Transition metal catalysts in the heterogeneous electro-Fenton process for organic wastewater treatment: a review

As a green and efficient advanced oxidation process, electro-Fenton (EF) has attracted extensive attention in the degradation and mineralization of organic pollutants. The design and application of heterogeneous catalysts allow EF to perform efficiently over a wide pH range and recycle in multiple reaction runs. This work reviews the reported transition metal catalysts such as natural minerals, synthetic monometallic or polymetallic composite particles and single-atom catalysts for the heterogeneous EF (Hetero-EF) process. Applied as suspended catalysts or modified cathodes for the 2e(-) ORR and formation of active species, the transition metal material performance and mechanism for H2O2 generation and activation are discussed exhaustively. The structure and composition, catalytic performance and degradation mechanism of these catalysts are summarized. Finally, we overview the design and action strategies of transition metal catalysts, and propose the present challenges and future prospects of the Hetero-EF to improve the wide applicability and practical implication for advanced wastewater treatment.