Structural Distortion in MnO₂ Nanosheets and Its Suppression by Cobalt Substitution

Shinya Suzuki; Masaru Miyayama

doi:10.3390/nano7100295

Structural Distortion in MnO₂ Nanosheets and Its Suppression by Cobalt Substitution

Nanomaterials (Basel). 2017 Sep 25;7(10):295. doi: 10.3390/nano7100295.

Authors

Shinya Suzuki¹, Masaru Miyayama²

Affiliations

¹ Department of Applied Chemistry, School of Engineering, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656, Japan. sin@fmat.t.u-tokyo.ac.jp.
² Department of Applied Chemistry, School of Engineering, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656, Japan. miyayama@fmat.t.u-tokyo.ac.jp.

Abstract

Co-Mn oxide nanosheets with the chemical composition H_0.23Co_0.23Mn_0.77O₂ (C23M77NS) and MnO₂ nanosheets (M100NS) were prepared by exfoliation of layer-structured oxides via chemical processing in an aqueous medium. The optical properties of C23M77NS and M100NS were compared using UV-Vis spectroscopy, and the valence states of Mn and Co and local structures around them were examined using X-ray absorption spectroscopy. M100NS with an average Mn valence of 3.6 exhibits large structural distortion, whereas C23M77NS with an average Mn valence of 4.0 does not exhibit structural distortion. Spontaneous oxidization of Mn occurs during ion-exchange and/or exfoliation into nanosheets. These results have originated the hypothesis that structural distortion determines the valence state of Mn in compounds with CdI₂-type-structured MnO₂ layers.

Keywords: Co–Mn oxide; MnO2; X-ray absorption spectroscopy; local structure; nanosheets; optical absorption.