Preparation Of ZnO-Ag Nanocomposite By Polymer Network Gel Method And Its Photocatalytic Activity

With the development of economics and technology,the problem of environmental pollution is becoming more and more worse.Traditional methods can not effectively remove contaminants,they usually just convert pollutants from one form to another.Using photocatalysts to degrade pollutants not only completely degrades the pollutants,but also does not cause secondary pollution to the environment.In recent years,TiO₂ and ZnO have been widely used as nano-catalysts,and ZnO has drawn more and more attention due to its lower cost.However,as a kind of wide bandgap semiconductor,ZnO nano-photocatalyst can excite photo-generated carriers only when the surface of the zinc oxide is irradiated with ultraviolet light,this will also inhibit its photocatalytic activity.Changing the preparation method is a kind of effective way to improve the catalyst's defects.Polymer-network gel method combines the advantages and avoids the drawbacks of other methods by all walks of life widespread concern in the past years.In this thesis,the polymer-network gel method with two-step synthesis,to synthesize ZnO nanopowders complexed with different materials.The samples were characterized by XRD,SEM,TEM,UV-vis,PL,XPS,BET,SPV and SPC.Our work mainly includes:?1?By a two-step polymer-network gel method,ZnO-Ag nano-photocatalyst was synthesized.Structural and optical properties of the samples were characterized by such techniques as X-ray diffraction,scanning electron microscope,transmission electron microscopy,X-ray photoelectron spectroscopy,UV-Vis diffuse reflectance spectroscopy,and room temperature photoluminescence spectra.The best Ag loading was found to be 3%.As evidenced by the XRD and UV-Vis,ZA3 have the higher crystallinity.The SPV and UV-vis spectra reveal that ZA3 produces more photo-induced electrons.Moreover,PL and SPC indicate that the electron–hole pairs of ZA3 can be separated effectively.The XPS results show that ZA3 have most surface hydroxyl groups.All the ZnO-Ag nanoparticles exhibit much higher photocatalytic activity than pure ZnO.Our research shows that the excellent performance of Ag nanoparticles is combined with ZnO semiconductors,and the photocatalytic activity of the catalyst is significantly improved by a two-step process.?2?The ZnO/TiO₂-1%Ag nanoparticle heterostructures with different TiO₂contents?0²%?were synthesized by two-step method.The structure and optical properties of the samples were characterized by X-ray diffraction,scanning electron microscopy,transmission electron microscopy,X-ray photoelectron spectroscopy,UV-visible diffuse reflectance spectroscopy and photoluminescence spectra.The best TiO2 loading occurs to the Ti concentration of 0.5%,while excessive TiO2 loading will does a harm to the photocatalytic activity.As XRD evidenced,the sample with0.5%Ti exhibits the best crystallinity.UV-visible spectrum reveals that ZAT0.5produces more photoelectrons.In addition,the PL spectrum shows that the electron-hole pairs of ZAT0.5 samples can be effectively separated.XPS results show that ZAT0.5 contains the most chemisorbed oxygen.Our results indicate that the appropriate amount of supported titania can effectively improve the photocatalytic activity of the ZnO-Ag nanoparticles.