The 3rd International Congress on Ionic Liquids

15 October 2009

Pre-Symposia

Chemistry in Japan

The Japanese pre-symposium workshop of COIL-3 was sponsored by a Grant-in-Aid of Scientific Research on the Priority Area "Science of Ionic Liquids" from the Ministry of Education, Culture, Sports, Science and Technology (MEXT) of Japan. The workshop included two full days of presentations (including a number of invited guest speakers) and over 80 posters, the highlights of which are summarised below, apart from speakers who presented in the main COIL-3.

Noriyoshi Matsumi (Nagoya University) discussed functional organoboron ionic liquids containing closo-1,2-carborane anions. These low-melting ionic liquids were prepared by reacting the appropriate carbene with closo-1,2-C2B10H12 under mild reaction conditions. 

Keiko Nishikawa (Chiba University) discussed a differential scanning calorimeter with nanowatt stability and sensitivity, which was able to detect the melting and crystallisation behaviours of 1-isopropyl-3-methylimidazolium bromide. The precision and accuracy of this calorimeter is quite remarkable, giving access to information about phase transitions otherwise inaccessible. 

A variety of structural studies of ionic liquids and their surfaces was presented. Osamu Yamamuro (University of Tokyo) described a neutron scattering study of fully deuteriated [C8mim]Cl, which revealed motions believed to be related to the local movement of the alkyl chains and diffusion of the ions, corresponding to fast and slow relaxations, respectively. Water mixtures with this ionic liquid, as well as with [C8mim]Br and [C12mim]Cl, were characterised by X-ray reflectivity with a liquid interface reflectometer (Yohko F. Yano, Ritsumeikan University) and showed reflectivity trends of [C8mim]Br > [C8mim]Cl > [C12mim]Cl. 

An interesting presentation came from Mitsuhiro Kanakubo (National Institute of Advanced Industrial Science and Technology) on the use of [C4mim][NTf2] for separating CO2 from gas mixtures by physical absorption. This system proved to be 20 % more efficient than one based on poly(ethylene glycol) (PEG 400). In a related talk, Yoshifumi Kimura (Kyoto University) reported a study of diffusion (thermal and translational) of solutions of CO2 in room temperature ionic liquids, using transient grating (TG) spectroscopy.

In an interesting and novel application of ionic liquids, Susumu Kuwabata (Osaka University) described the use of [C4mim][NTf2] to eliminate the surface charging effect, which commonly complicates scanning electron microscopy. 

The invited guest speakers delivered a range talks, more focused on applications. Jürgen Klakermayer (Aachen University, Germany) discussed rhodium-catalysed asymmetric hydrogenation with racemic tropoisomeric and atropoisomeric diphenylphosphine ligands in the presence of chiral ionic liquids; Mark Maroncelli (The Pennsylvania State University, USA) developed a new 4-site model meant to mimic the solvation behaviour of [C4mim][PF6]. Hyunjoo Lee (Energy & Environment Research Division, Republic of Korea) described ether-functionalised zwitterionic compounds as electrolyte additives for lithium batteries; Udo Kragl (University of Rostock, Germany) discussed the extraction of four well-characterised model proteins (bovine, serine, albumin or trypsin) from water using aqueous two-phase systems consisting of buffer, potassium phosphate and a water-miscible ionic liquid; Jennifer Pringle (Monash University, Australia) discussed the synthesis of conducting polymers in ionic liquids, specifically poly(3,4-ethylenedioxythiophene) (PEDOT), which is a potential alternative to platinum in the counter electrode catalyst role in dye-sensitised solar cells. 

Recent Advances in Theoretical Approaches to Ionic Liquids

In an afternoon session, ten lectures on theoretical studies of ionic liquids were delivered. These were surprisingly accessible to non-experts, which made for lively discussions. 

Brian Yates (University of Tasmania, Australia) described the importance of accurate ion-pair interactions in understanding ionic liquid properties such as conductivity and vapour pressure. Testing several basis sets and a variety of cations, Yates calculated that ionic liquids with the same anion generated similar ion pair energies. 

Patricia Hunt (Imperial College London, UK) explained that phosphonium ionic liquids have lower viscosities than their ammonium analogues (despite their larger molecular weights) because they have higher rotational freedom and a more open structure. Ralf Ludwig (University of Rostock, Germany) described how, in many cases, strong ion pairing due to hydrogen bonding can reduce viscosity, by blocking external hydrogen bonds, and used FTIR spectroscopy to probe hydrogen bonding differences between anions as a means of verifying force field predictions. 

The nature of melting in ionic liquids attracted a lot of attention. John Slattery (University of York, UK) suggested that molecular volumes are important not only for the determination of melting point, but also for the prediction of density, viscosity, heat capacity, conductivity, etc. Slattery calculated molecular volumes of ionic liquids in the gas phase and found a correlation, per anion type, between viscosities and molecular volumes. Philipp Eiden (University of Freiburg, Germany) presented predictions of melting points using the Born-Fajans-Haber cycle and a computational method which, while having an error margin of 20 °C, requires no experimental values and low computer costs. Edward Maginn (University of Notre Dame, USA) has developed a method for prediction of melting points, based on the free energy difference between liquid and solid states. This open source molecular dynamics code (LAMMPS) is available online. 

