Degradation of bisphenol A by Fe-doped BiOBr enhanced UV/persulfate system: Significant role of superoxide radicals

Abstract

Widely diffused pollution of endocrine disrupting chemicals (EDCs) has indeed threatened the safety of ecological environment and human health. A hydrangea-like Fe doped BiOBr (Fe-BiOBr) microsphere was synthesized and used to enhance the performance of UV/persulfate (PS) system using bisphenol A (BPA) as the targeted contaminant. The photochemical characterization of Fe-BiOBr showed that Fe doping markedly improved the separation efficiency of photoelectron and hole, and enhanced the utility rate of luminous energy of BiOBr. Degradation test demonstrated that with the assistance of Fe-BiOBr, the efficiency of UV/PS system was increased by 1.8 times, while 85.7% of BPA can be degraded within 10 min. Through scavenging experiments, sulfate radical (SO4•−), superoxide radical (O2•−), and hole were demonstrated as the dominate reactive species (RSs) in UV/Fe-BiOBr/PS system. Then, the role and mutual transformation of RSs was further clarified by radicals steady-state concentrations estimation and X-ray photoelectron spectroscopy (XPS) analysis. Based on the results, the produced O2•− can be subdivided into confined O2•− and free O2•− from the UV induced oxygen vacancy and photoelectron, respectively. Of which, SO4•− and confined O2•− were symbiotic via the redox cycle of Fe species. Significantly, only 2.6% of TOC can be simultaneously removed within 10 min treatment time, suggesting the incomplete degradation of BPA. For this, 16 organics was detected using LC-MS and the degradation route of BPA was also determined based on the intermediates analysis. Finally, the application possibility of the system was evaluated from the perspective of ecotoxicity by ECOSAR and T.E.S.T. softwares. This study investigates the dual effect of transition metal doped semiconductor on coupling system, and provides new insights into the role of O2•−.