Tunable Biogenic Manganese Oxides

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 ) is explored. Physical characterisation of MnO 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 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 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 minerals is examined and correlated with their structural properties.

Diversity in the Family of Manganese Oxides at the Nanoscale: From Fundamentals to Applications

“…The bacterial enzyme complex is responsible for the biomineralization and also for the production of manganese oxides at the nanoscale. 25 The manganese(IV) oxides so produced through microbial activity, often coined as biogenic manganese oxides or manganese biooxides, can mediate a variety of redox reactions with organic and inorganic compounds in the environment. The vacant sites at the octahedral layers of these biogenic mangenese oxides can lead to sequestration of several metallic elements.…”

“…At low pH and in the absence oxygen, Mn(II) is thermodynamically stable, whereas in the presence of O 2 , the formation of Mn(III) and Mn(IV) is favored, which occurs primarily as insoluble Mn (oxyhydr)oxides. Reprinted with permission from (a) refs ( 24 ) and (b) ( 25 ), respectively. Copyright (a) (2004) Annual Reviews and (b) (2017) Wiley-VCH, respectively.…”

“…Bacteria and fungi that produce manganese oxides are extraordinarily skilled engineers of nanomaterials that contribute significantly to global biogeochemical cycles. The bacterial enzyme complex is responsible for the biomineralization and also for the production of manganese oxides at the nanoscale . The manganese­(IV) oxides so produced through microbial activity, often coined as biogenic manganese oxides or manganese biooxides, can mediate a variety of redox reactions with organic and inorganic compounds in the environment.…”

“…The vacant sites at the octahedral layers of these biogenic mangenese oxides can lead to sequestration of several metallic elements. ,, The multicopper oxidase enzymes include a family of proteins that are found in plants, animals, bacteria, and fungi and are associated with the four stepwise single electron oxidations of O 2 to H 2 O. The cycle of different oxidation states of manganese found in nature and plausible mechanism of the MnO x mineralization catalyzed by multicoopper oxidase, MnxG are enunciated in Figure .…”

Synthesis and Characterization of a New Monometallic Manganese Layered Double Hydroxide with Unique Redox Properties

“…Due to coupling between the unpaired electron of the outer shell and unpaired core electron resulting from photoionization, high spin Mn ions give rise to multiplet splitting. Overlapping of these multiplets poses serious difficulty for qualitative and quantitative analysis of Mn valence state [47,48,49,50,51,52,53,54,55,56]. Figure 6 shows Mn2p 3/2 peak at 642.0 eV with shoulder at 643 eV, which suggests the coexistence of Mn II and Mn III valence states.…”