BACKGROUND: This research investigated the effect of platinum (Pt) on the reactivity of tungsten oxide (WO3) for the visible light photocatalytic oxidation of dyes. RESULTS: Nanocrystalline tungsten oxide (WO3) photocatalysts were synthesised by a sol-gel process and employed for the photocatalytic degradation of Methyl Orange under visible light. For comparison commercial bulk WO3 materials were also studied for the samereaction. These materials were fully characterised using X-ray diffraction (XRD), UV-visible diffuse reflection spectroscopy and transmission electron microscopy (TEM). The photocatalytic oxidation of iso-propanol was used as a model reaction to follow the concomitant reduction of molecular oxygen. No reactions occured in the absence of platinum, which is an essential co-catalyst for the multi-electron reduction of oxygen. The platinised WO3 catalysts were stable for multiple oxidation-reduction cycles. The results from the catalytic activity measurements showed that platinised nanocrystalline WO3 is a superior oxidation photocatalyst when compared with bulk WO3. Methyl Orange was completely decolourised in 4 h. CONCLUSIONS: The enhanced performance of nanocrystalline Pt-WO3 is attributed to improved charge separation in the nanosized photocatalyst. Platinum is an essential co-catalyst to reduce oxygen. This photocatalyst could be applied to the treatment of organic pollutants in wastewater, with the advantage of using visible light compared with the widely studied TiO2, which requires UV light. (C) 2011 Society of Chemical Industry