Rile Ge

Density-Viscosity Product of Small-Volume Ionic Liquid Samples Using Quartz Crystal Impedance Analysis

Quartz crystal impedance analysis has been developed as a technique to assess whether room-temperature ionic liquids are Newtonian fluids and as a small-volume method for determining the values of their viscosity-density product, rho eta. Changes in the impedance spectrum of a 5-MHz fundamental frequency quartz crystal induced by a water-miscible room-temperature ionic liquid, 1-butyl-3-methylimiclazolium trifluoromethylsulfonate ([C4mim][OTf]), were measured. From coupled frequency shift and bandwidth changes as the concentration was varied from 0 to 100% ionic liquid, it was determined that this liquid provided a Newtonian response. A second water-immiscible ionic liquid, 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide [C4mim][NTf2], with concentration varied using methanol, was tested and also found to provide a Newtonian response. In both cases, the values of the square root of the viscosity-density product deduced from the small-volume quartz crystal technique were consistent with those measured using a viscometer and density meter. The third harmonic of the crystal was found to provide the closest agreement between the two measurement methods; the pure ionic liquids had the largest difference of approximately 10%. In addition, 18 pure ionic liquids were tested, and for 11 of these, good-quality frequency shift and bandwidth data were obtained; these 12 all had a Newtonian response. The frequency shift of the third harmonic was found to vary linearly with square root of viscosity-density product of the pure ionic liquids up to a value of square root(rho eta) approximately 18 kg m(-2) s(-1/2), but with a slope 10% smaller than that predicted by the Kanazawa and Gordon equation. It is envisaged that the quartz crystal technique could be used in a high-throughput microfluidic system for characterizing ionic liquids.

Sulfur impregnated in a mesoporous covalent organic framework for high performance lithium–sulfur batteries

Undesirable cycling performance has been considered as the main bottleneck that has hindered the practical application of lithium–sulfur (Li–S) batteries, which mainly results from soluble polysulfides shuttling between the anode and the cathode (so-called shuttle effect). To solve this problem effectively, a covalent organic framework (COF), Azo-COF, with a regular pore distribution of 2.6 nm was prepared as the host for sulfur. Such small mesopores can not only confine the sulfur well in the nanopores but also supply Li+ with one-dimension (1D) transmission channels. Benefiting from this concept, even without a LiNO3 additive, the Li–S battery assembly with a S/Azo-COF cathode presented a high stable capacity of 741 mA h g−1 after 100 cycles while delivering a high initial discharge capacity of nearly 1536 mA h g−1 at 0.1C (1C = 1672 mA g−1). Additionally, when the capacity rate (C-rate) was increased to 2C, a high discharge capacity of 770 mA h g−1 can be still achieved after 20 cycles, proving excellent C-rate performance.

Channel-wall functionalization in covalent organic frameworks for the enhancement of CO2 uptake and CO2/N2 selectivity

A series of tailored covalent organic frameworks (COFs), i.e. [NN]X%–TAPH-COFs and [CC]X%–TAPH-COFs, were synthesized by post-fabrication of [HO]X%–TAPH-COFs with 4-phenylazobenzoyl chloride (PhAzo) and 4-stilbenecarbonyl chloride (PhSti), respectively. Powder X-ray diffraction (PXRD), FT-IR, and solution-state 1H NMR of the digested COFs were applied to clarify the functional groups integrated in the pore channels. Gas sorption isotherms confirmed that the [NN]X%–TAPH-COFs and [CC]X%–TAPH-COFs had moderate surface areas, narrow pore sizes, and good physicochemical stability. Compared with [CC]X%–TAPH-COFs, the [NN]X%–TAPH-COFs exhibited higher CO2 uptake capacities of up to 207 mg g−1 (273 K and 1 bar), isosteric heats of adsorption for CO2 (30.7–43.4 kJ mol−1), and CO2/N2 selectivities of up to 78 (273 K) because of the dipole interactions between the azo group and CO2 as well as the N2-phobic behavior of the azo group. Furthermore, although the decreased pore size was advantageous for increasing CO2 adsorption, the decreased surface area of the COFs would undoubtedly decrease CO2 adsorption if too many functional groups were introduced.

Small volume laboratory on a chip measurements incorporating the quartz crystal microbalance to measure the viscosity-density product of room temperature ionic liquids.

A microfluidic glass chip system incorporating a quartz crystal microbalance (QCM) to measure the square root of the viscosity-density product of room temperature ionic liquids (RTILs) is presented. The QCM covers a central recess on a glass chip, with a seal formed by tightly clamping from above outside the sensing region. The change in resonant frequency of the QCM allows for the determination of the square root viscosity-density product of RTILs to a limit of approximately 10 kg m(-2) s(-0.5). This method has reduced the sample size needed for characterization from 1.5 ml to only 30 mul and allows the measurement to be made in an enclosed system.

