Direct and indirect photodegradation of bisphenol-A in the presence of natural water components

Abstract

Abstract In this paper, the impact and mechanism of natural water constituents (humic acid, nitrate, iron and chloride ions) on the photodegradation of bisphenol A (BPA) was investigated in aqueous media under simulated UV light irradiation. Results suggested that the contributions of ·OH, 1O2, O2.− and BPA* to BPA photodegradation in pure water were 13.4%, 7.7%, 22.9% and 47.9%, respectively, indicating that direct photodegradation other than self-sensitized photodegradation was the main reaction pathway. Furthermore, the presence of humic acid (HA), nitrate, iron and chloride ions showed different impacts on BPA photodegradation. NO- 3 and NO- 2 both showed inhibitory effect but due to different ROS (reactive oxidization species). In the presence of HA, it was light-screening-induced direct photolysis not quenching effect dominated over the inhibited BPA photodegradation. The photodegradation of BPA was significantly enhanced by the addition of iron because iron-assisted indirect photolysis controlled the degradation process through promoting the production of ·OH and H2O2. Chloride had a dual effect on BPA photodegradation depending on the different concentration levels. Additionally, a simple linear model revealed that the interaction of these factors also significantly impacted BPA photodegradation. In natural water, the decreased photolytic rate of BPA was mainly attributed to triple-excited dissolved organic matter (3DOM*) and indirect photolysis was the primary transformation pathway of BPA. Finally, the detection of photolysis products including nitrate and chlorinated products suggested the possibility of increasing ecological risk of BPA photodegradation.