Study On The Reparation Of Ag And Ce Modified TiO₂-SiO₂composite Catalysts And Its Degradation Kinetics

TiO₂ has been widely used in such filed as photacatalisis,medicalscience,sensing,magnetics and biology because of it easy acceptance,stable physical and chemical property,no toxicity and superior photocatalytic activity.However,as photocatalyst,TiO₂ with wide band gap?Eg=3.0³.2 eV?only absorbs light in the ultraviolet which less than 5% of solar energy.Moreover,the recombination rate of photo-generate electron-hole pairs is particular high in the pure TiO₂ catalyst,wich lead to the low efficiency of its practical application.The photocatalytic efficiency of catalyst is related to the absorption range of catalyst,the life time of the carrier and the specific surface area of sample.In order to extend light responsive region and restrain the recombination rate of photoinduced electronhole pairs as well as enlarge the specific surface area of catalyst.In this thesis,some modification technique was taken such as semiconductor coupling and doping method.At the same time the effect of different modification methods were investigated.The main contents are illustrated as follow:?1?Ternary Ag-TiO₂-SiO₂ nanocomposites with enhanced visible-light photocatalytic activity were synthesized by sol-gel method.The obtained materials were characterized by XRD,TEM,FE-SEM,XPS,FT-IR,BET,and UV-vis DRS,respectively.All photocatalyst samples hold an anatase phase confirmed by XRD.The Ag-TiO₂-SiO₂ particles were highly dispersed and the particle size became smaller compared to the pure TiO₂,resulting in the enlargement of surface area.In addition,UV-vis absorption shifted to visible region after Ag doping.XPS and FTIR results demonstrated that Ti-O-Si bonds in the synthesized materials.Photocatalytic performance of the obtained Ag-TiO₂-Si O₂ nanoparticles were evaluated by the rate of decomposition of Rhodamine B?RhB?.Ag deposition significantly enhanced the RhB photodegradation under visible light irradiation due to the formation of Schottky barrier at the Ag-Ti O₂ interface,which serve as the electron trap,benefiting for the separation of electrons and holes.?2?The supported photocatalysts of?x wt%?Ce-TiO₂-Si O₂?x=0,0.1,0.3,0.5,0.8,1?were prepared with?Si?OC2H5?4?,?Ti?OC2H5??4 and Ce?NO3?3·6H2O as precursors via a facile sol-gel method.The XRD data showed that the phase transformation from anatase to rutile was inhibited which demonstrated the thermal stability was improved after introduced the Ce and carrier SiO₂ to TiO₂.The analytic result of XPS and FT-IR showed that the Si-O-Ti and Si-O-Si bonds were formed in the catalyst,it was suggested the strong chemical bonds was formed between TiO₂ and Si O₂.The morphology of SEM image demonstrated that Ce-TiO₂-SiO₂ had smaller particle size and uniform size distribution when compared to TiO₂.According to the BET data,the specific surface area of TiO₂-SiO₂ and 0.3% Ce-TiO₂/SiO₂ were increased from 17.55 m2/g to 174.98 m2/g and 194.98 m2/g,respectively.At the same time the pore size and pore volume were significantly increased.The effects of the Ce content on the photocatalytic activity were investigated by the photodegradation of rhodamine B?Rh B?irradiated by ultraviolet light and visible light.The results showed that the reaction accord with pseudo first-order model furthermore the composites with the constant of 10wt% SiO₂ and 0.5wt% Ce had the best ability of photo-degradation.The degradation efficiency could reach to 99% and 74% after reaction for 30 min under the ultraviolet light and 180 min visible light irradiation respectively.?3?Quarternary Ce-Ag-TiO₂-SiO₂ photocatalyst with super visible-light photocatalytic activity was synthesized by doping rare earth element Ce and decorating noble metal Ag nanoparticles.Samples were characterized by different techniques such as,X-ray diffraction?XRD?,Raman spectrum,FE-scanning electron microscope?FE-SEM?,transmission electron microscopy?TEM?,X-ray photoelectron spectroscopy?XPS?,nitrogen adsorption and desorption?N2-BET?,UV–vis absorption spectrum?UV-vis?measurements.The result of SEM,XRD,Raman,BET and UV-vis indicated that the crystallite size of modified samples was decreased,the phase transformation was inhabited,the specific surface area was increased,and extend the spectral response from UV to visible range.The photodegradation experiment showed that the resultant samples displayed a high photoctalytic activity for degradation of Rh B under the visible-light and UV-light irradiation,which can be ascribed to the surface plasma of Ag.The active 4f electrons and multi-electron configurationof Ce and the enhanced absorption capacity of large specific surface area of SiO₂.The results showed that the reaction of photo-degradation was accorded with pseudo first-order model.