Qingde Chen

Interaction between Ionic Liquids and β-Cyclodextrin: A Discussion of Association Pattern

We report herein the interaction of three ionic liquids, i.e., 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (11), 1-hexyl-2,3-dimethylimidazolium chloride (16), and 1-dodecyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (17), with beta-cyclodextrin (beta-CD). For 11 and 16, the 1:1 inclusion complexes were determined and the association constants were estimated through a competitive fluorescence method, conductivity, and (19)F NMR measurements. It was confirmed that the alkyl side chain on the imidazolium ring but not the imidazolium ring itself entered into the cavity of beta-CD. According to the association constants, the sequence of interaction strength of some ILs with beta-CD was obtained. We also found that the cation and the anion in 17 exhibited strong interactions with beta-CD simultaneously. Furthermore, a general interaction pattern of an IL with beta-CD was suggested.

Solvent extraction of thorium(IV) using W/O microemulsion

The extraction of thorium(IV) was investigated using two types of W/O microemulsion, one of which was formed by a surface-active saponified extractant sodium bis(2-ethylhexyl) phosphate (NaDEHP) and the other was formed by a mixture of an anionic surfactant sodium bis(2-ethylhexyl) sulfosuccinate (AOT) and an extractant bis(2-ethylhexyl)phosphoric acid (HDEHP) as the cosurfactant. The extraction capacities of the above two systems were higher than that of the HDEHP extraction system. High concentration of NaNO3 showed no influence on the extraction in the NaDEHP based W/O microemulsion system, whilst reduced the extractability in the AOT-HDEHP W/O microemulsion system. The mechanism in acidic condition was demonstrated by the log-log plot method. The structure of the aggregations and the water content in the organic phase after extraction were measured by dynamic light scattering and Karl Fischer water titration, respectively. It was found that NaDEHP based W/O microemulsion broke up after extraction, while AOT-HDEHP W/O microemulsion was reserved.

Separation Processes in the Presence of Cyclodextrins Using Molecular Imprinting Technology and Ionic Liquid Cooperating Approach

Recently, separation science in the presence of cyclodextrins (CDs) has been paid more and more attention. Two important technologies based on CDs, molecularly imprinted polymers (MIPs) and ionic liquid (IL) cooperating approach, have been studied exten- sively and not been reviewed. MIPs are significant and important in separation processes. MIPs based on cyclodextrins (CD-MIPs) take advantage of unique properties of cyclodextrins and are applied in the separation of various molecules. Different methods for preparation CD-MIPs and supramolecular interactions in the systems are reviewed. Furthermore, ILs have been also widely used in separation sci- ence. Cooperative effect of CDs and ILs together for separation usage is discussed in this paper. The related separation techniques are mainly capillary electrophoresis (CE) and gas chromatography (GC). CD-MIPs and cooperative effect of ILs in separation methods, which are two important aspects in cyclodextrins separation science, are summarized here. It is hoped that the discussion on the above two topics will stimulate further research.

Improvement of the cloud point extraction of uranyl ions by the addition of ionic liquids

The cloud point extraction (CPE) of uranyl ions by different kinds of extractants in Triton X-114 (TX-114) micellar solution was investigated upon the addition of ionic liquids (ILs) with various anions, i.e., bromide (Br(-)), tetrafluoroborate (BF4(-)), hexafluorophosphate (PF6(-)) and bis[(trifluoromethyl)sulfonyl]imide (NTf2(-)). A significant increase of the extraction efficiency was found on the addition of NTf2(-) based ILs when using neutral extractant tri-octylphosphine oxide (TOPO), and the extraction efficiency kept high at both nearly neutral and high acidity. However, the CPE with acidic extractants, e.g., bis(2-ethylhexyl) phosphoric acid (HDEHP) and 8-hydroxyquinoline (8-HQ) which are only effective at nearly neutral condition, was not improved by ILs. The results of zeta potential and (19)F NMR measurements indicated that the anion NTf2(-) penetrated into the TX-114 micelles and was enriched in the surfactant-rich phase during the CPE process. Meanwhile, NTf2(-) may act as a counterion in the CPE of UO2(2+) by TOPO. Furthermore, the addition of IL increased the separation factor of UO2(2+) and La(3+), which implied that in the micelle TOPO, NTf2(-) and NO3(-) established a soft template for UO2(2+). Therefore, the combination of CPE and IL provided a supramolecular recognition to concentrate UO2(2+) efficiently and selectively.

Stripping of uranium from an ionic liquid medium by TOPO-modified supercritical carbon dioxide

UO22+, which is extracted from the aqueous phase into the 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (C2mimNTf2) ionic liquid phase with octyl(phenyl)-N,N-diisobutylcarbamoylmethylphosphine oxide (CMPO), can be stripped by supercritical CO2. Trioctylphosphine oxide (TOPO), the modifier added to the supercritical CO2 phase, enhances the stripping efficiency by up to 99%.

