title: Influence of the molecular-oriented structure of ionic liquids on the crystallinity of aluminum hydroxide prepared by a sol-gel process in ionic liquids.
abstract: The influence of the structure of ionic liquids on the crystallinity of aluminum hydroxide (Al(OH)3) prepared by a sol-gel process with aluminum isopropoxide (Al(OPr(i))3) in imidazolium-based ionic liquids was investigated. When Al(OH)3 was prepared in ionic liquids having long alkyl chains, such as 1-butyl-3-methylimidazolium salts and 1-methyl-3-octylimidazolium salts, highly crystalline products were obtained. In contrast, Al(OH)3 obtained using the 1-ethyl-3-methylimidazolium salt was an amorphous material, indicating that hydrophobic interaction of the alkyl tail of the imidazolium cation of the ionic liquid strongly affects the crystallinity of sol-gel products and the local structure of the ionic liquid. Moreover, the crystallinity of Al(OH)3 prepared in ionic liquids increased relative to the amount of additional water (ionic liquid/water = 1.28/2.0-3.5/0.2, w/w). In the case of addition of a small amount of water (ionic liquid/water = 3.5/0.2, w/w), the product was amorphous. These results implied that the presence of an ionic liquid and a sufficient amount of water was crucial for the successful synthesis of sol-gel products with high crystallinity. (1)H NMR analyses revealed a shift of the peak associated with the imidazolium cation upon addition of water, which suggested that the molecular orientation of the ionic liquid was similar to that of a micelle.
authors.affiliation: Department of Chemical Science and Engineering, Graduate School of Engineering, Kobe University, Rokko, Nada, Kobe 657-8501, Japan. minamihi@kobe-u.ac.jp.
authors.forename: K
authors.initials: K
authors.lastname: Kinoshita
authors.forename: H
authors.initials: H
authors.lastname: Yanagimoto
authors.forename: T
authors.initials: T
authors.lastname: Suzuki
authors.forename: H
authors.initials: H
authors.lastname: Minami