The influence of dissolved transition metals on the photocatalytic degradation of phenol with TiO2

The influence of dissolved cupric and ferric ions on the photocatalytic degradation of phenol in aqueous dispersions of titanium dioxide was investigated. At pH 3.5 both ion species enhanced the TiO₂ photocatalytic activity until an optimum metal concentration was reached (1×10^?3 M for Cu²⁺ and 7×10^?6 M for Fe³⁺). Beyond these values the activity was observed to decrease, what was mainly attributed to precipitation of metal derivatives. A mechanism based in the formation of a complex between the metal and the organic compound adsorbed onto the titania surface is proposed to explain the observed positive effect of copper and iron ions addition.