Sergey Verevkin (University of Rostock, Germany) discussed the prediction of vapourisation enthalpies using a novel combination of theoretical and experimental values. The theoretical values were obtained using G3MP2, and experimental values from thermogravimetric analysis (TGA) of static vapourisation. 

Shyue Ping Ong (Massachusetts Institute of Technology, USA) presented a computational method to screen cations for viability in electrochemical applications. Cation stability was improved by the presence of electron-withdrawing groups and negatively affected by electron-donating groups. Hubert Valencia (National Institute of Advanced Industrial Science and Technology, Japan) described a theory of how some ionic liquids adsorb onto lithium electrode surfaces, focussing in depth on cation reactivity. 

Elaine Mindrup (University of Notre Dame, USA) presented a screening of ionic liquids with different tethered functional groups for CO2 absorption. Cation-tethered amines resulted in 1:2 (CO2 to ionic liquid) reactions, whereas anion-tethered amines resulted in 1:1 reactions. Amine structure and tethering point were found to be important parameters for tuning energies and reaction stoichiometries. 

Physical & Electrochemical Properties / Synthesis & Applications of Ionic Liquids

The third presymposium, run in parallel with Theoretical Approaches, was a diverse mixture of talks that could be grouped roughly as Electrochemistry and Other. 

Frank Endres (Technische Universität Clausthal, Germany) highlighted that the solvation layers of ILs at interfaces differ significantly from that observed in conventional solvents. Furthermore, such studies are extremely sensitive to impurities that are commonly present in industrially-supplied ionic liquid samples. For example, XPS studies highlighted the presence of vacuum grease in such samples, while lithium and potassium contaminants interfere with AFM studies dues to their electrodeposition. 

Vera Lockett (University of South Australia) gave a talk on the differential capacitance observed at electrode-liquid interfaces in aqueous, molten salt and ionic liquid systems. The differences between aqueous and ionic liquid systems were noted, and the similarities between ionic liquids and molten salts discussed. Ionic liquids were noted to follow the Lattice Saturation theory. Yasushi Katayama (Keio University, Japan) discussed the application of ionic liquids as replacement electrolytes for rechargeable lithium batteries, while increasing the storage value by replacing carbon anodes with tin. The IL-Sn system does not require the prior formation of a Solid Electrolyte Interface (SEI) film, but lithium dope-undope reactions were still observed. Addition of small quantities of glyme to the ionic liquid dramatically reduced the charge transfer resistance in the system, by altering the lithium coordination environment in the ionic liquid. Andrea Balducci (Westfälische Wilhelms University of Münster, Germany) discussed the move towards 'greener' batteries through the combination of ionic liquids as electrolytes with fluorine-free binders. Fluorine binders are state of the art, but toxic and relatively expensive. Sodium carboxylmethylcellulose has been investigated as a cheaper, greener replacement, which while possible still suffers from low capacity due to wettability problems. Abhishek Lahiri (University of Alabama, USA) discussed using nickel chloride-ionic liquid melts as a possible means of extracting nickel from its oxide at relatively low temperatures. To this end, the electrodeposition of nickel from such melts was investigated. The crystal phase of the nickel deposit could be altered by the presence or absence of moisture in the melt, its presence leading to the formation of hexagonal close packed crystalline nickel, a potential hydrogen storage material. 

Junhua Huang (Energy Technology CSIRO, Australia) gave an overview, from an industrial perspective, of current academic progress on the application of ionic liquids for CO2 capture. Amine solutions are currently employed by industry, and amine-functionalised ionic liquids were noted as potential improvements. Huang discussed the future requirements necessary for ionic liquids to find application on an industrial-scale, for example faster absorption-desorption rates, low corrosivity and high thermal stability. Her research group is currently focussing upon possible pilot-scale applications of amines, enzymes and solids in IL-based systems. 

Alexander Wulf (University of Rostock, Germany) gave a review of his extensive previous work, using IR, Raman and ab initio calculations to probe hydrogen-bonding in ionic liquid and protic ionic liquid systems, and its influence upon their physicochemical properties. The reason that an increase in hydrogen bonding can sometimes help to fluidise ionic liquids was highlighted and discussed. 

