Planar tetracoordinate carbon in CE42− (E = Al–Tl) clusters

The structures and bonding of the CE₄^2?clusters (E = Al, Ga, In, Tl) have been theoretically studied via B3LYP/def2-TZVP computations. Total energies were recalculated at the CCSD(T)/def2-TZVPP//B3LYP/def2-TZVP level in order to corroborate the energy differences. Our computations show that all the CE₄^2?and CE₄Li^?clusters (E = Al, Ga, In,Tl) have a planar tetracoordinate carbon structure. Interestingly, while the most stable form of CAl₄Li^? and CGa₄Li^? is planar with coordination of Li⁺ to an edge of the CE₄^2? fragment, for CIn₄Li^? and CTl₄Li^? the pyramidal structures with C_4v symmetry are the lowest-energy structures.     

Modelling (vapour + liquid) and (vapour + liquid + liquid) equilibria of {water (H2O) + methanol (MeOH) + dimethyl ether (DME) + carbon dioxide (CO2)} quaternary system using the Peng–Robinson EoS with Wong–Sandler mixing rule

The (vapour + liquid) equilibria (VLE) and (vapour + liquid + liquid) equilibria (VLLE) binary data from literature were correlated using the Peng–Robinson (PR) equation of state (EoS) with the Wong–Sandler mixing rule (WS). Two group contribution activity models were used in the PRWS: UNIFAC–PSRK and UNIFAC–Lby. The systems were successfully extrapolated from the binary systems to ternary and quaternary systems. Results indicate that the PRWS–UNIFAC–PSRK generally displays a better performance than the PRWS–UNIFAC–Lby.     

Vibrational relaxation rates for H on a Si(1 0 0):(2×1) surface: a two-dimensional model

The results of calculations based on perturbation theory of vibrational relaxation rates due to coupling to substrate phonons for hydrogen atoms adsorbed on a Si(1 0 0):(2×1) surface are presented. For this purpose a two-dimensional model is adopted in which both the H–Si stretching and bending motions are included. It is shown that within this model the multiphonon emission and absorption processes play a negligible role. The calculated lifetimes agree well with available experimental data.     

A potentiometric study of acid–base properties of the (phenol + phenolate) systems in acetonitrile and, (acetonitrile + cyclohexane) solvent system

Acid–base equilibria were studied potentiometrically in (phenol + phenolate) systems involving nine substituted phenols with both electron-donating and electron-accepting substituents in a polar protophobic aprotic solvent, acetonitrile. To estimate the influence of the polarity of the medium on acid dissociation and anionic homoconjugation equilibria, the equilibrium constants were also determined in an (acetonitrile + cyclohexane) solvent in which the latter was a diluent that lowered the dielectric permittivity of the reaction medium, and compared with those determined in acetonitrile.     

Ternary (liquid + liquid) equilibria for β-citronellol in aqueous alcohol at different temperatures

(Liquid + liquid) equilibrium (LLE) data for {water (1) + methanol (2) + β-citronellol (3)} and {water (1) + ethanol (2) + β-citronellol (3)} ternary systems at T = (283.15, 298.15, and 313.15) K are reported. The immiscible region of (water + methanol + β-citronellol) system was found to be larger than that for the ethanol system at the same temperature. The effect of the temperature on the ternary (liquid + liquid) equilibria was examined and discussed. The experimental (liquid + liquid) equilibrium data have been satisfactorily represented by using extended UNIQUAC and modified UNIQUAC models.     

Theoretical study of the stability of small triply charged carbon clusters Cn3+ (n = 3–12)

Using density functional theory, coupled cluster and multireference methods, dissociation energies and 3rd ionization potentials for, respectively, triply charged and neutral carbon clusters have been evaluated. The results show that the smaller C_n³⁺ clusters are metastable, i.e., they present a fragmentation channel with negative dissociation energy. The lowest dissociation channel always corresponds to evaporation of a singly charged carbon atom. Good agreement with available experimental data is found for most two-fragment channels. The third ionization potential of the corresponding neutral species decreases with cluster size.     

