From Molten Salts to Ionic Liquids: A "Nano" Journey
ABSTRACT Ionic liquids (ILs), a special group of classical molten salts, are widely used in various fields of science. Historically, researchers have tested ILs out of curiosity or to improve a specific property in a particular system in many areas of chemistry or materials science. However, today, ILs are far from being simple chemical curiosities and sit at the center of various green industrial innovation processes, where they play important roles in materials extraction, reactive catalytic supports, spatial devices, and biotransformations. In this Account, we describe a journey into a nanostructured universe to better understand the unique properties of ionic liquids and their modern applications. Because molten salts have been known for centuries and have found limited uses, we try to explain why modern nonaqueous ILs deserve increased interest and curiosity. We discuss the characteristics that distinguish modern nonaqueous ILs and compare them with classical molten salts. One of the main differences between room temperature ILs, especially those based on imidazolium cations, and simple molten salts, is the molecular asymmetry built into at least one of the ions. This asymmetry in modern, nonaqueous ILs opposes the strong charge ordering due to ionic interactions that normally would cause the system to crystallize. In addition, the presence of a cooperative network of hydrogen bonds between the cations and anions induces structural directionality (the entropic effect). Therefore, modern ILs form preorganized structures, mainly through hydrogen bonding, that induce structural directionality. In contrast, classical salts form aggregates only through ionic bonds. In other words, weak interactions order the structures in modern ILs while charges order the structure within classical salts. ILs cannot be regarded as merely homogeneous solvents. In fact, ILs form extended hydrogen-bond networks with polar and nonpolar nano domains and therefore are by definition "supramolecular" fluids. Thus, ILs are better described as hydrogen-bonded polymeric supramolecules of the type [(DAI)(m)(X)(m_n))](n+)[(DAI)(m_n)(X)(x))](n-). This structural pattern is a general trend for both the solid and the liquid phase and is apparently maintained to a large extent even in the gas phase. This structural organization of ILs can be used as entropic drivers (the "IL effect") for the preparation of well-defined nanoscale structures with extended order, either in the bulk phase or at the gas/vacuum interface.
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ABSTRACT: An overview of the recent advances in the field of polyoxometalate, ionic liquid hybrids, is proposed with a special attention paid to their application in catalysis, more precisely biphasic and heterogeneous catalysis. Both components of the hybrids are separately outlined pointing to their useful properties and potential for catalysis, followed by the description of the hybrids preparation and synergy between components in a large range of organic transformations. And finally a vision on the future developments is proposed.01/2014; DOI:10.1155/2014/963792
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ABSTRACT: The influence of the length of the cation alkyl chain on the dispersibility by ultrasonic treatment of TiO2 nanopowders in hydrophilic imidazolium-based room temperature ionic liquids was studied for the first time by dynamic light scattering and advanced rheology. TiO2 nanopowders had been synthesized by chemical vapor synthesis (CVS) under varied conditions leading to two different materials. A commercial nanopowder had been used for comparison. Characterizations had been done using transmission electron microscopy, X-ray diffraction, nitrogen adsorption with BET analysis, and FT-IR spectroscopy. Primary particle sizes were about 6 and 8 nm for the CVS-based and 26 nm for the commercial materials. The particle size distribution in the dispersion was strongly influenced by the length of the cation alkyl chain for all the investigated powders with different structural characteristics and concentrations in the dispersion. It was found that an increase of the alkyl chain length was beneficial, leading to a narrowing of the particle size distribution and a decrease of the agglomerate size in dispersion. The smallest average nanoparticle sizes in dispersion were around 30 nm. Additionally, the surface functionality of the nanoparticles, the concentration of the solid material in the liquid, and the period of ultrasonic treatment control the dispersion quality, especially in the case of the ionic liquids with the shorter alkyl chain. The influence of the nanopowders characteristics on their dispersibility decreases considerably with increasing cation alkyl chain length. The results indicate that ionic liquids with adapted structure are candidates as absorber media for nanoparticles synthesized in gas phase processes to obtain liquid dispersions directly without redispergation.Journal of Nanoparticle Research 03/2013; 15(3). DOI:10.1007/s11051-013-1463-2 · 2.28 Impact Factor
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ABSTRACT: Esterification of aromatic acid can be promoted via HSO3-functionalized Brønsted acidic ionic liquids (ILs). Under the optimum conditions, using 1-(3-sulfonic acid) propyl-3-methylimidazolium hydrogen sulfate ([MimC3SO3H][HSO4]) and 1-(4-sulfonic acid) butyl-3-methylimidazolium hydrogen sulfate ([MimC4SO3H][HSO4]) as dual solvent-catalysts, the conversion of esterification of aromatic acid was determined to be more than 90%, indicating that HSO3-functionalized ILs show much better catalytic ability than those of non-functionalized ionic liquids. The separation of desired product was easily performed by extraction with diethyl ether and these HSO3-functionalized ILs could be reused 7 times after vacuum drying. Our data represent an environmentally friendly method for the preparation of aromatic esters.Chinese Science Bulletin 09/2013; 58(26). DOI:10.1007/s11434-013-5888-x · 1.37 Impact Factor