Oxidative polymerization of bisphenol A (BPA) via H-abstraction by Bi2.15WO6 and persulfate: Importance of the surface complexes

Abstract

Bi2+xWO6 are a group of reactive photocatalysts in the photooxidation of various contaminants. However, their catalytic reactivity in the persulfate (PS)-based oxidation processes in the absence of light is still unknown. In this study, Bi2.15WO6 shows a high reactivity in the catalytic oxidation of bisphenol A (BPA) by PS in the absence of light under alkaline conditions, and 20 mg L-1 BPA can be rapidly removed within 30 min at pH 10.0 with the low stoichiometry ratio of 1.79 between consumed PS and removed BPA. Characterizations of the oxidation products indicate that 98.4% of soluble BPA has been oxidatively polymerized to BPA polymers, instead of being oxidized to CO2 and H2O. FTIR, Raman, XPS and electrochemical analyses confirm that surface Bi(III) is the reactive site for the adsorption of BPA and PS, which then initiates reactions between BPA and PS. DFT calculations reveal that the O-O bond in PS is moderately activated via the nonradical pathway after adsorbing on Bi(III), instead of being decomposed to SO4•−, followed by H-abstraction from BPA by the activated PS with the formation of phenoxyl radicals and the subsequent polymerization to BPA polymers. The apparently lower energy barrier from adsorbed BPA (ΔG = 0.056 eV) than that from dissolved BPA (ΔG = 0.263 eV) further reveals that H-abstraction from adsorbed BPA to the activated PS on the surface of Bi2.15WO6 is more favorable than that from dissolved BPA. This study gives new insight on the efficient removal of recalcitrant contaminants via the H-abstraction pathway.