Influence of ionic liquids under controlled water activity and low halide content on lipase activity

Room-temperature ionic liquids (ILs) can be used as reaction media for nonaqueous biocatalysis. However, the purity of ILs should be considered to understand the influence of ILs on enzyme activity. The major impurities in ILs are water and halide. In the transesterification of benzyl alcohol with vinyl acetate, the optimal water activities for lipases in [Omim][Tf₂N] were similar to those in organic solvents. The chloride impurity in [Omim][Tf₂N] seriously influenced the activity of lipase. In this work, the effect of ILs on lipase activity was investigated under controlled initial water activity and low halide content. The activity of lipase was highly dependent upon the anion structure of ILs. The initial reaction rate of lipases followed the order [Tf₂N]⁻>[PF6]⁻>[TfO]⁻>[SbF₆]⁻≈[BF₄]⁻. All tested lipases showed the highest activities in ILs containing [Tf₂N] anion. Particularly, [AAIM][Tf₂N] was shown as a suitable reaction medium for biocatalysis. Lipozyme IM showed the highest activity in this IL among tested ILs. Thermal stability of lipase was also investigated. The higher thermal stability of Novozym 435 was obtained in hydrophobic and water-immiscible ILs such as [Bmim][Tf₂N], [Edmim][Tf₂N], and [Bmim][PF₆].     

Textured CaBi4Ti4O15 ceramics with large piezoelectricity,excellent thermal stability and high resistivity

The bismuth layer-structured ferroelectrics (BLSF) are promising high-temperature piezoelectric materials, in which large piezoelectricity, good thermal stability and high electrical resistivity are desired. Here highly textured CaBi₄Ti₄O₁₅ BLSF ceramics with orientation factor of 82% have been fabricated by spark plasma sintering technique. The piezoelectric coefficient d₃₃ is significantly enhanced by 250%, from 7.2 pC/N for the texture-less sample to 25.3 pC/N for the textured one, accompanied by a high Curie temperature T_C= 788 °C. The variation of d₃₃ is below 5% in the temperature range of 25–500 °C, showing excellent thermal stability. The textured sample exhibits high electrical resistivity ρ = 2.1 × 10¹¹ Ω·cm, an order of magnitude larger than that of the texture-less sample. At the temperature as high as 500 °C, the textured sample still maintains excellent electrical properties of d₃₃ = 24.2 pC/N, tanδ = 9.9% and ρ = 2.7 × 10⁶ Ω·cm, suggesting that the textured CaBi₄Ti₄O₁₅ ceramics could be a potential candidate for high-temperature piezoelectric sensor or detector applications.     

Enhanced stability of <Emphasis Type="Italic">Candida antarctica</Emphasis> lipase B in ionic liquids

The activity and stability of lipase from Candida antarctica were investigated in the kinetic resolution of (R,S)-1-phenylethanol with vinyl acetate using ionic liquids (ILs) as reaction media. Among ILs tested, the highest activity of lipase was observed in [Edmim][Tf₂N]. In hydrophobic ILs such as [Edmim][Tf₂N], [Emim][Tf₂N] and [Pmim] [PF₆], lipase could retain its activity after 5 times reuse, while the activity of lipase in hydrophilic ILs and organic solvents was drastically decreased. The activities of lipase in [Edmim][Tf₂N], [Emim][Tf₂N] and [Pmim][PF₆] were also well maintained after 1 day incubation at 80 °C. The lipase suspended in [Edmim][Tf₂N] could be successfully reused 6 times without loss of activity.     

Piezoresistivity of n-type conductive ultrananocrystalline diamond

Recent developments of a piezoresistive sensor prototype based on n-type conductive ultrananocrystalline diamond (UNCD) are presented. Samples were deposited using hot filament chemical vapor deposition (HFCVD) technique, with a gas mixture of H₂, CH₄ and NH₃, and were structured using multiple photolithographic and etching processes. Under controlled deposition parameters, UNCD thin films with n-type electrical conductivity at room temperature (5 × 10^− 3 – 5 × 10¹ S/cm) could be grown. Respective piezoresistive response of such films was analyzed and the gauge factor was evaluated in both transverse and longitudinal arrangements, also as a function of temperature from 25 °C up to 300 °C. Moreover, the gauge factor of piezoresistors with various sheet resistance values and test structure geometries was evaluated. The highest measured gauge factor was 9.54 ± 0.32 at room temperature for a longitudinally arranged piezoresistor with a sheet resistance of about 30 kΩ/square. This gauge factor is well comparable to that of p-type boron doped diamond; however, with a much better temperature independency at elevated temperatures compared to the boron-doped diamond and silicon. To our best knowledge, this is the first report on piezoresistive characteristics of n-type UNCD films.     

