Imidazolium Imidazolium Ionic Liquids Research Articles

Ion selectivity regulation under confinement for electromagnetic pollution management

Ionic conductors are emerging as promising candidates in the field of microwave absorption, demonstrating significant potential in absorption efficiency and practical applications. In this study, we have synthesized a series of microwave absorption clays (AC) by incorporating 2D ZIF-L with four imidazolium ionic liquids (ILs). These materials not only exhibit outstanding absorption properties but also enhance our understanding of mechanisms associated with ion-based absorbers. The selective interaction of the ZIF-L framework results in distinct dielectric properties among imidazolium ILs with varying ion sizes and polarities. Analysis of relaxation behavior and ionic conductivity reveals that smaller ions facilitate better ionic transport and longer relaxation times by accessing the interior cavities, whereas larger ions experience extended charge transport distances within the framework gaps but shorter relaxation times due to the formation of short-range ordered structures. Moreover, these clay-like ionic conductors demonstrate excellent microwave absorption capabilities, with effective bandwidths of 2.3 GHz, 7.0 GHz, 6.7 GHz, and 7.4 GHz, respectively. This work presents a promising avenue for high-performance absorbers, advancing our understanding of ion-based absorption mechanisms.

Structure effects of imidazolium ionic liquids on integrated CO2 absorption and transformation to dimethyl carbonate

The integration of chemical absorption of CO2 and in situ transformation to highly valuable chemicals is a promising process as an alternative toward fossil fuels. Here, three imidazolium ionic liquids (ILs), 1-butyl-3-methylimidazolium acetate, 1-butyl-3-methylimidazolium 1,2,4-triazole ([Bmim][Tz]), and 1-butyl-2,3-dimethylimidazolium 1,2,4-triazole were synthesized to absorb and activate CO2 by the formation of CO2-adducts, which can be in situ converted into dialkyl carbonates with alcohols (ROH, R = CH3, C2H5, and C4H9) in solvent diiodomethane under ambient temperature and pressure. The results show [Bmim][Tz] exhibits the best CO2 absorption capacity and dimethyl carbonates (DMC) yield, where CO2 capacity is up to 0.216 gCO2/gIL and DMC yield (based on methanol) is as high as 20.2 %. The structures of imidazolium ILs have significant effects on the absorption of CO2 and subsequent transformation process. Fourier transform infrared and carbon nuclear magnetic resonance spectroscopies demonstrate ILs structures influence binding sites for CO2 absorption, which can combine with CO2 to form CO2-adducts, zwitterion [Bmim-CO2], and [Tz-CO2]−. Furthermore, density functional theory calculations verify the structure effects (binding sites and steric hindrance) of ILs on the activation of CO2 and methanol, through the elongated CO bond lengths of CO2-adducts and O-H bond lengths of methanol in IL-methanol complexes, respectively, leading to different DMC yields. The integrated process is promising for the energy-efficient capture and utilization of CO2 under ambient conditions.

The Influence of Imidazolium Ionic Liquids on the Chromatographic Behavior of Some Aromatic Acids under Reverse-Phase High-Performance Liquid Chromatography Conditions

Using reverse-phase high-performance liquid chromatography, some features of the chromatographic retention of polar aromatic acids (gallic, ferulic, benzoic, and salicylic) on hexadecylsilica gel from aqueous-acetonitrile eluents containing imidazolium ionic liquids (ILs) were studied. The following ILs were used: 1-butyl-3-methylimidazolium bromide [C4MIM][Br], 1-hexyl-3-methylimidazolium bromide [C6MIM][Br], 1-decyl-3-methylimidazolium bromide [C10MIM][Br], and 1-methyl-3-octylimidazolium bromide [MC8IM][Br]. The dependences of retention on the structure of imidazolium ILs and aromatic acids were studied. Based on the temperature dependences of the retention factor, the thermodynamic characteristics of the sorption process (standard enthalpy and entropy component) were calculated. The obtained thermodynamic characteristics of sorption were analyzed, and the influence of the structure of the IL and sorbate on their values was shown. The compensation relationships between the enthalpy and the entropy component of the sorption of the studied aromatic acids were analyzed.

