The Use of Nanomaterials in Electro-Fenton and Photoelectro-Fenton Processes

Abstract

Nowadays, electro-Fenton and photoelectro-Fenton are considered two of the best electrochemical advanced oxidation processes to ensure fast degradation of organic pollutants and inactivation of toxic pathogens. Despite their apparent simplicity, two critical factors must be carefully controlled in order to enhance the production of •OH from homogeneous Fenton’s reaction: the H2O2 electrogeneration from cathodic O2 reduction, and the characteristics of metal species employed to catalyze the quick decomposition of H2O2. In conventional electrochemical Fenton-based systems, the cathodes are made of either raw carbon powder or massive carbon pieces since these materials are known to promote the two-electron reduction of O2 to yield H2O2, whereas Fe(II) or Fe(III) salts are added to allow homogeneous catalysis at optimum pH ~3. On the basis of this concept, good progress has been made when working with nanomaterials because the increased specific surface area provides: (i) more active cathode surfaces to produce H2O2; (ii) better heterogeneous catalysts, which may react to a larger extent with H2O2, within a wider pH range; (iii) a larger absorption of photons, promoting photoreduction and photooxidation reactions; and (iv) a larger area to adsorb pollutants that can be further degraded. As will be discussed in this chapter, most of the work has addressed the use of pristine, functionalized, and decorated nanocarbons as cathodes; the synthesis of nanocatalysts containing iron since this is the best metal for Fenton’s reaction; and the preparation of nanostructured anodes.