Formation Of Brominated Phenolic Compounds Via Manganese Oxides Sand-catalyzed Oxidation Of Phenol In The Presence Of Bromide

The origins of bromophenol(BPs) and hydroxylated polybrominated diphenyl ethers(OH-PBDEs) had sparked increasing attention because of their wide distribution in the environment. To date, most of the studies suggested these compounds are the result of biological process. However, it is still unclear whether they can be formed from aboitic environmental processes, especially in soil and sediment. In this study, we explored the formation of brominated phenolic compounds via manganese oxides sand-catalyzed oxidation of phenol in the presence of bromide. Overall, this study includes:(1) The BET surface of the natural manganese oxides sand was characterized by the specific surface area measurement, scanning electron microscope(SEM) and an energy-dispersive X-ray spectroscopy(EDS) system. Results showed that the surface area of manganese oxides sand was 28.2 m2/g, the iron and manganese oxides were the main composition, and the appearance was nodositas or platy.(2) The products produced were identificated and quantified by gas chromatography coupled with a mass spectrometer(GC-MS). Results showed that BPs(such as 4-BP, 2,4-DBP, 2,4,6-TBP) were readily produced via manganese oxide sand-catalyzed oxidation of bromide and phenol. In addition, 11 different OH-PBDE/PBBs, such as 2′-OH-BDE-68, 6-OH-BDE-25 and 2,2′-OH-BB-80, were also detected as main products.(3) The possible formation pathways were proposed on the basis of the identified products. BPs were formed from electrophilic addition reaction between phenol and HOBr/Br2, which were generated via manganese oxides sand-catalyzed oxidation of bromide. OH-PBDE/PBBs were likely generated from the oxidative coupling of bromophenoxy radicals, which were formed from the oxidation of the BPs by manganese oxide sand. For example, 2′-OH-BDE-68 and 2,2′-OH-BB-80 can be produced from C-O and C-C coupling reaction between bromophenoxy radicals. All of the identified brominated organic compounds and Mn2+ increased with the increasing initial concentration of bromide and phenol. Although the influence of initial pH value varied with each compound, the total concentration of formation products increased as the pH increased.In view of the ubiquity of bromide, phenol and natural manganese oxide mineral in soil and sendiment, catalytic oxidation of phenol in the presence of bromide by natural manganese oxide mineral is likely an important abiotic route for the natural formation of BPs and OH-PBDE/PBBs in the environment.