Deciphering Evolution Pathway of Supported NO3 • Enabled via Radical Transfer from •OH to Surface NO3 - Functionality for Oxidative Degradation of Aqueous Contaminants.
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ABSTRACT: NO3 • can compete with omnipotent •OH/SO4 •- in decomposing aqueous pollutants because of its lengthy lifespan and significant tolerance to background scavengers present in H2O matrices, albeit with moderate oxidizing power. The generation of NO3 •, however, is of grand demand due to the need of NO2 •/O3, radioactive element, or NaNO3/HNO3 in the presence of highly energized electron/light. This study has pioneered a singular pathway used to radicalize surface NO3 - functionalities anchored on polymorphic α-/γ-MnO2 surfaces (α-/γ-MnO2-N), in which Lewis acidic Mn2+/3+ and NO3 - served to form •OH via H2O2 dissection and NO3 • via radical transfer from •OH to NO3 - (•OH → NO3 •), respectively. The elementary steps proposed for the •OH → NO3 • route could be energetically favorable and marginal except for two stages such as endothermic •OH desorption and exothermic •OH-mediated NO3 - radicalization, as verified by EPR spectroscopy experiments and DFT calculations. The Lewis acidic strength of the Mn2+/3+ species innate to α-MnO2-N was the smallest among those inherent to α-/β-/γ-MnO2 and α-/γ-MnO2-N. Hence, α-MnO2-N prompted the rate-determining stage of the •OH → NO3 • route (•OH desorption) in the most efficient manner, as also evidenced by the analysis on the energy barrier required to proceed with the •OH → NO3 • route. Meanwhile, XANES and in situ DRIFT spectroscopy experiments corroborated that α-MnO2-N provided a larger concentration of surface NO3 - species with bi-dentate binding arrays than γ-MnO2-N. Hence, α-MnO2-N could outperform γ-MnO2-N in improving the collision frequency between •OH and NO3 - species and in facilitating the exothermic transition of NO3 - functionalities to surface NO3 • analogues per unit time. These were corroborated by a greater efficiency of α-MnO2-N in decomposing phenol, in addition to scavenging/filtration control runs and DFT calculations. Importantly, supported NO3 • species provided 5-7-fold greater efficiency in degrading textile wastewater than conventional •OH and supported SO4 •- analogues we discovered previously.
SUBMITTER: Kim J
PROVIDER: S-EPMC8397361 | biostudies-literature |
REPOSITORIES: biostudies-literature
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