Steering radical pathways and molecular pre-organization enables efficient polymerization of polyvinyl alcohol in the ferric chloride-assisted heat/peroxydisulfate system

The heat-activated peroxydisulfate (PDS) system exhibits significant potential for removing polyvinyl alcohol (PVA) through polymerization in water treatment. However, excessive chain scission severely limits intermolecular crosslinking and oxidant utilization efficiency during the polymerization process. Herein, we demonstrated that introducing ferric chloride (FeCl₃) into the heat/PDS system dramatically enhanced PVA polymerization, achieving 22.2- and 11.5-fold improvements in TOC removal and PDS utilization efficiency, respectively. Mechanistic investigations revealed a dual-regulation mechanism involving Fe(III)-induced intermolecular pre-organization of PVA chains and a shift in the dominant radicals from sulfate radicals (SO₄^•⁻) to chlorine radicals (Cl^•). Fe(III)-mediated pre-organization shortened intermolecular distances, creating a favorable conformation for subsequent crosslinking, while Cl^• preferentially abstracted hydrogen atoms from PVA rather than cleaving the carbon backbone, thereby suppressing chain scission and promoting polymer growth. As a result, insoluble Fe-coordinated polymeric aggregates with porous, amorphous, and thermally stable characteristics were formed. Furthermore, the system was effective for treating real desizing wastewater containing PVA and exhibited broad applicability to hydroxylated aromatic compounds. Overall, this study provides a feasible strategy for enhancing PVA polymerization in the heat/PDS system by suppressing chain scission and promoting intermolecular crosslinking, offering new insights into improving oxidant utilization and selective polymerization in advanced oxidation processes.