Bioconcentration of imidazolium ionic liquids: In vivo evaluation in marine mussels Mytilus trossulus

Although imidazolium ionic liquids (ILs) are beginning to be used more widely in many industrial fields e.g., as reaction media, electrolytes, stationary phases in gas chromatography), there is still little information about their potential environmental fate. Among the uncertainties regarding the risks associated with these compounds, bioconcentration is one of the key issues, about which many doubts have been raised in recent years. While in vitro data suggest that permanently charged compounds can also bioconcentrate, conclusive evidence in the form of studies on organisms, at least for selected compounds, is needed. Therefore, the main objective of this work was to determine whether imidazolium cations of ILs, namely 1-methyl-3-octylimidazolium ([IM18]+) and 1-methyl-3-dodecylimidazolium ([IM1–12]+), can bioconcentrate in marine invertebrates tissues. During 21-day experiments, Mytilus trossulus mussels were exposed to these cations individually, at a concentration of 10 μg/L. In our study, it has been demonstrated for the first time during in vivo study, that long-chain imidazolium ionic liquids can bioconcentrate. The determined BCF value for [IM1–12]+ of 21,901 ± 3400 L/kg makes this compound to be considered highly bioaccumulative according to commonly accepted criteria. However, the obtained BCF for [IM18]+ (with the value below 100) suggests that this cation has little potential for bioconcentration. On the other hand, no salinity or anion influence on the bioconcentration of the tested cations was observed. Our tests also confirm that imidazolium ILs exhibit acute toxicity only at relatively high concentration levels, as LC50 reached 0.68 mg/L for [IM1–12][Br], and 11.66 mg/L for [IM18][C(CN)3]. This further confirms that the risks associated with the potential presence of these compounds in the environment should be attributed to their high persistence and potential bioconcentration, rather than acute toxicity.

Analysis of imidazolium ionic liquids in biological matrices: A novel procedure for the determination of trace amounts in marine mussels

Imidazolium ionic liquids (ILs) are chemical compounds beginning to be used on a mass scale. Although their presence in the environment is usually treated as only potential threat, there are already first evidences that this has become a real case. Taking into account their increasing use it might be expected that this problem will also increase in the nearest future. Given that some of the imidazolium cations exhibit high potential for bioconcentration, it is likely that they will accumulate in the tissues of wild organisms. Thus, there is no doubt that monitoring the presence of these compounds in organisms from potentially contaminated waters will be needed. Therefore, the aim of our study was to develop and fully validate a novel and reliable analytical procedure for the determination of the mixture of imidazolium ILs in Mytilus trossulus mussels. For this purpose, different extraction techniques were tested such as: microwave-assisted extraction (MAE), accelerated-solvent extraction (ASE) and bullet-blender homogenization (HOMO). Finally, the proposed procedure is based on the application of MAE technique for the extraction of imidazolium cations and SPE technique using Oasis HLB cartridges for the purification of the obtained extracts and LC-MS/MS technique with QqQ analyzer for their final determination. Absolute recoveries of the proposed analytical procedure reached 71–90%. The developed procedure is characterized with low limits of quantification, at 50–100 ng g−1 dry tissue and allows for reliable determination of trace amounts of the tested compounds in complex biological matrix. Matrix effects obtained for the optimized procedure ranged from 7.8 to 37.5%. As a result, this is the first study presenting the analytical procedure for the analysis of imidazolium ILs in aquatic animal tissues.

