Highly dispersed phase of SnO2 on TiO2 nanoparticles synthesized by polyol-mediated route: Photocatalytic activity for hydrogen generation

Abstract

Abstract TiO 2 –SnO 2 mixed oxides (Ti:Sn = 98:2 (TS2), 95:5 (TS5) and 90:10 (TS10) by atomic weight) of large surface area and small particle size, in which SnO 2 is in a dispersed phase on TiO 2 , have been synthesized by a polyol-mediated route. Characterization by various techniques has shown that a highly dispersed phase of SnO 2 on anatase TiO 2 is formed in TS2 sample. No separate discernible phases corresponding to cassiterite SnO 2 or rutile TiO 2 is seen in TS2 sample, whereas rutile TiO 2 and SnO 2 are observed besides the anatase phase of TiO 2 in TS5 and TS10 samples. The average particle size of the mixed oxide samples is ∼20 nm. All samples absorb visible light and the onset of absorption was ∼425 nm. These mixed oxides show emission from defect levels arising due to the anion vacancies present in TiO 2 . The visible light absorption of these samples is attributed to the presence of defect levels in the bandgap of TiO 2 . Photocatalytic activity of these samples for hydrogen generation from water using methanol as sacrificial reagent was studied under sunlight type radiation. The results indicate that mixed oxides have better activity compared to pure TiO 2 synthesized by the same method and the activity decreases with increasing SnO 2 concentration in TiO 2 . The enhanced activity of TS2 sample is ascribed to the efficient charge separation from TiO 2 to SnO 2 owing to the high dispersion of SnO 2 in TiO 2 . The decreased photocatalytic activity with increased SnO 2 concentration is due to the aggregation of SnO 2 on TiO 2 , which results in relatively poor dispersion of SnO 2 and decreased charge transfer efficiency, but still maintains better photocatalytic activity compared to TiO 2 . In addition loading Pd co-catalyst produces a pronounced increase in the hydrogen yield due to the accumulation of electrons in the metal from the TiO 2 and SnO 2 semiconductors and the increased reductive power of the Pd loaded mixed oxide nanoparticles.