Evolution of Singlet Oxygen by Activating Peroxydisulfate and Peroxymonosulfate: A Review.

Advanced oxidation processes (AOPs) based on peroxydisulfate (PDS) or peroxymonosulfate (PMS) activation have attracted much research attention in the last decade for the degradation of recalcitrant organic contaminants. Sulfate (SO4•-) and hydroxyl (•OH) radicals are most frequently generated from catalytic PDS/PMS decomposition by thermal, base, irradiation, transition metals and carbon materials. In addition, increasingly more recent studies have reported the involvement of singlet oxygen (1O2) during PDS/PMS-based AOPs. Typically, 1O2 can be produced either along with SO4•- and •OH or discovered as the dominant reactive oxygen species (ROSs) for pollutants degradation. This paper reviews recent advances in 1O2 generation during PDS/PMS activation. First, it introduces the basic chemistry of 1O2, its oxidation properties and detection methodologies. Furthermore, it elaborates different activation strategies/techniques, including homogeneous and heterogeneous systems, and discusses the possible reaction mechanisms to give an overview of the principle of 1O2 production by activating PDS/PMS. Moreover, although 1O2 has shown promising features such as high degradation selectivity and anti-interference capability, its production pathways and mechanisms remain controversial in the present literatures. Therefore, this study identifies the research gaps and proposes future perspectives in the aspects of novel catalysts and related mechanisms.

Periodate activation with manganese oxides for sulfanilamide degradation.

This study presents a novel periodate oxidation system mediated by manganese oxides for the rapid removal of aqueous contaminants. The catalytic activation of periodate on manganese oxides was demonstrated as an efficient advanced oxidation system for degradation of sulfanilamide. The reactivity of manganese oxides with different Mn valence followed the order of MnO2>Mn3O4>Mn2O3, all of which showed extraordinary reusability during repeated activation of periodate. Sulfanilamide was rapidly degraded along with stoichiometric transformation of IO4- to IO3-, and both processes exhibited good linear correlations with the dosage of manganese oxides. While the degradation of sulfanilamide in the MnO2/IO4- system was accelerated at lower solution pH, it was only slightly affected by ionic strength, water anions and humic acid. In contrast to the homogeneous system of Mn2+/IO4-, sulfanilamide degradation was not influenced in oxic and anoxic environment. It was evidenced by quenching studies and EPR tests that both singlet oxygen (1O2) and iodate radicals (IO3•) were generated when the metastable Mn(IV)-O-IO3 interacted with sulfanilamide. The XPS spectra of Mn 2p and O 1s before and after reactions indicated that the catalytic activation of periodate on MnO2 was not in company with the redox cycling of Mn(IV) species.