Effect of electrolytes on surface tension and surface adsorption of 1-hexyl-3-methylimidazolium chloride ionic liquid in aqueous solution

Surface and bulk properties of 1-hexyl-3-methylimidazolium chloride [C₆mim][Cl] as an ionic liquid (IL) have been investigated by surface tension and electrical conductivity techniques at various temperatures. Results reveal that the ionic liquid behaves as surfactant-like and aggregates in aqueous solution. Critical aggregation concentration (cac) values obtained by conductivity and surface tension measurements are in good agreement with values found in the literature. A series of important and useful adsorption parameters including cac, surface excess concentration (Γ), and minimum surface area per molecule (A_min) at the air + water interface were estimated from surface tension in the presence and absence of different electrolytes. Obtained data show that the surface tension as well as the cac of [C₆mim][Cl] is reduced by electrolytes. Also, values of surface excess concentration (Γ) show that the IL ions in the presence of electrolyte have much larger affinity to adsorption at the surface and this affinity increased in aqueous electrolyte solution in the order of I^? > Br^? > Cl^? for counter ion of salts that was explained in terms of a larger repulsion of chloride anions from interface to the bromide and iodide anion as well as difference in their excess polarizability.     

Experiments and model for the surface tension of (MDEA + [Bmim][BF4]) and (MDEA + [Bmim][Br]) aqueous solutions

The surface tension (γ) of 1-butyl-3-methylimidazolium tetrafluoroborate ([Bmim][BF₄]), 1-butyl-3-methylimidazolium bromide ([Bmim][Br]), (N-methyldiethanolamine(MDEA) + [Bmim][BF₄]) and (MDEA + [Bmim][Br]) aqueous solutions were measured by using the BZY-1 surface tension meter. The temperature ranged from (293.2 to 323.2) K. The mass fraction of MDEA ranged from 0.35 to 0.45. A thermodynamic equation was proposed to model the surface tension of (MDEA + ionic liquids) (ILS) aqueous solutions and the calculated results agreed well with the experiments. The effects of temperature, mass fractions of MDEA and ILS on the surface tension were demonstrated on the basis of experiments and calculations.     

Potential energy surface and rate constant of the inversion substitution reactions CH3X + O2 → CH3O2• + X• (X = SH,NO2)

The temperature dependence of the rate constant of the inversion substitution reactions CH₃X + O₂ → CH₃O₂^? + X^? (X = SH, NO₂), can be expressed as k = 6.8 × 10^–12(T/1000)^1.49exp(–62816 cal mol^–1/RT) cm³ s^–1 (X = SH) and k = 6.8 × 10^–12(T/1000)^1.26 × × exp(–61319 cal mol^–1/RT) cm³ s^–1 (X = NO₂), as found with the use of high-level quantum chemical methods and the transition state theory.     

Densities,surface tensions,and derived surface thermodynamics properties of (trimethylbenzene + propyl acetate,or butyl acetate) from T = 298.15 K to 313.15 K

Densities (ρ) for binary systems of (1,2,4-trimethylbenzene, or 1,3,5-trimethylbenzene + propyl acetate, or butyl acetate) were determined at four temperatures (298.15, 303.15, 308.15, and 313.15) K over the full mole fraction range. The excess molar volumes (V^E) calculated from the density data show that the deviations from ideal behaviour in the systems (all being positive, excepting 1,2,4-trimethylbenzene + butyl acetate system) become more positive with the temperature increasing. Surface tensions (σ) of these binary systems were measured at the same temperatures (298.15, 303.15, 308.15, and 313.15) K by the pendant drop method, the surface tension deviations (δσ) for all system are negative, and decrease with the temperature increasing. The V^E and δσ are fitted to the Redlich–Kister polynomial equation. Surface tensions were also used to estimate surface entropy (S_σ) and surface enthalpy (H_σ).     

