Review on the application of modified iron oxides as heterogeneous catalysts in Fenton reactions

Heterogeneous Fenton reaction is an advanced oxidation process which has gained wide spread acceptance for higher removal efficiency of recalcitrant organic contaminants under wide range of pH compared to homogeneous reactions. Conventionally, iron oxides are used as heterogeneous catalysts for Fenton oxidation system because of their abundance, easy separation and lower cost. This paper reviews the substitution of iron in an iron oxide with other transition metals as a mean to improve the properties of the iron oxide towards higher performance for contaminant degradation. Several studies have reported enhanced performance resulted from this substitution based on two possible mechanisms. First is the conjugation of redox pairs of iron species and imported active ion in hydroxyl radical production cycle. Second: the generation of oxygen vacancies as active sites on the surface of catalyst via adjustments for unequal charge substitutions. This class of catalysts is anticipated to work effectively for treatment of various recalcitrant wastewaters using Fenton oxidation system. Subsequently, the stability of the produced catalyst needs to be examined under various experimental conditions to prevent the adverse effects of transition metals on the receiving environment.