Alvise Perosa (Università Ca' Foscari, Italy) discussed the green synthesis of phosphonium and ammonium ionic liquids using dimethylcarbonate as the alkylating agent. Its advantages over conventional alkylating agents were highlighted, the necessary synthetic conditions described, and the resulting methylcarbonate ionic liquids could be used as both Michael Coupling catalysts and as halide-free precursors to other ionic liquids. Pedro Lozano (Universidad de Mercia, Spain) gave an in-depth review on enzymatic reactors in ionic liquid systems. While ionic liquids can provide a catalytic phase for enzymatic synthesis, mass transfer is limited and scaling up is difficult. Supercritical CO2 can act as a means to transport the substrate to the enzymes and chemical catalysts, which are immobilised in and protected by the ionic liquid. He discussed the favourable application of this system to continuous flow reactors, and gave relevant examples. 

Main Conference

Over five days of the main COIL-3 symposium, conference goers we were treated to 44 lectures and 355 posters all based on the latest advances of ionic liquid technology, much of which is strongly relevant to the field of green chemistry. A highlight of the conference organisation was the absence of parallel sessions and the unrelated nature of juxtaposed lectures, encouraging a continually full and diverse audience. We present below a summary of the principle talks, the abstracts of which are available on the COIL-3 website and a selection of speakers and organisers is shown in Figure 2. 

Figure 2. A selection of COIL-3 speakers and organisers

Peter Wasserscheid (University of Erlangen-Nuremberg, Germany) opened the official COIL-3 symposium on Sunday evening with cues to the research community on how to encourage successful new industrial processes with ionic liquids. He noted that, while interest in ionic liquids is continuing to grow-thanks to their high economic potential, wide range of applications, and advancing industrial development-the technology is still considered too risky by many potential industrial users. In order to encourage successful new industrial processes, it is important to develop new ionic liquids and reduce both development time and technical risk. He led off with examples from his laboratory, describing, for instance, how his group took advantage of cation-anion interactions to prepare a chiral ionic liquid from a prochiral one, via asymmetric hydrogenation of the cation's side chain (Figure 3). They also prepared new ionic liquids with a 4-fluorobutane sulfonate anion, starting from tetrabutylammonium fluoride and 1,4-butane sultone. 

Figure 3. Asymmetric hydrogenation of an ionic liquid

Synthesis

Koen Binnemans (K.U. Leuven, Belgium) presented new ionic liquids for metal coordination, with carboxylate or nitrile functional groups. These dissolved metal salts much better than conventional ionic liquids with weakly coordinating anions. Studies on single crystals revealed unusual coordination chemistry to be occurring within the functionalised ionic liquid. Binnemans proposed that the limits between low solubility of metal ions in ionic liquids with weakly coordinating anions, and the high viscosities and melting points imposed by strongly coordinating anions, could be circumvented by preparing ionic liquids with a coordinating functional group attached to the cation. The studies will further the understanding of solvation processes of metal ions in ionic liquids.

Nikolai Ignatiev (Merck KGaA, Germany) showcased Merck's new commercial range of hydrophobic and low-viscosity ionic liquid anions: [(C2F5)3PF3]- (FAP), [(C2F5)2PF4]-, [N{P(O)(C2F5)3}2]- (FPI), [(C2F5)BF3]-, and [B(CN)4]- (TCB), e.g. for use in extraction processes, lithium ion batteries, and other electrochemical devices. With these bulky, weakly-coordinating anions, the viscosity of 1,3-dialkylimidazolium ionic liquids no longer depended on the length of the alkyl side chain, but rather, predominately on the interaction (co-ordination) between cation and anion. Shiro Seki (CRIEPI, Japan) described ionic liquids based on a new cation, triethyl(2-methoxymethyl)phosphonium (TEMMP), which underwent structural changes with temperature increase and therefore display unusual conductivity-temperature behaviour. Anja-Verena Mudring (Ruhr-Universität Bochum, Germany) reported the syntheses of lanthanide-containing ionic liquids, phase-switchable magnetic ionic liquids, and transition metal-based luminescent ionic liquids. The transition metal-based ionic liquids, with tuneable emission colours, were suggested for use in manufacturing dye lasers and biomarkers. James Davis, Jr. (University of South Alabama, USA) drew on structure-function relationships of biological membranes to guide the design of new ionic liquids, as well as to challenge current computational models. Chain unsaturation, which lowers the melting point of phospholipid bilayers (and chocolate), was also demonstrated to lower melting points of lipidic ionic liquids. In contrast to computational studies of ionic liquids, which predict that hydrophobic compounds will only reside in the hydrophobic regions of ionic liquid, the hydrophobic part of long-chain fatty acids in biological membranes resides in both the hydrophobic and hydrophilic domain of a cell.

Hiroyuki Ohno (Tokyo University of Agriculture and Technology, Japan) presented his work on amino acid-derived ionic liquids (AAILs), pioneering work on ion-conductive polymers, and his experience in treating biopolymers such as cellulose with ionic liquids. While some hydrophobic AAILs / water mixtures show temperature dependent phase behaviour ("LCST"; lower critical solution temperature) that could be exploited for separation processes, his work on ion conductivity led to novel materials such as photoresponsive polymer gels. Concerning biopolymers in ionic liquids Ohno focused on enzymatic saccharification (conversion to glucose) of biomass. In conclusion, he proposed a new ionic liquid, [B]+[NO]-¬, which reflected the mood of the conference. 

