Insight into the electron transfer regime of periodate activation on MnO2: The critical role of surface Mn(IV)

At present, the potential mechanism of manganese oxide (MnO2) activation of PI and the key active sites of PI activation are still unclear and controversial. To this end, three different crystal forms of MnO2 were prepared in this study and used to activate PI to degrade pollutants. The results showed that different crystal types of MnO2 showed different catalytic abilities, and the order was gamma-MnO2 > alpha-MnO2 > beta-MnO2. Through quenching ex-periments, EPR tests, Raman experiments and in situ electrochemical experiments, it has been confirmed that electron transfer-mediated non-free radical process is the main mechanism of pollutant degradation, in which the active substance is the highly active metastable intermediate complex (MnO2/PI*). Hydroxyl radical (HO center dot), superoxide radical (O-2(-) ), singlet oxygen (O-1(2)) and iodine radical (IO3 center dot) did not participate in pollutant degra-dation. The quantitative structure-activity relationship analysis confirmed that the catalytic performance of MnO2 was highly positively correlated with the surface Mn(IV) content, which indicated that the surface Mn(IV) site was the main active site. Overall, this study will be of great help to the design and application of manganese dioxide activation for periodate degradation of pollutants.

Automated summary

In this study, three different crystal forms of MnO2 were prepared and used to activate PI for pollutant degradation, revealing the potential mechanism and key active sites of MnO2 activation. The results showed that MnO2 with different crystal types exhibited different catalytic abilities, with the order of gamma-MnO2 > alpha-MnO2 > beta-MnO2. Experimental tests including quenching, EPR, Raman, and in situ electrochemical experiments confirmed that electron transfer-mediated non-free radical process was the main mechanism for pollutant degradation, and the highly active metastable intermediate complex (MnO2/PI*) was the active substance. Hydroxyl radical (HO·), superoxide radical (O2-), singlet oxygen (O1(^2)), and iodine radical (IO3·) did not participate in pollutant degradation. The quantitative structure-activity relationship analysis indicated that the catalytic performance of MnO2 was highly positively correlated with the surface Mn(IV) content, suggesting that surface Mn(IV) site was the main active site. Overall, this study provides valuable insights for the design and application of manganese dioxide activation for periodate degradation of pollutants.