While abiotic processes are ubiquitous in nature, they have not thus far been considered as a fast route for formation of Mn(IV) oxides in environmental systems. Here, we report the photochemically-assisted fast oxidation of Mn2+ (aq) to Mn(IV) in a nitrate solution within hrs. Analyses of structures and oxidation states clearly indicated that a hitherto unconsidered inorganic abiotic process, nitrate photolysis, can enable the fast oxidation and the consequent formation of layered birnessite nanosheets, which are the most dominant phase of natural Mn(IV) oxide on the Earth’s surface. By using the scavengers of reactive oxygen species, we found that superoxide generated from nitrate photolysis plays the dominant role in the fast oxidation of Mn2+ (aq) to Mn(IV). We also confirmed that this oxidation occurs via an Mn(III) intermediate. Our findings elucidate the considerable effect of abiotic processes that occur with sunlight exposure on the fate of Mn in natural systems. The findings also have important implications for sustainably synthesizing layered birnessite nanosheets, which are very useful materials in many engineered applications.

Previously unexplored fast photochemical oxidation of Mn2+ (aq) in an abiotic inorganic process and consequent formation of birnessite nanosheets

255th National Meeting (2018)

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