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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 : The efficient assembly of nanoparticles by oriented attachment (OA) mechanism has attracted more and more attention. However, the morphological and structural coupling during the OA processes is not fully understood. Here, we propose the OA mechanism during the layer-based δ-MnO2 transformation to tunnel-based α-MnO2 using powder X-ray diffraction, X-ray atomic pair distribution function and transmission electron microscopy. It is suggested staged three-dimensional OA processes play a vital role in both morphological and concurrent structural evolution of δ-MnO2 into α-MnO2. In the initial stage of the evolution, the δ-MnO2 nanodots are found to spontaneously self-assemble into long nanosheet via OA process along a-b plane driven by hydrogen bonding through edge sites. Meanwhile, the Mn(IV) in the [MnO6] octahedral layers are reduced to Mn(III)/Mn(II) by H2O with the release of O2 and oxygen vacancies generation in the δ-MnO2 structure. The newly formed Mn(III) which migrates from layers to above/below the vacancies coordinate with three hydroxide oxygen. Therefore, the adjacent long nanosheets attach with each other driven by hydrogen bonding between hydroxide oxygen which coordinated with interlayer Mn(III) and form primary nanorods through face-to-face OA mechanism along c-axis. Concomitantly, the bonding of [Mn(III)O6] octahedra in interlayer of long nanosheets with adjacent [MnO6] octahedral layers were facilitated to construct the new 2  2 tunnel α-MnO2. These findings provide insight not only on mechanism of transformation of layer-based nanoparticles to tunnel-based nanoparticles but also on the efficient controlled synthesis and design of nanomaterials through different structures and morphologies.
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https://hal-insu.archives-ouvertes.fr/insu-02984568
Contributor : Bruno Lanson <>
Submitted on : Wednesday, November 25, 2020 - 1:35:21 PM
Last modification on : Thursday, November 26, 2020 - 3:28:57 AM

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Xinran Liang, Jeffrey Post, Bruno Lanson, Xiaoming Wang, Mengqiang Zhu, et al.. Coupled morphological and structural evolution of δ-MnO2 to α-MnO2 through multistage oriented assembly processes: the role of Mn(III). Environmental science‎.Nano, Royal Society of Chemistry, 2020, 7 (1), pp.238-249. ⟨10.1039/C9EN01000A⟩. ⟨insu-02984568⟩

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