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Mixtures of polyethylene oxide (PEO, M.W.~900,000) and imidazolium ionic liquids (ILs) are studied using high-pressure Fourier-transform infrared spectroscopy. At ambient pressure, the spectral features in the C-H stretching region reveal that PEO can disturb the local structures of the imidazolium rings of [BMIM] + and [HMIM] + . The pressure-induced phase transition of pure 1-butyl-3-methylimidazolium bromide ([BMIM]Br) is observed at a pressure of 0.4 GPa. Pressure-enhanced [BMIM]Br-PEO interactions may assist PEO in dividing [BMIM]Br clusters to hinder the aggregation of [BMIM]Br under high pressures. The C-H absorptions of pure 1-hexyl-3-methylimidazolium bromide [HMIM]Br do not show band narrowing under high pressures, as observed for pure [BMIM]Br. The band narrowing of C-H peaks is observed at 1.5 GPa for the [HMIM]Br-PEO mixture containing 80 wt% of [HMIM]Br. The presence of PEO may reorganize [HMIM]Br clusters into a semi-crystalline network under high pressures. The differences in aggregation states for ambient-pressure phase and high-pressure phase may suggest the potential of [HMIM]Br-PEO (M.W.~900,000) for serving as optical or electronic switches.

Ionic liquids (ILs) have been considered as "green" substitutes for traditional organic solvents in many existing biological and chemical areas. However, they have high solubility and poor biodegradability in water, suggesting that they could become persistent chemical pollutants in aquatic environment. The ability of two widely used imidazolium-based ILs to affect the growth and physiological characteristics of a marine diatom (Phaeodactylum tricornutum) was investigated in this study. The diatom was exposed to different concentrations of 1-butyl-3-methylimidazolium tetrafluoroborate ([C 4 mim]BF 4 ) and 1-octyl-3-methylimidazolium tetrafluoroborate ([C 8 mim]BF 4 ) for 96h within a batch-culture system. Results showed that [C 4 mim]BF 4 and [C 8 mim]BF 4 were very stable in seawater during 96h of exposure, and the compounds significantly inhibited the growth of P. tricornutum with 24, 48, 72 and 96h EC 50 values of 30.81, 28.53, 39.92, 45.88mgL -1 and 30.17, 23.36, 28.62, 31.37mgL -1 , respectively. In addition, the photosynthetic activity and chlorophyll a synthesis of P. tricornutum were inhibited by [C 4 mim]BF 4 and [C 8 mim]BF 4 , indicating that the structural integrity of chloroplasts of the diatom may be disrupted or damaged by the two ILs. Compared with that of the controls, reactive oxygen species (ROS) level was increased by 0.65, 1.17, 1.85, 3.13, 2.94 times and 0.55, 1.77, 2.42, 3.45, 3.47 times in 5, 10, 20, 40 and 60mgL -1 [C 4 mim]BF 4 and [C 8 mim]BF 4 treatments, respectively. The excessive ROS may cause lipid peroxidation, shortage of metabolic energy and decline of photosynthetic efficiency, which may be the main reason for toxicity of the two ILs to marine diatoms. To withstand the damaging effects of excessive ROS, remarkable physiological and biochemical responses occurred in treatments with the two ILs to protect the cells of P. tricornutum. Parameters such as soluble protein content, soluble sugar content, and superoxide dismutase (SOD) and peroxidase (POD) activities of the diatom increased significantly with increasing concentrations of the two ILs at 96h of exposure relative to the controls. These findings not only provide strong background for evaluating the ecological risks and toxicity of ILs in marine environment, but also help to unravel the toxic mechanism of the two ILs to marine diatoms., (Copyright © 2017 Elsevier B.V. All rights reserved.)

In this study, the possibility of using Tween 80 to disturb the microstructures of 1‐butyl‐3‐methylimidazolium tetrafluoroborate ([BMIM]BF4) and 1‐butyl‐3‐methylimidazolium hexafluorophosphate ([BMIM]PF6) was investigated under high pressures. The imidazolioum CH absorptions of pure ionic liquids (ILs) are significantly blue‐shifted under high pressures. However, mild changes in imidazolioum CH stretching frequencies were observed for IL/Tween 80 mixtures. Tween 80 may hinder cations of ILs to form network structures with anions under high pressures via pressure‐enhanced cation‐Tween 80 interactions. Based on the experimental results, Tween 80‐[BMIM]PF6 interactions are more effective in disturbing the local structure of imidazolium CH than Tween 80‐[BMIM]BF4 interactions. [ABSTRACT FROM AUTHOR]