Density and surface tension of pure 1-ethyl-3-methylimidazolium l-lactate ionic liquid and its binary mixtures with water

The density and surface tension of 1-ethyl-3-methylimidazolium l-lactate ([emim][l-lactate]) ionic liquid were determined from T = (283.15 to 333.15) K. The coefficients of thermal expansion were calculated from the experimental density results using an empirical correlation for T = (283.15 to 333.15) K. Molecular volume and standard entropies of the IL were calculated from the experimental density values. The surface properties of IL were investigated. The critical temperature and enthalpy of vaporization were also discussed. Density and surface tension have been measured over the whole composition range for {[emim][l-lactate] + water} binary systems at a temperature of 298.15 K and atmospheric pressure. Excess molar volumes V^E and the surface tension deviations δγ have been determined.     

Liquid–liquid equilibrium calculation in binary water + nonionic surfactant CiEj systems with a new mass-action law model based on continuous thermodynamics

A systematic study of the LLE for a number of aqueous solutions of n-alkyl polyglycol ethers (C_iE_j) with tail length i from 4 to 12 and head length j from 1 to 6 is presented. For calculation a new thermodynamic model was developed basing on the mass-action law and continuous thermodynamics. Besides the micellization the self association of water is taken into account. The resulting polydisperse mixture of micelles and water associates is described by two continuous aggregation-size distribution functions depending on temperature and surfactant concentration. The Gibbs energy of the mixture is calculated by the Flory-Huggins theory with a temparature dependent parameter χ. The model is applied to 13 water + C_iE_j systems with LCST behavior and to the three systems water + C₄E₁, water + C₁₀E₄ and water + C₁₀E₅ with closed-loop miscibility gaps. For the former 13 systems four parameters were fitted to the experimental equilibrium data. For the systems with closed-loop miscibility gaps two additional parameters were necessary, due two the more extended temperature range. The agreement between calculated and experimental data is very good for nearly all systems of both types.     

Temperature dependence of the surface tension and 0.1 MPa density for 1-Cn-3-methylimidazolium tris(pentafluoroethyl)trifluorophosphate with n = 2, 4, and 6

Experimental air–liquid interfacial tension data and density data are presented for three 1-C_n-3-methylimidazolium tris(pentafluoroethyl)trifluorophosphates (FAP), [C_nMIM][(C₂F₅)₃PF₃], with n = 2, 4, and 6, measured at atmospheric pressure in the temperature range from 267 K to 360 K using the Krűss K100MK2 tensiometer. The accuracy of the surface tension measurements was checked by employing the Wilhelmy plate and the du Noüy ring methods in parallel. The combined standard uncertainty associated with the Wilhelmy plate method is estimated to be ±0.1 mN · m⁻¹. The density data were obtained using buoyancy method with an estimated standard uncertainty less then ±0.4 kg · m⁻³ (3 · 10⁻⁴ϱ). The chloride anions decrease the density of the tris(pentafluoroethyl)trifluorophosphates of interest up to six times more effectively than they decrease the density of the imidazolium based tetrafluoroborates. A QSPR analysis of the surface tension of imidazolium based ionic liquids with BF₄, TFA, DCA, FAP, NTf₂, and PF₆ anions indicates, that the FAP ionic liquids fit well into the analyzed group of imidazolium based ionic liquids while those having hexafluorophosphate anion show anomalously high deviations of the experimental surface tension from the values predicted by the QSPR model.     

Reversibility of platinum voltammograms in aqueous electrolytes,ionic product and dissociative adsorption of water

Well-known reversibility of platinum voltammograms in supporting aqueous electrolytes formally contradicts the equilibrium defined by the ionic product of water: K_w = [H⁺] · [OH⁻] ≅ 1 × 10¹⁴, since at any pH value, concentration of one of these ions should be too low (⩽10⁷ M) to ensure reversibility in the whole potential region at usual scan rates. This contradiction could be overcome by allowing dissociative water adsorption on platinum. All available relevant data obtained by in situ physical methods appear to provide indirect experimental evidences for this hypothesis.     