Bio and Green

Yoon-Mo Koo (Inha University, Republic of Korea) used ionic liquids as solvents in biocatalysis of biodiesel and esterified sugars. Lipase-catalysed methanolysis of soyabean oil in [C2mim][OTf] proceeds (12 h, 50 °C) to 80 % yield of fatty acid methyl esters (FAMEs) - eight times higher than a solvent-free system and 15 % higher than using the conventional organic additive, tert-butanol. Esterification of glucose was studied in pure ionic liquids, using fatty acids and Novozym 435 (an immobilised lipase). Among several ionic liquids, a mixture of [C4mim][OTf] and [C4mim][NTf2] (1:1, v/v) achieved the optimal biocatalyst activity and stability and showed good recyclability (86 % residual activity after five biocatalyst recycles). Supersaturation of glucose in this mixture increased lipase activity from 1.1 to 2.9 mol min?1 g?1. Cristina Silva Pereira (Instituto de Tecnologia Química e Biológica, Portugal) presented the toxicity and metabolism-altering effects of ionic liquids toward filamentous fungi. As model eukaryotes, fungi (Penicillium sp.) were cultured in presence of sixteen ionic liquids. Some species were highly tolerant (up to 0.375 M) of some ionic liquids. Ionic liquid-induced alterations in the (ESI-mass spectra) profiles of fungal secondary metabolites suggested that ionic liquids might be used as metabolism-directing solvents for biosynthesis of biologically active molecules. 

Noleen Byrne (Arizona State University, USA) showed that certain proteins dissolve in protic ionic liquids keeping their native structure and activity. Hen egg white lysozyme dissolved in its native form in dimethylammonium ethanoate. After thermal denaturation, refolding was not spontaneous but could be induced (up to 97 %) and studied via the addition of guanadinium chloride (4.6 M), another protic salt and a typical protein denaturant that was here demonstrated as an excellent refolding agent. Toshiyuki Itoh (Tottori University, Japan) used a functionalised ionic liquid - a chiral imidazolium cation, with a D-proline moiety grafted onto the ring, and an alkyl-poly(ethylene glycol)-sulfate anion - to coat lipase for acceleration and enhanced enantioselectivity in the esterification of alcohols (in diisopropyl ether). With examples from his laboratory, Tim Liebert (University of Jena, Germany) showed how ionic liquids are opening the possibilities for cellulose chemistry under homogeneous conditions. [C4mim]Cl was a good solvent for esterifications with acyl chlorides, while 1-ethyl-3-methylimidazolium ethanoate was suitable for all acetylations, regardless of the acetylating reagent. Sulfation, silylation, and etherification were also successful in these ionic liquids, sometimes with improved performance by addition of a molecular organic co-solvent. The products thus obtained have potential for the generation of biomaterials, such as the capsules formed from sulfated cellulose and polycations, which can host active glucose oxidase.

Ionic Liquids as Solvents for Chemistry

Using design principles developed for neutral alkene ligands in palladium-based catalysis, John Slattery (University of York, UK) prepared several cationic ?-acidic alkene-doped ionic liquids (Figure 4A), which were found to be excellent reaction media for the palladium-catalysed Hiyama coupling reactions (Figure 4B).

Figure 4. (A) Novel alkene-containing ionic liquids used to catalyse (B) the Hiyami coupling reaction.

The alkene-ligand effects in these ionic liquids were similar to neutral-alkene systems, but the very different solubilities of alkene-doped ionic liquids to the cross-coupling products enabled clean and efficient product extraction using solvent washes, with minimal alkene ligand or Pd leaching. Reaction rates depended on the choice of substitution on the alkene ligands and correlated to the size of palladium nanoparticles.

Materials Applications

Ionic liquids were also being applied to novel materials chemistry, particularly with nanomaterials. Yong Soo Kang (Hanyang University, Republic of Korea) used ionic liquids to chemically activate silver and copper nanoparticles in facilitated transport membranes, resulting in robust olefin carriers for the separation of olefin/paraffin mixtures. Masayoshi Watanabe (Yokohama National University, Japan) presented on self-assembled, polymer-grafted, colloidal silica nanoparticles in ionic liquids. At sufficiently high concentration in a dispersion medium, colloidal crystalline arrays of mono-disperse particles reveal structural (diffraction-based) colour, which can be potentially applied in sensors, displays, optical switches, and photonic crystals. The quasi-ordered colloidal array formed in ionic liquids showed high ionic conductivity and very unique optical and viscoelastic features. Catherine Santini (Université de Lyon, France) showed how metallic nanoparticles (MNPs) of well-controlled size can be synthesised in dialkylimidazolium ionic liquids, due to strong solvent hydrogen bonding and self organisation. A direct relationship between the imidazolium chain length and nanoparticles size suggested that crystal growth is likely controlled by the local concentration of the organometallic, which is limited by the size of non-polar solvent domains. Alan Bond (Monash University, Australia) found [C4mim][BF4] to be a good medium for synthesising exceptionally long semiconducting nanowires made of silver tetracyanoquinodimethane (Ag[TCNQ]). The synthesis proceeds via a photo-catalysed redox couple, for which it was accidentally found that trace water in [C4mim][BF4] could act the sacrificial electron donor, photo-oxidising to hydrogen and oxygen. The implication that an ionic liquid environment may facilitate the photo-oxidation of water could lead to advances in the area of water splitting for cheap hydrogen fuel.