Diphenylphosphorylated PEG (DPPPEG) as a new support for generation of nano-Pd(0) as catalyst for carbon–carbon bond formation via copper-free Sonogashira and homocoupling reactions of aryl halides in PEG

In this study, synthesis and application of diphenylphosphorylated PEG₂₀₀ (DPPPEG₂₀₀) are described. Herein, we report a very simple procedure for the preparation of DPPPEG₂₀₀ as a stable solid through the reaction of PEG₂₀₀ with ClPPh₂. This compound was used as a very suitable ligand for the in situ generation of nano-Pd(0) particles through its reaction with PdCl₂ as a pre-catalyst. Isolation of this catalyst is very simple through addition of diethyl ether to the reaction mixture and centrifugations. Full characterization of the nano-Pd(0)/DPPPEG200 was performed by XRD spectra, UV–Vis spectra, and also by TEM image. This nano-complex was used as an efficient catalyst for copper-free Sonogashira and homocoupling reactions of aryl halides. The sonogashira reaction of aryl halides was conducted at 80 °C in PEG. However, the homocoupling reaction was performed at 100 °C for aryl iodides and activated aryl bromides and at 130 °C for deactivated aryl bromides and aryl chlorides in PEG. The catalyst was recovered and recycled for four consecutive runs.     

Excess molar volume,viscosity, and refractive index study for the ternary mixture {2-methyl-2-butanol (1) + tetrahydrofuran (2) + propylamine (3)} at different temperatures. Application of the ERAS-model and Peng–Robinson–Stryjek–Vera equation of state

Densities, viscosities, and refractive indices of the ternary mixture consist of {2-methyl-2-butanol (1) + tetrahydrofuran (THF) (2) + propylamine (3)} at a temperature of 298.15 K and related binary mixtures were measured at temperatures of (288.15, 298.15, and 308.15) K at ambient pressure. Data were used to calculate the excess molar volumes and the deviations of the viscosity and refractive index. The Redlich–Kister and the Cibulka equations were used for correlating binary and ternary properties, respectively. The ERAS-model has been applied for describing the binary and ternary excess molar volumes and also Peng–Robinson–Stryjek–Vera (PRSV) equation of state (EOS) has been used to predict the binary and ternary excess molar volumes and viscosities.     

Synthesis and electrochemical characteristics of xLi2MnO3–(1−x)Li(Mn0.375Ni0.375Co0.25)O2 (0.0 ≤ x ≤ 1.0) thin film cathode for lithium rechargeable micro batteries

We have compared the structure, microstructure, and electrochemical characteristics of xLi₂MnO₃–(1−x)Li(Mn_0.375Ni_0.375Co_0.25)O₂ (0.0 ≤ x ≤ 1.0) thin films with their bulk cathode laminate counterparts of identical compositions. Pure Li(Mn_0.375Ni_0.375Co_0.25)O₂ as well as the synthesized composite films partially transform into cubic spinel structure during charge–discharge cycling. In contrast, such layered to spinel phase transformation has only been identified in bulk cathode laminates with x ≥ 0.75. At a current density 0.05 mAcm⁻², the discharge capacity of Li(Mn_0.375Ni_0.375Co_0.25)O₂ thin film was measured to be ∼60 μAhcm⁻². The discharge capacity (∼217 μAhcm⁻²) was markedly improved in x∼0.5 composite thin film. The capacity retention after 20 charge discharge cycles are improved in composite films; however, their capacity fading could not be eliminated completely.     

