Selective degradation mechanism induced by stacked structure of phenanthrene aggregates in thermally activated persulfate oxidation

Persulfate-based advanced oxidation processes (PS-AOPs) are extensively employed for the remediation of soils contaminated with polycyclic aromatic hydrocarbons (PAHs). However, PAHs could form stable aggregates via π-π interactions, and how these aggregated structures dictate degradation pathways remains unexplored. This study reveals that phenanthrene (PHE) aggregates exhibit accelerated degradation kinetics, with a 3.78 - 25.79 % higher degradation rate than molecules within 3 hours. Structural characterization confirmed the formation of stable submicron aggregates (180.09 nm ± 23.8 nm to 532.03 nm ± 20.5 nm) with ordered lamellar stacking. Density functional theory (DFT) calculations disclosed that the compact architecture of aggregates enhances electrophilic reactivity by facilitating electron delocalization, which reduces the orbital energy gap by 14.34 %. Mechanistic investigations via reactive oxygen species (ROS) probing and electrochemical assays demonstrated that thermal activation preferentially promotes 1 O 2 accumulation (by 54.19 %) and direct electron transfer (by 8.82 %) in aggregates. The non-radical pathways synergistically facilitate the transformation of PHE into characteristic oxygenated products with potential ecotoxicity concerns. The findings elucidate a mechanistic nexus between aggregation-induced electronic effects and preferential non-radical oxidation, providing a fundamental basis for designing targeted remediation strategies for PAH pollutants.