Synergy of imidazolium ionic liquids and flexible anionic polymer for controlling facilely montmorillonite swelling in water

The hydration and swelling of clay minerals in the reservoir will probably bring about serious damage to stratum. Herein, a series of imidazolium ionic liquids (ILs) with different alkyl chains were synthesized to inhibit the swelling of montmorillonite (MMT). The relationship between the inhibitory property and ILs structure was determined through detailed studies. The combination of adsorption capacity, XPS and zeta potential demonstrated that ILs successfully adsorbed on MMT replacing Na+ ion. The adsorption behavior of ILs correlated well with Langmuir adsorption isotherm, implying the homogeneous monolayer adsorption. Besides, the presence of moderate amounts of flexible hydrolyzed polyacrylamide (HPAM) was favorable to improve the inhibition ability of ILs, where HPAM was adsorbed on the surface of MMT through ILs bridging, encapsulating the MMT particles. To understand inhibition mechanism in depth, the interlayer variation of dry and wet MMT and micromorphology of MMT particles were investigated to confirm the intercalation of ILs and stacking variation of MMT particles. Altogether, this study provides new insights into the structure-property relationships of imidazolium ILs and facilitates the design of excellent clay stabilizers.

Imidazolium ionic liquids as fracture toughening agents in DGEBA-TETA epoxy resin

Although epoxy resins are used in a broad variety of applications due to their good mechanical and thermal properties, their low fracture toughness is a limitation, exhibiting brittle behavior. This study explored the potential use of imidazolium ionic liquids (IL) as toughening agents for epoxy resin based on diglycidyl ether of bisphenol A (DGEBA) with triethylenetetramine (TETA) as curing agent. Fracture toughness was evaluated for DGEBA-TETA epoxy resins with eleven imidazolium IL and the best results were found for the IL with the chloride anion and the shortest N-alkyl side chain, C4MImCl. The use of 1.0 phr of C4MImCl lead to the reduction of the crosslink density of the post-cured resin, resulting in the increase of 25.5% in stress intensity factor and 8.2% in tensile strength with no significant loss in other mechanical properties.

The validity of high pressure IR for detecting the interactions between β-cyclodextrin and imidazolium based ionic liquids

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.

Assessment the ecotoxicity and inhibition of imidazolium ionic liquids by respiration inhibition assays

The ecotoxicity and inhibition of 12 imidazolium ionic liquids (ILs) with alkyl chain from C4 to C10 and chloride (Cl-), tetrafluoroborate (BF4-) and bis(trifluoromethanesulfonyl)imide (NTf2-) anions have been studied by means of respiration inhibition assays using activated sludge collected from a wastewater treatment plant. This test represents an alternative easy, economic and quick way to evaluate the true impact of ILs on activated sludge-based wastewater treatment. For comparison purposes, the EC50 values were also determined by the Microtox test (Vibrio fischeri). It was observed that this widely used microbial test overestimates the effect of the ILs on biological wastewater treatment facilities, especially in the case of ILs with lower ecotoxicity. The results of the biological tests showed that the alkyl chain length plays a crucial role in the ecotoxicity of ILs. A significant increase of the toxicity with the length of the n-alkyl chain was found. Regarding to the impact of the anion, the ecotoxicity measured by respiration inhibition assays follows the order NTf2- > Cl- > BF4-, being the anion effect higher as decreasing the length of cation alkyl chain. According to the hazard substances ranking for aquatic organisms (Passino and Smith, 1987), imidazolium ILs with C4 alkyl chain can be classified as “practically harmless” compounds whereas those with alkyl chains C8 or C10 correspond to “highly toxic” species.

Kluyveromyces marxianus, an Attractive Yeast for Ethanolic Fermentation in the Presence of Imidazolium Ionic Liquids.

Imidazolium ionic liquids (ILs) are promising solvents for lignocellulosic biomass (LCB) pretreatment and allow the achievement of higher ethanolic yields after enzymatic hydrolysis and ethanolic fermentation. However, residual ILs entrapped in pretreated biomass are often toxic for fermentative microorganisms, but interaction mechanisms between ILs and cells are still unknown. Here we studied the effects of 1-ethyl-3-methylimidazolium acetate [Emim][OAc] and 1-ethyl-3-methylimidazolium methylphosphonate [Emim][MeO(H)PO2] on Kluyveromyces marxianus, a thermotolerant ethanologenic yeast. Morphological impacts induced by ILs on K. marxianus were characterized by Scanning Electron Microscopy analysis and showed wrinkled, softened, and holed shapes. In Yeast-Malt-Dextrose (YMD) medium, K. marxianus tolerated IL additions up to 2% for [Emim][OAc] and 6% for [Emim][MeO(H)PO2]. Below these thresholds, some IL concentrations enhanced ethanolic yields up to +34% by switching the metabolic status from respiratory to fermentative. Finally, K. marxianus fermentation was applied on several substrates pretreated with [Emim][OAc] or [Emim][MeO(H)PO2] and enzymatically hydrolyzed: a model long fiber cellulose and two industrial LCBs, softwood (spruce) and hardwood (oak) sawdusts. The maximum ethanolic yields obtained were 1.8 to 3.9 times higher when substrates were pretreated with imidazolium ILs. Therefore K. marxianus is an interesting fermentative yeast in a second-generation bioethanol process implying IL pretreatment.

