The understanding of confined structure and flow property of ionic liquid (IL) in a nanochannel are essential for the efficient application of ILs in the green chemical processes. In this work, the ionic structure and various flow behaviors of ILs inside graphene nanochannels via molecular dynamics simulations are shown. The effect of the nanochannel structure on confined flow is explored, showing that the width mainly heightens the viscosity while the oxidation degree primarily enhances the interfacial friction coefficient. Tuning the width and oxidation degree of nanochannel, three different flow behaviors including Poiseuille, partial plunger and full plunger flow can be achieved, where the second one does not occur in water or other organic solvents. To describe the special flow behavior, an effective influence extent of the nanochannel (w EIE) is defined, whose value can distinguish the above flows effectively. Based on w EIE, the phase diagrams of flow behavior for the nanochannel structure and pressure gradient are obtained, showing that the critical pressure gradient decreases with width and increases with the oxidation degree. Based on the quantitative relations between confined structures, viscosity, friction coefficient, flow behavior, and nanochannel structure, the intrinsic mechanism of regulating the flow behavior and rational design of nanochannel are finally discussed.

AbstractCharacterization of structural heterogeneity of liquid solutions and the pursuit of its nature have been challenging tasks to solution chemists. In the last decade, an emerging method called excess spectroscopy has found applications in this area. The method, combining the merits of molecular spectroscopy and excess thermodynamic functions, shows the ability to enhance the apparent resolution of spectra, provides abundant information concerning solution structures and intermolecular interactions. In this review, the thinking and mathematics of the method, as well as its developments, are presented first. Then, research progress related to the exploration of the method is thoroughly reviewed. The materials are classified into two parts, small-molecular solutions and ionic liquid solutions. Finally, potential challenges and the perspective for further development of the method are discussed.

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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 ( 1 H 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.

While the depolymerization of lignin to chemicals catalyzed by ionic liquids has attracted significant attention, the relevant molecular mechanism, especially the cleavage of specific bonds related to efficient depolymerization, still needs to be deeply understood for the complexity of this natural aromatic polymer. This work presents a detailed understanding of the cleavage of the most abundant β-O-4 bond in the model system, guaiacylglycerol β-guaiacyl ether, by a Brønsted acidic IL (1-methyl-3-(propyl-3-sulfonate) imidazolium bisulfate ([C 3 SO 3 Hmim][HSO 4 ]) using density functional theory calculation and molecular dynamics simulation. It has been found that [C 3 SO 3 Hmim][HSO 4 ] generates zwitterion/H 2 SO 4 via proton transfer with an energy barrier of 0.38 kcal/mol, which plays a dominant role in the lignin depolymerization process. Subsequently, the reaction can be carried out via three potential pathways, including (1) the dehydration of α-C-OH, (2) dehydration of γ-C-OH, and (3) the protonation of β-O. The electrophilic attack of H 2 SO 4 and the hydrogen-bonding interaction between GG and zwitterion are the two most important factors to promote the depolymerization reaction. In all steps, the dehydration of α-C-OH route is computed to be favored for the experiment. The relatively higher energy barrier for β-O-4 bond dissociation among these reaction steps is attributed to the hindrance of the self-assembled clusters of GG in the mixed system. Further, the dense distribution of H13([C 3 SO 3 Hmim]) surrounding O21(GG), indicated by sharp peaks in RDFs, reveals that -SO 3 H in cations plays a substantial role in solvating lignin. Hopefully, this work will demonstrate new insights into lignin depolymerization by functionalized ILs in biomass conversion chemistry.

The utilization of ionic liquids (ILs) as electrolytes in lithium-ion batteries is of great academic and industrial significance. Previous studies have shown that clusters can be formed in IL electrolytes. However, the influence of clusters on [Li] solvation and transport is still ambiguous, especially under external electric fields. The structural, dynamical, and transport properties of mixed organic compound/IL electrolytes, consisting of lithium salts ([Li][TFSI], [Li][BF 4 ], and [Li][PF 6 ]), organic solvents (ethylene carbonate (EC) and dimethyl carbonate (DMC)), and ILs ([EMIM][TFSI], [EMIM][BF 4 ], [EMIM][PF 6 ], and [PYR 14 ][TFSI]) under external electric fields were investigated using molecular dynamics (MD) simulations. The results suggest a strong relationship between the cluster structures and the applied external electric fields. Under low electric fields, no obvious change of cluster structures was observed, but due to the electrophoretic effect, [Li] diffusion was weakened. Under high electric fields, the anions around [Li] could be partially substituted by DMC molecules, and it was found that [Li] diffusion could be increased significantly. The physical insights provided in the study demonstrate that the original larger ion clusters tend to be smaller on increasing the strength of the external electric fields, thereby enhancing the transport of [Li].

Electrochemical degradation mechanism of phenolic lignin model compounds with typical Caryl–O bond in a protic IL-water system is clarified, including direct oxidation of substrates at the electrode and indirect oxidation by in situ generated H2O2.