Measurement and correlation of the (p, ρ, T) relation of liquid cyclohexane,toluene, and ethanol in the temperature range from 233.15 K to 473.15 K at pressures up to 30 MPa for use as density reference liquids

Comprehensive (p, ρ, T) measurements on cyclohexane, toluene, and ethanol were carried out in the homogeneous liquid phase for temperatures from 233.15 K to 473.15 K at pressures up to 30 MPa. The measurements were performed by using an accurate single-sinker densimeter based on the Archimedes’ buoyancy principle. The total uncertainty of the measurements in density was estimated to be 0.015% (level of confidence 95%). Based on the experimental results, accurate correlation equations for the density of the three liquids have been established; their uncertainty is 0.020%. Comparisons with previous results of other experimentalists and with values calculated from current equations of state are presented. In this context it is also shown that the density of a liquid can vary slightly depending on the batch of the liquid used for the measurements. The purpose of this work was to provide accurate correlation equations for the densities of the three selected liquids so that these liquids can be used as density reference liquids for the calibration of densimeters and, in particular, for the calibration of vibrating-tube densimeters.     

Theoretical approach on ceria-based two-phase electrolytes for low temperature (300–600 °C) solid oxide fuel cells

Recently, extensive studies on the ceria-based two-phase composites as functional electrolytes have created excellent 300–600 °C fuel cell technology. There is an emergence need to deepen the knowledge and to develop theoretical methodologies in this field. The feasibility to design and develop two-phase materials as superionic conductors for 300–600 °C solid oxide fuel cells (LTSOFCs) is reported. The superionic conductivity at 300–600 °C in two-phase materials where the interfaces between the constituent phases are constructed as “superionic highways” resulting in interfacial high ionic conduction. The material architecture and design presented in this report thus reaches beyond the conventional molecular way to synthesize new compounds.     

Measurement of the 238U(n,γ)239U reaction cross sections in the energy range of 2.0–5.0 MeV by using a neutron activation technique

The neutron capture cross-sections of ²³⁸U at the neutron energies of 4.38?±?0.05 MeV, 3.02?±?0.49 MeV and 2.04?±?0.26 MeV have been measured using the activation method and off-line gamma-ray spectrometric technique. The effects of neutron flux fluctuation, multiple scattering, flux self-shielding and gamma-ray self-absorption were corrected. The excitation function of the ²³⁸U(n,γ)²³⁹U reaction was also calculated using the TALYS-1.9 code. The experimental results were compared with the evaluated data, the theoretical data and the previous experimental data.

     

Preparation of an ionic liquid-mediated carbon nanotube-poly(dimethylsiloxane) fiber by sol–gel technique for determination of polycyclic aromatic hydrocarbons in urine samples using head-space solid-phase microextraction coupled with gas chromatography

A novel ‘ionic liquid-mediated multi-walled carbon nanotube (MWCNT)-poly(dimethylsiloxane) (PDMS)’ hybrid coating was prepared by the covalent functionalization of MWCNTs with hydroxyl-terminated PDMS using the sol–gel technique. The prepared fiber was successfully used for the separation and determination of trace amounts of polycyclic aromatic hydrocarbon compounds (PAHs) in four urine samples using head-space solid-phase microextraction coupled to gas chromatography-flame ionization detection. The proposed fiber has high thermal stability and long durability and it can be used more than 210 times without any significant change in its sorption properties. The effects of important parameters such as the exposure time, sampling temperature, sample ionic strength and stirring rate on the extraction efficiency have been studied and optimized. Under the optimal conditions, the method detection limits (S/N = 3) were in the range of 0.0005–0.004 ng mL^?1 and the limits of quantification (S/N = 10) between 0.002 and 0.01 ng mL^?1. The relative standard deviations for one fiber (repeatability, n = 5) were 4.9–7.5 % and for the fibers obtained from different batches (reproducibility, n = 3), 6.1–8.9 %. The developed method was successfully applied to determine trace levels of PAHs in real urine samples. The obtained relative recoveries for the spiked samples with 0.05 ng mL^?1 of each of the PAH compounds were 89.3–107.2 %.     

