A Microbial‐Mineralization‐Inspired Approach for Synthesis of Manganese Oxide Nanostructures with Controlled Oxidation States and Morphologies

Abstract

aqueous solution at room temperature. We focus on a biomimetic synthesis inspired by microbial mineralization of manganese oxides.Recently, biomimetic approaches have facilitated the generation of a wide variety of hierarchical crystals with the cooperation of organic molecules and polymers. [5][6][7][8][9][10][11][12][13] As well as construction of hierarchical structures, control over both nanostructures and oxidation states in an aqueous solution is important for syntheses of transition metal oxides. In nature, microorganisms have synthesized manganese and iron oxides with designed nanostructures and controlled oxidation states. [14][15][16][17] We can obtain ideas from the microbial mineralization of transition metal oxides. Biomineralization of transition metal oxides has attracted much interest from a wide area of researchers such as from biology, geology, and mineralogy. Microbial mineralization contributes to the natural cycles of manganese, iron, nitrogen, carbon, sulfur, and precious metals. [ 14,15 ] Both enzyme-mediated and abiotic oxidation processes involve biomineralization of manganese and iron oxides. [ 14 b,c] In synthetic systems, however, it is not easy to synthesize transition metal oxides with controlled nanostructures and oxidation states in an aqueous solution as demonstrated by bacteria. As well as the development of synthetic routes, one of our next challenges is to fi nd potential applications of the resultant materials through biomimetic routes.Manganese oxides with diverse crystal structures and oxidation states are important materials because of their broad range of applications, such as adsorbents and catalysts. Many researchers have studied synthesis, characterization, and application of a wide variety of trivalent and tetravalent manganese oxides. [18][19][20][21][22][23][24][25][26][27][28] In nature, tetravalent manganese oxides (MnO 2 ) are synthesized from divalent manganese ions through biological oxidation processes. [ 14,15 ] Earlier works have proposed two models for mineralization of manganese oxides in nature. [ 14 b,c] One proposed model is "enzymemediated direct synthesis" of tetravalent

Single-unit-cell thick Mn3O4 nanosheets

“…S4b, ESIw) demonstrate that the binding energy of O 1s is 530.2 eV and attributed to the lattice oxygen of manganese oxide. 11,16 The binding energies of Mn P 3/2 and Mn P 1/2 are 641.1 and 652.3 eV, respectively, with the spin orbit splitting between Mn P 3/2 and Mn P 1/2 levels of 11.1 eV. These results are well matched with those of the reported Mn 3 O 4 .…”

“…Platelet Mn 3 O 4 nanocrystals structures had been formed by the selective attachment of oleylamine onto the (001) planes. 11 Similar results were also reported for the formation of metal oxide or oxyhydroxide nanosheet structures by controlling the interaction between the inorganic and organic species. 6,11 The magnetic properties of Mn 3 O 4 nanomaterials are directly dependent on their size and shape.…”

“…11 Similar results were also reported for the formation of metal oxide or oxyhydroxide nanosheet structures by controlling the interaction between the inorganic and organic species. 6,11 The magnetic properties of Mn 3 O 4 nanomaterials are directly dependent on their size and shape. 11,18 However, previous research focused mainly on the effect of size on magnetic properties and found that decreases in size lower the blocking temperature (T B ) and Curie-Weiss temperature (T C ).…”

“…These results are well matched with those of the reported Mn 3 O 4 . 11,15 These Raman and XPS results provide further evidence that the nanosheets are in the Mn 3 O 4 phase.…”

Bioinspired palladium-doped manganese oxide nanocorns: a remarkable antimicrobial agent targeting phyto/animal pathogens

“…This may be due to intermediate levels forming between the CB and VB of the host Mn 3 O 4 matrix 62 , 63 . Pd atoms act as an accepter to decrease the band gap of Mn 3 O 4 NPs 64 , 65 . Therefore, variation in the energy band gap of Mn 3 O 4 NPs by Pd doping may have applications in photocatalytic activity 66 .…”