Using high-pressure infrared methods, we have investigated close interactions of charge-enhanced C-H-O type in ionic liquid/dimethyl sulfoxide (DMSO) mixtures. The solvation and association of the 1-butyl-3-methylimidazolium tetrafluoroborate (BMI+BF4-) and 1-butyl-2,3-dimethylimidazolium tetrafluoroborate (BMM+BF4-) in DMSO-d6 were examined by analysis of C-H spectral features. Based on our concentration-dependent results, the imidazolium C-H groups are more sensitive sites for C-H-O than the alkyl C-H groups and the dominant imidazolium C-H species in dilute ionic liquid/DMSO-d6 should be assigned to the isolated (or dissociated) structures. As the dilute mixtures were compressed by high pressures, the loss in intensity of the bands attributed to the isolated structures was observed. In other words, high pressure can be used to perturb the association-dissociation equilibrium in the polar region. This result is remarkably different from what is revealed for the imidazolium C-H in the BMM+BF4-/D2O mixtures. DFT-calculations are in agreement with our experimental results indicating that C4-H-O and C5-H-O interactions seem to play non-negligible roles for BMM+BF4-/DMSO mixtures. [ABSTRACT FROM AUTHOR]

The effects of alkyl side-chain length on the interactions between imidazolium ionic liquids (ILs) and β-cyclodextrin (β-CD) were studied at ambient pressure and up to 2.5GPa. No noticeable changes in the C-H band frequencies of 1-methyl-3-propylimidazolium hexafluorophosphate ([MPIM][PF6]) were observed upon β-CD addition under ambient pressure. Nevertheless, β-CD addition inhibited the formation of the [MPIM][PF6] aggregated structure under pressures of ≤0.7 GPa. As the pressure was raised to 1.1–2.5 GPa, [MPIM][PF6] aggregated and formed self-associated configurations. This pressure-induced dissociation was not detected in the 1-butyl-3-methylimidazolium hexafluorophosphate and β-CD mixture ([BMIM][PF6]-β-CD) due to the long side chain in the [BMIM] cation. This indicates that the alkyl side-chain length of the imidazolium ILs plays a non-negligible role in controlling the order and strength of IL-β-CD interactions. It is well known that the validity of infrared spectroscopy for detecting the inclusion complexation is questionable in the literature. However, this study demonstrates that the combination of high pressure and IR spectroscopy may provide a suitable way to monitor the IL-β-CD interactions. [ABSTRACT FROM AUTHOR]

Magnetic ionic liquids are a group of magneto-responsive compounds that typically possess high ionic conductivities and low vapor pressures. In spite of the general interest in these materials, a number of questions concerning the fundamental interactions among the ions remain unanswered. We used vibrational spectroscopy to gain insight into the nature of these interactions. Intramolecular vibrational modes of the ions are quite sensitive to their local potential energy environments, which are ultimately defined by cation–anion coordination schemes present among the ions. Ambient pressure Fourier transform infrared (FT-IR) spectroscopy indicates comparable interaction motifs for 1-ethyl-3-methylimidazolium tetrachloroferrate(III), [emim]FeCl4, and 1-ethyl-3-methylimidazolium tetrabromoferrate(III), [emim]FeBr4, magnetic ionic liquids. However, the vibrational modes of [emim]FeCl4 generally occur at slightly higher frequencies than those of [emim]FeBr4. These differences reflect different interaction strengths between the [emim]+ cations and Fe Cl 4 - or Fe Br 4 - anions. This conclusion is supported by gas-phase ab initio calculations of single [emim]FeCl4 and [emim]FeBr4 ion pairs that show longer C–H···Br–Fe interaction lengths compared to C–H···Cl–Fe. Although the IR spectra of [emim]FeCl4 and [emim]FeBr4 are comparable at ambient pressure, a different series of spectroscopic changes transpire when pressure is applied to these compounds. This suggests [emim]+ cations experience different types of interaction with the anions under high-pressure conditions. The pressure-dependent FT-IR spectra highlights the critical role ligands attached to the tetrahalogenoferrate(III) anions play in modulating cation–anion interactions in magnetic ionic liquids. [ABSTRACT FROM AUTHOR]

