Spatially decoupled MgFe2O4carbon interfaces promote interfacial electron transfer for concurrent BHA degradation and As(III) oxidation-immobilization.

Arsenic-organic co-contamination in mineral-processing wastewater remains difficult to remediate because organic collectors compete with As(III) for oxidants, reactive species, and surface sites. Here, MgFe2O4-modified biochar (MF-BC) was developed as a peroxydisulfate (PDS) activator for the concurrent degradation of benzohydroxamic acid (BHA) and oxidation-immobilization of As(III). MF-BC formed functionally differentiated but electronically coupled carbonaceous and MgFe2O4 domains. BHA showed a relative association preference for the carbonaceous domains and was degraded predominantly through a singlet oxygen-mediated nonradical pathway, whereas PDS activation and arsenic retention mainly occurred at the MgFe2O4-associated domains. Electrochemical measurements, X-ray photoelectron spectroscopy, and density functional theory calculations collectively indicated that electrons released during BHA oxidation were transferred through the carbonaceous framework to MgFe2O4, promoting Fe(III)/Fe(II) cycling and sustaining PDS activation. As(III) was oxidized to As(V) through combined radical and nonradical pathways, followed by immobilization primarily via inner-sphere As-O-Fe complexation. Multilevel ecotoxicological assays confirmed a substantial reduction in the biological toxicity of the treated water. This study demonstrates that spatially decoupling organic oxidation from arsenic transformation can alleviate competitive interactions in co-contaminated systems, while cross-domain electron transfer couples the two processes to enhance overall treatment performance.