Enhanced visible light responsive photocatalytic activity of TiO2-based nanocrystallites: impact of doping sequence

Non-metal doping is an effective approach to improve the visible light responsive photocatalytic activity of TiO2-based materials. To investigate the effect of doping sequence on the photocatalytic activity of nonmetal doped TiO2, four TiO2-based nanocrystallites were fabricated with both doping-in-sol and doping-in-gel (adsorption-calcination) methods. Experimental results demonstrate that the doping-in-gel method could effectively suppress the growth of crystallite size and the resultant photocatalyst had higher dopant content. The TiO2 nanoparticle obtained from the doping-in-gel approach had a much better photocatalytic performance than the three doping-in-sol counterparts, although the band gap of the former was larger than those of the other three. The enhanced photocatalytic activity could be attributed to the synergetic effects of the higher dopant content, the smaller crystallite size, the larger specific surface area, and the better dispersion in dye solutions. The results indicate that adsorption exhausted TiO2 gel might be a good precursor for TiO2-based photocatalysts. The consequent utilization of the TiO2-based materials as adsorbents and photocatalysts may endow them with renascent vitality. Besides, the results here shed light on the morphology and activity control of non-metal doped TiO2 with the sol-gel process.