Nanoconfinement-driven enrichment of surface-bound radicals for efficient natural organic matter exclusion and selective pollutant degradation.

Developing effective strategies to enhance the interference resistance and selective degradation performance of advanced oxidation processes (AOPs) in complex water matrices remains a critical challenge for practical water treatment. Herein, we design a confinement-effect-based catalyst by encapsulating MoS2/Fe3O4 heterostructures with a polydopamine (PDA) coating, aiming to address the issue of natural organic matter (NOM)-induced radical quenching and improve pollutant degradation selectivity. The polymer PDA coating not only endows a porous architecture composite but also induces a strong confinement effect, which significantly elevates the concentration of surface-bound hydroxyl radicals (OH) by 7.2-fold compared to the uncoated MoS2/Fe3O4 heterostructures. In complex water matrices containing 5 mg L-1 NOM, the apparent rate constant (kₐₚₚ) of the uncoated material decreases sharply by 80%, whereas that of the PDA-coated composite only declines by 14.3%, demonstrating superior anti-interference capability. Except for HCO3-, the effects of Cl-, NO3-, and SO42- on the reaction were negligible. Systematic characterizations combined with density functional theory calculations reveal that the PDA coating creates a confined reaction microenvironment, which effectively modulates the adsorption affinity of peroxymonosulfate (PMS) and facilitates interfacial electron transfer. Moreover, OH generated by PMS activation preferentially binds to Fe sites within the PDA layer, where they are converted into surface-bound OH and enriched in the confined space. Meanwhile, the size-exclusion effect of the PDA porous network effectively blocks NOM from accessing the internal reaction region, thereby suppressing the competition quenching of surface-bound OH by NOM. This study provides novel insights into the improving the rational design of confinement-effect-based catalysts to enhance the selectivity and robustness of radical-driven AOPs for practical application in the treatment of complex real water matrices.