Continued growth and development of ionic liquids requires a thorough understanding of how cation and anion molecular structure defines the liquid structure of the materials as well as the various properties that make them technologically useful. Infrared spectroscopy is frequently used to assess molecular-level interactions among the cations and anions of ionic liquids because the intramolecular vibrational modes of the ions are sensitive to the local potential energy environments in which they reside. Thus, different interaction modes among the ions may lead to different spectroscopic signatures in the vibrational spectra. Charge organization present in ionic liquids, such as 1-butyl-3-methylimidazolium trifluoromethanesulfonate ([C 4 mim]CF 3 SO 3 ), is frequently modeled in terms of a quasicrystalline structure. Highly structured quasilattices enable the dynamic coupling of vibrationally-induced dipole moments to produce optical dispersion and transverse optical-longitudinal optical (TO-LO) splitting of vibrational modes of the ionic liquid. According to dipolar coupling theory, the degree of TO-LO splitting is predicted to have a linear dependence on the number density of the ionic liquid. Both temperature and pressure will affect the number density of the ionic liquid and, therefore, the amount of TO-LO splitting for this mode. Therefore, we test these relationships through temperature- and pressure-dependent FT-IR spectroscopic studies of [C 4 mim]CF 3 SO 3 , focusing on the totally symmetric S O stretching mode for the anion, ν s (SO 3 ). Increased temperature decreases the amount of TO-LO splitting for ν s (SO 3 ), whereas elevated pressure is found to increase the amount of band splitting. In both cases, the experimental observations follow the general predictions of dipolar coupling theory, thereby supporting the quasilattice model for this ionic liquid. [ABSTRACT FROM AUTHOR]

A simple one-pot method was developed to prepare PtNi alloy nanoparticles, which can be self-decorated on multiwalled carbon nanotubes in [BMIm][BF] ionic liquid. The nanohybrids are targeting stable nanocatalysts for fuel cell applications. The sizes of the supported PtNi nanoparticles are uniform and as small as 1-2 nm. Pt-to-Ni ratio was controllable by simply selecting a PtNi alloy target. The alloy nanoparticles with Pt-to-Ni ratio of 1:1 show high catalytic activity and stability for methanol electro-oxidation. The performance is much higher compared with those of both Pt-only nanoparticles and commercial Pt/C catalyst. The electronic structure characterization on the PtNi nanoparticles demonstrates that the electrons are transferred from Ni to Pt, which can suppress the CO poisoning effect. Graphical Abstract: [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

TiO-supported PdAu bimetallic nanoparticles (NPs) with small size and good dispersity were prepared by the room-temperature ionic liquid-assisted bimetal sputtering, which is simple, environmentally friendly, and free of additives and byproducts. Pd/Au atomic ratio can be tuned by controlling the sputtering conditions simply. High catalytic activity was found in PdAu-NPs-TiO hybrids for solvent-free selective oxidation of 1-phenylethanol using O as the oxidant at the low temperature of 50 °C and low pressure of 1 atm. It was found that Pd/Au ratio strongly affected the catalytical activity, and the highest conversion of about 35 % and turnover frequency of about 421 h were achieved at 1:1 of Pd/Au atomic ratio. The synergistic effect in PdAu NPs was also discussed based on the comprehensive characterization results. The present approach may offer an alternative platform for future development of green-chemistry compatible bimetallic nanocatalysts. [ABSTRACT FROM AUTHOR]

In this study, we used high-pressureinfrared spectroscopy to probe the local structures formed betweenthe ionic liquid [BMI][PF6] and the triblock PEO–PPO–PEOcopolymer P123. The signals for the imidazolium C–H units of[BMI][PF6] underwent anomalous frequency shifts upon dilution,induced by order-to-order transitions. Appreciable changes in therelative band intensities of the signals for the imidazolium moietiesoccurred upon compression. Upon increasing the pressure, the etherC–O–C stretching band underwent dramatic changes, witha shoulder peak appearing near 1097 cm–1with relativelyincreasing intensity. It appears that high pressures somehow stabilizethe hydrogen bonds formed between [BMI] and P123, possibly forcingthe P123 molecules to dissociate the clusters of ionic liquid throughenhanced hydrogen bonding with the imidazolium C–H units. Analogousto temperature-dependent behavior, we suggest the possibility of pressure-inducedassociation of P123 molecules through elevation of pressure. [ABSTRACT FROM AUTHOR]

Highlights: [•] Pd-nanoparticle–graphene hybrid is simply prepared by room-temperature ionic liquid assisted sputtering method. [•] The supported Pd nanoparticles have high loading density and uniformly small sizes of 1–2nm. [•] The hybrid is in situ characterized by the surface-sensitive ambient pressure X-ray photoelectron spectroscopy. [•] The Pd-nanoparticle–graphene hybrid shows high catalytic activity for CO oxidation. [Copyright &y& Elsevier]

