Formation and Oxidation Reactivity of MnO2+(HCO3-)n in the MnII(HCO3-)-H2O2 System.
Inorg Chem
; 59(5): 3171-3180, 2020 Mar 02.
Article
em En
| MEDLINE
| ID: mdl-32077694
The MnII(HCO3-)-H2O2 (MnII-BAP) system shows high reactivity toward oxidation of electron-rich organic substrates; however, the predominant oxidizing species and its formation pathways involved in the MnII-BAP system are still under debate. In this study, we used the MnII-BAP system to oxidize As(III) in that As(III), Mn2+, and HCO3- are common components in As(III)-contaminated groundwater. Kinetic results show that MnII(HCO3-)n [including MnII(HCO3)+ and MnII(HCO3)2] is a key factor in the MnII-BAP system to oxidize As(III). Quenching experiments rule out contributions of OH⢠and 1O2 to As(III) oxidation and reveal that O2â¢- and the oxidizing species generated from O2â¢- play predominant roles in the oxidation of As(III). We further reveal that the MnO2+(HCO3-)n intermediate generated in the reaction between MnII(HCO3-)n and O2â¢-, instead of O2â¢-, is the predominant oxidizing species. Although CO3â¢- also contributes to As(III) oxidation, the high reaction rate constant between CO3â¢- and O2â¢- indicates that CO3â¢- is not the predominant oxidizing species in the As(III)-MnII-BAP system. In addition, the presence of Mn(III) further indicates the important Mn(II)-Mn(III) cycling in the MnII-BAP system. We therefore suggest two important roles of MnII(HCO3-)n in the MnII-BAP system: (i) MnII(HCO3-)n reacts with H2O2 to form the MnIII(HCO3)3 intermediate, followed by a subsequent reaction between MnIII(HCO3)3 and H2O2 to produce O2â¢-; (ii) MnII(HCO3-)n can also stabilize O2â¢- with the formation of MnO2+(HCO3-)n. MnO2+(HCO3-)n is an electrophilic reagent and plays the predominant role in the oxidation of As(III) to As(V).
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MEDLINE
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En
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Inorg Chem
Ano de publicação:
2020
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Article