Rapid Determination of Pyrrolidinium Cations by Ion-Pair Chromatography With Imidazolium Ionic Liquids.

This article describes a pioneering ion-pair chromatography with indirect ultraviolet detection with imidazolium ionic liquids (ILs) as ultraviolet absorption reagent and eluting agent for determination of pyrrolidinium cations. Three pyrrolidinium cations were analyzed on a reversed-phase silica-based monolithic column by isocratic elution with imidazolium ILs-ion-pair reagents-methanol mixtures. The effects of the ultraviolet absorption reagents, detection wavelength, ion-pair reagents, imidazolium ILs, organic solvents, column temperature and flow rate on the separation and determination of pyrrolidinium cations were investigated. Under the selected chromatographic conditions, the separation time was reduced to <2.5 min while maintaining excellent peak shapes and sufficient resolution. The detection limits for N-methyl-N-ethylpyrrolidinium cation, N-methyl-N-propylpyrrolidinium cation and N-methyl-N-butylpyrrolidinium cation were 0.12, 0.08 and 0.19 mg/L, respectively. Relative standard deviations for peak area were <0.59%. This simple and practical method has been successfully applied to the determination of three IL samples synthesized by the chemistry laboratory. The method is accurate, reliable and meets the requirements for quantitative analysis. In general, the analytical system and its associated methods appear to be widely applicable to determination of pyrrolidinium cations.

Determining mushroom tyrosinase inhibition by imidazolium ionic liquids: A spectroscopic and molecular docking study

The inhibition effects of imidazolium ionic liquids (ILs) on the enzyme kinetics of mushroom tyrosinase is reported. A simple UV-VIS spectrophotometric assay was used to measure the reaction kinetics of the reaction between mushroom tyrosinase and L-dopa. Seven different imidazolium ILs, comprised of 1-alkyl-3-methylimidazolium ([Imn1+], n=2, 4, 6) cations paired with several anions that included Cl−, [NO3−], methanesulfonate ([MeSO3−]), trifluoromethanesulfonate (or triflate, [TFMS−]), and bis(trifluoromethylsulfonyl)imide ([Tf2N−]). Lineweaver-Burk plots were generated from the recovered kcat and Km parameters using four to six substrate concentrations per measurement. The results show that mushroom tyrosinase activity was consistently inhibited by all of the ILs and that the type of inhibition was non-competitive in nearly all cases. Only the data for [Im21+][Tf2N−] suggested that the inhibition mechanism was competitive with the substrate. Molecular docking simulations were performed using AutoDock4.2 and AutoDock Vina and revealed that all cations docked in the L-dopa active site. Anions showed varied results that included locations both within and outside of the active site.

