Experimental Discovery of Magnetoresistance and Its Memory Effect in Methylimidazolium-Type Iron-Containing Ionic Liquids

The ordering and interactions of charge carriers play a critical role in many physicochemical properties. It is, therefore, interesting to study how a magnetic field affects these physicochemical processes and the consequent behavior of the charge carriers. Here, we report the observation of positive magnetoresistance and its memory effect in methylimidazolium-type iron-containing ionic liquids (ILs). Both the electrical transport and magnetic properties of ILs were measured to understand the mechanism of magnetoresistance behavior and its memory effect. The magnetoresistance effect of [BMIM]­[FeCl4] was found to increase with increasing applied currents. This observed memory effect can be ascribed to the slow order and disorder processes in these ILs due to the large viscosity caused by the interactions among ions

Hydrogen-Bonding Interactions in Pyridinium-Based Ionic Liquids and Dimethyl Sulfoxide Binary Systems: A Combined Experimental and Computational Study

The addition of highly polar and aprotic cosolvents to ionic liquids has proven to considerably decrease the viscosity of the solution and improve mass transfer in many chemical reactions. In this work, the interactions between a representative pyridinium-based ionic liquid, N-butylpyridinium dicyanamide ([Bpy]­[DCA]), and a cosolvent, dimethylsulfoxide (DMSO), were studied in detail by the combined use of attenuated total reflection Fourier transform infrared spectroscopy, hydrogen nuclear magnetic resonance (1H NMR), and density functional theory calculations. Several species in the [Bpy]­[DCA]–DMSO mixtures have been identified, that is, ion clusters can translate into ion pairs during the dilution process. DMSO formed hydrogen bonds (H bonds) simultaneously with [Bpy]+ cations and [DCA]− anions but stronger hydrogen-bonding interactions with the [Bpy]+ cations than the [DCA]− anions, and the intrinsic hydrogen-bond networks of IL were difficult to interrupt at low DMSO concentrations. Interestingly, hydrogen-bonding interactions reach the strongest when the molar fraction of DMSO is 0.4–0.5. Hydrogen-bonding interactions are prominent in the chemical shifts of hydrogen atoms in [Bpy]+ cations, and anisotropy is the main reason for the upfield shifts of DMSO in the presence of [Bpy]­[DCA]. The theoretical calculations offer in-depth studies of the structural evolution and NMR calculation

Physicochemical Characterization of MF_<i>m</i>^–‑Based Ammonium Ionic Liquids

A series of ammonium-based ionic liquids (ILs), which share a homologous series of cations (CH₃CH₂)₃N⁺(C_<i>n</i>H_2<i>n</i>+1) with <i>n</i> = 2, 4, 6, 8 and the anions with either BF₄^–, PF₆^–, or SbF₆^–, was synthesized. Their structures were confirmed by ¹H and ¹³C NMR, ESI-MS, and elemental analysis. Meanwhile, the content of impurity (e.g., water and bromide ions) was also determined using Karl Fischer titrator and ion chromatography. The thermal properties of the ILs were determined by TGA and DSC. Five of the investigated ILs have been shown to have a low melting point (< 100 °C): <i>N</i>,<i>N</i>,<i>N</i>,<i>N</i>-tetraethylammonium tetrafluoroborate, [N₂₂₂₂]­BF₄, <i>N</i>,<i>N</i>,<i>N</i>,<i>N</i>-tetraethylammonium hexafluorophosphate, [N₂₂₂₂]­PF₆, <i>N</i>,<i>N</i>,<i>N</i>-triethylhexylammonium tetrafluoroborate, [N₂₂₂₆]­BF₄, <i>N</i>,<i>N</i>,<i>N</i>-triethyloctylammonium hexafluorophosphate, [N₂₂₂₈]­PF₆ and <i>N</i>,<i>N</i>,<i>N</i>-triethyloctylammonium hexafluoroantimonate, [N₂₂₂₈]­SbF₆. Densities, refractive indices, and miscibility of these 12 ILs were well studied systematically. Moreover, from the analysis of the structure–property relationship, the role of the alkyl chain length of the cation on these physical properties of the ILs has been assessed, and the influence of the nature of the anions on these experimental data of the ILs has been discussed. The studies may provide valuable contributions for the design and study of ILs

Improved Catalytic Lifetime of H₂SO₄ for Isobutane Alkylation with Trace Amount of Ionic Liquids Buffer