Molecular insight into the effect of ion structure and interface behavior on the ammonia absorption by ionic liquids

Molecular dynamics simulations were performed to elucidate the roles of ion structure and interface behavior in absorption of gases (NH₃, N₂, H₂) by ILs (protic IL [Bim][Tf₂N] and conventional IL [Bmim][Tf₂N]). The results indicated that NH₃ compete with [Tf₂N]⁻ to interact with N3-H site of [Bim]⁺ cation, forming a strong N3 H∙∙∙N(NH₃) hydrogen bond with the energy of −79 kJ/mol, which is twice as much as the energy of the hydrogen bond between C2 H of [Bmim]⁺ and NH₃ (−33.2 kJ/mol). Moreover, there is a dramatic increase in the number density of cations near the IL-gas interface, resulting in the NH₃ molecules permeate into the bulk rapidly and effectively and achieving the high selective absorption of NH₃ to H₂ and N₂. Considering the inevitable trace water in the raw gases, the influence of water was studied and it was shown that trace water can enhance the absorption of NH₃ by [Bim][Tf₂N].     

Three-dimensional numerical simulation of a horizontal rotating fluidized bed

Three-dimensional numerical simulations of a horizontal rotating fluidized bed (RFB) containing glass bead particles (d_s = 82 μm, ρ_s = 2450 kg/m³) and washed alumina (d_s = 89 μm, ρ_s = 1550 kg/m³) were performed. FLUENT 6.1 software was used to carry out our simulation. The numerical results were compared with the experimental data of Qian and Pfeffer et al. [G.H. Qian, I. Bagyi, I.W. Burdick, R. Pfeffer, H. Shaw, Gas-Solid Fluidization in a Centrifugal Field.” AIChE J. 47 (5) (2001) 1022-1034]. The rotating speed of the RFB was set at 325 rpm (34 rad/s), which is equivalent to a centrifugal acceleration of 7 g.The flow behavior of the solid particles was analyzed; the bed thickness and the calculated pressure drop were compared with the experimental results. Our calculated pressure drop agreed very well with the experimental results.     

Structural, Electrical and Optical Properties of p-Type Transparent Conducting SnO2:Zn Film

Highly transparent, p-type conducting SnO₂:Zn films were deposited on quartz substrates by radio frequency (RF) magnetron sputtering using a 12 wt% ZnO doped with 88 wt% SnO₂ ceramic target followed by annealing at various temperatures. The effect of annealing temperature on the structural, electrical and optical performances of SnO₂:Zn films has been studied. XRD results show that all the SnO₂:Zn films possess tetragonal rutile structure with the preferred orientation of (101). Hall effect results indicate that at 873 K for 3 h was the optimum annealing parameters for p-type SnO₂:Zn films with relatively high hole concentration and low resistivity of 3.334 × 10¹⁹ cm⁻³ and 3.588 Ω cm, respectively. The average transmission of the p-type SnO₂:Zn films were above 80% in the visible light range. In addition, p-type conductivity was also confirmed by the non-linear characteristics of a p-type SnO₂:Zn/n-type SnO₂:Sb structure.     

