Patricia C. Marr

Ionic liquid gel materials: applications in green and sustainable chemistry

Ionic liquid gel materials offer a way to further utilise ionic liquids in technological applications. Combining the controlled and directed assembly of gels, with the diverse applications of ionic liquids, enables the design of a heady combination of functional tailored materials, leading to the development of task specific/functional ionic liquid gels. This review introduces gels and gel classification, focusing on ionic liquid gels and their potential roles in a more sustainable future. Ionic liquid gels provide the ability to build functionality at every level, the solid component, the ionic liquid, and any incorporated active functional agents. This allows materials to be custom designed for a vast assortment of applications. This diverse class of materials has the potential to yield functional materials for green and sustainable chemistry, energy, electronics, medicine, food, cosmetics, and more. The discussion of the development of ionic liquid gel materials for applications in green and sustainable chemistry centres on uses of ionic liquid gels in catalysis and energy.

Clean preparation of nanoparticulate metals in porous supports: a supercritical route

Here we present the synthesis of nanometre sized silver particles which have been trapped within porous substrates; poly(styrene-divinylbenzene) beads and silica aerogels. This is the first time that supercritical carbon dioxide has been used to impregnate such porous materials with silver coordination complexes. In this paper we demonstrate that control over the resultant nanoparticles with respect to size, loading and distribution in the support material has been achieved by simple choice of the precursor complex. The solubility of the precursor complexes in the supercritical solvent is shown to be one of the key parameters in determining the size of the nanoparticles, their distribution and their homogeneity within the support matrix. Moreover, we demonstrate that the same methodology can be applied to two very different substrate materials. In the particular case of aerogels, conventional organic solvents could not be used to prepare nanoparticles because the surface tension of the solvent would lead to fracturing of the aerogel structure.Controlled decomposition of the coordination complexes in situ leads to metallic silver nanoparticles with a narrow size distribution, typically 10–100 nm that are homogeneously dispersed throughout the porous substrate. The whole process is carried out at near ambient temperature and no solvent residues are introduced into the porous media. The silver precursors are specifically designed to be both CO2 soluble and sufficiently labile to ensure facile decomposition to the metal. In-depth characterisation by X-ray diffraction and transmission electron microscopy has been applied to illustrate the homogeneous dispersion of particles throughout the composite material, determine the range and variation in particle size within the solid matrices and fully identify the resultant particles as metallic silver. This enables visualisation of dispersion and concentration, and control over particle size of the fabricated nanocomposite materials.

Supercritical fluids: A route to palladium-aerogel nanocomposites

Supercritical carbon dioxide (scCO2) is used to prepare novel silica aerogel composites containing nano-particles of palladium. The material produced has been found to exhibit a Pd loading of 8% by wt. The particles deposited fit within two discrete size ranges of <6 nm and 15–20 nm as analysed by XRD and TEM. We demonstrate that scCO2 may be successfully applied to prepare catalytic support materials based upon aerogels and that the catalyst is active in a continuous flow reactor leading to effective hydrogenation of cyclohexene.

The Co‐Entrapment of a Homogeneous Catalyst and an Ionic Liquid by a Sol–gel Method: Recyclable Ionogel Hydrogenation Catalysts

Molecular hydrogenation catalysts have been co-entrapped with the ionic liquid [Bmim]NTf(2) inside a silica matrix by a sol-gel method. These catalytic ionogels have been compared to simple catalyst-doped glasses, the parent homogeneous catalysts, commercial heterogeneous catalysts, and Rh-doped mesoporous silica. The most active ionogel has been characterised by transmission electron microscopy, X-ray photoelectron spectroscopy, and solid state NMR before and after catalysis. The ionogel catalysts were found to be remarkably active, recyclable and resistant to chemical change.

Dissociative electron attachment to HCCCN

Dissociative electron attachment to cyanoacetylene (propiolonitrile) HCCCN has been observed in the electron energy range 0-12 eV. Negative ions are formed in two main bands with maxima at ∼1.6 eV (CCCN − ) and ∼5. 3e V (CCCN − ,C N − , HCC − and CC − ). There are also weaker resonances which lead to dissociative electron attachment to form CN − , HCC − and CC − with a maximum intensity at ∼8.1 eV and CCCN − , CN − and CC − at ∼11. 2e V. A trace of CCN − is observed at ∼9. 1e V. The positions of the main dissociative attachment bands observed are close to positions of π ∗ resonances recently calculated by Sommerfeld and Knecht. Calculations have also been performed in this work, which confirm the position of the π ∗ orbitals. The electron affinity of the CCCN radical is determined as 4.59 ± 0.25 eV from the threshold for CCCN − formation at 1.32 ± 0.15 eV. Dissociative electron attachment to this molecule will act as a source of negative ions in extraterrestrial environments where electrons are present with more than 1.3 eV energy.

Dissolving biomolecules and modifying biomedical implants with supercritical carbon dioxide

We describe two methodologies for dissolving ionic/polar species in scCO2. Both lead to a broadening of the range of applications for scCO2. Fluorinated surfactants may be used to prepare water in carbon dioxide microemulsions to allow solubilization of ionic and biological species. We outline also the preparation of scCO2 soluble metal precursors that can be impregnated efficiently into polymeric substrates. Further processing by heat or UV light leads to metallic particles distributed throughout a polymer substrate. The clean synthesis of such composites can be applied to the development of improved medical implants.

Minimizing side reactions in chemoenzymatic dynamic kinetic resolution: organometallic and material strategies

Chemoenzymatic dynamic kinetic resolution (DKR) of rac-1-phenyl ethanol into R-1-phenylethanol acetate was investigated with emphasis on the minimization of side reactions. The organometallic hydrogen transfer (racemization) catalyst was varied, and this was observed to alter the rate and extent of oxidation of the alcohol to form ketone side products. The performance of highly active catalyst [(pentamethylcyclopentadienyl)IrCl(2)(1-benzyl,3-methyl-imidazol-2-ylidene)] was found to depend on the batch of lipase B used. The interaction between the bio- and chemo-catalysts was reduced by employing physical entrapment of the enzyme in silica using a sol-gel process. The nature of the gelation method was found to be important, with an alkaline method preferred, as an acidic method was found to initiate a further side reaction, the acid catalyzed dehydration of the secondary alcohol. The acidic gel was found to be a heterogeneous solid acid.

A low molecular weight hydro and organogelator derived from an isohexide and sol-gel transcription of the alcogel

Heating 2,5-di-O-methanesulfonyl-1,4:3,6-dianhydro-D-sorbitol (1) in a range of solvents led to the formation of a gel state at low concentrations. 1 was found to gel aromatics, alcohols and water. The structure of 1 in the solid state was solved by single crystal X-ray crystallography; no strong hydrogen bonds or associated solvents were found in the crystal. Electron micrographs revealed the morphology of the gels to be predominantly rod-like. The ethanol alcogel was used to template silica by sol–gel transcription.

Low molecular weight gelators (LMWGs) for ionic liquids: the role of hydrogen bonding and sterics in the formation of stable low molecular weight ionic liquid gels

Low molecular weight gelators capable of forming a gel with an ionic liquid are rare. We report the ability of 3 sugar based gelators from renewable resources (derived from isosorbide and mannitol) to form gels with 21 ionic liquids comprising a range of cations and anions that are commonly applied in a variety of technologies. It was found that the combined consideration of Kamlet–Taft values with ionic liquid size and shape gives a useful predictor of successful gel formation.