Enhanced oxidative degradation of emerging pollutants sulisobenzone (BP-4) by sodium phosphate-assisted ozonation

Sulisobenzone (BP-4) is a widely used ultraviolet filter in sunscreens and has emerged as a contaminant of concern due to its persistence and potential ecological risks in aquatic environments. This study investigates the ozonation of sulisobenzone in the presence of sodium phosphate dibasic to enhance its degradation and mineralization. Ozonation was conducted for 60 min at an ozone flow rate of 0.48 L min^-1 using sodium phosphate concentrations ranging from 0.001 to 0.1 M. Increasing phosphate concentration significantly improved degradation efficiency, with 0.1 M sodium phosphate achieving 96% chemical oxygen demand (COD) and 93% total organic carbon (TOC) removal. The degradation followed pseudo-first-order kinetics, with the rate constant increasing from 1.43 ± 0.15 × 10^-2 min^-1 in the absence of phosphate to 2.97 ± 0.15 × 10^-2 min^-1 at 0.1 M sodium phosphate. Quenching experiments confirmed that hydroxyl radicals were the dominant reactive species, with additional contribution from phosphate-derived radicals. Complete removal of sulisobenzone was verified by high-performance liquid chromatography with photodiode array detection (HPLC-PDA). Liquid chromatography-mass spectrometry (LC-MS) identified multiple transformation products, indicating degradation pathways involving oxidative desulfonation and aromatic ring cleavage. This study demonstrates that phosphate-assisted ozonation significantly enhances radical generation and mineralization efficiency without the need for additional oxidants or catalysts, offering a simple and effective strategy for the removal of persistent pharmaceutical and personal care products (PPCPs) from aqueous systems.