Visible-light-absorbing Evonik P-25 nanoparticles modified with tungstophosphoric acid and their photocatalytic activity on different wavelengths

For the first time, Evonik P-25 nanoparticles were impregnated with tungstophosphoric acid (TPA) (30% w/w) and annealed at two different temperatures, 200 degrees C (P25-TPA-200) and 500 degrees C (P25-TPA-500) for 1 h. Samples were characterized by different analytical techniques. Their photocatalytic activity was evaluated in the degradation of malachite green (MG) solutions at pH 5.0 upon three different irradiations: lambda(1) >320 nm, lambda(2) > 450 nm and lambda(3) > 590 nm. Only sample P25-TPA-500 showed visible-light absorption. This absorption could be related to the formation of a surface complex TPA Keggin anion-TiO2. P25-TPA-500 and P25-TPA-200 samples showed an important dark adsorption of MG dye (similar to 30%); however, sample P25-TPA-500 exhibited the highest photocatalytic activity either under irradiation lambda(1) or lambda(2). The presence of tert-butyl alcohol (TBA), an (OH)-O-center dot scavenger affected the photocatalytic reaction upon irradiation lambda(1), but just slightly upon irradiation lambda(2). Finally, P25-TPA-200 exhibited a higher leaching of TPA than P25-TPA-500 samples. (C) 2016 Elsevier Ltd. All rights reserved.