Xiaofu Sun

Water sorption in ionic liquids: kinetics, mechanisms and hydrophilicity

Most of the ionic liquids (ILs) are hygroscopic in air. The effects of structural factors of ILs (cation, anion, alkyl chain length at cation, and C2 methylation at cation) and external factors (temperature, relative humidity, and impurity) on the kinetics of water sorption by 18 ILs were investigated. A modified two-step sorption mechanism was proposed to correlate the water sorption data in the ILs. Three type of parameters (sorption capacity, sorption rate and degree of difficulty to reach sorption equilibrium) based on the modified two-step mechanism were derived to comprehensively characterize the water sorption processes. These parameters have similar tendencies, providing an efficient way to evaluate them by one parameter that can be easily obtained. The hydrophilicity of the ILs was classified to four levels (super-high, high, medium, low) according to the water sorption capacity. The results show that cation of the ILs also plays an important role in water sorption, and the impurities affect the water sorption enormously. Acetate and halogen-based ILs have the highest hydrophilicity when combined with the imidazolium or pyridinium cation.

Studies on staged precipitation of cellulose from an ionic liquid by compressed carbon dioxide.

An efficient method to precipitate and refine cellulose from ionic liquids (ILs) using compressed CO2 as a gas anti-solvent was proposed. 1-Butyl-3-methylimidazolium acetate ([Bmim]OAc) was used as the solvent of microcrystalline cellulose (MCC). The yield and degree of polymerization (DP) value of the regenerated cellulose can be finely tuned by controlling the temperature, pressure, reaction time and addition of aprotic polar solvents. For gaining a better understanding of the possible cellulose precipitation mechanism, the possible carboxylation reaction, volume expansion and solvatochromic parameters of the solution caused by compressed CO2 were investigated. The solvent strength of the system can be adjusted by the pressure and temperature of CO2. The regenerated cellulose samples from [Bmim]OAc by addition of different anti-solvents were characterized by solid-state cross-polarization/magic angle spinning (CP/MAS) 13C NMR, X-ray diffraction (XRD) and atomic force microscopy (AFM). In addition, the energy consumption analysis during the anti-solvent process was discussed. The precipitation and staged bio-refining of cellulose from IL is easy, sustainable and cost-efficient.

Molybdenum–Bismuth Bimetallic Chalcogenide Nanosheets for Highly Efficient Electrocatalytic Reduction of Carbon Dioxide to Methanol

Methanol is a very useful platform molecule and liquid fuel. Electrocatalytic reduction of CO2 to methanol is a promising route, which currently suffers from low efficiency and poor selectivity. Herein we report the first work to use a Mo-Bi bimetallic chalcogenide (BMC) as an electrocatalyst for CO2 reduction. By using the Mo-Bi BMC on carbon paper as the electrode and 1-butyl-3-methylimidazolium tetrafluoroborate in MeCN as the electrolyte, the Faradaic efficiency of methanol could reach 71.2 % with a current density of 12.1 mA cm(-2) , which is much higher than the best result reported to date. The superior performance of the electrode resulted from the excellent synergistic effect of Mo and Bi for producing methanol. The reaction mechanism was proposed and the reason for the synergistic effect of Mo and Bi was discussed on the basis of some control experiments. This work opens a way to produce methanol efficiently by electrochemical reduction of CO2 .

Synthesis of Functional Nanomaterials in Ionic Liquids.

Utilization of ionic liquids (ILs) in material synthesis is a promising field. The unusual properties of ILs provide new opportunities for the design of functional materials, and much excellent work has been reported. Here, the progress in material design and synthesis using ILs, especially nanomaterials, is discussed, including the unitization of ILs as synthetic media, templates, precursors, or components in the synthesis of various categories of nanomaterials. The challenges and opportunities in this interesting and rapid developing area are also discussed.

Efficient Reduction of CO2 into Formic Acid on a Lead or Tin Electrode using an Ionic Liquid Catholyte Mixture

Highly efficient electrochemical reduction of CO2 into value-added chemicals using cheap and easily prepared electrodes is environmentally and economically compelling. The first work on the electrocatalytic reduction of CO2 in ternary electrolytes containing ionic liquid, organic solvent, and H2 O is described. Addition of a small amount of H2 O to an ionic liquid/acetonitrile electrolyte mixture significantly enhanced the efficiency of the electrochemical reduction of CO2 into formic acid (HCOOH) on a Pb or Sn electrode, and the efficiency was extremely high using an ionic liquid/acetonitrile/H2 O ternary mixture. The partial current density for HCOOH reached 37.6 mA cm(-2) at a Faradaic efficiency of 91.6 %, which is much higher than all values reported to date for this reaction, including those using homogeneous and noble metal electrocatalysts. The reasons for such high efficiency were investigated using controlled experiments.

