Accelerating Fe(III)/Fe(II) redox cycling in heterogeneous electro-Fenton process via S/Cu-mediated electron donor-shuttle regime

Abstract

In this study, we developed a Cu0.5Fe2.5S4 nanocatalyst through facile sulfidation of the Cu-MIL-88B(Fe) precursorto expedite surface Fe(III) reduction and enhance H2O2 activation in the heterogeneous electro-Fenton(HEF). The as-prepared catalyst possesses relatively large specific surface area and uniformly dispersed metalactive sites. The Cu0.5Fe2.5S4-catalyzed HEF system allowed complete removal of naproxen with minimal metalleaching, surpassing that of Cu-MIL-88B(Fe) or Fe3S4. Quantitative XPS analysis, electrochemical characterizationand density functional theory calculations reveal an electron donor-shuttle regime in which S2- and Cuspecies serve as the electron donor and shuttle, respectively. The Cu species significantly accelerate the internalelectron transfer between S and Fe and mitigate the dissolution of the adjacent iron sites, securing the sustainablereducing capacity. Moreover, Cu0.5Fe2.5S4-based HEF exhibits great practicability for treatment of various organicsin urban wastewater. This study opens new avenue for addressing the challenge of sluggish Fe(III)/Fe(II)cycling in HEF.