In Situ Regulation of MnO2 Structural Characteristics by Oxyanions to Boost Permanganate Autocatalysis for Phenol Removal

Oxyanions,a class of constituents naturally occurring in water,have been widely demonstrated to enhance permanganate (Mn(VII)) decontaminationefficiency. However, the detailed mechanism remains ambiguous, mainlybecause the role of oxyanions in regulating the structural parametersof colloidal MnO2 to control the autocatalytic activityof Mn(VII) has received little attention. Herein, the origin of oxyanion-inducedenhancement is systematically studied using theoretical calculations,electrochemical tests, and structure-activity relation analysis.Using bicarbonate (HCO3 (-)) as an example,the results indicate that HCO3 (-) can acceleratethe degradation of phenol by Mn(VII) by improving its autocatalyticprocess. Specifically, HCO3 (-) plays asignificant role in regulating the structure of in situ produced MnO2 colloids, i.e., increasing the surfaceMn(III)(s) content and restricting particle growth. Thesestructural changes in MnO2 facilitate its strong bindingto Mn(VII), thereby triggering interfacial electron transfer. Theresultant surface-activated Mn(VII)* complexes demonstrate excellentdegrading activity via directly seizing one electron from phenol.Further, other oxyanions with appropriate ionic potentials (i.e.,borate, acetate, metasilicate, molybdate, and phosphate) exhibit favorableinfluences on the oxidative capability of Mn(VII) through an activationmechanism similar to that of HCO3 (-). Thesefindings considerably improve our fundamental understanding of theoxidation behavior of Mn(VII) in actual water environments and providea theoretical foundation for designing autocatalytically boosted Mn(VII)oxidation systems. Thisstudy demonstrates the mechanism of oxyanion-boostedMn(VII) autocatalysis to guide the efficient application of Mn(VII)and the development of oxyanion-assisted Mn(VII) water treatment systems.

Automated summary

Oxyanions, natural constituents in water, have been shown to enhance the decontamination efficiency of permanganate. However, the mechanism behind this enhancement is not well understood. This study systematically investigated the role of oxyanions in regulating the structural parameters of colloidal MnO2, leading to increased autocatalytic activity of Mn(VII). The results showed that oxyanions such as bicarbonate can improve the degradation of phenol by Mn(VII) through improved autocatalytic processes and structural changes in MnO2. Other oxyanions with appropriate ionic potentials also showed similar activation mechanisms. These findings enhance our understanding of Mn(VII) oxidation behavior and provide a theoretical foundation for designing enhanced Mn(VII) oxidation systems.