Abstract: We report a generic strategy to make hybrids incorporating metal nanoparticles and carbon nanosupports with large surface area, which is a one-step, universal approach totally free of additives and by-products. Utilizing this approach, we show that small Au, Ag and Pd nanoparticles of uniform size can be self-assembled on diverse carbon nanostructures such as graphene oxide, reduced graphene oxide, and multiwalled carbon nanotubes by simply sputtering metal onto room-temperature ionic liquids. The size of metal nanoparticles can be controlled by the composition of room-temperature ionic liquids, and the surface density of metal nanoparticles can be controlled by the sputtering conditions. The self-assembly is demonstrated to be driven by the interlinking interactions among the metal nanoparticles, ionic liquid cations and carbon nanostructures. [Copyright &y& Elsevier]

The nanostructures of ionic liquids (ILs) have been the focus of considerable research attention in recent years. Nevertheless, the nanoscale structures of ILs in the presence of polymers have not been described in detail at present. In this study, nanostructures of ILs disturbed by poly(vinylidene fluoride) (PVdF) were investigated via high-pressure infrared spectra. For 1-(2-hydroxyethyl)-3-methylimidazolium bis(trifluoromethanesulfonyl)imide ([HEMIm][TFSI])-PVdF mixtures, non-monotonic frequency shifts of the C4,5-H vibrations upon dilution were observed under ambient pressure. The experimental results suggest the presence of microheterogeneity in the [HEMIm][TFSI] systems. Upon compression, PVdF further influenced the local structure of C4,5–H via pressure-enhanced IL–PVdF interactions; however, the local structures of C2–H and hydrogen-bonded O–H were not affected by PVdF under high pressures. For choline [TFSI]–PVdF mixtures, PVdF may disturb the local structures of hydrogen-bonded O–H. In the absence of the C4,5–H⋯anion and C2–H⋯anion in choline [TFSI]–PVdF mixtures, the O–H group becomes a favorable moiety for pressure-enhanced IL–PVdF interactions. Our results indicate the potential of high-pressure application for designing pressure-dependent electronic switches based on the possible changes in the microheterogeneity and electrical conductivity in IL-PVdF systems under various pressures. [ABSTRACT FROM AUTHOR]

The nanoscale ion ordering of ionic liquids at confined interfaces under high pressures was investigated in this study. 1-Hexyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([HMIM][NTf2])/poly(vinylidene fluoride-co-hexafluoropropylene) (PVdF-co-HFP) and 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([EMIM][NTf2])/PVdF-co-HFP were prepared and characterized by using high-pressure infrared spectroscopy. Under ambient pressure, imidazolium C2–H and C4,5–H absorptions were blue-shifted in frequency due to the presence of PVdF-co-HFP. However, the absorption of anionic νa SO2 did not reveal any significant shifts in frequency upon dilution by PVdF-co-HFP. The experimental results suggest that PVdF-co-HFP disturbs the local structures of the imidazolium C–H groups instead of the anionic SO2 groups. The frequency shifts of C4,5–H became dramatic for the mixtures at high pressures. These results suggest that pressure-enhanced ionic liquid–polymer interactions may play an appreciable role in IL-PVdF-co-HFP systems under high pressures. The pressure-induced blue-shifts due to the PVdF-co-HFP additions were more obvious for the [HMIM][NTf2] mixtures than for [EMIM][NTf2] mixtures. [ABSTRACT FROM AUTHOR]

1-Butyl-3-methylimidazolium hexafluorophosphate ([C4MIM][PF6])/DNA and 1-methyl-3-propylimidazolium hexafluorophosphate ([C3MIM][PF6])/DNA mixtures were prepared and characterized by high-pressure infrared spectroscopy. Under ambient pressure, the imidazolium C2–H and C4,5–H absorption bands of [C4MIM][PF6]/DNA mixture were red-shifted in comparison with those of pure [C4MIM][PF6]. This indicates that the C2–H and C4,5–H groups may have certain interactions with DNA that assist in the formation of the ionic liquid/DNA association. With the increase of pressure from ambient to 2.5 GPa, the C2–H and C4,5–H absorption bands of pure [C4MIM][PF6] displayed significant blue shifts. On the other hand, the imidazolium C–H absorption bands of [C4MIM][PF6]/DNA showed smaller frequency shift upon compression. This indicates that the associated [C4MIM][PF6]/DNA conformation may be stable under pressures up to 2.5 GPa. Under ambient pressure, the imidazolium C2–H and C4,5–H absorption bands of [C3MIM][PF6]/DNA mixture displayed negligible shifts in frequency compared with those of pure [C3MIM][PF6]. The pressure-dependent spectra of [C3MIM][PF6]/DNA mixture revealed spectral features similar to those of pure [C3MIM][PF6]. Our results indicate that the associated structures of [C4MIM][PF6]/DNA are more stable than those of [C3MIM][PF6]/DNA under high pressures. [ABSTRACT FROM AUTHOR]

