The effect of Cu2+ on the photocatalytic oxidation of 1,4-dioxane was evaluated. The addition of Cu2+ led to an enhancing effect in the photocatalytic degradation and mineralisation of 1,4-dioxane for both pH 3 and 5. This positive role of Cu2+ was attributed to its involvement in the ligand-to-metal charge transfer (LMCT) process, where Cu2+ formed complexes with 1,4-dioxane and/or its intermediate products, providing an alternative routes for the oxidation reaction via photoredox mechanism. The supporting evidence to the complexes formation has been confirmed using an electron spin resonance (ESR) spectroscopy and the semi-empirical PM3 calculation. (c) 2007 Elsevier B.V. All rights reserved.