The mineralisation of functionalised (hydroxyl and carboxylic) organic compounds by platinum deposits on titanium dioxide (Pt/TiO2) was investigated to study the catalytic and photocatalytic roles of platinum and the effect of organic molecular structure on these properties. Under dark conditions Pt/TiO2 catalysed the complete mineralisation of formic acid and partial mineralisation of oxalic acid and 1,2,3-trihydroxybenzene (1,2,3-THB). Under irradiated conditions, platinum deposits improved the mineralisation rate of each organic considered. Increasing carbon chain length of aliphatic compounds decreased mineralisation rates by both bare TiO2 and Pt/TiO2, attributed to steric hindrance effects for alcohols and the formation of rate limiting intermediates for carboxylic acids. Increasing the number of hydroxyl groups in aliphatic compounds increased mineralisation rates only by Pt/TiO2. This effect was not evident for hydroxylated aromatics. The findings suggest the degree of catalysis invoked by platinum deposits during photocatalysis is governed by the structural and functional characteristics of the target organic. (c) 2006 Published by Elsevier B.V.