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Coupled Morphological and Structural Evolution of δ-MnO2 to α-MnO2 through Multistage Oriented Assembly Processes: the Role of Mn(III)

Abstract

α-MnO2 is a typical tunneled Mn oxide (TMOs) which frequently associated with δ-MnO2 in the environment exhibits strong adsorption and oxidation activity. The morphology of α-MnO2 which controlled by oriented attachment process (OA) is one of the key factors affecting its reactivity. However, the detailed crystal growth process and coupling between morphology and structure of α-MnO2 during OA processes remain poorly understood. We propose that the transformation of the layer-based δ-MnO2 to tunnel-based α-MnO2 occurs via a multistage OA process. In the initial stage, the produced δ-MnO2 nanoflakes are found to spontaneously self-assemble into a nanoribbon with a large number of lattice defects via edge-to-edge OA. The presence of lattice defects promotes the generation of oxygen vacancies, and the Mn(IV) ions in the [MnO6] octahedral layers of δ-MnO2 is reduced to Mn(III)/Mn(II). The reduced ions subsequently migrate from the [MnO6] octahedral layers to the interlayers during this process. Driven by hydrogen bonding between hydroxide which acts in coordination with the interlayer Mn(III)/Mn(II) and oxygen atoms coordination with adjacent nanoribbons attach to each other and form primary nanorods through a face-to-face OA mechanism along the c-axis. Concomitantly, the bonding of [Mn(III)O6] octahedra in the interlayer of the nanoribbons with adjacent [MnO6] octahedral layers lead to the fabrication of a new 2 * 2 α-MnO2 tunnel structure from the original δ-MnO2. These findings provide insights into both the transformation mechanisms of the layer-based to the tunnel-based nanoparticles and methods for efficient and controlled synthesis of nanomaterials.

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Publication details

The article was received on 04 Sep 2019, accepted on 20 Nov 2019 and first published on 21 Nov 2019


Article type: Paper
DOI: 10.1039/C9EN01000A
Environ. Sci.: Nano, 2019, Accepted Manuscript

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    Coupled Morphological and Structural Evolution of δ-MnO2 to α-MnO2 through Multistage Oriented Assembly Processes: the Role of Mn(III)

    X. Liang, J. Post, B. Lanson, X. Wang, M. Zhu, F. Liu, W. F. Tan, X. Feng, G. Zhu, X. Zhang and J. De Yoreo, Environ. Sci.: Nano, 2019, Accepted Manuscript , DOI: 10.1039/C9EN01000A

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