Preparation And Catalytic Research Of Ag,TiO₂ Nanoparticles And Their Nanocomposites

In recent years,noble metal?Ag,Au etc.?and TiO₂ nanomaterials have been widely applied to the purification of the organic pollutants because of their unique properties,such as non-toxicity,high chemical stability,and excellent activity.In this disseration,our work mainly carried out the following four parts work in synthesis of Ag nanoparticles and TiO₂ nanostructures and their nanocomposites,as follows:In the first part,a novel Ag@TiO₂ nanostructure with multiple Ag nanoparticles as core and a crystalline TiO₂ as outer shell has been successfully achieved via a facile and one-step solvothermal route.The as-prepared Ag@TiO₂ products show an uniform and spherical morphology as well as a large specific surface area?226m²/g?.The synthetic approach is simple,rapid,and environmentally friendly,in which no any sacrificial template,toxic reagent or surfactant is emploited.Moreover,The time-dependent experiments reveal that the formation of Ag@TiO₂ nanospheres includes a nucleation,aggreagation and self-assembly process.Apart form this,the rattle-type Ag@TiO₂ nanoparticles can be also obtained by only tuning the amount of tetrabutyl titanate?TBOT?added in the precursor.When employed as catalyst for reduction of 4-nitrophenol?4-NP?,the Ag@TiO₂ nanospheres prepared exhibit a superior catalytic activity and a good cycle stability,benefiting from their unique multiple-cored nanostructure and the effective synergistic effect between Ag nanoparticles and TiO₂ shell.The present method also provides a great possiblility for preparation of other metal@TiO₂ nanocomposites with the multiple metal nanoparticles as cores.In the second part,a facile chemical self-etching route is presented for syntheisi of yolk-shell Ag@carbon nanostructures with uniform morphology.The space and the average size of theAg cores can be readily tuned by changing the amount of HCl,reaction time or the reaction temperature.Here,HCl as the etching agent extends the internal space by selective etching Ag cores of Ag@carbon core-shell nanoparticles.The penetrable carbon shell and empty inner space provide a homogenous environment for a heterogeneous catalysis,facilitate the diffusion of reactants,guarante the fully contact of the silver cores and the substrate molecules.Besides that,more crystal faces of the silver cores are able to expose providing more active sites for catalysis.When employed as catalyst for reduction of 4-nitrophenol?4-NP?,the yolk-shell Ag@carbon nanoparticles exhibite high catalytic performance and good cycle stability benefiting from their unique yolk-shell nanostructure.In the third part,an environmentally friendly and template-free route based on a simple hydrothermal process has been developed for preparing rattle-type TiO₂hollow microspheres by using the titanium?IV?sulfate?Ti?SO₄?₂?as the titanium source and acetic acid/water as the cosolvent.A possible formation mechanism involving the Ostwald ripening process was proposed.Ag/TiO₂ was also prepared for improving the catalytic performance.The photocatalytic results indicated that the Ag/TiO₂ microspheres exhibited higher photocatalytic activity for the photodegradation of methyl orange?MO?than the pure TiO₂ and commercial Degussa P25.In the fourth part,the flower-like and dendritic Ag nanoparticles are successfully prepared by a simple one-step method.According to the results of the experiment,ascorbic acid,as the reducing agent and structure-directing agent,promotes the formation of the flower-like structure.Besides that,ethanol reduces the surface free energy and changes the growth direction of the Ag nanoparticles,thus the dendritic Ag nanoparticles are obtained.The Ag nanoparticles with the unique structures have more potential applications in photocatalysis and surface-enhanced Raman scattering.