A binder-free thin film anode composed of Co2 +-intercalated buserite grown on carbon cloth for oxygen evolution reaction

We present a binder-free catalytic anode for highly efficient and stable oxygen evolution reaction in alkaline media. The catalyst consists of a thin film of buserite-type layered manganese dioxide (MnO₂) intercalated with Co^2 + ions, resulting from electrodeposition of the layered MnO₂ film with tetrabutylammonium (Bu₄N⁺) ions on a carbon cloth, followed by ion-exchange of the initially incorporated Bu₄N⁺ with Co^2 + in solution. The electrode is capable to produce a current density of 10 mA cm^− 2 at an overpotential (η) of 377 mV with a Tafel slope of 48 mV dec^− 1, much superior to the layered MnO₂ without Co^2 +.     

Measurement of the (pressure,density, temperature) relation of two (methane + nitrogen) gas mixtures at temperatures between 240 and 400 K and pressures up to 20 MPa using an accurate single-sinker densimeter

Comprehensive (p, ρ, T) measurements on two gas mixtures of (0.9CH₄ + 0.1N₂) and (0.8CH₄ + 0.2N₂) have been carried out at six temperatures between 240 and 400 K and at pressures up to 20 MPa. A total of 108 (p, ρ, T) data for the first mixture and 134 for the second one are given. These measurements were performed using a compact single-sinker densimeter based on Archimedes’ buoyancy principle. The overall uncertainty in density ρ is estimated to be (1.5 · 10⁻⁴ · ρ + 2 · 10⁻³ kg · m⁻³) (coverage factor k = 2), the uncertainty in temperature T is estimated to be 0.006 K (coverage factor k = 2), and the uncertainty in pressure p is estimated to be 1 · 10⁻⁴·p (coverage factor k = 2). The equipment has been previously checked with pure nitrogen over the whole temperature and pressure working ranges and experimental results (35 values) are given and a comparison with the reference equation of state for nitrogen is presented.     

A study of the photodeposition over Ti/TiO2 electrode for electrochemical detection of heavy metal ions

Here we reported that UV light irradiation can significantly enhance sensitivity of Ti/TiO₂ electrode for determination of trace heavy metal ions (such as Cu^2 +, Pb^2 + and Cd^2 +) owing to the photodeposition of metal ions on the surface of electrodes. The sensitivity of heavy metal ions can be selectively enhanced over the Ti/TiO₂ electrode, which is attributed to matching between potential of heavy metal ions and the position of the conduction band of TiO₂.     

Isothermal (vapour + liquid) equilibrium (VLE) for binary mixtures containing diethyl carbonate,phenyl acetate,diphenyl carbonate,or ethyl acetate

The isothermal (vapour + liquid) equilibrium (VLE) (P–T–x_i–y_i) was determined the binary systems of (ethyl acetate + diethyl carbonate) from T = (373.2 to 453.2) K, (ethyl acetate + phenyl acetate) at T = 373.2 K, and (diethyl carbonate + phenyl acetate) at T = 373.2 K, while the VLE (P–T–x_i) of three diphenyl carbonate-containing binary systems was also determined experimentally at temperatures from (373.2 to 453.2) K. The experimental results show no azeotrope formation and near ideal solution behaviour for each binary system. These new VLE (P–T–x_i–y_i) data have been passed by the point, area, and infinite dilution thermodynamic consistency tests. The Wilson-HOC, the NRTL-HOC, and the UNIQUAC-HOC models were applied to correlate the VLE results and the optimal values of the model parameters have been determined through data reduction. Comparable results were obtained from these three models.     

A (vapor + liquid) equilibria of the {carbon dioxide + isopropoxyethanol (iC3E1)} and the {carbon dioxide + isobutoxyethanol (iC4E1)} systems

Binary (vapor + liquid) equilibrium data were measured for the {carbon dioxide + isopropoxyethanol (iC₃E₁)} and the {carbon dioxide + isobutoxyethanol (iC₄E₁)} systems at temperatures ranging from (313.15 to 333.15) K. These experiments were performed with a circulating-type apparatus with on-line gas chromatography. The experimental data correlated well with the Peng–Robinson equation of state using the Wong–Sandler mixing rules.     

