Degradation mechanism, reaction pathways and kinetics for the mineralization of Bisphenol A using hybrid ZnO/graphene oxide nano-catalysts

Abstract

Removal of Bisphenol A (BPA) from surface waters is necessary before consumption. A study, therefore, was conducted to degrade BPA using graphene oxide, ZnO and ZnO decorated on graphene oxide. Hydrothermal method was used to synthesize the hybrid nano-catalysts. 99.5% photocatalytic degradation of BPA was achieved by using ZG0.6 nano-catalyst in comparison to bare ZnO and GO nano-catalysts at natural pH of 7.5 in 60 min of UV irradiation. The higher photocatalytic activity of ZG0.6 nano-catalyst could be ascribed to an improved surface area, efficient charge separation as well as the decreased recombination rate of electron-hole charge carriers, leading to the generation of highly reactive hydroxyl radicals for the degradation of BPA. Photocatalytic degradation followed Langmuir-Hinshelwood model with pseudo-first-order kinetics. The degradation mechanism is also detailed with identification of reaction intermediates. Degradation pathways, based on LCMS analysis, have been proposed. The pathways revealed the formation of smaller by-products such as phenol, hydroquinol and (Z)-3-hydroxyacrylaldehyde. The developed ZG0.6 nano-catalyst were found to be reusable for consecutive five runs without much loss in the activity and have the advantage of effective charge separation.