Catalytic oxidation of Bisphenol A with Co3+ rich spinel Co3O4: Performance evaluation with peroxymonosulfate activation and mineralization mechanism

Abstract

Bisphenol A (BPA) is a toxic substance that is released into the environment mainly from paint, polymer, plastics and pharmaceutical industries. In this study, spinel Co3O4 consisting of Co2+/(Co3+)2O4 nanospheres with excellent specific surface properties were systematically synthesized via a simple hydrothermal approach preceded by calcination. The as-synthesized Co3O4 spinels were used for peroxymonosulfate (PMS) activation to reduce the bisphenol A (BPA). The effects of operating parameters including PMS dosage, initial pH, catalyst dosage, and co-existing ions were detected during the BPA degradation. It was observed that at neutral pH, the nano-Co3O4/PMS system effectively degrades the BPA (∼92%) with very low cobalt leaching and excellent recyclability. Control experiment analysis confirms the magnificent performance of the Co3O4/PMS system and the synergistic interaction between Co3O4 and PMS. Various characterization techniques were used to determine the thermal, textural and structural properties. A chemical quenching study confirmed that both hydroxyl radicals (•OH) and sulfate radicals (SO4•−) promotes BPA oxidation. The chloride (Cl-) ions and dihydrogen phosphate ions (H2PO4-) have little inhibition effect while adding humic acid (HA) and HCO3- inhibits the BPA oxidation. Separation techniques such as high-performance liquid chromatography (HPLC) coupled with mass spectroscopy (MS) were used to identify the oxidative by-products and the mineralization pathway of BPA reduction. First-order pseudo-kinetics were observed for BPA degradation. However, the power law model also fits nth-order kinetics models.