Stable iminonitroxide biradicals: Building blocks for organic heterospin,heteromolecular complexes

A stable cationic biradical has been designed and synthesized, and its magnetic property and crystal structure have been examined. An iminonitroxide derivative of 3,5-disubstituted pyridine (1) with a triplet ground state has been cationized by a reaction with methyl trifluoromethanesulfonate (MeTfO), which gave a salt of N-methylated pyridinium 2⁺, 2⁺ · TfO⁻. The ground state of the cation 2⁺ has been found to be triplet with 2J/k_B = 7.5 K from magnetic susceptibility measurements for 2⁺ · TfO⁻ in a magnetically diluted organic matrix. The magnetic susceptibility of neat crystalline solids of 2⁺ · TfO⁻ has been explained by an exchange coupling model based on the X-ray crystal structure. It is well known that the energy preference for a high-spin ground state for a m-phenylene coupling unit is disturbed by heteroatomic substitution and an ionic charge. The present experimental results show that the high-spin preference in 1 is little affected by the ionic charge in 2⁺. The ground-state triplet biradical serves as building blocks for molecule-based magnets of S > 1/2 of molecular assemblages based on electrostatic interactions between molecular ions.     

Reply to comment on the possible role of the reaction H+H2O→H2+OH in the radiolysis of water at high temperatures

In reply to “Comment on the possible role of reaction H+H₂O→H₂+OH in the radiolysis of water at high temperatures” (Bartels, 2009 Comment on the possible role of the reaction H+H₂O→H₂+OH in the radiolysis of water at high temperatures. Radiat. Phys. Chem. 78, 191–194) we present an alternative thermodynamic estimation of the reaction rate constant k. Based on the non-symmetric standard state convention we have calculated that the Gibbs energy of reaction Δ_rG=57.26 kJ mol^?1 and the reaction rate constant k=7.23×10^?5 M^?1 s^?1 at ambient temperature. Re-analysis of the thermodynamic estimation (Bartels, 2009 Comment on the possible role of the reaction H+H₂O→H₂+OH in the radiolysis of water at high temperatures. Radiat. Phys. Chem. 78, 191–194) showed that the upper limit for the rate constant at 573 K is k=1.75×10⁴ M^?1 s^?1 compared to the value predicted by the diffusion-kinetic modelling (3.18±1.25)×10⁴ M^?1 s^?1 (Swiatla-Wojcik, D., Buxton, G.V., 2005. On the possible role of the reaction H+H₂O→H₂+OH in the radiolysis of water at high temperatures. Radiat. Phys. Chem. 74(3–4), 210–219). The presented thermodynamic evaluation of k(573) is based on the assumption that k can be calculated from Δ_rG and the rate constant of the reverse reaction which, as discussed, are both uncertain at high temperatures.     

Correlation between capacitances of porous carbons in acidic and aprotic EDLC electrolytes

A study based on a total of 41 nanoporous carbons shows that there exists a good correlation between the limiting gravimetric capacitances C_o at low current densities j (1 mA cm⁻²) measured in aprotic (1 M (C₂H₅)₄NBF₄ in acetonitrile) and in acidic (2 M aqueous H₂SO₄) electrolytes. The comparison of the surface-related capacitances (F m⁻²) of well characterized samples with the amount of thermodesorbed CO suggests a strong contribution of CO generating surface groups to charge storage in the acidic electrolyte, but a negligible contribution in the aprotic medium. It also appears that the decrease of the capacitance with current density is similar in both electrolytes. This confirms that the average micropore width and the CO₂ generating surface groups are the main factors which limit the ionic mobility in both electrolytes.     

