Synergizing Surface-Bound Radicals with Singlet Oxygen to Expedite Emerging Organic Contaminant Degradation in Soil-Based Heterogeneous Surface Oxidation

The inefficient degradation of emerging organic contaminants (EOCs) in complex soil environments is mainly due to the improper consumption of reactive oxidative species (ROS) by non-target background substances and limited mass transfer. Herein, we developed iron sulfide (FeS) as a structurally stable heterogeneous catalyst to selectively and continuously generate ROS via peroxydisulfate (PDS) activation. Synthesized FeS demonstrated exceptional PDS activation, achieving 95.44% carbamazepine (CBZ) removal, with high resistance to coexisting soil substances and strong pH tolerance. Mechanistic studies confirmed that CBZ degradation was driven by surface-bound SO₄^•- radicals and singlet oxygen (¹O₂). The presence of sulfide species in Fe_xS_y significantly enhanced the electrochemical performance of the catalyst, accelerating the Fe(III)/Fe(II) cycle. The results suggested that oxidation of target pollutants occurs near the soil surface rather than in bulk solution, reducing the mass transfer distance and improving ROS utilization. Two degradation pathways for CBZ were proposed, resulting in a considerable reduction in CBZ toxicity, and the oxidation system has little effect on the soil matrix. Heterogeneous surface oxidation demonstrates stronger oxidative capacity, electron transfer, and mass-transfer efficiency in comparison to homogeneous systems, suggesting its significant potential for remediating EOCs in soil throughout a broad pH range.