Surface-bonded amide-functionalized imidazolium ionic liquid as stationary phase for hydrophilic interaction liquid chromatography

The amide group modified silica materials are popular stationary phases for hydrophilic interaction liquid chromatography (HILIC). Meanwhile, surface-confined imidazolium ionic liquids (ILs) have been proved to be useful HILIC stationary phases and possess many unique properties. In this study, the synthesis of an amide-functionalized imidazolium IL was conducted which was then bonded onto silica surface to obtain a novel imidazolium-embedded amide stationary phase for HILIC. The combination of the amide group and imidazolium IL moiety might bring some advantages in selectivity or retention and therefore extended its applications. After characterizing the prepared IL and the resulting modified silica materials, the chromatographic performance and separation selectivity of the packed column were evaluated and compared with a commercial amide column. Then, the retention behavior was investigated through observing the retention factors at different chromatographic conditions using a wide range of compounds. Exceptionally, the prepared amide IL column exhibited superior separation performance towards complex samples such as flavonoids mixture, soybean flavonoids and human urine. All the results indicated that the novel amide IL column possessed an anion-exchange/HILIC mixed-mode retention mechanism and could be useful in the sample analysis as a promising candidate for HILIC stationary phase.

Highly Efficient CO2 Capture by Imidazolium Ionic Liquids through a Reduction in the Formation of the Carbene–CO2 Complex

A strategy for improving CO2 capture by imidazolium ionic liquids (ILs) through a reduction in the formation of carbene–CO2 complex was reported. The carbene–CO2 complex content in CO2 capture by imidazolium ILs was determined by a quantitative NMR method, and the carbene–CO2 complex formation was decreased through a reduction in the basicity of the anion and an enlargement in the steric hindrance of the cation. Thus, both enhanced absorption capacity and improved desorption were achieved, where an ideal IL, [Ipmim][Triz], exhibited a very high capacity of 0.21 g of CO2/g of IL and excellent reversibility.

Real-Time X-ray Imaging Reveals Interfacial Growth, Suppression, and Dissolution of Zinc Dendrites Dependent on Anions of Ionic Liquid Additives for Rechargeable Battery Applications.

The dynamic interfacial growth, suppression, and dissolution of zinc dendrites have been studied with the imidazolium ionic liquids (ILs) as additives on the basis of in situ synchrotron radiation X-ray imaging. The phase contrast difference of real-time images indicates that zinc dendrites are preferentially developed on the substrate surface in the ammoniacal electrolytes. After adding imidazolium ILs, both nucleation overpotential and polarization extent increase in the order of additive-free < EMI-Cl < EMI-PF6 < EMI-TFSA < EMI-DCA. The real-time X-ray images show that the EMI-Cl can suppress zinc dendrites, but result in the formation of the loose deposits. The EMI-PF6 and EMI-TFSA additives can smooth the deposit morphology through suppressing the initiation and growth of dendritic zinc. The addition of EMI-DCA increases the number of dendrite initiation sites, whereas it decreases the growth rate of dendrites. Furthermore, the dissolution behaviors of zinc deposits are compared. The zinc dendrites show a slow dissolution process in the additive-free electrolyte, whereas zinc deposits are easily detached from the substrate in the presence of EMI-Cl, EMI-PF6, or EMI-TFSA due to the formation of the loose structure. Hence, the dependence of zinc dendrites on anions of imidazolium IL additives during both electrodeposition and dissolution processes has been elucidated. These results could provide the valuable information in perfecting the performance of zinc-based rechargeable batteries.

Metallosurfactant Ionogels in Imidazolium and Protic Ionic Liquids as Precursors To Synthesize Nanoceria as Catalase Mimetics for the Catalytic Decomposition of H2 O2.

The gelation behavior of cationic surfactants with different counterions, Br- , [FeCl3 Br]- , and [CeCl3 Br]- , in imidazolium ionic liquids (ILs) and protic ethylammonium nitrate was investigated. Small-angle X-ray scattering measurements and freeze-fracture transmission electron microscopy observations revealed the lamellar phases of metallosurfactant ionogels. The characteristics of imidazolium ILs, including the size and type, have effects on metallosurfactant ionogel properties, such as transformation temperatures, interlayer spacing, and mechanical strength. Cubic fluorite structured cerium oxide nanoparticles (CeO2 NPs) were produced by using metallosurfactant ionogels as precursors. Cubic fluorite CeO2 exhibited good catalase mimetic activity toward H2 O2 to generate O2 , providing more multiple mimetic enzyme activities of CeO2 NPs for H2 O2 .

