Preparation And Performance Study Of Metal Embedded Modified Ordered Mesoporous TiO₂ Materials

Novel metal modified semiconductors（NMS）have a wide range of applications in environmental restoration,catalysis and conversion of solar energy due to their excellent optical,electrical and magnetic properties.Recently,a large number of works about NMS have been reported,including design of special morphology materials,performance optimization and mechanism exploration.At present,depositing novel metals on the surface of metal oxide semiconductors is most frequently employed to synthesize NMS.However,this method usually shows shortcomings in big-sized noble metal,the poor dispersion of metal particles,and the low stability against leaching and agglomeration etc.To solve these problems,the metal-embedded ordered mesoporous materials have been synthesized by in-situ modification.Their photocatalytic performances have also been studied systematically in this thesis.1.Ag-modified ordered mesoporous TiO₂（Ag/TiO₂）was successfully prepared by evaporation-induced self-assembly method.The catalyst exhibited ordered two-dimensional hexagonal mesoporous structure and large specific surface area.Compared with the catalyst prepared by traditional impregnation method,the active sites of the present catalyst are uniformLy dispersed and the pore channels are not blocked,which favored the mass diffusion and transfer.The photocatalytic properties were studied by using the degradation of pollutants and the selective oxidation of benzaldehyde as probes.The results demonstrated that,in the Ag/TiO₂ with Ag-loading of 1.0%,the Ag particles were uniformLy embedded in the pore walls of ordered mesoporous TiO₂.The Ag/TiO₂ exhibited the regular pore structure and high specific surface area,which could significantly improve the catalytic performance.Compared with irregular porous materials,such a unique structure was conducive to expose active sites.Meanwhile,the ordered channels also favored light absorption and solute transport.Theorefore,the as-prepared Ag/TiO₂ exhibited high activity.Fuethermore,the Ag and TiO₂ pocessessed strong interaction,which could effectively inhibit the loss and gaithering of Ag nanoparticles during reaction process.2.An Fe-doped TiO₂ composite with ordered mesoporous structure（FT）were prepared by in-situ modification.FT composites had a wide range of visible light response range and strong ability for visible light absorption.The photo-induced Fenton oxidation technology was developed for the selective oxidative cleavage of olefins.During photofenton reaction process,the photoelectrons could be rapidly transferred,so that the electron-hole recombination could be effectively inhibited.Meanwhile,the conversion between Fe³⁺and Fe²⁺also rapid priceeded.As a result,the present photo-induced Fenton reaction could greatly improve the olefins conversion efficiency in comparison with the conventional way used in oxidative cleavage of olefins.3.A novel ordered mesoporous compsite with Pd nanoparticles uniformly embedded in TiO₂ walls were successfully prepared by evaporation-induced self-assembly.Due to the confinement of the pore walls,the Pd particle size and distribution were greatly improved by inhibiting the agglomeration.The average Pd metal particle size was about 0.7 nm.The catalytic performance of the catalyst was studied by photocatalytic coupling reaction of chlorobenzene（Ullmann reaction）.The influence of Pd-loading and solvents were investigated.Compared with the traditional Ullmann reactions,Photocatalytic Ullmann reaction on the as-prepared Pd/TiO₂exhibited excellent activity and selectivity as well as stability.4.Cu and Pd co-doped TiO₂ with ordered mesoprous structure（Cu/PT）was successfully synthesized and applied in photocatalytic coupling reaction of iodobenzene（Stiller reaction）for the first time.The effects of metal-loading,solvent and alkali on the reaction were carefully investigated.The Cu/PT with Cu/Pd molar ratio of 1.5 exhibited the highest conversion and excellent selectivity.It was found that the introduction of Cu promoted the separation and transfer efficiency of photo-generated charge of TiO₂.Meanwhile,the Cu also promoted the metal transfer rate of the tin reagent and the oxidative addition intermediate.As a result,the photocatalytic Stirling reaction over Cu/PT exhibited much higher activity and selectivity comparing the conventional Stiller reactions.