A new approach of ionic liquid containing polymer sorbents for post-combustion CO2 scrubbing

Room temperature task-specific ionic liquids (TSIL) of 1-(2-hydroxylethyl)-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([Im₂₁OH][Tf₂N]) or 2-hydroxyethyl(dimethyl)-isopropylammonium bis(trifluoromethylsulfonyl)imide ([N_ip,211OH][Tf₂N]) with superbase, 1,8-diazabicyclo-[5.4.0]undec-7-ene (DBU), has been combined with Torlon^® powders (<106 um) to simulate the potential benefits of integrating equimolar amounts of ionic liquids and superbase into hollow fibers in terms of both sorption uptake and kinetics. Approximately 44 wt% of an equimolar [Im₂₁OH][Tf₂N]-DBU in Torlon^® powders achieved CO₂ sorption uptake of 0.57 mmol CO₂/g at a CO₂ feed pressure of 0.1 atm and at 35 °C. Similar amounts of an equimolar [N_ip,211OH][Tf₂N]-DBU in Torlon^® powders showed CO₂ sorption uptake of 0.45 mmol CO₂/g at the same condition. The half time (time to reach M_t/M_∞ of 0.5) for Torlon^®, Torlon^®(62 mg)/[Im₂₁OH][Tf₂N]-DBU(48 mg) and [Im₂₁OH][Tf₂N]-DBU at low feed pressure (～1.5 psia CO₂) was approximately 4, 55, and 298 s, respectively demonstrating that imbibing an equimolar [Im₂₁OH][Tf₂N]-DBU into polymer powders substantially improved sorption kinetics compared to the neat counterpart. The sorption half time is expected to be even shorter for fibers with smaller characteristic polymer morphology domains. The current study also demonstrates a new experimental approach to characterize CO₂ sorption in an equimolar mixture of ionic liquids and superbase.     

Growth,doping and characterization of epitaxial thin films and patterned structures of AlN,GaN, and AlxGa1−xN

Advancements in the doping of GaN and Al_xGa_1−xN thin films, and the growth of GaN and Al_xGa_1−xN structures on patterned heterostructure substrates via metalorganic vapor phase epitaxy are reported. The acceptor-type behavior of Mg-doped GaN films grown in N₂ diluents is presented. Net ionized impurity concentrations up to 8×10¹⁸ cm⁻³ and Hall mobilities up to ≈14 cm² V⁻¹ s⁻¹ were measured for Mg-doped films grown in N₂ in the as-grown condition. Donor and acceptor doping of Al_xGa_1−xN alloys was performed. Acceptor doping of Al_xGa_1−xN for x≤0.13 and donor doping for x≤0.58 were achieved for films deposited at 1100 °C. Lateral epitaxial overgrowth of GaN and Al_xGa_1−xN layers was investigated. The growth and coalescence of GaN and Al_xGa_1−xN stripes patterned in SiO₂ and/or SiN_x masks deposited on GaN, including aligned second lateral epitaxial overgrowth on initial laterally overgrown GaN layers, are discussed.     

Ionic Liquids for Chloromethane/Isobutane Distillative Separation: Express Screening

The present study centres on room‐temperature ionic liquids (ILs) as entrainers in extractive distillation of chloromethane/isobutane mixtures. The binary system, chloromethane/isobutene, is an azeotropic system. In this study, IL entrainers are shown to be able to break the azeotrope and, thus, assure the separation in the whole range of chloromethane/isobutane ratios. ILs formed from different cations and anions are considered and their influence on chloromethane/isobutane separation is explored. Among the ILs studied, those containing the trifluoromethanesulfonate ([CF₃SO₃]^–) or tricyanomethanide ([C(CN)₃]^–) anion are demonstrated to exhibit an enhanced potential for chloromethane/isobutane separation compared to the corresponding ILs based on the bis(trifluoromethylsulfonyl)imide ([Tf₂N]^–) anion. Moreover, the ILs enclosing these anions are cheaper than those with the [Tf₂N]^– anion. Thus, the separation ability, solubility of chloromethane/isobutane mixtures, and costs of IL entrainers can be adjusted by the right choice of cations and anions.     

