Interface-confined multi-layered reaction centers between Ce-MOFs and Fe3O4@C for heterogeneous electro-Fenton at wide pH 3–9: Mediation of Ce3+/Ce4+ and oxygen vacancy

A bifunctional catalyst with Ce-based metal–organic frameworks deposited on carbon encapsulated Fe 3 O 4 particles (Ce-MOFs/Fe 3 O 4 @C) was prepared for heterogeneous electro-Fenton (EF), which exhibited high H 2 O 2 generation efficiency (over 90% selectivity and 80.7% current efficiency), high sulfamethazine (SMT) removal with very low electric energy consumption (7.65 kWh kg −1 SMT), and wider pH suitability to alkaline environment (pH 9). The highest content of oxygen vacancies (O V ), Ce 3+ and Fe 2+ was simultaneously exhibited when the Fe/Ce ratio in precursor was 2:1. Interface-confined between Ce-MOFs and Fe 3 O 4 @C and presence of O V promoted the O 2 adsorption for oxygen reduction reaction and O 2 ∙- generation, and electron transfer between Fe and Ce. Meanwhile, the presence of Fe 2+ /Fe 3+ and Ce 3+ /Ce 4+ simultaneously facilitated the sequential catalysis induced by H 2 O 2 to generate ∙ OH, and Ce 4+ could promote O 2 ∙- to generate 1 O 2 . This work provides new insight into the design and synthesis of Fe-based catalysts in EF with interface confinement and multi-layered reaction centers to improve the generation and the decomposition of H 2 O 2 at the same time at a low cathode potential.