Influence of Aqueous Chloride and Bromide Anions on the Reactivity of ZnO on Bisphenol a Degradation

Zinc oxide (ZnO) nanoparticles have been widely investigated for applications in photocatalytic degradation of organic pollutants in wastewater. Despite the advantages of robust ZnO material, its photocatalytic activity is greatly affected by environmental factors. Halogen ions are commonly found in wastewater, which directly influence the pollutant aggregation and sedimentation, therefore it is necessary to discuss their effect on the photodegradation. The current study assesses the halogen ions effect on the photocatalytic degradation of BPA using different dosage of sodium chloride (NaCl) and sodium bromide (NaBr). The microstructural characterization of ZnO was conducted by transmission electron microscopy and hydrodynamic size was analyzed through dynamic light scattering. Degradation reactions of BPA with ZnO nanoparticles followed pseudo-first-order kinetics. The increase of ZnO dosage from 0.01 g/L to 0.1 g/L enhanced the degradation rate constant of BPA up to 0.089 min-1 (14.8 folds). In order to evaluate the the role halogen ions to degrade BPA, NaBr and NaCl were used. The degradation rate was reduced up to 26 folds (0.0034 min-1) after the addition of NaBr, which was attributed to the increase in hydrodynamic particle size leading, thereby restricting the light adsorption capacity. Noteworthy, upon addition of NaCl from 10 mM to 500 mM concentration, there was only a slight decrease (2.4 folds, 0.037 min-1) on the degradation rate of BPA. Therefore, this study unveils the role of chloride ions as an effective medium for BPA degradation by ZnO nanoparticles, without aggregation, and provides a novel platform for the treatment of organic pollutants in saline water.