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Self-Assembly of Birnessite Nanoflowers by Staged Three-Dimensional Oriented Attachment


Birnessite (layer type Mn(III, IV) oxides with ordered sheet stacking) is the most common mineral species of manganese (Mn) oxides, and has been demonstrated to be among the strongest sorbents and oxidants in surface environments. The morphology of birnessite is one of the key factors affecting its reactivity. Either biotic or abiotic birnessite samples usually consists of nanoflower-like crystals. However, governing factors and mechanisms of morphological evolution of the nanoflower-shaped birnessite remain poorly understood. In this work, birnessite nanoflowers, as a natural birnessite analog, were synthesized and the intermediate products during birnessite crystallization were captured by instant freezing using liquid nitrogen. The processes and mechanisms of crystal growth of birnessite nanoflowers were investigated using a combination of high-resolution transmission electron microscopy (HRTEM), field-emission scanning electron microscopy (FESEM), powder X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). Results indicate that the primary hexagonal nanoflakes rapidly agglomerate to form nuclei-like substrates at the initial stages, and subsequently, these nanoflakes aggregate laterally and link serially on the substrates to form nanopetals through both rotation and edge-to-edge oriented attachment (OA) mechanism. This process is likely driven by hydrogen bonding between unsaturated O at the edge planes of [MnO6] sheets. Meanwhile, the OA mechanism along the (001) plane is likely driven by Coulombic interactions and hydrogen bonding during assembling process of the adjacent nanopetals. The morphological evolution occurred by the staged three-dimensional OA process that plays an essential role in the self-assembly of flower-like birnessite crystals. The findings provide further understanding of how nanoparticle assembly is directed to achieve desired shapes and sizes by fabricating nanomaterials through three-dimensional OA processes.

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Publication details

The article was received on 29 Nov 2016, accepted on 05 Jun 2017 and first published on 14 Jun 2017

Article type: Paper
DOI: 10.1039/C6EN00619A
Citation: Environ. Sci.: Nano, 2017, Accepted Manuscript
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    Self-Assembly of Birnessite Nanoflowers by Staged Three-Dimensional Oriented Attachment

    X. Liang, Z. Zhao, M. Zhu, F. Liu, L. Wang, H. Yin, G. Qiu, F. Cao, X. Liu and X. Feng, Environ. Sci.: Nano, 2017, Accepted Manuscript , DOI: 10.1039/C6EN00619A

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