Clays and oxide minerals as catalysts and nanocatalysts in Fenton-like reactions — A review

Advanced oxidation processes (AOP), involving the generation of highly oxidizing radical species, have attracted much attention because of their potential in eliminating recalcitrant organic pollutants from different environmental matrices. Among the most investigated AOP is the Fenton reaction in which hydroxyl radicals (HO) are generated through the catalytic reaction of Fe(II)/Fe(III) in the presence of hydrogen peroxide. The use of clays and iron-oxide minerals as catalysts of Fenton-like reactions is a promising alternative for the decontamination of soils, groundwaters, sediments, and industrial effluents. The low cost, abundance, and environmentally friendly nature of clay minerals and iron oxides are an added advantage. Additionally, the introduction of nanoparticles in heterogeneous catalytic processes has led to appreciable improvements in catalytic efficiency. Here we review the application of clays and iron-oxide minerals as supports or active catalysts in Fenton-like reactions, and summarize the latest advances in nanocatalyst development. We also evaluate the potential use of allophane nanoparticles, coated with iron oxides, as catalysts of Fenton-like reactions.