A further understanding of the cation exchange mechanism for the extraction of Sr 2+ and Cs + by ionic liquid

The cation exchange mechanism was further investigated during the extraction of Sr2+ and Cs+ using the extractant dicyclohexano-18-crown-6 (DCH18C6) in an ionic liquid (IL) 1-ethyl-3-methyimidazolium bis[(trifluoromethyl)sulfonyl]imide (C2mimNTf2). The concentrations of both the cation C2mim+ and the anion NTf2− in aqueous phase were detected. The concentration of NTf2− in the aqueous phase decreased as Sr2+ or Cs+ exchanged into the IL phase. Addition of C2mim+ or NTf2− as well as the variation of the solubility of C2mimNTf2 influenced the extraction efficiency of Sr2+ or Cs+.

Supramolecular Structures in the Presence of Ionic Liquids

Supramolecular chemistry is defined as “chemistry beyond the molecule”, bearing on the organized entities of higher complexity that result from the association of two or more chemical species held together by intermolecular forces (Lehn, 1988, 1995). Supramolecular chemistry may be divided into two broad and partially overlapping areas concerning: (1) supermolecules, well-defined and discrete oligomolecular species that result from the intermolecular association of a few components (a receptor and its substrate(s)) following a built-in scheme based on the principles of molecular recognition; (2) supramolecular assemblies, polymolecular entities that result from the spontaneous association of a large undefined number of components into a specific phase having more or less well-defined microscopic organization and macroscopic characteristics depending on its nature (such as micelles, microemulsions, vesicles, films, layers, membranes, mesomorphic phase and so on) (Lehn, 1995). Investigation on supramolecular systems is receiving more and more attention (Beletskaya et al., 2009; Constable, 2008; Descalzo et al., 2006; He et al., 2008b; Metrangolo et al., 2008; Oshovsky et al., 2007). Different from simple inorganic salts (such as NaCl) who often melt at very high temperature, ionic liquids (ILs) are a kind of organic salts that are liquid at or near room temperature, always taking 100 oC as an upper limit. Figure 1 shows the structures of some typical cations and anions of ILs. The imidazolium, especially 1-alkyl-3-methylimidazolium (Cnmim+), is one of the most popular cations. So far, ILs have attracted much attention and been widely used as an attractive class of green solvents in the filelds of chemical reactions, organic and material syntheses, solvent extraction, and electrochemistry because of their negligible vapor pressure, nonflammability, high thermal and chemical stability, high polarity, wide electrochemical window and tunable physicochemical properties (Chiappe & Pieraccini, 2005; Dupont, 2004; Leclercq & Schmitzer, 2009a; Weingartner, 2008; Welton, 1999; Zhao et al., 2002). In the field of supramolecular chemistry, ILs could either participate directly in the assembly of supramolecular organizations, or influence the assembly of various supramolecular structures in a certain way, leading to the appearance of many novel and interesting phenomena. In addition, there exist three-dimensional supramolecular networks with polar and non-polar regions in imidazolium ILs, which can be used as powerful supramolecular receptors (Dupont, 2004; Leclercq & Schmitzer, 2009a). Therefore, this review will summarize the work in the literature, concerning the above novel and

Synthesis and characterization of a new ion-imprinted polymer for the selective separation of thorium(IV) ions at high acidity

A new ion-imprinted polymer (IIP) was synthesized by thermal copolymerization of bis(2-methacryloxyethyl) phosphate as functional ligand and ethylene glycol dimethacrylate as cross-linker in the presence of Th4+ as a template ion. The molar ratio of the functional ligand to Th4+ was optimized to be 4 by 31P NMR titration, elemental analysis, and EXAFS, which was verified by comparing the adsorption capacities and selectivities of IIPs with different composition. Thorium(IV) ions were leached out using 0.1 mol L−1 ethylenediaminetetraacetic acid disodium salt and the prepared IIP was characterized by infra-red spectroscopy, thermogravimetric analysis and Brunauer–Emmett–Teller surface area measurement. It was found that the IIP could extract Th4+ from high acidity solution. The maximum adsorption capacity was as high as 33.3 mg g−1 in 1.0 mol L−1 HCl. Even in 6.0 mol L−1 HCl, its adsorption capacity was still considerable. Moreover, the IIP exhibited good selectivity towards Th4+, especially in the presence of competing ions such as La3+, Eu3+, Yb3+, UO22+, and Fe3+.

Characterization of reversed micelles formed in solvent extraction of thorium(IV) by bis(2-ethylhexyl) phosphoric acid. Transforming from rodlike to wormlike morphology

Abstract The reversed micelles formed in solvent extraction of thorium(IV) by bis(2-ethylhexyl) phosphoric acid (HDEHP) in n-heptane were studied. IR spectra, dynamic/static light scattering and zero shear viscosity measurements indicated that thorium complexes formed rodlike reversed micelles, and both the size of aggregates and the viscosity of the organic phase increased with the increasing loadage of thorium(IV). The entanglement of reversed micelles resulted in their transformation to wormlike reversed micelles, inducing the very high viscosity of the organic phase. The structural composition of thorium complexes was proposed to be Th(DEHP)3(NO3) according to the results of log -log  plot and job method analysis. Furthermore, molecular modeling was employed to clarify the structures of reversed micelles as well as the state of water inside. It was found that the complexes linked together via hydrogen bonding and van der Waals forces and that the existence of NO3– and H2O improved the stability of reversed micelles.