Tertiary amine-mediated chlorination of dissolved organic matter: Unraveling molecular reorganization and enhanced photochemical reactivity.

The transformation behaviors of dissolved organic matter (DOM) were investigated during chlorination accelerated by trimethylamine (TMA, a representative tertiary amine). This study explored the transformation patterns of DOM during TMA-accelerated chlorination using Suwannee River fulvic acid (SRFA) and humic acid (SRHA) as model DOM. Spectroscopic techniques, FT-ICR MS, and machine learning were combined to reveal molecular property evolution. TMA enhanced the oxidative degradation of aromatic structures and quenched characteristic fluorophores, leading to reduced molecular weight and aromaticity. Notably, this molecular fragmentation generated photoactive moieties (e.g., aromatic ketones and quinones), resulting in elevated apparent quantum yields of triplet-state DOM and hydroxyl radicals. At the molecular level, FT-ICR MS revealed that chlorination fragmented high-molecular-weight compounds. This process was further intensified by TMA, increasing the diversity and abundance of CHO, CHON, and chlorinated species. The predominant transformation shifted from lignin/CRAM structures toward aromatic and tannin-like compounds. SHAP analysis identified molecular weight, nitrogen content, and chlorine content as key factors associated with product formation in TMA/chlorination systems. Reaction network analysis elucidated oxygenation and dealkylation as dominant pathways in TMA addition. These findings advance the mechanistic understanding of how tertiary amines mediate DOM transformation during chlorination, and provide a scientific basis for environmental risk assessment of their interactions.