This work explores thoroughly the reaction network of the partial oxidation of phenylmethanol at the TiO(2)-solvent interface under photocatalytic conditions by using a first-principles continuum solvation method. We demonstrate that the photocatalytic oxidation of phenylmethanol has a complex reaction network with dual pathways. The dimer pathway dominates the mechanism under aerobic conditions and a [C(6)H(5)CH(OH)O](2) peroxo dimer is the key intermediate, the decomposition of which leads to an unusual O exchange phenomenon.