Sulfonated imidazolium ionic liquid-catalyzed transesterification for biodiesel synthesis

Four kinds of imidazolium ionic liquids (ILs) were employed to catalyze the transesterification reaction of rapeseed oil. The effects of molar ratio of methanol to rapeseed oil, catalyst dosage, reaction temperature, and reaction time, and the deactivation of water on catalytic activity were explored. The results showed that imidazolium ILs with long alkyl chains and sulfonated groups exhibited the best catalytic activities due to their strong Brønsted acidity. The catalytic activity was depend on the SO3H group in the cation, not the anion HSO4−. Water molecules competed with the anion to bind with the protons of the imidazolium cation. This results in the disruption of the structure of ILs, leading to deactivation; increasing the reaction temperature could alleviate this negative effect of water. The yield of fatty acid methyl ester (FAME) remained constant (∼85%) at 130°C, when the water content increased from 1wt% to 5wt%. The highest yield of FAME for the catalyst 1-butylsulfonate-3-methyl imidazolium hydrogen sulfate ([BSO3HMIM][HSO4]) could reach 100% under optimum conditions.

Evaluation of thermodynamic properties for non-crystallizable ionic liquids

Heat capacity of three glass-forming imidazolium ionic liquids (ILs) was studied by adiabatic calorimetry in the temperature range (5–370)K. Using the experimental data obtained in this work and those available in literature it was demonstrated that for all the studied glass-forming imidazolium ILs except [C8mim]BF4 the Tg/Tfus quotient is close to 2/3. The anion symmetry and the alkyl chain length were found to be the most important factors affecting heat capacity changes at the glass transition. The values of the residual entropy for the [C4mim]An ILs can be explained by conformational disorder of the ions. However, since no statistically significant dependence of this quantity of the alkyl chain length was observed it is possible that the conformational disorder of the alkyl chains in ILs is lower than in molecular liquids or gases.

Ionothermal Stability of Mesoporous Silica Films

We have examined the ionothermal stability of mesoporous silica films (MSFs) in four different imidazolium ionic liquids (ILs) and compared it to their hydrothermal stability in liquid water. Ionothermal treatment of MSFs in anhydrous 1-butyl-3-methylimidazolium acetate, bromide, chloride, and thiocyanate reveals that MSFs are thermochemically stable in these ILs up to 175 °C for 24 h. Solvothermal stability of MSFs in imidazolium IL–water compositional mixtures was also investigated, and mesoporous silica is found to be stable in compositions greater than 25 mol % IL. A kinetic acceleration in MSF dissolution occurs at suitably low IL compositions relative to water for all ILs used and depends on the IL anion. Our findings suggest that anhydrous imidazolium ILs are unable to solvolytically depolymerize mesoprous silica, possibly making these better solvents than water for use with mesoporous silica.

Facile synthesis of size controllable dendritic mesoporous silica nanoparticles.

The synthesis of highly uniform mesoporous silica nanospheres (MSNs) with dendritic pore channels, particularly ones with particle sizes below 200 nm, is extremely difficult and remains a grand challenge. By a combined synthetic strategy using imidazolium ionic liquids (ILs) with different alkyl lengths as cosurfactants and Pluronic F127 nonionic surfactants as inhibitors of particle growth, the preparation of dendritic MSNs with controlled diameter between 40 and 300 nm was successfully realized. An investigation of dendritic MSNs using scanning electron microscopy (SEM), transmission electron microscopy (TEM), and nitrogen physisorption revealed that the synthesis of dendritic MSNs at larger size (100-300 nm) strongly depends on the alkyl lengths of cationic imidazolium ILs; while the average size of dendritic MSNs can be controlled within the range of 40-100 nm by varying the amount of Pluronic F127. The Au@MSNs can be used as a catalyst for the reduction of 4-nitrophenol by NaBH4 into 4-aminophenol and exhibit excellent catalytic performance. The present discovery of the extended synthesis conditions offers reproducible, facile, and large-scale synthesis of the monodisperse spherical MSNs with precise size control and, thus, has vast prospects for future applications of ultrafine mesostructured nanoparticle materials in catalysis and biomedicine.