Tunable Biogenic Manganese Oxides

Alexandr N Simonov; Rosalie K Hocking; Lizhi Tao; Thomas Gengenbach; Timothy Williams; Xi-Ya Fang; Hannah J King; Shannon A Bonke; Dijon A Hoogeveen; Christine A Romano; Bradley M Tebo; Lisandra L Martin; William H Casey; Leone Spiccia

doi:10.1002/chem.201702579

Tunable Biogenic Manganese Oxides

Chemistry. 2017 Sep 27;23(54):13482-13492. doi: 10.1002/chem.201702579. Epub 2017 Aug 28.

Authors

Affiliations

¹ School of Chemistry and the ARC Centre of Excellence for Electromaterials Science, Monash University, Victoria, 3800, Australia.
² Discipline of Chemistry, College of Science and Engineering, James Cook University, Queensland, 4811, Australia.
³ Department of Chemistry, University of California, One Shields Avenue, Davis, California, 95616, USA.
⁴ Commonwealth Scientific and Industrial Research Organisation Manufacturing Flagship, Clayton, Victoria, 3168, Australia.
⁵ Monash Centre for Electron Microscopy, Monash University, Victoria, 3800, Australia.
⁶ Division of Environmental and Biomolecular Systems, Institute of Environmental Health, Oregon Health & Science University, Portland, Oregon, 97239, USA.
⁷ Department of Earth and Planetary Sciences, University of California, One Shields Avenue, Davis, California, 95616, USA.

PMID: 28722330
DOI: 10.1002/chem.201702579

Abstract

Influence of the conditions for aerobic oxidation of Mn2+(aq) catalysed by the MnxEFG protein complex on the morphology, structure and reactivity of the resulting biogenic manganese oxides (MnO_x ) is explored. Physical characterisation of MnO_x includes scanning and transmission electron microscopy, and X-ray photoelectron and K-edge Mn, Fe X-ray absorption spectroscopy. This characterisation reveals that the MnO_x materials share the structural features of birnessite, yet differ in the degree of structural disorder. Importantly, these biogenic products exhibit strikingly different morphologies that can be easily controlled. Changing the substrate-to-protein ratio produces MnO_x either as nm-thin sheets, or rods with diameters below 20 nm, or a combination of the two. Mineralisation in solutions that contain Fe2+(aq) makes solids with significant disorder in the structure, while the presence of Ca2+(aq) facilitates formation of more ordered materials. The (photo)oxidation and (photo)electrocatalytic capacity of the MnO_x minerals is examined and correlated with their structural properties.

Keywords: MnxEFG protein complex; biogenic materials; manganese; structural disorder; structure elucidation; tunable morphology.