Highly conductive SiC ceramics containing Ti2CN

Highly conductive SiC ceramics were fabricated by sintering β-SiC and TiN powder mixture in N₂ atmosphere. SiC ceramics exhibited decreased electrical resistivity (ρ) with increasing TiN content. X-ray diffraction data indicated that the specimens consisted of β-SiC grains without a detectible secondary phase for low TiN content (≤2 vol%) but contained a Ti₂CN phase as the TiN content increased. The temperature-dependent resistivity ρ(T) of specimens revealed semiconductor-like behavior for TiN content up to 10 vol% and metal-like behavior above 20 vol%. For the specimen with TiN content of 15 vol%, ρ(T) remained almost constant (2.06 ± 0.01 × 10⁻³ Ω cm) in the 4–300 K range. The resistivity of metal-like specimens were as low as 3.5 × 10⁻⁴ Ω cm for TiN content of 20 vol%. For semiconductor-like specimens, ρ(T) was primarily affected by N donors in the β-SiC grains. Metal-like specimens were primarily affected by metallic Ti₂CN clusters.     

CaMn0.05Zr0.95O3–NiMn2O4 composite ceramics with tunable electrical properties for high temperature NTC thermistors

A series of novel high temperature negative temperature coefficient (NTC) composite ceramics based on (1-x)CaMn_0.05Zr_0.95O₃-xNiMn₂O₄ (x = 0, 0.1, 0.2, 0.3) were fabricated by using the solid-state method. The Rietveld refinement method and backscattered electron (BSE) image confirmed the absence of any other phase. The conduction mechanism of the composite ceramics was determined by analyzing the complex impedance and resistance-temperature characteristics, which could be related to the formation of a continuous Mn³⁺-O-Mn⁴⁺ network. The effect of spinel content on the high temperature stability was analyzed using aging tests. The ρ_400°C, ρ_700°C and B_400/700 values of the NTC thermistors were determined to be 4.9 × 10⁶–1.2 × 10⁴, 1.4 × 10⁵–0.8 × 10³ Ω cm and 12739-5712 K, respectively. This indicated that the electrical properties could be tuned by adjusting the weight ratio of CaMn_0.05Zr_0.95O₃ and NiMn₂O₄. The findings obtained in this study reveal that the composite NTC thermistor exhibits a good application potential at high temperatures and under harsh environments.     

Fabrication and characterization of MOCVD (In1-xAlx)2O3 (0.1≤x≤0.6) ternary films

A series of (In_1-xAl_x)₂O₃ (0.1 ≤ x ≤ 0.6) films with tunable bandgap were grown on MgO (100) substrates by MOCVD. The influences of chemical compositions and growth temperatures on the film properties were studied systematically. XRD analyses indicated that the film quality degraded from crystalline to amorphous structure as Al concentration (x) increased. The (In_1-xAl_x)₂O₃ films prepared at 700 °C exhibited better film crystallinity than those of the ones grown at 600 °C. The films prepared at 700 °C with x = 0.1–0.3 showed an epitaxial In₂O₃ <111> orientation with the corresponding growth relationship of In₂O₃ (111)∥MgO (100). The film with x = 0.2 exhibited the best crystallinity and the largest grain size of 25.9 nm. The Hall mobilities and resistivities of the films were influenced evidently by Al concentrations. The Hall mobility showed a monotonous decrease from 12 to 1.1 cm²V^?1s^?1 as x increased from 0.1 to 0.6. The lowest resistivity of 9.2 × 10^?3 Ω cm was acquired for the film with x = 0.2. The average transmittances in the visible region for all the films were beyond 83%. The bandgap of the (In_1-xAl_x)₂O₃ films can be regulated in the range of 3.85–4.88 eV by changing Al concentrations from 0.1 to 0.6.     

Rheological properties of cellulose/ionic liquid/dimethylsulfoxide (DMSO) solutions