Trace amounts of ionic liquids have been mixed in sulfuric acid to enhance the catalytic performance for the alkylation of isobutane with butene. The experimental results from batch reactors indicated that the reaction efficiency was significantly improved. The effective catalytic lifetime of concentrated H₂SO₄ mixed with [Bmim]­[SbF₆] was twice compared with pure H₂SO₄. Under the optimal conditions, the alkylate research octane (RON) reached 98, and the selectivity of C8 was 90%. The ionic liquids with SbF₆ anion worked similar to buffer agents, which were in favor of keeping the acid strength of catalytic system, slowing the growth of acid soluble oil, and reducing acid consumption. In conclusion, the new catalytic system of acid and trace amounts of ionic liquids is very promising to substitute the old catalytic system of concentrated H₂SO₄ alone for the alkylation

Insight into the Cosolvent Effect of Cellulose Dissolution in Imidazolium-Based Ionic Liquid Systems

Recently, it has been reported that addition of a cosolvent significantly influences solubility of cellulose in ionic liquids (ILs), but little is known about the influence mechanism of the cosolvent on the molecular level. In this work, four kinds of typical molecular solvents (dimethyl sulfoxide (DMSO), <i>N</i>,<i>N</i>-dimethylformamide (DMF), CH₃OH, and H₂O) were used to investigate the effect of cosolvents on cellulose dissolution in [C₄mim]­[CH₃COO] by molecular dynamics simulations and quantum chemistry calculations. It was found that dissolution of cellulose in IL/cosolvent systems is mainly determined by the hydrogen bond interactions between [CH₃COO]⁻ anions and the hydroxyl protons of cellulose. The effect of cosolvents on the solubility of cellulose is indirectly achieved by influencing such hydrogen bond interactions. The strong preferential solvation of [CH₃COO]⁻ by the protic solvents (CH₃OH and H₂O) can compete with the cellulose–[CH₃COO]⁻ interaction in the dissolution process, resulting in decreased cellulose solubility. On the other hand, the aprotic solvents (DMSO and DMF) can partially break down the ionic association of [C₄mim]­[CH₃COO] by solvation of the cation and anion, but no preferential solvation was observed. The dissociated [CH₃COO]⁻ would readily interact with cellulose to improve the dissolution of cellulose. Furthermore, the effect of the aprotic solvent-to-IL molar ratio on the dissolution of cellulose in [C₄mim]­[CH₃COO]/DMSO systems was investigated, and a possible mechanism is proposed. These simulation results provide insight into how a cosolvent affects the dissolution of cellulose in ILs and may motivate further experimental studies in related fields

Synergistic Effects in Nanoengineered HNb₃O₈/Graphene Hybrids with Improved Photocatalytic Conversion Ability of CO₂ into Renewable Fuels

Layered HNb₃O₈/graphene hybrids with numerous heterogeneous interfaces and hierarchical pores were fabricated via the reorganization of exfoliated HNb₃O₈ nanosheets with graphene nanosheets (GNs). Numerous interfaces and pores were created by the alternative stacking of HNb₃O₈ nanosheets with limited size and GNs with a buckling and folding feature. The photocatalytic conversation of CO₂ into renewable fuels by optimized HNb₃O₈/G hybrids yields 8.0-fold improvements in CO evolution amounts than that of commercial P25 and 8.6-fold improvements than that of HNb₃O₈ bulk powders. The investigation on the relationships between microstructures and improved photocatalytic performance demonstrates that the improved photocatalytic performance is attributed to the exotic synergistic effects via the combination of enhanced specific BET surface area, increased strong acid sites and strong acid amounts, narrowed band gap energy, depressed electron–hole recombination rate, and heterogeneous interfaces

Thermodynamic Modeling and Assessment of Ionic Liquid-Based CO₂ Capture Processes

Ionic liquid (IL)–amine hybrid solvents have been experimentally proved to be effective for CO2 capture. This Article provided rigorous thermodynamic models, process simulation, and cost estimation of a potential design of IL-based CO2 capture processes. Three ILs ([Bmim]­[BF4], [Bmim]­[DCA], and [Bpy]­[BF4]) were investigated to blend with MEA aqueous solution. The physicochemical properties of the ILs were predicted by several temperature-dependent correlations. Phase equilibria were modeled based on Henry’s law and NRTL equation, and the calculated values were in good agreement with the experimental data. The simulation results show that the [Bpy]­[BF4]–MEA process can save about 15% regeneration heat duty as compared to the conventional MEA process, which is attributed to the reduction of sensible and latent heat. Moreover, a modified [Bpy]­[BF4]–MEA process via adding intercooling and lean vapor recompression presents 12% and 13.5% reduction in overall equivalent energy penalty and capture cost as compared to the conventional MEA process, respectively

