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Structural Evolution in a Hydrothermal Reaction between Nb2O5 and NaOH Solution: From Nb2O5 Grains to Microporous Na2Nb2O6•⅔H2O Fibers and NaNbO3 Cubes

Zhu, Huai Yong, Zheng, Zhanfeng, Gao, Xueping, Huang, Yining, Yan, Zhimin, Zou, Jin, Ying, Hongming, Zou, Qingdi, Kable, Scott H., Zhao, Jincai, Xi, Yunfei, Martens, Wayde N., & Frost, Ray L. (2006) Structural Evolution in a Hydrothermal Reaction between Nb2O5 and NaOH Solution: From Nb2O5 Grains to Microporous Na2Nb2O6•⅔H2O Fibers and NaNbO3 Cubes. Journal of the American Chemical Society, 128(7), pp. 2373-2384.

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Abstract

Niobium pentoxide reacts actively with concentrate NaOH solution under hydrothermal conditions at as low as 120 degrees Celsius. The reaction ruptures the corner-sharing of NbO7 decahedra and NbO6 octahedra in the reactant Nb2O5, yielding various niobates, and the structure and composition of the niobates depend on the reaction temperature and time. The morphological evolution of the solid products in the reaction at 180 degrees Celsius is monitored via SEM: the fine Nb2O5 powder aggregates first to irregular bars, and then, niobate fibers with an aspect ratio of hundreds form. The fibers are microporous molecular sieve with a monoclinic lattice, Na2Nb2O6 ⅔H2O. The fibers are a metastable intermediate of this reaction, and they completely convert to the final product NaNbO3 cubes in the prolonged reaction of 1 h. This study demonstrates that by carefully optimizing the reaction condition, we can selectively fabricate niobate structures of high purity, including the delicate microporous fibers, through a direct reaction between concentrated NaOH solution and Nb2O5. This synthesis route is simple and suitable for the large-scale production of the fibers. The reaction first yields poorly crystallized niobates consisting of edge-sharing NbO6 octahedra, and then the microporous fibers crystallize and grow by assembling NbO6 octahedra or clusters of NbO6 octahedra and NaO6 units. Thus, the selection of the fibril or cubic product is achieved by control of reaction kinetics. Finally, niobates with different structures exhibit remarkable differences in light absorption and photoluminescence properties. Therefore, this study is of importance for developing new functional materials by the wet-chemistry process.

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ID Code: 3501
Item Type: Journal Article
Additional Information: This article is freely available from the American Chemical Society website 12 months after the publication date. See links to publisher website in this record.
Keywords: Niobate, Fibers, Wet, chemical reaction, Kinetic control, Structural evolution
DOI: 10.1021/ja056301w
ISSN: 1520-5126
Subjects: Australian and New Zealand Standard Research Classification > CHEMICAL SCIENCE (030000)
Divisions: Past > QUT Faculties & Divisions > Faculty of Science and Technology
Copyright Owner: Copyright 2006 American Chemical Society
Copyright Statement: The contents of this journal can be freely accessed online via the ACS web page 12 months after publication. See hypertext link. Author contact details: r.frost@qut.edu.au
Deposited On: 11 Jul 2006
Last Modified: 25 Feb 2013 12:51

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