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Frame Stability of Tunnel‐Structured Cryptomelane Nanofibers: The Role of Tunnel Cations
Author(s) -
Gao Tao,
Norby Poul
Publication year - 2013
Publication title -
european journal of inorganic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.667
H-Index - 136
eISSN - 1099-0682
pISSN - 1434-1948
DOI - 10.1002/ejic.201300602
Subject(s) - cryptomelane , nanofiber , recrystallization (geology) , dissolution , hydrothermal circulation , chemical engineering , microstructure , aqueous solution , chemistry , nanotechnology , ion , hydrothermal synthesis , materials science , crystallography , geology , oxide , organic chemistry , paleontology , manganese oxide , engineering
The role of tunnel K + ions on the growth and stability of tunnel‐structured cryptomelane‐type MnO 2 nanofibers (denoted as cryptomelane nanofibers hereafter) has been discussed by means of X‐ray diffraction and electron microscopy. Cryptomelane nanofibers with typical diameters of 20–80 nm and lengths of 1–6 μm have been synthesized by means of a simple hydrothermal reaction of KMnO 4 and MnSO 4 aqueous solutions at 140 °C. The growth of cryptomelane nanofibers under hydrothermal conditions follows a dissolution–recrystallization process and involves a morphological transformation from a layered precursor to the tunnel‐structured cryptomelane, in which the K + ions play important roles in templating and stabilizing the tunneled framework. The presence of tunnel K + ions also enhances the frame stability of the cryptomelane nanofibers at elevated temperatures. The formation of a layered K x Mn 2 O 4 ( x ≈ 0.26) with a hexagonal phase structure has been observed at about 900 °C. The transformation from tunneled cryptomelane to layered K x Mn 2 O 4 also follows the dissolution–recrystallization growth mechanism, in which the diffusion of K + ions at high temperatures represents a critical process. The topological correlation between the tunneled and layered MnO 2 materials might provide useful information for the synthesis of MnO 2 nanomaterials with controlled microstructures for different applications.