Preparation And Application Of Nano-tio₂ Photocatalyst With A Visible-light Activity

The preparation methods of photocatalysts——sol-gel (SG) and precipitation-dipping (PD) were studied. The results showed that nano-TiO₂s'particle size, lattice distortion degree, the specific surface area are very similar which were prepared by two methods; And in terms of the photocatalytic activity and preparation process, PD method is better than SG. But the immobilized effect of nanometer photocatalyst by the SG method is good, while the PD for the effect of difference.In order to expand TiO₂'s visible light absorption property which was only of UV activity, co-doped photocatalysts were studied. Thus, four co-doped photocatalyst of Ni, S, Ni, N, Co, N and Co, N, S were studied.The results show that modified TiO₂ by doping have an excellent visible light photocatalytic activity, and the scope of its absorption can be expanded. By contrast, Ni/S/TiO₂ and Ni/N/TiO₂'s photocatalytic activity under visible light is in general; Co/N/TiO₂'s visible activity is very good, and its degradation for T1 probe come to 87.5% under the purely visible light(λ>400nm) . Compared to single-doped TiO₂ with Co or N, its UV absorption properties do not change much, but the visible light absorption properties has been significantly increased; Co/N/S/TiO₂ have the best visible light activity, and the degradation come to 88.4% under the purely visible light. Compared to Co, N single-doped or N/S doped TiO₂, the catalyst's absorption capacity in the ultraviolet and visible light were markedly improved.The modified photocatalyst's absorption properties, crystal morphology, grain size, surface morphology and doping other elements were studied by the characterized means of DRS, XRD, TEM, EDX and XPS. The results showed that the four new catalysts were anatase, and the elements will not affect the TiO₂'s transition temperature, and the catalysts'average particle sizes are about 6 to 11 nm. Compared to the P25 with 20nm's particle size, the modified catalysts'particle sizes are smaller, and the surface areas are larger, it helps to improve the catalytic performance in visible light. DRS results showed that all catalysts have the phenomenon of different degrees's red shift, the order of red shift from small to large is: Ni/S/TiO₂≈Ni/N/TiO₂ <Co/N/TiO₂ <Co/N/S/TiO₂, the same order as its visible absorption properties.When modified photocatalyst Co/N/TiO₂ or Co/N/S/TiO₂ were loaded on activated carbon, its photocatalytic activity decreased, but the difference was not significant. Co/N/TiO₂-AC and Co/N/S/TiO₂-AC's catalytic properties of visible light are much higher than the TiO₂-AC.And it has a good visible light activity of humic acid——the major organic pollutants in water, the degradation rates reached 87.72% and 85.94% respectively after 3h's light. Photocatalyst can better load on AC by SG method, and can reach the purposes of nanometer photocatalyst's separation, recycling.