A MOF-derived Fe3O4/Fe0/Fe3C-2-600 dual-cathode electro-Fenton system construction: Revealing the mechanism for active centers linked by Fe0 as an electronic transfer station for enhancing Fenton reaction

• Fe 3 O 4 /Fe 0 /Fe 3 C-2-600 derived from MIL-88B(Fe) was prepared as the catalytic cathode. • The mechanism of electron transfer in the catalysis process was revealed. • The Fe 0 induced electron transfer to Fe(III), boosting the Fe(III)/Fe(II) cycle. • Fe 0 , as an electron transfer station, exported e - from the core to the surface. • Fe 3 O 4 /Fe 0 /Fe 3 C-2-600 cathode could efficiently remove TC at a wide pH range. Conventional heterogeneous iron-based catalysts face challenges such as insufficient catalytic activity, sluggish Fe(Ⅲ)/Fe(Ⅱ) cycle, and hindered electron transfer during Fenton catalytic reactions. Herein, Fe 3 O 4 /Fe 0 /Fe 3 C-2-600, obtained by calcining MIL-88B (Fe) in-situ growth on stainless-steel mesh at varying temperatures, was served as a catalytic electrode in a dual-cathode electro-Fenton system. The catalytic mechanism was elucidated by density functional theory (DFT) calculations. Based on the calculations, the presence of Fe 0 could induce electron transfer to Fe(Ⅲ), accelerating the Fe(Ⅲ)/Fe(Ⅱ) cycle. Simultaneously, Fe 0 was functioned as an electron transfer station, rapidly exporting electrons from the internal Fe 3 O 4 core to the surface graphite layer, further activating H 2 O 2 . Due to the rapid electron transfer, the Fe 3 O 4 /Fe 0 /Fe 3 C-2-600 cathodes demonstrated remarkable catalytic activity, achieving a 97.7 % degradation of tetracycline (TC) within 12 min. According to electron spin resonance tests and quenching experiments, hydroxyl radicals (·OH) was identified as the main active species. In addition, the possible degradation pathways of TC were proposed, according to the results of high-performance liquid chromatography-mass spectrometry (HPLC-MS). The Fe 3 O 4 /Fe 0 /Fe 3 C-2-600 cathode presented a promising strategy for developing an efficient and straightforward method to construct internal electric fields that could accelerate electron transfer in Fenton reactions. Moreover, the integration with the double-cathode electro-Fenton system, realizes the concept of reagent-free and sustainable catalysis, enhancing its practical application value.