Bottom-up preparation of gold nanoparticle-mesoporous silica composite nanotubes as a catalyst for the reduction of 4-nitrophenol

Abstract Gold (Au) nanoparticle (NP)-mesoporous silica (SiO2) composite nanotubes were prepared by a bottom-up approach, in which Au NPs were anchored to the inner wall of mesoporous SiO2 tubular shells. In this composite, the agglomeration, exfoliation, and grain growth of Au NPs were restricted, and the loading and size of the catalyst NPs were easily tuned. The mesoporous shell, open ends, and one-dimensional passage of the SiO2 nanotubes all promote the diffusion of reactants, which enhanced the catalytic efficiency of this composite in the reduction of 4-nitrophenol. The Au NP-mesoporous SiO2 composite nanotubes also demonstrated good reusability, and no leaching or agglomeration of the Au NPs was observed during the catalytic reaction.

First application of bis(oxalate)borate ionic liquids (ILBOBs) in high-performance dye-sensitized solar cells

A series of bis(oxalate)borate ionic liquids (ILBOBs) were developed for the first time as the necessary components of the electrolyte system for dye-sensitized solar cells (DSCs). It was found that the photovoltaic performances of DSCs were significantly improved by 26% to 45% with these ILBOBs in the organic solvent electrolytes. Systematic investigations were carried out to reveal the effects of the chain lengths of the quaternary ammonium BOB as well as the cations of the ILBOBs on the performances of the DSCs. Among them, the highest power conversion efficiency (PCE) was achieved by the DSC based on the electrolyte containing 1-ethyl-3-methylimidazolium bis(oxalate)borate (EmimBOB). Specifically, the addition of EmimBOB increased the short circuit current densities (Jsc) from 11.87 mA cm−2 to 15.99 mA cm−2, and the open-circuit voltage (Voc) from 0.721 V to 0.742 V, accompanied by a final 45% improvement of the overall PCE from 6.01% to 8.73% under AM 1.5, 100 mW cm−2 illumination. As an ionic liquid, EmimBOB was also used to develop a solvent-free electrolyte system. Compared with the one containing pure 1-methyl-3-propylimidazolium iodide (PMII), the hybrid solvent-free electrolyte system based on the EmimBOB/PMII combination notably increased the PCE of the DSCs from 3.48% to 5.38%. Finally, using solvent-free electrolytes, the long-term stability of the DSC devices were remarkably improved.

Separate density and viscosity determination of room temperature ionic liquids using dual Quartz Crystal Microbalances

The drive towards cleaner industrial processes has led to the development of room temperature ionic liquids (RTIL) as environmentally friendly solvents. They comprise solely of ions which are liquid at room temperature and with over one million simple RTIL alone it is important to characterize their physical properties using minimal sample volumes. Here we present a dual Quartz Crystal Microbalance (QCM) which allows separate determination of viscosity and density using a total sample volume of only 240µL. Liquid traps were fabricated on the sensing area of one QCM using SU-8 10 polymer with a second QCM having a flat surface. Changes in the resonant frequencies were used to extract separate values for viscosity and density. Measurements of a range of pure RTIL with minimal water content have been made on five different trap designs. The best agreement with measurements from the larger volume techniques was obtained for trap widths of around 50 µm thus opening up the possibility of integration into lab-on-a-chip systems.

Bimetallic docked covalent organic frameworks with high catalytic performance towards tandem reactions

Mn/Pd bimetallic docked covalent organic frameworks were fabricated via a programmed synthetic procedure. Within the framework, MnCl2 could only coordinate with the bipyridine ligands, while Pd(OAc)2 could occupy the rest of the nitrogen sites. Such bimetallic docked materials showed high catalytic activity in a Heck-epoxidation tandem reaction.

Determination of the physical properties of room temperature ionic liquids using a love wave device

In this work, we have shown that a 100 MHz Love wave device can be used to determine whether room temperature ionic liquids (RTILs) are Newtonian fluids and have developed a technique that allows the determination of the density-viscosity product, ρη, of a Newtonian RTIL. In addition, a test for a Newtonian response was established by relating the phase change to insertion loss change. Five concentrations of a water-miscible RTIL and seven pure RTILs were measured. The changes in phase and insertion loss were found to vary linearly with the square root of the density-viscosity product for values up to (ρη)(1/2) ~ 10 kg m(-2) s(-1/2). The square root of the density-viscosity product was deduced from the changes in either phase or insertion loss using glycerol as a calibration liquid. In both cases, the deduced values of ρη agree well with those measured using viscosity and density meters. Miniaturization of the device, beyond that achievable with the lower-frequency quartz crystal microbalance approach, to measure smaller volumes is possible. The ability to fabricate Love wave and other surface acoustic wave sensors using planar metallization technologies gives potential for future integration into lab-on-a-chip analytical systems for characterizing ionic liquids.

Density and viscosity measurements of room temperature ionic liquids using patterned Quartz Crystal Microbalances

Ionic liquids are becoming of increasing interest for an extensive range of applications. Small scale characterization processes are being continually researched to find cheap and efficient methods for processing ever smaller sample volumes. This work presents a dual Quartz Crystal Microbalance (QCM) setup with one smooth, and one patterned surface using chemically compatible materials allowing separate viscosity and density measurements of room temperature ionic liquids. Measurements were corroborated with standard measurement techniques and show good agreement, demonstrating the merit of the dual QCM setup in determining the physical properties of these exciting new solvents.