Formation of hydroxyl radicals catalyzed by clay surfaces

The formation of superoxide and hydroxyl radicals at the surface of smectite clays due to oxygen reduction is demonstrated by electron paramagnetic resonance spectroscopy. The yield of hydroxyl radicals is mainly a function of particle size of the clays and depends, to a lesser extent, on the clay lattice iron. Synthetic laponite clay with small platelet size (similar to20 nm) and without lattice iron is leading in the formation of hydroxyl radicals followed by montmorillonite (similar to200 nm). Fluorohectorite (similar to2000 nm) was inactive to hydroxyl radical formation by oxygen reduction.