Preparation And Investigation On Photocatalytic Reactivity Of Transition Metal Lon Doped TiO₂

Titanium dioxide(TiO2) has been considered as one of the most promising materials for its application in photocatalysis and photo conversion because of its high chemical stability, corrosion resistance, nontoxicity and low cost. However, it shows photo catalytic activity only under the UV irradiation due to its wide band gap(3.0-3.2eV). In order to improve the photocatalytic activity or extend the photo absorption to the visible light region, in this paper, transition metal(element 24 to 30) ion doped TiO2 had been prepared by sol-gel method. X-Ray diffraction, UV-Vis absorption spectrum, BET method were used to understand the crystallization behavior, optical property and specific surface area. By using Mn/TiO2 thin film deposited on porous nickel as positive electrode, carbon rod as negative electrode, arsenic as as target oxidation material, UV lamp(λ=253.7nm) as light source, experiments had been done to test the catalytic activity.The results of UV-Vis scanned by Mn/TiO2 indicated that catalysts showed the best optical properties when ion molar fraction was 1.5%, calcining temperature was 500℃, calcining time was 3h. UV-visible spectra of TiO2 doped with various transition metal ions showed that the absorption of the doped TiO2 had been improved in the visible-light range, the degree of improvement were decreasing by Cr3+, Mn2+, Cu2+, Co2+,Ni2+, Fe3+, Zn2+. The results of XRD showed that TiO2 and doping TiO2 were anatase crystal, and there were no typical characteristic diffraction peaks of doping ions because of the low doping rates. BET results showed that the display order of specific surface area was Cr/TiO2>Mn/TiO2> Ni/TiO2>Cu/TiO2> Co/TiO2>Zn/TiO2>Fe/TiO2.The standard curve of arsenite determined by electrochemical stripping voltammetry had the best linearity. Photocatalytic activity evaluation indicated that degradation of arsenite by photoelectrocatalytic method was better than photocatalytic method because electrifying could hinder the reuniting of photogenerated electron and photogenerated hole. Catalytic activity of Mn/TiO2 inhenced because of the increasment of BET and optical absorption.Using density function theory, pure TiO2, Mn/TiO2 and were calculated to investgate the geometry, the band structure, the electronic density of states, the orbit and the optical properties. The results indicated that the hybridization between O-2p and Mn-3d lead to some new bands between valence bands and conduction bands, besides, the valence bands become wider and the conduction bands shift downwards in Mn doped anatase TiO2, These changs lead to the narrowing of band gap and a red shift of the absorption band in Mri/TiO, experiments of Mn/TiO2 were also been done, the red-shift of Mn doped TiO2 in the experiments agreed with our calculation result. Calculated results of Cu/TiO2 are similar to Mn/TiO2. It was indicated that Mn was the best doping element by the caculation of transition metal ions doping Ti16O32 supercell.