The effect of confining ionic liquids (ILs) such as 1-ethyl-3-methylimidazolium tetrafluoroborate [C2C1Im][BF4] or 1-butyl-3-methylimidazolium tetrafluoroborate [C4C1Im][BF4] in silica matrices was investigated by high-pressure IR spectroscopy. The samples were prepared via the sol-gel method, and the pressure-dependent changes in the C–H absorption bands were investigated. No appreciable changes were observed in the spectral features when the ILs were confined in silica matrices under ambient pressure. That is, the infrared measurements obtained under ambient pressure were not sufficient to detect the interfacial interactions between the ILs and the porous silica. However, dramatic differences were observed in the spectral features of [C2C1Im][BF4] and [C4C1Im][BF4] in silica matrices under the conditions of high pressures. The surfaces of porous silica appeared to weaken the cation-anion interactions caused by pressure-enhanced interfacial IL-silica interactions. This confinement effect under high pressures was less obvious for [C4C1Im][BF4]. The size of the cations appeared to play a prominent role in the IL-silica systems. [ABSTRACT FROM AUTHOR]

The interfacial interactions between ionic liquids (1,3-dimethylimidazolium methyl sulfate and 1-ethyl-3-methylimidazolium trifluoromethanesulfonate) and solid surfaces (mesoporous aluminum oxide and mica) have been studied by infrared spectroscopy at high pressures (up to 2.5 GPa). Under ambient pressure, the spectroscopic features of pure ionic liquids and mixtures of ionic liquids/solid particles (Al2O3 and mica) are similar. As the pressure is increased, the cooperative effect in the local structure of pure 1,3-dimethylimidazolium methyl sulfate becomes significantly enhanced as the imidazolium C–H absorptions of the ionic liquid are red-shifted. However, this pressure-enhanced effect is reduced by adding the solid particles (Al2O3 and mica) to 1,3-dimethylimidazolium methyl sulfate. Although high-pressure IR can detect the interactions between 1,3-dimethylimidazolium methyl sulfate and particle surfaces, the difference in the interfacial interactions in the mixtures of Al2O3 and mica is not clear. By changing the type of ionic liquid to 1-ethyl-3-methylimidazolium trifluoromethanesulfonate, the interfacial interactions become more sensitive to the type of solid surfaces. The mica particles in the mixture perturb the local structure of 1-ethyl-3-methylimidazolium trifluoromethanesulfonate under high pressures, forcing 1-ethyl-3-methylimidazolium trifluoromethanesulfonate to form into an isolated structure. For Al2O3, 1-ethyl-3-methylimidazolium trifluoromethanesulfonate tends to form an associated structure under high pressures. [ABSTRACT FROM AUTHOR]

• Pressure-dependent infrared spectroscopy is used to clarify ionic liquid interactions with the pore walls of AAO. • Confinement-induced modifications to the phase behavior of the ILs are observed as pressure is increases. • Confinement effects are observed for both planar and nonplanar cations, with both long and short alkyl side chains. • Interactions between both cations and anions with the Al O and Al OH surface groups are observed. Pressure-dependent infrared (IR) spectroscopy is used to clarify ionic liquid-pore wall interactions in a model anodized aluminum oxide (AAO) nanoporous host. Our high-pressure IR spectroscopic studies reveal confinement-induced modifications to the phase behavior of the ILs. Cation-wall interactions have a prominent role in directing pressure-induced solidification for confined ILs. For example, C H stretching modes for 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide ([C 2 MIM][TFSI]) are split under high pressure and undergo band shifting. Confinement eliminates band splitting and modulates the rate of band shifting due to pressure. Thus, the structural reorganization that accompanies pure ILs when subjected to pressure is impeded upon confinement. Confinement effects on the phase transition process are observed for both planar (imidazolium) and nonplanar (pyrrolidinium) cations as well as cations that contain short and long alkyl side chains. Thus, our observations appear to be broadly applicable to a variety of cation types. Interactions between both cations and anions with the Al O and Al OH surface groups are observed in the IR spectra. These likely play a crucial role in the phase transformations that transpire when the samples are pressurized. [ABSTRACT FROM AUTHOR]