Photochemical formation of hydroxyl radicals catalyzed by montmorillonite.

In this work, the photooxidation of benzene and the formation of phenol in aqueous suspensions of the iron-rich montmorillonite under irradiation of a 250W metal halide lamp (lambda> or = 365nm) were investigated. We confirmed that hydroxyl radicals (()OH) were produced by illuminating montmorillonite and was responsible for the photooxidation of benzene in aqueous suspensions of montmorillonite. Low pH value facilitated the formation of hydroxyl radicals in the pH range of 2.0-10.0. The ()OH concentration increased with increasing the concentration of montmorillonite in aqueous solutions in the range of 0-20.0gl(-1). Higher concentration like 25.0gl(-1) montmorillonite inhibited the ()OH production. Iron, predominantly free iron in the clays, is believed to be one of the most important factors determining ()OH formation. Structural irons in montmorillonite have contributions to ()OH formation, especially in the presence of carboxylate ions. The formation of ()OH from montmorillonite under irradiation of near UV and visible light indicates that clays might play important role not only in transfer through adsorption but also in transformation through oxidation of organic compounds on the surface of clay particles in air, water, soil or even top sediments.