Photochemical transformation of tetrabromobisphenol A under simulated sunlight irradiation: Kinetics, mechanism and influencing factors

A systematic study on photolysis of tetrabromobisphenol A (2,2',6,6'-tetrabromo-4,4'-isopropylidendiphenol, TBBPA) in water was investigated under simulated sunlight irradiation. The results showed that the photolysis of TBBPA followed apparent pseudo-first-order kinetics. The photolysis rate constants (k) changed from 2.80 x 10(-2) to 0.70 x 10(-2) min(-1) with the concentrations of TBBPA varying from 0.1 to 10 mg L-1. Increasing humic acid (HA) concentration from 0-100 mg L-1 led to the decrease of k from 2.53 x 10(-2) to 0.39 x 10(-2) min(-1), which was due to the competitive adsorption for photons between HA and TBBPA molecules. The photolysis rate was faster at near-neutral conditions (pH = 6 and 7) than that in either acidic or basic conditions. Electron spin resonance (ESR) and reactive oxygen species (ROS) scavenging experiments indicated that TBBPA underwent self-sensitized photooxidation via ROS (i.e., (OH)-O-center dot, O-1(2) and O-2(center dot-)), and the process was mainly controlled by O-2(center dot-). After irradiation of 180 min, about 35.0% reduction of TOC occurred accompanied with approximate 99.1% of TBBPA removed. The detection of products (i.e., Br-, bisphenol A, 2,6-dibromophenol, 2-bromophenol and phenol) revealed that the main photolytic pathways of TBBPA were debromination and breakage of C-C bond. (C) 2014 Elsevier Ltd. All rights reserved.