Sulfur-doped FeP enables a pH-induced switch from ·OH to Fe(IV)=O for efficient sulfamethoxazole degradation via Fenton-like catalysis

This study presents a pH-switchable Fenton-like system based on sulfur-doped FeP synthesized via a confined gas–solid strategy, where ·OH dominates at pH 3.0 and Fe(IV)=O prevails at pH 6.0. Sulfur incorporation modulates the FeP electronic structure by expanding the lattice, enhancing Fe–P covalency, and increasing electron density, thereby promoting charge transfer and reducing the activation barrier for H 2 O 2 activation. The optimized FePS 15 catalyst achieved ~99% sulfamethoxazole degradation (150   mg/L) within 15   minutes, exhibiting a reaction rate 2.54 times higher than that of undoped FeP. When further supported on lignin-derived carbon spheres (FePS 15 @LC), it exhibited enhanced structural integrity, suppressed iron leaching, and improved reusability. These findings demonstrate that sulfur doping drives pH-dependent ROS switching from ·OH to Fe(IV)=O, supporting adaptable Fenton-like catalysis. This work improves mechanistic insight into ROS modulation and enables pH-adaptable advanced oxidation processes for pollutant removal.