2D nanoporous Ni(OH)2 film as an electrode material for high-performance energy storage devices.

A two-dimensional (2D) nanoporous Ni(OH)2 film was successfully developed from triethanolamine (TEA) as the alkali source and soft template using a scalable hydrothermal technique. The nanostructured Ni(OH)2 film was flexible and translucent, and could be directly compressed on a current collector. Owing to the uniform well-defined morphology and stable structure, the Ni(OH)2 film binder-free electrode displayed a high specific capacity, exceptional rate capability, and admirable cycle life. The specific capacitance was 453.6 mA h g-1 (1633 F g-1) at 0.5 A g-1. The assembled Ni(OH)2//activated carbon (AC) asymmetric supercapacitor (ASC) device had an energy density of 58.7 W h kg-1 at a power density of 400 W kg-1. These prominent electrochemical properties of Ni(OH)2 were attributed to the high electrical conductivity, high surface area, and unique porous architecture. Free tailoring, binder-free, and direct pressing were the most significant achievements of the Ni(OH)2 film in the development of high-performance energy storage devices.

Nanoreactors stable up to 200 °C: a class of high temperature microemulsions composed solely of ionic liquids.

It is a challenge to develop microemulsions which can serve as nanoreactors for the synthesis of nanoparticles and chemical reactions at high temperature. In this work, a class of novel high temperature microemulsions consisting solely of ionic liquids have been designed and prepared for the first time. It is found that nanoscale droplets formed in the ionic liquid microemulsions can be maintained up to 200 °C, and the size distribution of the droplets can be easily tuned by selection of the ionic liquids and varying compositions of the systems. By using such microemulsions as nanoreactors, porous metals such as Pt have been prepared at 180 °C without using any purposely added reductant.

A green separation strategy for neodymium (III) from cobalt (II) and nickel (II) using an ionic liquid-based aqueous two-phase system.

It is significant to develop sustainable strategies for the selective separation of rare earth from transition metals from fundamental and practical viewpoint. In this work, an environmentally friendly solvent extraction approach has been developed to selectively separate neodymium (III) from cobalt (II) and nickel (II) by using an ionic liquid-based aqueous two phase system (IL-ATPS). For this purpose, a hydrophilic ionic liquid (IL) tetrabutylphosphonate nitrate ([P4444][NO3]) was prepared and used for the formation of an ATPS with NaNO3. Binodal curves of the ATPSs have been determined for the design of extraction process. The extraction parameters such as contact time, aqueous phase pH, content of phase-formation components of NaNO3 and the ionic liquid have been investigated systematically. It is shown that under optimal conditions, the extraction efficiency of neodymium (III) is as high as 99.7%, and neodymium (III) can be selectively separated from cobalt (II) and nickel (II) with a separation factor of 103. After extraction, neodymium (III) can be stripped from the IL-rich phase by using dilute aqueous sodium oxalate, and the ILs can be quantitatively recovered and reused in the next extraction process. Since [P4444][NO3] works as one of the components of the ATPS and the extractant for the neodymium, no organic diluent, extra etractant and fluorinated ILs are used in the separation process. Thus, the strategy described here shows potential in green separation of neodymium from cobalt and nickel by using simple IL-based aqueous two-phase system.

Visible Light-Controlled Inversion of Pickering Emulsions Stabilized by Functional Silica Microspheres.

A new class of donor-acceptor Stenhouse adduct (DASA)-functionalized silica microspheres (SMs) is designed and described to formulate Pickering emulsions with inversion property and large polarity change upon visible light irradiation. By tuning the hydrophilicity of the functional SM particles with visible light, these Pickering emulsions can easily perform inversion from water-in-oil to oil-in-water. The inversion performance of the emulsions is ascribed to DASA photoisomerization from an extended, hydrophobic, and intensely purple-colored triene to a compact, zwitterionic, and colorless cyclopentenone upon irradiation with visible light. This unique inversion behavior has been applied to control encapsulation and the release of fluorescein sodium salt.

Solvothermal synthesis of NiWO4 nanostructure and its application as a cathode material for asymmetric supercapacitors.

This study proposes a facile solvothermal synthesis of nickel tungstate (NiWO4) nanowires for application as a novel cathode material for supercapacitors. The structure, morphology, surface area and pore distribution were characterized and their capacitive performances were investigated. The results showed that the NiWO4 nanowires synthesized in ethylene glycol solvent could offer a high specific capacitance of 1190 F g-1 at a current density of 0.5 A g-1 and a capacitance retaining ratio of 61.5% within 0.5-10 A g-1. When used as a cathodic electrode of an asymmetric supercapacitor (ASC), the NiWO4 nanowire based device can be cycled reversibly in a high-voltage region of 0-1.7 V with a high specific capacitance of 160 F g-1 at 0.5 A g-1, which therefore contributed to an energy density of 64.2 W h kg-1 at a power density of 425 W kg-1. Moreover, 92.8% of its initial specific capacitance can be maintained after 5000 consecutive cycles (5 A g-1). These excellent capacitive properties make NiWO4 a credible electrode material for high-performance supercapacitors.

