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In this study, we developed a Cu 0.5 Fe 2.5 S 4 nanocatalyst through facile sulfidation of the Cu-MIL-88B(Fe) precursor to expedite surface Fe(III) reduction and enhance H 2 O 2 activation in the heterogeneous electro-Fenton (HEF). The as-prepared catalyst possesses relatively large specific surface area and uniformly dispersed metal active sites. The Cu 0.5 Fe 2.5 S 4 -catalyzed HEF system allowed complete removal of naproxen with minimal metal leaching, surpassing that of Cu-MIL-88B(Fe) or Fe 3 S 4. Quantitative XPS analysis, electrochemical characterization and density functional theory calculations reveal an electron donor-shuttle regime in which S2- and Cu species serve as the electron donor and shuttle, respectively. The Cu species significantly accelerate the internal electron transfer between S and Fe and mitigate the dissolution of the adjacent iron sites, securing the sustainable reducing capacity. Moreover, Cu 0.5 Fe 2.5 S 4 -based HEF exhibits great practicability for treatment of various organics in urban wastewater. This study opens new avenue for addressing the challenge of sluggish Fe(III)/Fe(II) cycling in HEF. [Display omitted] • Cu 0.5 Fe 2.5 S 4 designed from MOF sulfidation serves as novel HEF catalyst. • S2- provides many electrons to boost the Fe(III)/Fe(II) cycling in HEF. • Cu species acts as the electron shuttle to accelerate the internal electron transfer. • The Cu-doping stabilizes the adjacent iron sites and enhances the •OH production. • The high porosity and dispersibility of Cu 0.5 Fe 2.5 S 4 promote the mass transport in HEF. [ABSTRACT FROM AUTHOR]