Peroxymonosulfate activated by FeOx/MnOy modified kaolinite for the degradation of polyvinyl alcohol: Catalytic performance, mechanism and DFT study

Abstract

In this work, FeOx/MnOy modified kaolinite catalyst (FeMn@K) was prepared by impregnation and pyrolysis processes, and its potential to activate peroxymonosulfate (PMS) for the degradation of polyvinyl alcohol (PVA) was evaluated. The properties of the prepared catalysts were characterized by scanning electron microscope (SEM), energy dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). Overall, FeMn@K has a higher specific surface area, a larger pore volume and more hydroxyl groups than the bare MnFe2O4, which led to a higher catalytic activity for PMS and a better PVA degradation efficiency. MnFe2O4 was uniformly fixed on the kaolinite surface because of Fe-O-Al bonds, which avoided the leaching of metal ions for the good reusability of FeMn@K. The presence of Mn and Fe active sites and hydroxyl groups on FeMn@K surface could efficiently promote the electron transfer, thus accelerating the redox cycles of Mnn+1/Mnn and Fe3+/Fe2+. In FeMn@K/PMS system, •OH and SO4•- played the dominant role for PVA degradation. The mechanism was elaborately elucidated through density functional theory (DFT) calculations, which may be due to natural mineral carrier effects. The degradation intermediates of PVA were identified, and two possible degradation pathways were proposed based on DFT calculations.