In-Situ Synthesis Of TiO₂-Based Catalysts And Their Catalytic Properties

As one of the earliest studied metal oxides,TiO2 has many excellent properties such as high redox potential,non-toxic,cheap,high catalytic efficiency and excellent stability.Consequently,TiO2 has attracted much attention in the field of environmental protection field including photocatalysis and gas catalysis.Compared with the corresponding bulk form,nanostructured TiO2 owns larger surface area and more active sites,making it promising in catalytic field.It has been eported that TiO2 nanomaterials can be synthesized by sol-gel,hydrothermal process,and hydrolysis method and so on.However,most TiO2 nanomaterials mainly exist in powder form,which is not desirable for cyclic application in industry due to the degradation of catalytic activity and life as a result of the possible mass loss and second pollution in the separation step.Hence,it is technologically important to find a suitable way to immobilize the TiO2 catalyst for long-time recycle utilization.In this thesis,TiO2 nanomaterials were prepared via PEO method,hydrothermal process,ion exchange and heat treatment,and investigated the influence of synthesis conditions on morphology,phase,crystallinity and photodegradation activity.In addition,the in-situ grown TiO2 nanosheets were used as supporters to synthesize TiO2-based gas catalyst(Au/TiO2 and CuO/TiO2).The relationship between morphology,composition,structure and catalytic performance of TiO2-based catalyst and the mechanism of CO catalytic oxidation reaction of TiO2-based catalyst were analyzed,which paves a solid way of TiO2-based catalysts towards gas catalysis.The main research contents are summarized as follows:(1)TiO2 nanostructures have been in-situ grown on Ti foil substrate through a multiple-step method based on conventional plasma electrolytic oxidation(PEO)technology,hydrothermal reaction,ion exchange process and heat process.And,the effects of pH value and hydrothermal time on the morphologies of intermediate product(sodium titanate)were systematically studied.It's found that sodium titanate nanostructures can be easily tailored into nanoparticles,nanofiber,nanowire and nanosheet.Meanwhile,optimizing of heat process was performed to tailor the crystallinity and phase of TiO2 nanostructures.In addition.Ag/TiO2 catalysts were also achieved via decorating Ag nanoparticles on the surface of TiO2 nanosheets.It's found that TiO2 nanostructures belonged to anatase phase and showed good crystallinity when the annealing temperature reached 500 ?.Moreover,the decoration of Ag cocatalyst can further improve the photocatalytic performance of TiO2 nanosheets.The Ag/TiO2 composite shows best photocatalytic performance and stability and can decompose methyl orange under irradiation of 100 mW/cm2.(2)Based on above work,we realized the in-situ growth of TiO2 nanosheet and the the decoration of Au cocatalyst,which can also further verify this feasibility of the new technology in preparing supported catalysts.The size and density of Au nanoparticles were effectively tailored by regulating the concentration of chloroauric acid solution.It was found that Au nanoparticles with a size of 3 nm show the best performance,which could completely oxidize CO at room temperature and exhibit excellent performance stability?(3)In order to prepare CuO/TiO2 nano catalysts,ion exchange and heat process were performed to decorate CuO nanoparticles on TiO2 nanosheets.The crystallinity of CuO NPs can be effectively tailored by adjusting annealing temperature.XRD result shows that the crystallinity of CuO becomes higher with the increase of temperature.It was found that CO catalytic oxidation activity was closely associated with the crystallinity of CuO nanoparticles.When the annealing temperature reaches 400 ? or 500 ?,CO can be completely removed at 120 ? and the catalytic stability is excellent.According to TEM analysis and Raman spectra,CuO nanoparticles have strong contact with TiO2 supporter,and this special structure can prevent the growth of CuO particles,greatly slowing down the decay of the catalytic performance.