Treatment of Aqueous Bromate by Superparamagnetic BiOCl-Mediated Advanced Reduction Process

Bromate (BrO3−) contamination in drinking water is a growing concern. Advanced reduction processes (ARPs) are reportedly promising in relieving this concern. In this work, UV/superparamagnetic BiOCl (BiOCl loaded onto superparamagnetic hydroxyapatite) assisted with small molecule carboxylic acid (formate, citrate, and acetate), a carboxyl anion radical (CO2•−)-based ARP, was proposed to eliminate aqueousBrO3−. Formate and citrate were found to be idealCO2•−precursor, and the latter was found to be safe for practical use.BrO3−(10 μg·L−1, WHO guideline for drinking water) can be completely degraded within 3 min under oxygen-free conditions. In this process,BrO3−degradation was realized by the reduction ofCO2•−(major role) and formyloxyl radical (minor role) in bulk solution. The formation mechanism of radicals and the transformation pathway ofBrO3−were proposed based on data on electron paramagnetic resonance monitoring, competitive kinetics, and degradation product analysis. The process provided a sustainable decontamination performance (<5% deterioration for 10 cycles) and appeared to be more resistant to common electron acceptors (O2,NO3−, and Fe3+) than hydrated electron based-ARPs. Phosphate based-superparamagnetic hydroxyapatite, used to support BiOCl in this work, was believed to be applicable for resolving the recycling problem of other metal-containing catalyst.Keywords:bromate;carboxyl anion radical;reduction;magnetic recovering