Abstract
NO(3) (•) can compete with omnipotent (•)OH/SO(4) (•-) in decomposing aqueous pollutants because of its lengthy lifespan and significant tolerance to background scavengers present in H(2)O matrices, albeit with moderate oxidizing power. The generation of NO(3) (•), however, is of grand demand due to the need of NO(2) (•)/O(3), radioactive element, or NaNO(3)/HNO(3) in the presence of highly energized electron/light. This study has pioneered a singular pathway used to radicalize surface NO(3) (-) functionalities anchored on polymorphic α-/γ-MnO(2) surfaces (α-/γ-MnO(2)-N), in which Lewis acidic Mn(2+/3+) and NO(3) (-) served to form (•)OH via H(2)O(2) dissection and NO(3) (•) via radical transfer from (•)OH to NO(3) (-) ((•)OH → NO(3) (•)), respectively. The elementary steps proposed for the (•)OH → NO(3) (•) route could be energetically favorable and marginal except for two stages such as endothermic (•)OH desorption and exothermic (•)OH-mediated NO(3) (-) radicalization, as verified by EPR spectroscopy experiments and DFT calculations. The Lewis acidic strength of the Mn(2+/3+) species innate to α-MnO(2)-N was the smallest among those inherent to α-/β-/γ-MnO(2) and α-/γ-MnO(2)-N. Hence, α-MnO(2)-N prompted the rate-determining stage of the (•)OH → NO(3) (•) route ((•)OH desorption) in the most efficient manner, as also evidenced by the analysis on the energy barrier required to proceed with the (•)OH → NO(3) (•) route. Meanwhile, XANES and in situ DRIFT spectroscopy experiments corroborated that α-MnO(2)-N provided a larger concentration of surface NO(3) (-) species with bi-dentate binding arrays than γ-MnO(2)-N. Hence, α-MnO(2)-N could outperform γ-MnO(2)-N in improving the collision frequency between (•)OH and NO(3) (-) species and in facilitating the exothermic transition of NO(3) (-) functionalities to surface NO(3) (•) analogues per unit time. These were corroborated by a greater efficiency of α-MnO(2)-N in decomposing phenol, in addition to scavenging/filtration control runs and DFT calculations. Importantly, supported NO(3) (•) species provided 5-7-fold greater efficiency in degrading textile wastewater than conventional (•)OH and supported SO(4) (•-) analogues we discovered previously.