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 Fe3O4 particles (Ce-MOFs/Fe3O4@C) was prepared for heterogeneous electro-Fenton (EF), which exhibited high H2O2 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 (OV), Ce3+ and Fe2+ was simultaneously exhibited when the Fe/Ce ratio in precursor was 2:1. Interface-confined between Ce-MOFs and Fe3O4@C and presence of OV promoted the O2 adsorption for oxygen reduction reaction and O2∙- generation, and electron transfer between Fe and Ce. Meanwhile, the presence of Fe2+/Fe3+ and Ce3+/Ce4+ simultaneously facilitated the sequential catalysis induced by H2O2 to generate ∙OH, and Ce4+ could promote O2∙- to generate 1O2. 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 H2O2 at the same time at a low cathode potential.