Oxygen Doping Enables Tailored Built‐In Electric Fields in FeOCl/g‐C 3 N 4 Heterojunctions for Enhanced Peroxymonosulfate Activation

Abstract Regulating metal‐support interactions enables rational design of catalysts with enhanced performance in Fenton‐like oxidation reactions. Here, a novel oxygen‐doped, stalactite‐like g‐C 3 N 4 supported FeOCl (FeOCl‐OCN) is successfully synthesized. Due to the modulation of O doping to the work function ( Φ ) of g‐C 3 N 4 support, a delicate built‐in electric field (BIEF) oriented from OCN to FeOCl is constructed. Driven by large work function difference (Δ Φ = 3.235 eV), the interfacial charge transfer manipulates electron redistribution to achieve a rearrangement of structural Fe(II)/Fe(III). Based on theoretical calculations and mechanism insight, the interaction between FeOCl and OCN exhibits a stronger binding ability to peroxymonosulfate (PMS) and reduces the energy barriers for *O formation, therefore favoring a higher yield of singlet oxygen ( 1 O 2 ) and high‐valent iron‐oxo (Fe(IV)═O)− species. As a result, the FeOCl‐OCN/PMS system demonstrates a nonradical‐dominated pathway, delivering high activity ( k obs = 0.250 min −1 ), robust tolerance to pH variation and resistance, and excellent stability.