Maria Forsyth (Monash University, Australia) used tetraalkylphosphonium bis(trifluoromethylsulfonyl)amide or organophosphate ionic liquids in corrosion-resistant films for magnesium alloy surfaces. The anion dominated the chemical interaction with the surface, but cation size was also important in film formation. James Wishart (Brookhaven National Laboratory, USA) discussed ionic liquids as potential media for processing spent nuclear fuel. Since current technology uses only 3% of uranium energy, nuclear fuel reprocessing is an urgent field of research. Ionic liquids could be useful for chemical speciation, redox chemistry, selective extractions, solvation and plating out by electrodeposition. Wishart explores what happens when ionic liquids are irradiated and have found that solvation times for electrons in ionic liquids are much (e.g. fifty times!) slower than in molecular solvents. His group also looks at how ionic liquids differ from molecular solvents for charge transfer processes.

Electrochemistry

Frank Endres (Technische Universität Clausthal, Germany) discussed the attraction ionic liquids hold for various electrochemical purposes (electrodeposition, fabrication of functional nanostructures, such as nanodots, nanoparticles, nanowires, and photonic crystals), due to negligible vapour pressures, acceptable viscosities, and electrochemical windows which are wide enough (±3 V vs. NHE), in principle, to allow the electrodeposition of all metals. Of course, not all ionic liquids are excellent solvents for electrochemistry, and chemical aspects of the metal salts must be considered. Endres showed that variation of the ionic liquid anion or cation could achieve different deposit morphologies or reduction pathways. As an example, novel electrodeposited germanium photonic crystals showed potential to improve the efficiency of silicon based solar cells.

David Mecerreyes (Centre for Electrochemical Technologies, Spain) overviewed how polymeric electrolytes can be applied to a plethora of electrochemical technologies and nanomaterials. Imidazolium- or pyrrolidinium-containing monomers can be polymerised or co-polymerised with other monomers to generate versatile polyelectrolyte materials. Dye-sensitised solar cells, electrochromic devices, batteries, field effect transistors, light-emitting electrochemical cells, or vehicles for nanoparticles or nanorods, were among the many applications mentioned. Finally, he described in more detail the possibilities of combining ionic liquid chemistry with poly(3,4-ethylenedioxythiophene) (PEDOT) conducting organic polymers, or hybrid PEDOT/poly(styrene sulfonate) polymers. Ionic liquids can be used for the electropolymerisation of such materials, as electrolytes in devices constructed based on them, or as conductivity enhancers. Furthermore, including imidazolium groups tethered to the PEDOT chains, functional materials can be obtained, as for example, conducting films with switchable wettability. David Officer (University of Wollongong, Australia) talked about the utilisation of ionic liquids for porphyrin and ruthenium dye-sensitised solar cells. Ionic liquids have proven to be effective in both applications, despite their major limitation of relatively high viscosity. However, this limitation was overcome for porphyrin dye-sensitised solar cells. Using ionic liquid electrolytes for the synthesis of organic conducting polymers (OCPs) and the operation of electrochemical devices based on OCPs has been the main topic and interest of Gordon Wallace's (University of Wollongong, Australia) group. In his presentation, he reported unusual fractal forms of conducting polymers that have been produced from the selected compositions of ionic liquid electrolytes. Using ionic liquid electrolytes during electro-polymerisation has also enabled co-solubilisation of monomers and other active components such as dyes, which was not possible with simple solvents. Hence, both the physical nature and the composition of conducting polymers can be manipulated by use of ionic liquid electrolytes. Furthermore, he showed that using ionic liquids as electrolytes in electrochemical devices reduces the problems of electro-degradation which are common to conducting polymers synthesised from conventional electrolytes. In the field of dye-sensitized solar cells (DSSCs), Yang Soo Kang (Hanyang University, Republic of Korea) showed that ionic liquids can be used as electrolyte solvents, replacing solutions of M+, I- and I3- in volatile organic solvents.

Corinne Lagrost (University of de Rennes, France) used non-haloaluminate room-temperature ionic liquids, which are inherently ion-conducting and generally electrochemically robust, to highlight their unique effects on the transport properties of solutes, the kinetics of electron transfer, and associated chemical reactions, relative to these processes in conventional organic media. 