Rheological properties of cellulose dissolved in two ionic liquids (ILs), 1-allyl-3-methylimidazolium chloride (AmimCl) and 1-butyl-3-methylimidazolium chloride (BmimCl), with co-solvent dimethylsulfoxide (DMSO), are studied in the concentration range of cellulose from 0.070 to 6.0 wt%. The viscosities of ILs are exponentially decreased by adding DMSO in the concentration range of 0–100 wt%. The co-solvent DMSO decreases the monomer friction coefficient in cellulose solutions and has no significant change for the entanglement state of cellulose, thus results in the reduced solution viscosity, shortened relaxation time and unchanged moduli of the cross-over point. For cellulose solutions, dilute regime, semidilute unentangled regime and semidilute entangled regime were determined by steady shear experiments. In semidilute entangled regime, the specific viscosities η_sp, relaxation time τ, and plateau modulus G_N, exhibit concentration dependences as η_sp ～ C^4.4, τ ～ C^2.2, andG_N ～ C^1.9, respectively, in AmimCl-DMSO (80/20 w/w); and η_sp ～ C^4.3, τ ～ C^2.0, and G_N ～ C^2.1, respectively, in BmimCl–DMSO (80/20 w/w). Therefore, the rheological properties of cellulose/IL/DMSO solutions are approximately of IL-independence in this study. The dependence of η_sp upon cellulose concentration shows that the IL–DMSO mixture is more like a θ solvent for cellulose, and the thermodynamic properties of IL–DMSO mixtures are similar with those of ILs for cellulose at 25 °C. The conformation of cellulose in ILs would not be changed with the addition of DMSO not only in the dilute regime but also in the entanglement regime.     

Microwave-Assisted Esterification of N-Acetyl-L-Phenylalanine Using Modified Mukaiyama's Reagents: A New Approach Involving Ionic Liquids

Inspired by the concept of ionic liquids (ILs), this study modified the original Mukaiyama''s reagent, 2-chloro-1-methylpyridinium iodide (m.p. 200-dec), from ionic solid into liquids by changing its anion. The esterification of N-acetyl-L-phenylalanine was investigated as a model reaction. The microwave irradiation was more effective in esterifying N-acetyl-L-phenylalanine than the conventional reflux method. The original Mukaiyama''s reagent was modified into ILs through manipulating its anion. However, only non-nucleophilic anions (such as EtSO₄^– and Tf₂N^–) were favorable since nucleophilic ones (such as CF₃COO^– and CH₃COO^–) could exchange with chlorine resulting in non-reactive coupling reagents. Two modified Mukaiyama''s compounds (i.e. hydrophilic [2-ClMePy][EtSO₄] and hydrophobic [2-ClMePy][Tf₂N]) have been identified as the best ILtype coupling reagents. The esterification reaction was greatly enhanced by using 1- methylimidazole as the base instead of conventional toxic tertiary amines, and by using excess amount of alcohols as solvents instead of dichloromethane. Overall, the method reported is effective and ‘greener’.     

The effect of annealing on electrical properties of fluorinated amorphous carbon films

Fluorinated amorphous carbon (a–C:F) films have been deposited by electron cyclotron resonance chemical vapor deposition (ECR–CVD) at room temperature using C₄F₈ and CH₄ as precursor gases. The chemical compositions and electrical properties of a–C:F films have been studied by X-ray photoelectron spectroscopy (XPS), capacitance–voltage (C–V) and current-voltage (I–V) measurements. The results show that C–CF_x and C–C species of a–C:F films increase and fluorine content decreases after annealing. The dielectric constant of the annealed a–C:F films increases as a result of enhancement of film density and reduction of electronic polarization. The densities of fixed charges and interface states decrease from 1.6 × 10¹⁰ cm^− 2 and (5–9) × 10¹¹ eV^− 1 cm^− 2 to 3.2 × 10⁹ cm^− 2 and (4–6) × 10¹¹ eV^− 1 cm^− 2 respectively when a–C:F films are annealed at 300 °C. The magnitude of C–V hysteresis decreases due to reduced dangling bonds at the a–C:F/Si interfaces after heat treatment. The conduction of a–C:F films shows ohmic behavior at lower electric fields and is explained by Poole–Frankel (PF) mechanism at higher electric fields. The PF current increases indicative of reduced trap energy when a–C:F films are subjected to higher annealing temperatures.     