Preparation and characterization of regenerated cellulose from ionic liquid using different methods.

In this study, regenerated cellulose was prepared from ionic liquid 1-butyl-3-methylimidazolium acetate ([Bmim]Ac) solution using anti-solvent compressed CO2 of different pressures. And other anti-solvents like water, ethanol and acetonitrile were also employed to regenerate cellulose to provide comparisons. The two-dimensional nuclear magnetic resonance (2D NMR), namely heteronuclear single quantum coherence (HSQC) and heteronuclear multiple bond coherence (HMBC), and attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR) indicated that carboxylate zwitterions [Bmim(+)-COO(-)] formed through the chemical reactions between CO2 and [Bmim]Ac. Besides, FTIR, wide-angle X-ray diffraction (XRD), thermal gravimetric analysis (TGA), differential scanning calorimetry (DSC), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were used to provided structure characterization of native and regenerated cellulose using different anti-solvents. The results show that the crystallinity of cellulose decreases during the dissolution and regeneration process. And a crystal transformation of cellulose I to cellulose II was verified. The stability of the regenerated cellulose is lower than that of native cellulose. A higher compressed CO2 pressure results in a smoother surface, a thicker shape and a more homogeneous texture of regenerated cellulose.

Precipitation of chitosan from ionic liquid solution by the compressed CO2 anti-solvent method

The utilization of compressed CO2 as an anti-solvent to precipitate chitosan from acetate-based ionic liquid (IL) solution is presented. Volume expansion and solvatochromic behavior of IL are investigated to explain the precipitation mechanism. The regenerated chitosan is characterized and utilized as a catalyst in the formation of imines efficiently.

The dissolution behaviour of chitosan in acetate-based ionic liquids and their interactions: from experimental evidence to density functional theory analysis

The searches for sustainable solvents of chitosan have drawn wide attention in recent years. In this study, nine acetate-based ionic liquids (ILs) varying in their cation are used to explore the dissolution behavior of chitosan and the interactions between IL and chitosan. The solubilities of chitosan in these ILs have been determined in the temperature range from 40 °C to 140 °C with 10 °C intervals. For the imidazolium-based ILs, the solution thermodynamic parameters of chitosan have been calculated from the solubility data. The effects of cation type, alkyl chain structure, temperature and water content on the dissolution were investigated. Hydrogen bond donating and accepting abilities of ILs have been estimated by 1H nuclear magnetic resonance (NMR) spectroscopy and solvatochromic ultraviolet-visible (UV-vis) spectroscopy probe measurements. Temperature dependence of 13C NMR spectra and density functional theory (DFT) computations show that both cations and the OAc− anion of ILs play significant roles in the chitosan dissolution process by the disruption of the inherent hydrogen bonds of chitosan. And the interchain hydrogen bonds may be disrupted prior to the intrachain hydrogen bonds in the process of chitosan dissolution. In addition, low ionicity and special hydrogen bond interactions are used to explain the low chitosan solubility in the four quaternary ammonium-based ILs.

Synthesis of Supported Ultrafine Non-noble Subnanometer-Scale Metal Particles Derived from Metal-Organic Frameworks as Highly Efficient Heterogeneous Catalysts.

The properties of supported non-noble metal particles with a size of less than 1 nm are unknown because their synthesis is a challenge. A strategy has now been created to immobilize ultrafine non-noble metal particles on supports using metal-organic frameworks (MOFs) as metal precursors. Ni/SiO2 and Co/SiO2 catalysts were synthesized with an average metal particle size of 0.9 nm. The metal nanoparticles were immobilized uniformly on the support with a metal loading of about 20 wt%. Interestingly, the ultrafine non-noble metal particles exhibited very high activity for liquid-phase hydrogenation of benzene to cyclohexane even at 80 °C, while Ni/SiO2 with larger Ni particles fabricated by a conventional method was not active under the same conditions.

Extraction of 5-HMF from the conversion of glucose in ionic liquid [Bmim]Cl by compressed carbon dioxide

The efficient extraction of 5-hydroxymethylfurfural (HMF) from the conversion products of glucose in an ionic liquid has been achieved via charging compressed CO2 into the mixtures. The targeted and tunable extraction of HMF could be realized because of the insolubility of glucose and the tunable solubility of HMF in compressed CO2.