Study Of Modification With Doping And Immobilization Of Nanometer Titanium Dioxide Photocatalyst

Semiconductor TiO₂ can degrade organic pollutants in water efficiently, which is difficult to be degraded by biologic methods. In the current work, pure, transition metal ions single-doped, rare earth metal ions single-doped, transition metal ions and rare earth metal ions co-doped TiO₂ were prepared by sol-gel method. And activated carbon fibers (ACF) as the support for TiO₂ loading, TiO₂-loaded ACF (TiO₂/ACF) samples were prepared, also. The dye molecules were chosen as the model to evaluate the photacatalytic activity of all samples.The photocatalytic activity of samples was influenced greatly by processing parameter using tetra-n-butyl titanate as the precursor, acetic acid as the hydrolyzed inhibitor and ethanol as solvent. The influence factors from primary to secondary were calcined temperature, adding quantity of acetic acid, distilled water and ethanol. Calcined temperature could influence phase transformation, crystal size, the property of light absorption of TiO₂, and then influence the photocatalytic activity of TiO₂.Transition metal ions, Cr and Fe single-doping restrained the crystal size increase, led to distortion and change of crystal volume, and broaden light absorption range of TiO₂. The photocatalytic activity of TiO₂ was improved by doping with appropriate content Cr or Fe. The optimal doped molar fraction of two kinds of transition metal ions both were 0.05 percent. Rare earth metal ions doping restrained the crystal size increase, prevented phase transformation, led to distortion and expansion of crystal lattice and begot absorption profile red-shift of TiO₂. The photocatalytic activity of TiO₂ was improved by doping with appropriate content rare earth metal ions. The optimal doped molar fractions of Y, Ce, Sm and Eu were 0.1, 0.05, 0.1 and 0.1 percent in turns. Calcined temperature could influence crystal size, phase transformation, light absorption property, distortion and expansion degree of crystal lattice and the ability of doped ions entering into lattice TiO₂, and then influenced the photocatalytic activity of TiO₂. The optimal calcined temperature was 600℃in our experiment. Sm-doped TiO₂ was provided with good photocatalytic activity under visible light irradiation.In the systems of Fe, Ho co-doped and V, La co-doped TiO₂, transition metal ions doping promoted phase transformation, however rare earth metal ions doping restrained it. Two kinds of function counteracted and restrained function got the run upon promoted function when two kinds of ions were co-doped into TiO₂. Compare to single-doped TiO₂, photocatalytic activity of TiO₂ could be improved further by co-doping. This was ascribed to the fact that there was a cooperative action in the two doped elements. Transition metal ions doping broaden the absorption profile, rare earth metal ions doping retards the recombination of photo-generated electrons and holes. The photacatalytic activity of Fe and Ho co-doped TiO₂ was superior to V and La co-doped TiO₂. This was attributed to that hydroxyl group's quantity on the surface of Fe and Ho co-doped TiO₂ was more than that of V and La co-doped TiO₂. The photacatalytic activity of co-doped TiO₂ was influenced not only doped concentration of two doped ions, but also their concentration ratio. The optimal concentration ratios were 0.05 percent Fe and 0.5 percent Ho in Fe and Ho co-doped system, and 0.05 percent V and 0.05 percent La in V and La co-doped system. The photocatalytic activity of co-doped TiO₂ could be influenced greatly by calcined temperature. The optimal calcined temperature was 600℃. Two kinds of co-doped TiO₂ could photodegradate methyl orange under visible light irradiation, furthermore, their photacatalytic activity were superior to pure TiO₂, which was related to decrease of crystal size, recombination retardance of photo-generated electrons and holes and enhancement of visible light absorption because of doping.In immobilization system, TiO₂ film covered on the surface of ACF. TiO₂ film located groove in ACF easy to craze and the crack was the combination weakness of support system. Calcined temperature played an important influence on supported quantity of TiO₂ and finial structure and morphology of film. The diameter of immobilized samples was mainly below 2 nm and had two peaks at 0.82 nm and 1.17 nm. 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, and then a dynamic balance of desorption and photocatalytic degraded reaction would be established. When molecular size of pollutants was larger than the pore size of immobilized samples, pollutants couldn't be catch effectively by immobilization system because of pore screening. So the photocatalytic activity of immobilization system was influenced.