Peroxy-type disinfectants initiate chain reactions upon activation, but the underlying mechanisms of organic radical formation remain difficult to fully elucidate. In this study, we combine Density Functional Theory (DFT) with machine learning-based interatomic potentials to automate the construction of the reaction network for peroxyacetic acid (PAA). Using double-hybrid functionals, wavefunction analysis, we reveal that peroxide bond cleavage is primarily driven by an electronic excitation from the HOMO to the LUMO+1 orbital, resulting in bond dissociation. A pretrained machine learning model, refined through active learning, efficiently captures reaction pathways in molecular dynamics simulations. Conventional gas-phase calculations often neglect solvent effects and environmental factors, such as explicit solvation and dissolved oxygen, both of which are essential for accurately predicting chemical reactivity. Notably, O₂ facilitates the formation of CH₃OO·, which in turn produces CH₂O and ·OH radicals, further propagating the radical network. N₂/O₂ aeration experiments further highlight the crucial role of oxygen in driving reactivity, consistent with our computational predictions. The integrated approach of this study can readily be extended to issues of reaction mechanisms under microscopic media in environmental systems. Accordingly, we provide a research framework and have developed accompanying software for use.
Natural pectin, derived from fruit residue, presented a certain flocculation performance in previous studies. However, the process of extraction and treatment affected the flocculation performance considering the uncontrollable chemical composition and the molecule structure. In this study, degree of esterification (DE), degree of amidation (DA) were used as the internal factors affecting flocculation performance. The DE/DA values of pectin were obtained through FTIR, elemental analyses, H-NMR, and titration measurements. The kaolin suspension was employed for the coagulation jar tests, and the removal of NTU (Nephelometric Turbidity Unit) was used as the index of the flocculation performance. Results showed that the flocculation performance of pectin arising from different fruits was different, which was associated with the various preparation processes. By introducing polar groups into pectin, the flocculation was found to be related to bridging, adsorption, and charge neutralization. Based on the trends of three-dimensional response surfaces, the flocculation effect was improved with the decreased DE and the increased DA. The optimized amidated pectin was obtained by the amidation experiment, the turbidity reduction in wastewater was 99.63%. PRACTITIONER POINTS: The internal influencing factors of pectin as a flocculant were investigated. Different sources of pectin show different flocculation ability. Amidation modification can improve the flocculation performance of pectin. Response surface method to study the interaction of different influencing factors. Pectin may replace synthetic flocculants in water treatment.
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