Orbital modulation and coupled redox cycling in Fe–Mn dual-atom catalysts for efficient Fenton-like water purification

Abstract

Single-atom catalysts (SACs) offer ideal active sites for advanced oxidation processes, yet their practical applications are hindered by synthetic complexity, isolated centers, and limited redox and charge-transfer dynamics. Here, we report a scalable synthesis of a Fe–Mn dual-atom catalyst (Fe–Mn/N-C) featuring a symmetric Fe–Mn–N₆ coordination structure. This unique configuration establishes a sustainable bimetallic redox cycle that enables efficient activation of peracetic acid (PAA) for pollutant degradation. The catalyst achieves nearly complete removal of sulfamethoxazole (99.9%) with an apparent rate constant of 0.3226 min⁻¹—7.7 and 8.5 times higher than those of Fe/N-C and Mn/N-C counterparts, respectively. Density functional theory calculations reveal that Mn–N coordination promotes electronic delocalization and fine-tunes the electronic structure of adjacent Fe centers, leading to distinct PAA adsorption geometries on Mn and Fe sites that favor the selective formation of hydroxyl radicals (˙OH) and singlet oxygen (¹O₂) species. The optimized Mn d-band center further lowers the energy barrier for ¹O₂ generation. Moreover, the Fe³⁺/Fe²⁺ and Mn⁴⁺/Mn³⁺ redox cycles are coupled through electron transfer between Fe and Mn centers, ensuring self-regeneration of active sites and sustained catalytic stability. The Fe–Mn/N-C catalyst exhibits outstanding activity across a wide pH range, strong tolerance to competing inorganic ions, excellent recyclability, and broad substrate applicability. Collectively, this work establishes a durable bimetallic redox-coupling strategy that leverages electronic structure modulation to realize synergistic oxidation and provides insights for the rational design of robust Fenton-like catalysts for complex environments.