Novel Synthesis of Aluminium Oxide Nanofibers
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Novel Synthesis of Aluminium Oxide Nanofibers Huai. Y. Zhu and Gao. Q. Lu* Nanomaterials Centre and Department of Chemical Engineering, The University of Queensland, Brisbane, 4072 Australia ABSTRACT This report presents a novel synthesis method of alumina nanofibers at moderate conditions in aqueous systems through a surfactant-directed crystal growth process. In the presence of polyethylene oxide (PEO) surfactants, boehmite nanofibers of about 3 nm thick and 30-60 nm long formed from aluminium hydrate colloids. During the subsequent heating, the surfactant was evaporated and boehmite nanofibers were converted into γ-alumina nanofibers. The function of the PEO surfactant and the formation mechanism of the nanofibers are discussed. Alumina nanofibers are an ideal structural reinforcement for various nanocomposite materials. They are potential adsorbents with high adsorption capacity. Furthermore, their unique structure exhibits strong resistance to heating at high temperatures. The BET surface area of a typical sample after heating at 1200°C is as high as 68 m2/g. This makes the material very promising as excellent substrates for catalysts of high thermal stability. INTRODUCTION In recent years, nanomaterials have attracted great attention from academe and industry because of their superior properties and their potential for a wide range of applications. Surfactants have been widely used as templates in developing uniform mesoporous structure at a scale of several nano-meters [1-3]. The concept of surfactant templating was also applied to the synthesis of mesoporous alumina molecular sieves, because activated alumina is extensively used as industrial adsorbents, catalysts and catalyst supports [4]. Successes were achieved by using neutral surfactants [5,6)] or carboxylic acids [7], as templates and aluminium alkoxide as the alumina precursor. It would be of great interest to construct alumina nano-structures of other geometry (morphology). The alumina with other geometry in nano-meter level, for instance, nano-fibers, could be important advanced engineering materials. The unique aspect ratio of nanofibers can lead to a wide range of applications in advanced ceramics, electronic, adsorption, and catalysis etc. Here we report the first synthesis of alumina nanofibers with very large porosity from inorganic salts with non-ionic polyethylene oxide (PEO) surfactants. In such a synthesis, the surfactant micelles induce important changes in morphology and growth of the nano-sized crystallite, rather than acting as templates for gel particles to condense around them. The formation mechanism of alumina nanofibers is distinctly different from the templating mechanism as observed in M41S synthesis. This new mechanism could constitute a new strategy of nano-structuring inorganic solids. EXPERIMENTAL The PEO surfactant, with a general chemical formula C12-14H 25-29O(CH2CH2O)nH (n = 5-30) was mixed with aluminium hydrate cake prepared from common inorganic salts like NaAlO2, in a designed molar ratio of surfactant to aluminium (P
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