Oxidative degradation of endocrine disruptor bisphenol-A on MnO2 nanosheets under ambient conditions

Abstract

Removal of bisphenol A (BPA) from water was studied using manganese dioxide nanoparticles prepared through co-precipitation using MnCl₂ and KMnO₄. The nanoparticles were observed to consist of nanosheets and are poorly crystalline as seen from the SEM and TEM images, XRD analysis, and SAED pattern. The pH_zpc of MnO₂ nanoparticles was observed to be 3.9. TGA studies of MnO₂ showed 13.5% weight loss. Specific capacitance was found to be 188 F g⁻¹ at a current of 1 A g⁻¹. The BPA–MnO₂ reaction was carried out under constant stirring under ambient conditions in an open-mouth glass tube. It was observed that about 80% of BPA was removed in 60 min for a MnO₂ dose of 1 g L⁻¹ and an initial BPA concentration of 50 mg L⁻¹. With an increase in the dosage of MnO₂, the removal efficiency increased, whereas it showed a decrease in the removal efficiency with an increase in the initial concentration of BPA. The rate of reaction was shown to be increasing with an increase in temperature and a decrease in pH. Kinetic studies indicated that it was a second-order reaction. Total organic carbon (TOC) removal was studied, and about 75% of TOC was removed in 60 minutes for the same dose and initial concentration. Metal ions such as Ca²⁺ and Fe³⁺ decreased the final removal efficiency. A slight leaching of Mn²⁺ ions was observed during the course of the reaction, which confirmed the oxidative degradation of BPA. The reaction was carried out in a nitrogen environment. It was observed that oxygen had a minor role in the BPA degradation. Transformation products were identified by mass spectrometric studies.