The Design of Nanoscale Inorganic Materials with Controlled Size and Morphology by Ionic Liquids

Abstract

Recently, ionic liquids have successfully been employed in the preparation of inorganic materials (Antonietti et al., 2004, Taubert & Li, 2007). Ionic liquids often act as solvents, reactants or morphology templates, which enable the synthesis of inorganic materials with novel morphologies or improved properties. So far only a handful of studies have reported on the fabrications of nanoor micro-scaled materials including particles of metal oxide (Ding et al., 2007, Buhler & Fledmann, 2006) and sulfide (Jiang, et al., 2005, Jiang & Zhu, 2005). Many metal nanoparticles (NPs) such as Ir (Buhler & Fledmann, 2006), Rh (Wang & Zhu, 2005), Ru (Jiang, et al., 2005), Te (Jiang &. Zhu, 2005), Al (Mu, et al., 2004), Ag (Zhu et al., 2004), Pt (Foneca et al., 2003), and Au (Dupont et al., 2002) have been prepared in the presence of ionic liquids. Novel nanostructures can be produced by selecting suitable ionic liquid reaction systems: TiO2 (Nakashima & Kimizuka, 2003, Yoo et al., 2004, Zhou & Antonietti, 2003), Te nanorods (Zhu et al., 2004), Si (Abedin et al., 2004), CoPt nanorods (Wang &Yang, 2005), and porous silica (Zhou, et al., 2004, Zhou & Antonietti, 2004) have recently been synthesized, as reported. Žilkova et al. have used 1-methyl-3-octylimidazolium chloride (C8mimCl, an ionic liquid) as a template to prepare γ-Al2O3 from the hydrolysis and condensation of Al2Cl(OH)5 (Žilkovά, et al., 2006). It was shown that the molar ratio of Al/C8mimCl was important to define the porosity, i.e. the framework or textural type. Mumalo-Djokic and coworkers have put forward the concept of “all-in-one” solvent-reactant(-template)s, (Taubert & Li, 2007, Taubert 2004), that is ionic liquids or ionic liquid crystals (Binnemans, 2005) that are at the same time the solvent, the reactant, and the template for the fabrication of an inorganic. These special systems have been termed ionic liquid precursors and ionic liquid crystal precursors respectively (Taubert 2004, Zhu et al., 2006). Ionic liquid crystal precursors allow for the controlled mineralization of inorganics with complex structure and morphology. For example, they have made CaF2 tubes, CuCl platelets, and Au platelets from ionic liquid crystal precursors or their crystalline analogues (Taubert 2004, Taubert et al., 2007, Taubert et al., 2006, Taubert et al., 2005, Taubert 2005). Furthermore, other research groups have extended this concept of reactive ionic liquid crystals to other compounds (Zhu et al., 2006, Dobbs et al., 2006, lee et al., 2006, Kem et al., 2006).