Understanding the mechanism of LCST phase separation of mixed ionic liquids in water by MD simulations.

Recently, it has been found experimentally that two different amino acid ionic liquids (ILs) can be mixed to show unique lowest critical solution temperature (LCST) phase separation in water. However, little is known about the mechanism of phase separation in these IL/water mixtures at the molecular level. In this work, five kinds of amino acid ILs were chosen to study the mechanism of LCST-type phase separation by molecular dynamics (MD) simulations. Toward this end, a series of all-atom MD simulations were carried out on the ternary mixtures consisting of two different ILs and water at different temperatures. The various interaction energies and radial distribution functions (RDFs) were calculated and analyzed for these mixed systems. It was found that for amino acid ILs, the -NH2 or -COOH group of one anion could have a hydrogen bonding interaction with the -COO(-) group of another anion. With the increase of temperature, this kind of hydrogen bonding interaction between anions was strengthened and then the anion-H2O electrostatic interaction was weakened, which led to the LCST-type phase separation of the mixed ILs in water. In addition, a series of MD simulations for [P6668]1[Lys]n[Asp]1-n/H2O systems were also performed to study the effect of the mixing ratio of ILs on phase separation. It was also noted that the experimental critical composition corresponding to the lowest critical solution temperature was well predicted from the total electrostatic interaction energies as a function of mole fraction of [P6668][Lys] in these systems. The conclusions drawn from this study may provide new insight into the LCST-type phase behavior of ILs in water, and motivate further studies on practical applications.

Formation of ether-functionalized ionic-liquid-based aqueous two-phase systems and their application in separation of protein and saccharides.

Ionic-liquid (IL)-based aqueous two-phase systems (ATPSs) have attracted much attention in the separation technology. In this work, we synthesized five novel ether-functionalized ILs and studied their applications in ATPS formation. The phase diagrams for several systems were determined at 298.15 K. An as-prepared IL (1-(2-butoxy-ethyl)-3-methylimidazolium chloride) was chosen as a representative to construct ATPSs for separation of bovine serum albumin (BSA) from aqueous saccharide solutions. Results showed that 76.1-94.3% of BSA was enriched into the IL-rich top phase and almost all the saccharides were extracted into the salt-rich bottom phase in a one-step separation process. The main factors affecting the separation process, such as kinds of saccharides and the amount of inorganic salts, were discussed. Furthermore, the size distributions of aggregates in the IL-rich top phase were determined by dynamic light scattering (DLS), and accordingly the possible mechanism for the separation was investigated.

Selective electrodes for [PF6](-) and [BF4](-) anions based on the associates formed by ionic liquid and cationic dyes.

The feasibility of the newly synthesized ionic associates L1 and L2 formed by ionic liquid [C4mim][PF6] and cationic dyes (malachite green and methylene blue) has been tested as a novel ionophore for the preparation of anion-selective polymeric membrane electrodes. The electrode exhibits Nernstian response and enhanced potentiometric selectivity towards [PF6](-) compared to many other anions. The influence of some experimental parameters such as membrane composition, nature of plasticizer and amount of additive on the potential response of the [PF6](-) sensor are investigated. Under the optimized conditions, the response slopes of the membrane electrodes towards [PF6](-) are 59.7±0.5 and 58.1±0.5 mV/decade based on ionophore L1 and L2, respectively, in 1.0×10(-5)-1.0×10(-1) or 1.0×10(-6)-1.0×10(-1) mol/L concentration range. Interestingly, the optimized electrodes based on ionophores L1 and L2 also exhibit Nernstian response characteristics (60.3±0.5 and 56.0±0.5 mV/decade) for tetrafluoroborate anion [BF4](-) in a wide concentration range. Thus, the proposed sensor has been used for the determination of [PF6](-) and [BF4](-) in aqueous ionic liquids samples and the solubility of the [PF6](-) and [BF4](-) based ionic liquids in water. The satisfactory results are obtained.

Partitioning behavior of amino acids in aqueous two-phase systems formed by imidazolium ionic liquid and dipotassium hydrogen phosphate.

Partition coefficients of amino acids, including glycine, alanine, 2-aminobutyric acid, valine, leucine, threonine, methinoine, tryptophan and tyrosine, in [C(n)mim]Br (n=4, 6, 8)+K(2)HPO(4) aqueous two-phase systems (ATPSs) have been determined, and the relative hydrophobicity of the equilibrium phases in the ionic liquids-based aqueous two-phase systems has been characterized by the Gibbs energies of transfer for methylene group from the bottom salt-rich phase to the top ionic liquid-rich phase. Based on these results, factors affecting the partitioning behavior of the amino acids have been investigated. It is shown that partition coefficients of the amino acids increase with the increase of hydrophobicity of the amino acids and the ionic liquids, solution pH value, tie-line length of the ATPSs and temperature of the systems. The possible driving forces and the thermodynamic parameters for the partitioning of amino acids in the ionic liquids-based ATPSs have also been discussed.

