Decay of an Ir(II) complex and methylviologen radicals catalyzed by colloidal platinum. A pulse radiolytic investigation

Various platinum colloid preparations, stabilized by PVA or PSS, were tested with respect to their reactivity toward MV⁺ and Ir(II)²⁺. The latter were produced in aqueous solutions by pulse radiolysis, and the decay of their optical absorptions was followed. The results show large differences between various preparation methods, beyond the expected effects of the colloid particles sizes. The order of the reaction with respect to [Pt] changes from one, at low [MV²⁺] and [Ir(III)²⁺], to nearly two, upon increasing the concentrations of these ions. The results support the recent suggestion that adsorption of solutes to the colloid particles may affect the reaction order. Our results indicate, however, that additional factors may be involved.