From the field of batteries, Michel Armand (University of Picardie Jules Verne, France) described the preparation of the most popular positive electrode, based on oxyanions, lithium transition metal phosphates LiMPO4 and silicates Li2MSiO4 (where M = Fe, Mn, Co, etc). All the compounds studied showed high electrochemical activity. Shiro Seki (CRIEPI, Japan) showed that lithium secondary batteries and organic field-effect transistors, using room temperature ionic liquids as electrolytes, were safer and performed better than electrochemical devices which used conventional commercial electrolytes. Adam Best (CSIRO, Australia) presented efforts to prepare structurally flexible, high energy density batteries. Flexible batteries are generally polymer-based and suffer limitations such as low energy density and lack of robustness. Best's group used [C1C4pyrr][NTf2] as a solvent medium to codeposit polypyrrole (a high density, high-capacitance polymer) with PEDOT (a highly conductive, low capacitance polymer) to create copolymer with improved properties. They also used a distillable ionic liquid, [H2NMe2][O2CNMe2], to dissolve and deposit silver into polypyrrole, as well as to deposit lithium metal electrodes onto fabric substrates.

Separations

Jared Anderson (The University of Toledo, USA) discussed the utilisation of ionic liquids in various novel microextraction techniques. In one example, robust absorbent coatings were prepared with polymeric ionic liquids for solid-phase microextraction, e.g. the extraction of esters and fatty acid methyl esters in red and white wines. In another example, hydrophobic ionic liquids were used, via liquid microextraction, to detect organic pollutants (e.g. polyaromatic hydrocarbons) at extremely low (ppb) concentrations in sediment. The partitioning behaviour of various analytes to monocationic and dicationic imidazolium-based micellar aggregates was presented. 

Joan Brennecke (University of Notre Dame, USA) explained the key properties required for CO2 capture in ionic liquids, presented gas solubility studies, and discussed the engineering aspects of gas separations with ionic liquids having amine-functionalised cations or anions. She showed that these ionic liquids performed better than traditional aqueous amines (monoethanolamine, monodiethanolamine, etc.) and that CO2 solubility in the ionic liquids is higher than that in molecular solvents. FTIR spectroscopic studies revealed a 1:1 complexation between a molecule of CO2 and a single amine functionality on an ionic liquid anion. Brennecke examined the effect of water content of the ionic liquids' capacity to remove CO2, as well as their selectivity toward CO2 in the presence of N2 and O2, which are typically found in post-combustion flue gas. Richard Noble (University of Colorado at Boulder, USA) reported on CO2 separation using a 1:1 mol mixture of monodiethanolamine and [Cnmim][NTf2]. Noble also demonstrated a supported ionic liquid membrane, prepared with [C6mim][NTf2] and 12-hydroxystearic acid (98.5:1.5 wt %), which outperformed many polymer membranes in separating CO2 from N2.

Computational / Physical Chemistry

The development of new and better applications of ionic liquids requires an increasingly informed understanding of their fundamental properties. Hence, computational models and experimental data on physico-chemical properties were major topics in presentations and posters. 

Christopher Hardacre (QUILL, UK) summarised the use of neutron scattering techniques combined with molecular dynamics simulations for liquid structure determination in ionic liquids. It has been shown that pyridinium ionic liquids with an electron-withdrawing nitrile group in the cation (e.g: [1-alkyl-3-cyanopyridinium][NTf2]) lead to the formation of a highly coloured charge transfer (CT) complexes with electron rich donor (e.g. naphthalene), compared with the analogous alkylpyridinium systems. The structural information obtained in the liquid phase by these techniques can be used to design new ionic liquids for gas solubility. Rob Atkin (University of Newcastle, Australia) spoke on bulk and interfacial nanostructure in simple protic ionic liquids (e.g. ethylammonium nitrate). These were shown to possess both bulk and interfacial nanostructure, which are due to electrostatic and solvophobic interactions and are comparable to surfactant self-assembly. Small angle neutron scattering experimental data of the bulk ionic liquid showed a repeating length scale, indicating some structure therein; whereas, atomic force microscopy indicated a lamellar arrangement of the ionic liquid at the interface. Atkin also discussed the effect of temperature variation and changing the interactions between the cation and anion. Atkin's results help to inform the design of ionic liquids for interface-dependent applications, such as heterogeneous catalysis, electrodeposition, lubrication and dye-sensitised solar cells. Yansen Lauw (CSIRO, Australia) likewise discussed the structure of ionic liquids at charged interfaces in order to better rationalise the transport processes in electrochemical systems. Self-consistent mean field theory (SCMFT) indicated that electrical double layer capacities commonly found in aqueous electrolytes resembled the self-ordering in alternating layers found with ionic liquids, suggesting that SCMFT can be used as a fast and efficient method of predicting complex ionic liquids structures at charged interfaces. Using atomistic molecular dynamics simulations, Grant Smith (University of Utah, USA) presented studies on ionic liquids doped with lithium salts (promising materials as electrolytes in lithium-ion batteries), both in the bulk and at an interface with LiFePO4 (an important cathode material for lithium-ion batteries). The studies give insight into the mechanisms of lithium transport and how it differs in IL-based electrolytes compared to conventional organic electrolytes. Furthermore, the compiled simulations of numerous bulk ionic liquids have improved the understanding of transport mechanisms in ionic liquids and shown a correlation between transport and thermophysical properties. 