First-Row Transition Metal-Containing Ionic Liquids as Highly Active Catalysts for the Glycolysis of Poly(ethylene terephthalate) (PET)

First-row transition metal-containing ionic liquids (ILs) were synthesized and used to catalyze the degradation of poly­(ethylene terephthalate) (PET) in ethylene glycol (EG). One important feature of these IL catalysts is that they have good thermal stability, and most of them, especially [bmim]₂[CoCl₄] (bmim = 1-butyl-3-methyl-imidazolium) and [bmim]₂[ZnCl₄], exhibit higher catalytic activity, compared with traditional catalysts, conventional IL catalysts, and some functional ILs. For example, utilizing [bmim]₂[CoCl₄] as catalyst, the conversion of PET, selectivity of bis­(hydroxyethyl) terephthalate (BHET), and mass fraction of BHET in products reach up to 100%, 81.1%, and 95.7%, respectively, under atmospheric pressure at 175 °C for only 1.5 h. Another important feature is that BHET can be easily separated from these IL catalysts and has high purity. Moreover, recycling results show that [bmim]₂[CoCl₄] worked efficiently after being used six times. These all show that [bmim]₂[CoCl₄] is an excellent IL catalyst for the glycolysis of PET. Finally, based on in situ IR spectra and experimental results, the possible mechanism of degradation with synthesized IL is proposed

Core–Shell Structured <i>o</i>‑LiMnO₂@Li₂CO₃ Nanosheet Array Cathode for High-Performance, Wide-Temperature-Tolerance Lithium-Ion Batteries

To develop a high-capacity, high-rate, cycle-stable cathode material has long been the focus for lithium-ion battery (LIB) research. Recently, layer-structured orthorhombic-LiMnO₂ (<i>o</i>-LMO) has attracted extensive interest owing to its large discharge capacities. However, poor cycle performance greatly hinders its practical application, especially at high temperatures. Conventional strategies to address this issue often lead to sacrificed rate performance and mostly work at low temperatures. Herein, we report a novel core–shell structured, <i>o</i>-LiMnO₂@Li₂CO₃ (<i>o</i>-LMO@Li₂CO₃) nanosheet array cathode, where the Li₂CO₃ shell improves cycle performance by preventing <i>o</i>-LMO dissolution in the electrolyte (even at an elevated temperature), the <i>o</i>-LMO core provides high capacities and the nanosheet array architecture ensures rate performance (to the best of our knowledge, this <i>o</i>-LMO nanosheet array architecture is reported for the first time). The above features work synergistically to give well-balanced cycle performance (79% capacity retention at 60 °C, 400 cycles), capacity (207 mAh g^–1 at 0.5C) and rate performance (128 mAh g^–1 at 5C) of the <i>o</i>-LMO@ Li₂CO₃ cathode as well as remarkable full-cell performance (∼67% capacity retention for 400 cycles at ∼2C, 60 °C). Our work demonstrates that the synergistic effect between the <i>o</i>-LMO core, Li₂CO₃ coating and the nanoarray structure is an effective strategy for developing high-energy/power density, high-stability LIB cathodes

Density Prediction of Mixtures of Ionic Liquids and Molecular Solvents Using Two New Generalized Models

Engineers often demand generalized models without sophisticated and long-time computations. To date, such models are still lacking for the density prediction of ionic liquid (IL) mixtures. In this paper, corresponding states principle combining with new mixing rules is employed to develop two new generalized models for density prediction of IL mixtures, including an extended Riedel (ER) model and an artificial neural network (ANN) model. A total of 1985 data points of binary and ternary mixtures of IL with molecular solvents, such as water, alcohols, ketones, ethers, hydrocarbons, esters, and acetonitrile, are used to verify the models. Average absolute relative deviations of the ER model and the ANN model are 0.92% and 0.37%, respectively, which indicates both the developed models can achieve a universal and accurate density prediction of IL mixtures. Moreover, the ER model does not contain any fitted parameters and thus provides a real predictive method