Repurposing Waste Chemicals to Engineer Redox Mediators for Selective Active Species Modulation in Photo‐Fenton‐Like Systems

Abstract Resource recovery from chemical wastes offers significant economic and environmental opportunities. In particular, repurposing recycled materials to construct light‐driven oxidant activation systems presents a promising strategy for organic wastewater remediation. However, in such a photo‐Fenton‐like system, precise regulation of active species remains a major challenge, limiting performance optimization. Here, we propose a sustainable approach using catalysts derived from deteriorated potassium iodide (KI) reagents. Theoretical analyses reveal that I − and I 3 − species from degraded KI function as effective redox mediators, generating internal electric fields that substantially lower energy barriers for carrier separation. The resulting catalytic system exhibits outstanding decontamination performance, achieving complete removal of the antibiotic sulfamethoxazole with a pseudo‐first‐order rate constant of 0.79 min −1 , representing 3.76‐ and 79.00‐fold enhancements over systems using standard KI and single‐based catalysts, respectively. Mechanistic studies confirm the efficient utilization of photogenerated carriers and the selective generation of singlet oxygen through non‐radical pathways. Notably, this novel mechanism shows broad applicability across various oxidant activation systems, with the I − /I 3 − redox mediator effectively modifying substrate electronic structures to enhance reactive oxidant interactions. This work introduces an innovative strategy for converting chemical wastes into high‐value materials, advancing sustainable wastewater treatment, and opening new avenues for resource‐efficient chemical applications.