Structural studies of the aeschynite–euxenite transformation in the series Ln(TiTa)O6 Ln = Lanthanide

Ceramics based on LnTiTaO₆ (Ln = La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu) were prepared using a conventional solid-state ceramic route. The structure and microstructure of the samples were analyzed using scanning electron microscopy, synchrotron X-ray powder diffraction and neutron diffraction techniques. The unit cell volume of the ceramics decreased with a decrease in ionic radius of the rare-earth ions until a phase change was seen at Ho where the space group changed from Pnma to Pbcn. The results confirmed that the boundary of the aeschynite to euxenite phase change that lies between DyTiTaO₆ and HoTiTaO₆ and demonstrate that this is a result of distortion of the channels in the aeschynite structure.     

Synthesis and electrochemical characterization of xLi(Ni0.8Co0.15Mg0.05)O2–(1−x)Li[Li1/3Mn2/3]O2 (0.0 ≤ x ≤ 1.0) cathodes for Li rechargeable batteries

Using solution based processing route, we have successfully synthesized xLi(Ni_0.8Co_0.15Mg_0.05)O₂–(1?x)Li[Li_1/3Mn_2/3]O₂ (0.0 ≤ x ≤ 1.0) cathode materials for lithium rechargeable batteries. The phase formation behavior of these cathode materials is characterized by X-ray diffraction measurements. The Galvanostatic charge–discharge characteristic of these cathodes is reported in various cut-off voltage limits. When these composite cathodes are charged to 4.8 V, electrochemical extraction of lithium takes place from active (Li[Ni_0.8Co_0.15Mg_0.05]O₂) as well as inactive (Li[Li_1/3Mn_2/3]O₂) components. Good cycleability of these cathodes is obtained when cycled in the cut-off voltage limits of 4.6–3.0 V. The cycleability of these cathodes are deteriorated when charged above 4.8 V and deep discharged up to 1.2 V followed by repeated cycling in these voltage limits. Based on the analyses of impedance spectra at various charge and discharge states, the probable reasons for such findings are discussed.     

Determination of non-steroidal anti-inflammatory drugs in water samples by solid-phase microextraction based sol–gel technique using poly(ethylene glycol) grafted multi-walled carbon nanotubes coated fiber

In this study, poly(ethylene glycol) (PEG) grafted multi-walled carbon nanotubes (PEG-g-MWCNTs) were synthesized by the covalent functionalization of MWCNTs with hydroxyl-terminated PEG chains. PEG-g-MWCNTs was used as a novel stationary phase to prepare the sol–gel solid-phase microextraction (SPME) fiber in combination with gas chromatography–flame ionization detector (GC–FID) for the determination of ibuprofen, naproxen and diclofenac in real water samples.     

Ebulliometric determination and prediction of (vapor + liquid) equilibria for binary and ternary mixtures containing alcohols (C1–C4) and dimethyl carbonate

(Vapor + liquid) equilibrium (VLE) data for a ternary mixture, namely {methanol + propan-1-ol + dimethyl carbonate (DMC)}, and four binary mixtures, namely an {alcohol (C₃ or C₄) + DMC}, containing the binary constituent mixtures of the ternary mixture, were measured at p = (40.00 to 93.32) kPa using a modified Swietoslawski-type ebulliometer. The experimental data for the binary systems were correlated using the Wilson model. The Wilson model was also applied to the ternary system to predict the VLE behavior using parameters from the binary mixtures. The modified UNIFAC (Dortmund) model was also tested for the predictions of the VLE behavior of the binary and ternary mixtures. In addition, the experimental VLE data for the ternary and constituent binary mixtures were correlated using the extended Redlich–Kister (ERK) model, which can completely represent the azeotropic points. For the ternary system, a comparison of the experimental and the predicted or correlated boiling points obtained using the Wilson and ERK models showed that the ERK model is more accurate. The valley line, i.e., the curve which divides the patterns of vapor–liquid tie lines, was found in the (methanol + propan-1-ol + DMC) system. This valley line could be represented by the ERK model. Finally, the composition profile for simple distillation of this ternary mixture was obtained by analysis of the residue curves from the estimated Wilson parameters of the constituent binary mixtures.