On oxoacidic properties and solubilities of beryllium and magnesium oxides in molten (CsCs + KCl + NaCl) eutectic at T = 783 K

Reactions of Be²⁺ and Mg²⁺ with O^2– in molten eutectic mixture (CsCs + KCl + NaCl) (0.455:0.245:0.30) at T = 783 K were studied by a potentiometric method using Pt(O₂)|ZrO₂(Y₂O₃) indicator electrode. Addition of O^2– ions to the melt containing Mg²⁺ results in precipitation of MgO (pK_s,MgO = 11.89 ± 0.3, molality) whereas interaction of Be²⁺ with O^2– is accompanied with sequential formation of Be₂O²⁺ (pK = 15.68 ± 0.5, molality) and precipitation of BeO (pK_s,BeO = 9.62 ± 0.3, molality). On the basis of the obtained and known data pK_s,MgO–T⁻¹ dependence in molten (CsCs + KCl + NaCl) eutectic is constructed. The slope of the said dependence in T/K = (from 583 to 1073) range is in good agreement with the value predicted by the Shreder equation, that extends the range of use of the Shreder equation for predictions of metal oxide solubilities in molten halides.     

Molar heat capacities of some aqueous (2-amino-2-hydroxymethyl-1,3-propanediol + glycol) systems

A new set of molar heat capacity data for aqueous {2-amino-2-hydroxymethyl-1,3-propanediol (TRIS) + glycol} at (30 to 80) °C and different concentrations (4% to 16% by weight TRIS or 56% to 44% by weight water, in a fixed amount of glycol – 40% by weight) were gathered via reliable measurement method and are presented in this report. The glycols considered were diethylene glycol (DEG), triethylene glycol (TEG), tetraethylene glycol (T₄EG), propylene glycol (PG), dipropylene glycol (DPG), and tripropylene glycol (TPG). The 198 data points gathered fit the equation, C_p = C_p,a + B₁m + B₂m² + B₃m³, where C_p and C_p,a are the molar heat capacities of the (TRIS + glycol + water) and (water + glycol) systems, respectively, B_i the temperature-dependent parameters, and m the mole TRIS per kilogram (glycol + water). The overall average absolute deviation (AAD) of the experimental data from the corresponding values calculated from the correlation equation was 0.07%.     

Oxidation of aliphatic alcohols by triethylammonium chlorochromate in non-aqueous medium – A kinetic and mechanistic study

The oxidation of some aliphatic alcohols by triethylammonium chlorochromate (TriEACC) in dimethyl sulfoxide leads to the formation of the corresponding carbonyl compounds. The reaction is first order with respect to TriEACC. The reaction exhibited Michaelis–Menten type kinetics with respect to alcohol. The reaction is catalyzed by hydrogen ions. The hydrogen-ion dependence has the form: k_obs = a + b[H⁺]. The oxidation of [1,1-²H₂] ethanol (MeCD₂OH) exhibits a substantial primary kinetic isotope effect. Oxidation of aliphatic alcohol was studied in 19 different organic solvents. The solvent effect has been analysed using Kamlet’s and Swain’s multi-parametric equation. A suitable mechanism has been proposed.     

Study on electrochemical performance of activated carbon in aqueous Li2SO4, Na2SO4 and K2SO4 electrolytes

The electrochemical performances of activated carbon (AC) in 0.5 mol/l Li₂SO₄, Na₂SO₄ and K₂SO₄ aqueous electrolytes were investigated. The cyclic voltammetric results at different scan rates show that the rate behaviors of AC in the three electrolytes improve in the order of Li₂SO₄ < Na₂SO₄ < K₂SO₄. This improvement can be mainly ascribed to the following two reasons: (1) the decreasing equivalent series resistance in the order of Li₂SO₄ > Na₂SO₄ > K₂SO₄, which is the main factor influencing the maximum output power, and (2) the increasing migration speed of hydrated ions in the bulk electrolyte and in the inner pores of AC electrode in the order of Li⁺ < Na⁺ < K⁺. Their cycling behaviors do not show any differences in capacitive fading. The above results provide valuable information to explore new hybrid supercapacitors.