Improved visible light photocatalytic activity of TiO_2 nano powders with metal ions doping for glazed ceramic tiles

摘要

Self-cleaning and anti-bacterial activities of the photo-catalyst titanium dioxide make it a superior compound for use in the ceramics and glass industry. In order to achieve high self-cleaning efficiency for building products, it is important that Titania is present as anatase phase. Moreover, it is desirable that the particle sizes are in Nano-range, so that a large enough surface area is available for enhanced catalytic performance. In the present paper, Cobalt and Nickel co-doped (4%mol Ni and 4%mol Co doped TiO_2) and un-doped TiO_2 Nano powders have been prepared by sol-gel technique. They were calcined at the temperatures in the range of 475-1075 °C. Ni/Co co-doped TiO_2 postponed the anatase to rutile transformation of TiO_2 by about 200-300°C, such that before calcination at 775°C, no rutile was detected for 4 mol% Ni/Co co-doped TiO_2. A systematic decreasing on crystallite size and increasing on specific surface area of Ni/Co co-doped TiO_2 were observed. Photo-catalytic activity of anatase polymorph was measured by the decomposition rate of methylene blue under visible light. The results showed enhanced catalysis under visible light for Ni/Co co-doped TiO_2 as compared to pure TiO_2. The enhanced performance was attributed to surface chemistry change associated with a slight shift in the band gap. Depending on the temperatures ranging from 475 to 1075 °C, band gap energy of Ni and Co doped TiO_2 crystals decreased. For all samples there is a general reduction of the band gap energy from 3.00 to 2.96 eV.