Facilitated Activation of Peroxymonosulfate by Loading ZIF-8 on Fe3O4-MnO2 for Deep Mineralization of Bisphenol A

The hierarchically structured Fe3O4-MnO2-ZIF-8 composite was successfully synthesized and applied to activate peroxymonosulfate (PMS) for the degradation of bisphenol A (BPA) and other organic pollutants for the first time. Catalytic experiments revealed that the as-prepared Fe3O4-MnO2-ZIF-8 showed highly efficient catalytic activity and deep mineralization for BPA because of the loading of ZIF-8. When 60 mg/L BPA was degraded by the Fe3O4-MnO2-ZIF-8/PMS system, the removal efficiency of BPA reached 100% within 15 min and the TOC removal efficiency reached 80% within 9 min, values that were much higher than those of the catalysts reported recently. Fe3O4-MnO2-ZIF-8 can be separated conveniently from the aqueous phase under magnetic field control and shows better recyclability. Simultaneously, the Fe3O4-MnO2-ZIF-8/PMS system shows an excellent removal capability for other organic pollutants, such as phenol, tetracycline, p-hydroxybenzoic acid, and rhodamine B. Through radical quenching experiments and electron paramagnetic resonance tests, the mechanism of activation of PMS by Fe3O4-MnO2-ZIF-8 was investigated. ZIF-8 loaded on the surface of the Fe3O4-MnO2 composite can accept electrons generated from the Mn(II)/Mn(III)/Mn(IV) redox conjugate triplet and react with PMS to generate more •OH and SO4•–, thus significantly enhancing the catalytic performance. Additionally, on the basis of GC-MS analysis, the intermediates in the process of BPA degradation were tested and the possible degradation pathway was determined. This study indicates that Fe3O4-MnO2-ZIF-8 is a highly efficient catalytic material for PMS-based AOPs for the removal of various pollutants from water.