In a tandem oral presentation, Bernard Gilbert (University of Liège, Belgium) and Hélène Olivier-Bourbigou (IFP Lyon, France) talked about acidity in ionic liquids and its implications in catalytic petrochemical reactions. The difficulty in measuring Hammett acidities in ionic liquids was assessed, given the interaction between the indicator and the ionic liquid medium, and an alternative method was suggested: the measurement of the redox potential of the H+/H2 couple. In addition, the acidity levels measured by potentiometry were higher than the ones measured by the Hammett method, though the order of acidity of anions remained unaltered. From these results, the acid-catalysed dimerisation of isobutene in dialkylimidazolium ionic liquids was studied, and it was shown that the appropriate acidity of the system is crucial to achieve a good compromise for selectivity and conversion. This was accomplished by a careful selection of both the anion and the corresponding acid, the optimum ones being [CF3SO3]- and CH3SO3H, respectively. A further improvement to this approach was the incorporation of the acidic functionality covalently bonded to the ionic liquid cation. Lorna Crowhurst (Imperial College London, UK) presented the effect of various ionic liquids on Brønsted acidity and showed a new approach to measuring proton activity in ionic liquids. An acidity scale was established using 13C NMR spectra of mesityl oxide in ionic liquids. The differences in effective Brønsted acidity of ionic liquids depended mainly on the anion and to a much smaller extent on the cation.

José Nuno Canongia Lopes (University of Nova de Lisboa, Centro de Quimica Estrutural, Portugal) talked on ionic liquid phase diagrams from a molecular perspective. He stressed how the discovery of ionic liquids that can be distilled at low pressure and high temperature changed the belief that ionic liquids never occurred in the gas phase. Characterisation studies of ionic liquids in the gas phase gave the evidences to strengthen the idea of ionic liquids as nano-segregated fluids. Lopes explained complex liquid-liquid and solid-liquid phase behaviours of ionic liquid mixtures by using their phase diagrams. The examples given were the systems of [C2mim]+ mixed with aromatic molecules (solvent) which sometimes showed the existence of extremely stable congruent-melting inclusion crystals. This behaviour can be explained from selective cation- and anion- interactions with aromatic compounds. Seki (CRIEPI, Japan) discussed influence of cation and anion on physical properties of ionic liquids, in particular viscosity and density, and correlation between summary molecular volume and free volume of RTILs. 

Gregory Voth (University of Utah, USA) explored an array of ionic liquid physical properties through a systematic computational approach in order to describe the relationship of molecular structures and interactions with the measured liquid state properties such as interfacial structure, self diffusion, and viscosity. In his work, molecular-level simulation was used to investigate ionic liquid structural and dynamical correlations, which are then linked to systematic coarse-grained model at the mesoscale. From this study, it was found that ionic liquids exhibit high anisotropic liquid-state structure as well as significant spatial and dynamic heterogeneities. Furthermore, the electronic polarisation in these ionic liquids described the molecular-level simulation suggest a significant effect and importance in the dynamical (diffusion, viscosity) and interfacial (structural, surface tension) properties of the ionic liquid. 

Hiro-o Hamaguchi (University of Tokyo, Japan) presented several examples of how macroscopically homogenous ionic liquids were found to be heterogeneous at the nanoscale. Irradiation studies of trans-stilbene in [C4mim][PF6] showed that viscosity (macroscopic property) did not represent the microscopic solvation environment (related to the photoisomerisation rate). Secondly, UV-Vis and Raman spectroscopic studies of elemental iodine in various organic solvents and in [C4mim][NTf2] showed that the ionic liquid has three solvation sites for I2, corresponding to different polarity regions. Finally, it was concluded that the nanostructure of ionic liquids may closely resemble their crystal structures. 

The compositional variability of ionic liquids makes predictive software essential for selecting and designing ions to give the desired physical properties to fit processes. David Rooney (QUILL, UK) is developing microfluidic devices to measure key physical properties (viscosity, density, heat capacity) of ionic liquids, measurements which can then feed into predictive models, using CosmoThermX, Unifac, Aspen, etc. These devices are being further developed to determine water content, chloride content, thermal conductivity, etc. Ekaterina Izgorodina (Monash University, Australia) compared the performances of various ab initio and DFT-based methods in simulating short-range (van der Waals and hydrogen bonding) and long-range (Coulombic) interactions in ionic liquids. 

