Oxidation of bisphenol A by nonradical activation of peroxymonosulfate in the presence of amorphous manganese dioxide

This work demonstrated that bisphenol A (BPA) was rapidly degraded by peroxymonosulfate (PMS) in the presence of amorphous manganese dioxide (MnO2). Chemical quenching experiments and electron paramagnetic resonance spectroscopy (EPR) suggested that hydroxyl radical (OH), sulfate radical (SO4−), and singlet oxygen (1O2) were unlikely responsible for BPA oxidation. As such, a nonradical mechanism involving the formation of reactive complexes between amorphous MnO2 and PMS was tentatively proposed based on the PMS decomposition and Raman spectra. The presence of phosphate ions (H2PO4−) remarkably suppressed the degradation of BPA, while the addition of divalent metal ions (Ca2+, Mg2+, and Zn2+) appreciably enhanced BPA degradation. The discrepancy was likely resulted from their contrasting influences on the formation of reactive PMS-MnO2 complexes. Based on identified oxidation products (i.e., dimers, 4-hydroxycumyl alcohol, mono-hydroxylated BPA and its quinone derivative) by liquid chromatography tandem mass spectrometry, the transformation pathways of BPA in amorphous MnO2/PMS system involving one-electron oxidation, radical coupling, bond cleavage, and hydroxylation were proposed. In addition to BPA, thirteen other selected phenolic compounds were also efficiently degraded by amorphous MnO2/PMS system, and good correlations between apparent pseudo-first-order reaction rate constants (kobs) and descriptor variables (i.e., Hammett constants σ+ and half-wave potentials E1/2) were obtained.