UV-C-Activated bromine oxidation: A promising strategy for efficient degradation of methyl paraben —parameter optimization, kinetic behavior, and Quantum-Chemical Mechanistic insights

Abstract

Methyl paraben (MeP), an endocrine-disrupting preservative widely present in pharmaceuticals and personal care products (PPCPs), is frequently detected in aquatic environments and thus necessitates efficient remediation strategies. In this study, a UV-C-activated bromine (UV-C/bromine) process was investigated for the abatement of MeP, and its performance benchmarked against the UV-C/chlorine (UV-C/Cl), UV-C/hydrogen peroxide (UV-C/H₂O₂), and UV-C/persulfate (UV-C/PMS) processes under equivalent UV-C exposure conditions. The UV-C/bromine process achieved 91.3% MeP removal within 60 min, outperforming UV-C/Cl, UV-C/H₂O₂, and UV-C/PMS by 23.5%, 62.3%, and 31.7%, respectively; response surface methodology (RSM) optimization further elevated the removal efficiency to 92.7%. A steady-state kinetic model established in MATLAB was employed to quantify radical contribution ratios, which identified HO· and Br· as the dominant oxidants and revealed a bromine dosage-dependent kinetic shift toward ·Br-dominated degradation. Liquid chromatography-tandem mass spectrometry (LC-MS/MS) analysis identified hydroxylation, decarboxylation and ring-opening as the primary degradation pathways. Brominated byproducts were transient intermediates, with Br-MeP and Br₂-MeP reaching peak concentrations of 0.039 and 0.034 mmol·L⁻¹, respectively, whereas chlorinated analogues remained at negligible levels. ECOSAR-based toxicity predictions highlighted a clear performance-toxicity trade-off: oxidative/ring-opening intermediates were generally less toxic than the parent MeP compound, whereas brominated intermediates—particularly dihalogenated species—exhibited enhanced toxicity. The steady-state kinetic model developed in MATLAB quantitatively resolves the contributions of dominant radicals and predicts their steady-state concentrations under diverse water conditions, which provides a robust theoretical tool for revealing the intrinsic degradation mechanism of MeP in the UV-C/bromine system and guiding the rational design and operational optimization of halogen-based advanced oxidation processes.

Keywords

UV-C irradiation / Bromine radicals / Methyl paraben / Response surface methodology / Steady-state kinetic modeling / Degradation mechanism / Toxicity assessment

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Funding

Shanxi Provincial Natural Science Foundation project(202403021211189)

Patent Conversion Plan Project of Shanxi Province(202406023)

National Natural Science Foundation of China(22206149)

The Central Government Guides the Special Fund Projects of Local Scientific and Technological Development(YDZJSX2025D022)

National Natural Sclence Foundation of China(52200048)

The Open Project of State Key Laboratory of Urban-rural Water Resources and Environment, Harbin Institute of Technology(MS202533)

RIGHTS & PERMISSIONS

The Author(s), under exclusive licence to the International Society of Energy and Environmental Science

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