Manganese (Mn) oxides are a group of ubiquitous metal oxides with great environmental significance. Due to their small particle size, large surface area, and high sorptive and oxidative capacities, Mn oxides can participate in a wide range of sorption and redox reactions, and exert significant influences on the biogeoc hemical cycling of metals, nutrients, and organics. The majority of natural Mn oxides are thought to be formed from microbial activities and the predominant form of biogenic Mn oxides is a highly disordered nanocrystalline phase similar to hexagonal birnessite. This phase is highly reactive and can undergo abiotic ripening or transformations to form phases with higher structural order and less reactivity.<br/> <br/>Numerous efforts have been dedicated to understand the structure and reactivity of pure Mn oxides, yet much still remain unknown regarding the formation, structure, and reactivity of the oxide phases formed biologically and under conditions representative of complex environmental systems. Due to the negative surface charge of Mn oxides across a wide range of pH, metal cations have strong tendency to interact with and affect the oxide surface and structure properties. In order to develop predictive biogeochemical models involving Mn oxides as an active component, it is critical to develop a systematic understanding of the impacts of metal cations on the structure-reactivity relationship of Mn oxides.<br/> <br/>Our research systematically investigated the role of a common metal cation Zn on the formation, structure, and transformation pathways of biotic and abiotic Mn oxide phases. Zn almost exclusively existed as surface adsorbed species at vacancy sites due to its high structural incompatibility. Its presence significantly altered the morphological and structural properties of the oxides, which resulted in altered sorptive and oxidative reactivities, as well as Mn(II)-induced transformation kinetics and pathways. Such effects were also phase specific, i.e. different oxide phases show different degrees of alteration. Taken together, our study demonstrated the importance of understanding the structure-reactivity relationship of Mn oxides under environmentally relevant conditions.

Effects of metal impurities on the structure and reactivity of Mn oxide nanoparticles

Macromolecular Chemistry: The Second Century

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ACS Spring 2020 National Meeting & Expo

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.