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

- The photolysis behavior of TBBPA in surface water is investigated.
- Photolysis of TBBPA follows pseudo-first-order kinetics.
- The influencing factors including pH and HA are investigated.
- Reactive oxygen species (ROS) generated in the photolysis process are examined.
- Decomposition of TBBPA is accompanied by debromination and breakage of C-C bond.

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 × 10−2 to 0.70 × 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 × 10−2 to 0.39 × 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, 1O2 and O2−), and the process was mainly controlled by O2−. 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.