Application of iron-based materials in heterogeneous advanced oxidation processes for wastewater treatment: A review

Advanced oxidation processes (AOPs) can produce a large number of active and non-selective free inorganic radicals in the reaction, which makes them widely used in wastewater treatment, especially in the removal of refractory organic pollutants. In the presence of activator and depending on the type of oxidants (H2O2, persulfate, and percarbonate), AOPs often generate different radicals such as HO• and SO4•−, but the oxidation activity of inactivated oxidants is low. The applications of iron-based materials for activation of heterogeneous AOPs to effectively remove refractory organic pollutants have been extensively concerned due to their environmental friendliness and cost-effectiveness. In addition, the supplementary of light, electricity and reducing agents can greatly promote the redox cycle of iron in the reaction and generate in situ H2O2 (precursors for HO• radicals) to further improve the reactivity of iron-based materials in AOPs. In this review, the possible applications of different iron-based materials (e.g., zero-valent iron, iron (hydr)oxides, and iron composite materials) in AOPs and their activation and catalytic mechanisms are introduced. By providing an overview of the applications of iron-based materials in AOPs, this review helps researchers choose and develop more effective iron-based catalysts suitable for different AOP systems, and suggests that iron-based catalysts can play an excellent role in large-scale practical applications.