Due to their unique physical, chemical and biological properties the application of ionic liquids covers some 3,387 topics, according to Robin Rogers' (QUILL, UK) estimation. He ended the conference proceedings by challenging the audience to come up with a true definition of an ionic liquid. For example, in the field of pharmaceutical co-crystals, the so-called protic ionic liquids could exist as a complex that is simply hydrogen bonding between an acid and base, as a salt, or somewhere in between.

Poster Sessions

Two large and excellent poster sessions, for which five poster awards were presented (see Figure 5), contributed significantly to the success of the conference-with just over 350 posters, broken down into the categories "Bio/Green Applications in Ionic Liquids," "Electrochemistry/Device Applications of Ionic Liquids," "Materials Chemistry Applications of Ionic Liquids," "Physical Chemistry of Ionic Liquids," "Synthesis of and in Ionic Liquids," and "Theoretical Approaches to Ionic Liquids and their Properties" (see Figure 6). A surprising number of posters dealt with ionic liquids for biological or pharmaceutical applications, such as pharmaceutically active ionic liquids (from the groups of Robin Rogers and Doug MacFarlane) or protein stabilisation and crystallisation in protic ionic liquids (CSIRO, Australia). The Green Chemistry Award for Best Poster in Green and Bio Applications of Ionic Liquids went to Tim Stahlberg (Technical University of Denmark) for a contribution about the direct metal-catalysed dehydration of glucose in ionic liquids. 

Figure 5. The winners of the poster prizes (L to R): Wei Zhou, Takashi Iwahashi, Takashi Iwahashi, Tim Stahlberg, Alexander Wulf

The electrochemical section was dominated by solar cell and lithium battery applications. One of the highlights was an approach towards "greener" batteries, using fluorine-free battery electrodes in combination with ionic-liquid-based electrolytes, a poster by the Balducci group. Wei Zhou (Nagoya University, Japan) received the Endres / Abbott / MacFarlane Award for the Best Poster in Electrochemistry of Ionic Liquids, to honour his fundamental study on the potential-dependent ionic liquid anion- and cation- adsorption onto the surface of platinum electrodes, using in situ sum frequency generation (SFG) spectroscopy. 

Figure 6. Statistical breakdown of COIL-3 poster submissions

The many emerging applications of ionic liquids, presented throughout the conference, were appropriately complemented with a majority of conference posters (more than one third) reporting on their physical chemistry - ranging from thermophysical properties, spectroscopic studies and optical properties to their carbon dioxide capture and absorption behaviour. The Australian Journal of Chemistry Award for Best Poster in Physical Chemistry of Ionic Liquids was given to Alexander Wulf (University of Rostock, Germany) for a study on the hydrogen bonding in protic ionic liquids revealing three-dimensional hydrogen bonding networks which resemble those of water. The Topics in Current Chemistry Award for Best Poster in Theory and Spectroscopy of Ionic Liquids was awarded to Takashi Iwahashi (Nagoya University, Japan) on for his contribution on infrared-visible sum frequency generation spectroscopy on the interfaces of molecular liquids and ionic liquids. 

It was noticeable that there were hardly any posters on organic synthesis in ionic liquids. Rather, inorganic and materials chemists seemed to have discovered the benefits of ionic liquids, e.g. for nanomaterials synthesis, for interesting new polymer composite materials, or as metal-containing ionic liquids. The Chemical Communications Award for the best poster on Synthesis of and in Ionic Liquids was given to Kai Richter (Ruhr-Universität Bochum, Germany) for his contribution on the nanoparticle synthesis in ionic liquids via physical vapour deposition and microwave. 

Figure 7. The passing of the COIL sodium chloride crystal

The meeting closed with the ceremonial passing of the Salzburg sodium chloride crystal (Figure 7) from Doug MacFarlane to Robin Rogers, who will be hosting COIL-4 in Washington, D.C., in 2011. COIL 5 will be held in Oeiras, Portugal, in 2013, and it was announced for the first time that COIL-6 will be held in South Korea in 2015, continuing the international nature of the meeting. It has been interesting to see how the focus of the presented materials has shifted with conference location, from synthesis in Europe, to polymers in Japan, to electrochemistry in Australia, reflecting the breadth of the field. 

With thanks to the following members of QUILL,  The Queen's University of Belfast, for providing this article: Mahpuzah Abai, Norfaizah Ab Manan, Gabriela Adamová, Leigh Aldous, Kris Anderson, Tayeb Belhocine, Martyn J. Earle, Julien Estager, Jamie L. Ferguson*, Ramesh L. Gardas, Gertie Ge, Peter Goodrich, H. Q. Nimal Gunaratne, John D. Holbrey, Peter McGuicken, Andreas Metlen, Shieling Ng, Audrey-Flore Ngomsik, Peter Nockemann, Sarah Norman, Natalia V. Plechkova*, Alberto V. Puga, Héctor Rodríguez, Kenneth R. Seddon, Azlan Shah Hussain, Malgorzata Swadzba-Kwasny, Mohd. Faisal Taha, Alina A. Tomaszowska, David Wassell, and Yiran Zou.