Crystallinity-dependent transformation of layered manganese oxides: implications for the mineral diversity of manganese oxides in nature

Abstract

Manganese (Mn) oxides are crucial for the cycling of trace metals and nutrients. Over 30 types of Mn oxide minerals with distinct crystal structures have been identified across a variety of biogeochemical settings, yet the mechanisms underlying their formation are poorly understood. By incubating three layered Mn oxides of varying particle size and crystallinity under identical solution conditions, we observed the formation of distinct tunneled Mn oxides. The nanoscale mineral property, particularly vacancy density and surface energy, modulates the adsorption geometry of Mn(II) and subsequent electron transfer and structural rearrangement. These findings indicate that mineral structural properties associated with crystallinity are critical and previously underappreciated for the transformation of Mn oxides. Our study provides a mechanistic basis for understanding the natural diversity of Mn oxide minerals, suggesting that they likely derive from the transformation of biogenic layered Mn oxides that experienced dynamic variations in mineral crystallinity and local environmental conditions.