Photodegradation of 2,4,4′-tribrominated diphenyl ether in various surfactant solutions: kinetics, mechanisms and intermediates

Abstract

Currently, photodegradation has been proven to be an important way of eliminating polybrominated diphenyl ethers (PBDEs) from the environment. However, the mechanism of PBDE photodegradation in surfactants by UV light is still unclear. In this study, 2,4,4′-tribrominated diphenyl ether (BDE-28) was selected as the target pollutant to investigate the photodegradation of PBDEs in Triton X-100 (TX-100), sodium dodecylbenzenesulfonate (SDBS) and cetyltrimethylammonium bromide (CTAB) solutions. All photolysis experiments were performed above the critical micelle concentration (CMC). The results showed that photodebromination was the major pathway of BDE-28 photodestruction in different surfactants. From 1.5 CMC to 4 CMC, the photodegradation rates of BDE-28 increased as the concentration of TX-100 increased, and the increased concentration of SDBS has a negative effect on the photodegradation rate of BDE-28 due to the light barrier of SDBS. There was no obvious change in the case of CTAB. BDE-28 was debrominated to 4,4′-dibrominated diphenyl ether (BDE-15), 4-dibrominated diphenyl ether (BDE-3) and diphenyl ether (DE), subsequently. In addition, 2,8-dibrominated dibenzofuran (2,8-BDF), 2-monobrominated dibenzofuran (2-monoBDF), and dibenzofuran (DF) were produced via an intramolecular elimination of HBr from the PBDEs that had an ortho-bromine substituent. Moreover, DF can also be formed from DE and the generated amount of DF in CTAB was higher than that generated in SDBS and TX-100. We have also detected ortho-hydroxydiphenyl and para-hydroxydiphenyl during the photodegradation process.