Cooperative Spin Alignment Enhances Selective Singlet Oxygen Generation in Wastewater Pre‐Oxidation System

Abstract

ABSTRACT Selective nonradical oxidation to enhance biodegradability is an attractive route for wastewater pretreatment, but molecular control of peroxymonosulfate (PMS) activation remains elusive. Here we report a Fe‐N 4 catalyst with second‐shell boron coordination (FeN 4 /B) synthesized by supramolecular self‐assembly. The second‐shell B imposes long‐range electronic regulation and cooperative spin alignment, shifting the Fe‐PMS * adduct to a high‐spin configuration and promoting spin‐allowed interfacial charge transfer. Concomitantly, covalent B─H bonding with PMS generates the key SO 5 * intermediate that channels PMS activation toward singlet oxygen. This structural control delivers ≥96% 1 O 2 selectivity with an observed rate constant k obs = 1.64 min −1 , a 1 O 2 production rate of 227 µmol L −1 min −1 , and 98% PMS‐to‐ 1 O 2 conversion. FeN 4 /B rapidly degrades 15 highly biotoxic pollutants within 10 min and retains activity under pH fluctuations, common ion/DOM interference, and across diverse natural waters. Implemented as a hydrogel‐immobilized ALICR‐FeN 4 /B module, the catalyst operated continuously for 168 h, increased effluent biodegradability (BOD/COD > 0.50), reduced acute toxicity, and lowered downstream biological treatment load at an estimated pretreatment cost of ∼$0.14 t −1 . These results establish cooperative spin alignment as a central lever of second‐shell engineering, bridging atomistic design and scalable water treatment to enable practical, economically favorable pretreatment based on selective PMS‐to‐ 1 O 2 conversion.