Sticking probability of CN radicals

The sticking probability, s, of CN(X²Σ⁺) radicals which were the precursor of the formation of amorphous carbon nitride films with high [N]/([N]+[C]) ratios (≤ 0.5) was re-evaluated. CN(X²Σ⁺) radicals were generated from the decomposition of BrCN with the microwave discharge flow of Ar of the pressure of 0.2-0.4 Torr. The number density of CN(X²Σ⁺), n_CN(X), was evaluated from the intensity of the CN(A²Π_i-X²Σ⁺) laser-induced fluorescence spectrum calibrated against Rayleigh scattering intensity of Ar. The weight of the C and N components of films, w, was evaluated from the compositional analysis for the deposited films using Rutherford back scattering and elastic recoil detection analysis. The [N]/([N]+[C]) ratios of films were 0.4-0.5. Based on n_CN(X), w, and the flow speed measured by a time-resolved emission, s was evaluated both under the desiccated and H₂O-added conditions as (8.5 ± 2.1) × 10^− 2 − (6.1 ± 1.2) × 10^− 2 and (11.4 ± 1.3) × 10^− 2 − (7.4 ± 1.8) × 10^− 2, respectively. The variation of s under various experimental conditions was discussed based on the electron densities in the reaction region.     

Optimization of Enzymatic Synthesis of Tricaprylin in Ionic Liquids by Response Surface Methodology

Ten 1,3‐dialkylimidazolium‐based ionic liquids (ILs) have been investigated as media for the enzymatic synthesis of tricaprylin, in comparison with the conventional organic solvent hexane. The results suggested that the esterification activity of Novozym 435 was higher than Lypozyme RM IM in all the ILs assayed. Novozym 435 showed higher catalytic activity in ILs with anions Tf₂N^? and PF₆^? than in BF₄^? and hexane. FTIR analysis of the secondary structure of the lipase indicated that a smaller decrease of the α‐helix was observed in [C₄MIM] Tf₂N and [C₄MIM] PF₆ than [C₄MIM] BF₄ and hexane, indicating that the anions of ILs might be a key factor for the activity of lipase in ILs. Process parameters (amount of lipase, caprylic acid/glycerol molar ratio, temperature and their interactive effects) were optimized in 1‐butyl‐3‐methylimidazolium hexafluorophosphate ([C₄MIM]PF₆) using Novozym 435 by response surface methodology. When the reactions were performed with the lipase amount of 6.1 % substrate mass at a caprylic acid/glycerol molar ratio of 4.5:1 and 66.7 °C, a higher yield was reached up to 92.4 %.     

Microstructure and multiferroic properties of BaTiO3/CoFe2O4 films on Al2O3/Pt substrates fabricated by electrophoretic deposition

BaTiO₃/CoFe₂O₄ bilayer films on high temperature resistant Al₂O₃/Pt substrates were fabricated using the electrophoretic deposition (EPD) method. Powder synthesis, suspension preparation and kinetics of deposition were investigated in detail. Two different sintering temperatures were tested and the resultant microstructure and properties of ceramic films were investigated. The composite films sintered at a temperature of 1200 °C/2 h yielded optimal microstructures and properties. The obtained bilayer films had a dense structure with no phase diffusion or passive layer. Besides to ferroelectric and magnetic properties, magnetoelectric (ME) coupling properties were also confirmed by the magnetic anisotropy and magnetic field induced polarization investigation. The composite films showed a increased P_s from 16.2 to 16.85 μC/cm² with variations ΔP_s of 4% when the magnetic field was applied in parallel direction and a decreased P_s from 16.2 to 14.9 μC/cm² with variations ΔP_s of ?8% when a normal direction field was applied.     

Synthesis of poly(ethylene terephthalate) in benzyl imidazolium ionic liquids

In order to improve the method of synthesis of poly(ethylene terephthalate) (PET), a series of ionic liquids (ILs) based on benzyl imidazolium ([YBMIM][X], Y = NO₂, CH₃, F; B = benzyl; X = Tf₂N) were used to investigate the formation of PET at low temperature and pressure. High molecular weight PET (M_w up to 2.6 × 10⁴ g mol^?1) was obtained by two‐step polycondensation in these ILs at lower temperature (230–240 °C) than with traditional melt polycondensation (270–290 °C). Moreover, the molecular weight of the resulting PET was found to depend on the activities of the catalysts used in the ILs. The catalysts (Sb₂(OCH₂CH₂O)₃, Sb(OAc)₃, Sb₂O₃) used in the preparation of PET have little effect on the thermostability of the ILs. The ILs can decrease the viscosity of the reaction system, and thus small molecules can be easily removed. Copyright © 2012 Society of Chemical Industry