degradation time was analyzed by UV-vis absorption spectra.