Application of inorganic materials as heterogeneous cocatalyst in Fenton/Fenton-like processes for wastewater treatment

Traditional Fenton reaction refers to the activation of H2O2 by Fe2+ to generate hydroxyl radicals, but Fe2+ is easily oxidized to Fe3+ and the reduction of Fe2+ is a difficult challenge. Recently, more and more scientists have been trying to resolve this problem by adding inorganic heterogeneous cocatalyst into the reaction and establish heterogeneous co-catalytic system. We reviewed the latest evolution of inorganic heterogeneous co-catalytic Fenton methods in wastewater treatment. The two distinct kinds of heterogeneous cocatalyst, transition metals (Single-atom, zero-valent metal, metal sulphide, and metal phosphide) and non-metal (carbon, boron, and phosphorus materials) cocatalysts are summarized, and the reaction mechanisms of each type are discussed, then the advantages and disadvantages of practical applications are assessed. Four optimization methods for the co-catalytic system are proposed, including material optimization, operational optimization, synergy with other advanced oxidation processes, and novel Fenton-like process construction. Finally, future research needs for Fenton-like systems are presented.