Photocatalytic dye-degradation activity of nano-crystalline Ti M O (M =Ag, Pd, Fe, Ni and = 0, 0.01) for water pollution abatement.

Nanocrystalline metal-ion (M = Fe, Ni, Ag, and Pd) doped and undoped anatase-TiO powders were prepared using a solution combustion method. The photocatalytic degradation of different dyes such as methylene blue (MB), rhodamine B (RB), rhodamine B base (RBB), and thionine acetate (TA) was investigated under UV exposure. The degradation rate of the dyes were found to be better in the case of Ag and Pd doped TiO, whereas Fe and Ni doped TiO showed lower photocatalytic activity compared to undoped TiO nanoparticles. Combustion synthesized catalysts exhibited much better activity compared to the commercial Degussa P25 (75% anatase + 25% rutile) TiO photocatalyst. The intermediate states created in the band gap of the TiO photocatalyst due to doping of first row transition metal ions (such as Fe and Ni) into the TiO lattice act as recombination centres and the electrons present in the d-orbital quench the photogenerated holes by indirect recombination, hence increasing e-h recombination rates. As a result, a decrease in the photocatalytic activity of TiO doped with first row transition metal ions is observed. However, in the case of noble metal ions (such as Ag and Pd) in TiO, photoreduction of Ag and Pd ions occurs upon UV irradiation, hence the noble metal-ions act as electron scavengers. Consequently, the lifetime of the holes (h) increases and hence higher photocatalytic oxidation activity of the dyes is observed. A novel strategy of electron scavenging is envisaged here to develop Ag and Pd doped TiO to increase the photocatalytic oxidation of organic dyes for the development of better water pollution abatement catalysts. Redox-pair stabilization in the TiO lattice similar to photo-chromic glasses play a defining role in enhancing the photocatalytic activity of the catalyst and is a key finding for the development of superior photocatalysts. With the help of UV-vis and fluorescence spectroscopy, the mechanisms of the superior oxidation activity of Pd and Ag doped TiO nanoparticles are explained.