Effect of anionic structure on the phase formation and hydrophobicity of amino acid ionic liquids aqueous two-phase systems.

Compared with the conventional ionic liquids, amino acid ionic liquids are more biodegradable and biocompatible, and can enhance stability of biomaterials. In this work, amino acid ionic liquids 1-butyl-3-methylimidazolium L-serine ([C(4)mim][Ser]), 1-butyl-3-methylimidazolium glycine ([C(4)mim][Gly]), 1-butyl-3-methylimidazolium L-alanine ([C(4)mim][Ala]) and 1-butyl-3-methylimidazolium L-leucine ([C(4)mim][Leu]) have been synthesized. These ionic liquids are found to form aqueous two-phase systems (ATPSs) by the salted-out of K(3)PO(4) in aqueous solutions. Phase diagram of the ATPSs and the Gibbs energies of transfer of methylene group from the bottom salt-rich phase to the top ionic liquid-rich phase have been determined at 298.15K and pH 14, and the effect of anionic structure of the ionic liquids on phase formation of the ATPSs and the relative hydrophobicity between the top and the bottom phases are then examined. In order to understand the effect of relative hydrophobicity of the phases in equilibrium in the ATPSs on the extraction/separation capability of biomolecules, the partition coefficients of cytochrome-c (as a model biomolecule) in the ATPSs are measured by spectrophotometry. It is suggested that hydrophobic interactions are mainly responsible for the higher partition coefficients of cytochrome-c in aqueous two-phase systems at pH 14, and the extraction and separation capacity of biomolecules can be improved by the modulation of the relative hydrophobicity of the phases and/or the pH of the system.

Theoretical study on cation-anion interaction and vibrational spectra of 1-allyl-3-methylimidazolium-based ionic liquids.

In order to deepen the understanding of the cation-anion interaction in ionic liquids, the structures of cation, anions, and cation-anion ion-pairs of 1-allyl-3-methylimidazolium-based ionic liquids are optimized using density functional theory (DFT), and their most stable geometries are discussed. The structural parameters, hydrogen bonds and interaction energies of 1-allyl-3-methylimidazolium dicyanamide ([Amim]DCA), 1-allyl-3-methylimidazolium chloride ([Amim]Cl), 1-allyl-3-methylimidazolium formate ([Amim]FmO) and 1-allyl-3-methylimidazolium acetate ([Amim]AcO) ion pairs are studied. The vibrational frequencies of [Amim]DCA and [Amim]Cl have been calculated and scaled values have been compared with experimental FT-IR and FT-Raman spectra. The complete assignments were performed on the basis of the potential energy distribution (PED) of the vibrational modes.

Ionic association of the ionic liquids [C4mim][BF4], [C4mim][PF6], and [Cnmim]Br in molecular solvents.

Considering the ionic nature of ionic liquids (ILs), ionic association is expected to be essential in solutions of ILs and to have an important influence on their applications. Although numerous studies have been reported for the ionic association behavior of ILs in solution, quantitative results are quite scarce. Herein, the conductivities of the ILs [Cnmim]Br (n=4, 6, 8, 10, 12), [C4mim][BF4], and [C4mim][PF6] in various molecular solvents (water, methanol, 1-propanol, 1-pentanol, acetonitrile, and acetone) are determined at 298.15 K as a function of IL concentration. The conductance data are analyzed by the Lee-Wheaton conductivity equation in terms of the ionic association constant (KA) and the limiting molar conductance (Lambda(m)(0)). Combined with the values for the Br- anion reported in the literature, the limiting molar conductivities and the transference numbers of the cations and [BF4]- and [PF6]- anions are calculated in the molecular solvents. It is shown that the alkyl chain length of the cations and type of anion affect the ionic association constants and limiting molar conductivities of the ILs. For a given anion (Br-), the Lambda(m)(0) values decrease with increasing alkyl chain length of the cations in all the molecular solvents, whereas the KA values of the ILs decrease in organic solvents but increase in water as the alkyl chain length of the cations increases. For the [C4mim]+ cation, the limiting molar conductivities of the ILs decrease in the order Br- > [BF4]- > [PF6]-, and their ionic association constants follow the order [BF4]- > [PF6]- > Br- in water, acetone, and acetonitrile. Furthermore, and similar to the classical electrolytes, a linear relationship is observed between ln KA of the ILs and the reciprocal of the dielectric constants of the molecular solvents. The ILs are solvated to a different extent by the molecular solvents, and ionic association is affected significantly by ionic solvation. This information is expected to be useful for the modulation of the IL conductance by the alkyl chain length of the cations, type of anion, and physical properties of the molecular solvents.