Study On The Preparation Of TiO₂-SiO₂ Composite Oxide And Photocatalytic Property

Pure titania, TiO2-SiO2 composite oxide, doped with transition metal Fe3+ and rare earth metal Ho3+ were prepared by sol-gel method. The catalysts obtained were characterized by TG-DTA, XRD, DRS and FTIR. And activated carbon fibers (ACFs) as the support for TiO2-SiO2 composite oxide loading, TiO2-SiO2 composite oxide-loaded ACFs (TS/ACF)samples were prepared, also. The dye molecules were chosen as the model to evaluate the photocatalytic activity of all samples.The TiO2 and TiO2-SiO2 composite oxide calcined for 2h were totally anatase structure, The results showed that adding silicon could inhibite the crystal transformation form anatase to rutile, restrain the increase of grain size and refine grains; it could also broad band gap, which could improve the ability of reduction-oxidation. It was found that the samples calcined at 900℃and doped with 20% Si (in mole) possessed the highest photocatalytic activity among of all the prepared samplesThe optimal doping amount (in molar ratio) for Fe and Ho was Fe:Si:TiO2 =0.05%:20%:1 and Ho:Si:TiO2 =0.05%:20%:1 respectively. The optimal temperature of heat treatment for Fe doped TiO2-SiO2 composite oxide and Ho doped TiO2-SiO2 composite oxide both were 900℃. The photocatalysis properties of TiO2-SiO2 composite oxide prepared under this condition can be enhanced largely than TiO2-SiO2 composite oxide and pure TiO2 . The result of XRD showed that doping of Fe and doping of Ho both restrained the growth of the grains, promoted forming of nanoparticles and changed the crystalline transformation of TiO2 from anatase to rutile. The result of DRS showed that doping of Fe and doping of Ho both changed the spectrum absorption in ultraviolet light region and visible light region.In immobilization system, TiO2-SiO2 composite oxide film covered on the surface of ACFs. TiO2-SiO2 composite oxide film located groove in ACFs easy to crase and the crack was the combination weakness of support system. Organic pollutants in water could be degraded fleetly because of the dual function of adsorption and photocatalysis. Pore structure of immobilized samples influenced the photocatalytic activity. When molecular size of pollutants matched with the pore size of immobilized samples, pollutants could be absorbed into pores of immobilized samples; when molecular size of pollutants was larger than the pore size of immobilized samples, pollutants couldn't be caught effectively by immobilization system because of pore screening. So the photocatalytic activity of immobilization system was influenced.