Photochemical redox reactions at the zinc oxide-water interface in additive-free systems

Abstract

When aqueous ZnO suspensions, saturated with oxygen, are irradiated with u.v. light, hydrogen peroxide is formed and a decrease in pH is observed. The effects of different gases (O₂, N₂, and N₂O) on the course of this heterogeneous reaction and also the pH dependence of the reaction have been examined. On the basis of the results obtained, the mechanism which had been previously suggested was modified to allow for the hydrolysis of the zinc(II) ions removed from the crystal lattice during irradiation. A general reaction mechanism proposed to account for H₂O₂ production in systems with various additives present is extended to additive-free systems where interstitial zinc (Zn₁⁺) is the effective reductant.