Preparation Of Nano-sized Zno Photocatalyst Via A Novel Polymer-assisted Freeze-drying Process And Its Application In Dye Wastewater Treatment

Synthesis of semiconductors holds an important place in present material science research.Different preparation processes have a significant influence in the microstructure,macroscopic property and application of the semiconductor materials.Using the third generation semiconductor ZnO as the photocatalysis to photodegrade organic dyes wastewater is one of the research hotspots in recent years.This thesis has synthesized a kind of zinc oxide(ZnO)with enhanced dispersity and photocatalytic performance via a novel polymer-assisted freeze-drying process based on the conformational entropy and group chemical characteristic of high-molecular polymer.The obtain ZnO was used as a photocatalysis to degrade the single dye solution and mixed dyes wastewater.Mechanism models and kinetics equations of dyes photocatalytic degradation reaction has also been specifically investigate.The main work includes:(1)Nano-sized zinc oxide(ZnO)with enhanced dispersibility was prepared by a novel polymer-assisted freezing drying process.According to the controlling variable method,the effects of preparation condition on the photocatalytic performance of nano-sized ZnO were investigated.The optimum conditions of the polymer-assisted freeze-drying method were obtained:polyvinyl alcohol(PVA)is used as the polymer,mass fraction of polymer solution is 2%,the mass ratio of raw materials is 1:4,the calcination temperature is 550?,and the calcination time is 4 h.The intermediates and final nano-ZnO photocatalyst products were analyzed by X-ray diffraction(XRD),thermogravimetric differential thermal analysis(TGA-DTA),Fourier transform infrared spectroscopy(FT-IF)and scanning electron microscopy(SEM).Through the characterization of the intermediates,the chain conformation of the polymer and the dispersion properties of the freeze-drying process and the synergistic effect between these two effects were analyzed.The mechanism and characteristics of the polymer-assisted freeze-drying method were also elucidated.(2)The prepared nano-ZnO powders were used to degrade single component dye wastewater and multi-component mixed dyes wastewater,and influencing factors of the photocatalytic degradation reaction were studied.The interaction between different components in the process of degradation of multi-component mixed dyes was analyzed.The kinetic properties of the photocatalytic degradation were studied.It was found that the experimental data were in good agreement with the Langmuir-Hinshelwood(L-H)equation,and the correlation coefficients(R2)of the nonlinear fitting were more than 0.99.The degradation process of single component dye wastewater and multi-component mixed dye was discussed and analyzed by photocatalytic degradation mechanism.