Mutual diffusion coefficients of alkaline-earth and third-family metal chlorides in aqueous solutions

Measurements of mutual diffusion coefficients of several metal chlorides in aqueous solutions close to infinite dilution have been made with the Taylor dispersion technique. Data were obtained for alkaline earth metal chlorides. BeCl₂/H₂O, MgCl₂/H₂O, CaCl₂/H₂O, SrCl₂/H₂O, and BaCl₂/H₂O, and for third-family metal chlorides, AlCl₂/H₂O, and GaCl₃/H₂O. All the measurements were obtained at five temperatures between 298.15 and 318.15 K. A linear dependence between the mutual diffusion coefficient and temperature was found. In the range of temperatures studied here, the values of the mutual diffusion coefficients follow a sequence: BaCl₂ > SrCl₂ > CaCl₂ > MgCl₂ > BeCl₂ for alkaline-earth metal chlorides and GaCl₃ > AlCl₃, for third-family metal chlorides. That is, the higher the atomic weight of the cation. the higher the mutual diffusion coefficient. A comparison of mutual diffusion coefficients of alkaline, alkaline earth, and third-family metal chlorides is presented.     

Temperature dependence of the mutual diffusion coefficients in aqueous solutions of alkali metal chlorides

Measurements of mutual diffusion coefficients at infinite dilution in aqueous solutions of alkali-metal chlorides have been made with the Taylor dispersion technique. Data were obtained for the series LiCl/H₂O, NaCl/H₂O, KCl/H₂O, RbCl/H₂O, and CsCl/H₂O, at five temperatures between 298.15 and 318.15 K. A linear dependence with temperature was found. This technique is very convenient in comparison with other more time-consuming techniques.     

Critical behavior of nonionic micellar solutions

The critical behavior of micellar solutions of triethylene glycol monon-hexylether in water has been investigated in view of the issue of critical-point universality for such systems close to their critical mixing point. The values of the critical exponents obtained in this work are in excellent agreement with the theoretical ones for three-dimensional Ising-like systems. The dynamical critical behavior is also discussed.Paper presented at the Tenth Symposium on Thermophysical Properties, June 20–23, 1988, Gaithersburg, Maryland, U.S.A.     

Binary Diffusion Coefficients of Acetone in Carbon Dioxide at 308.2 and 313.2 K in the Pressure Range from 7.9 to 40 MPa

Binary diffusion coefficients of acetone in carbon dioxide were measured by the Taylor dispersion method at 308.2 K and 7.9 to 40 MPa and at 313.2 K and 8.0 to 37 MPa. The D ₁₂ values obtained from the response curves by the method of fitting in the time domain were more accurate than those obtained by the moment method. At pressures lower than about 8.3 MPa at 308.2 K or 9.1 MPa at 313.2 K, the accuracy in the D ₁₂ values was found to decrease significantly with decreasing pressure by examining (peak area)×u _{a, cal}, the values of S ₁₀, the fitting error , and u _{a, cal}/u _{a, exp} as a function of pressure. The D ₁₂ values at pressures higher than 8.3 MPa at 308.2 K or 9.1 MPa at 313.2 K were well represented with the Schmidt number correlation. The D ₁₂ data with larger fitting errors (>0.01) showed larger deviations from the values predicted by this correlation.     

Infinite Dilution Binary Diffusion Coefficients of Benzene in Carbon Dioxide by the Taylor Dispersion Technique at Temperatures from 308.15 to 328.15 K and Pressures from 6 to 30 MPa

Infinite dilution binary diffusion coefficients, D₁₂, of benzene in carbon dioxide were measured by the Taylor dispersion technique at temperatures from 308.15 to 328.15 K and pressures from 6 to 30 MPa. The diffusion coefficients were obtained by the method of fitting in the time domain from the response curves measured with a UV–vis multidetector by scanning from 220 to 280 nm at increments of 1 or 4 nm. The wavelength dependences on the binary diffusion coefficient and the uncertainty were examined. The detector linearity, in terms of the relationship between the absorbance intensity and the product of the peak area of the response curve and CO₂ velocity, was found to fail at some characteristic absorption wavelengths such as 243, 248, 253, and 259 nm, even when the maximum absorbance intensities of the response curves were less than 0.5 and the fits were good. Although the D₁₂ values obtained from the response curves measured at 253 nm were almost consistent with some literature data, the D₁₂ values measured at wavelengths showing the detector linearity to be satisfactory, i.e., at 239 nm, were higher than those at 253 nm. The present D₁₂ data at 239 nm were well represented by the Schmidt number correlation, except for those showing the anomalous decrease in a plot of D₁₂ vs density in the density range from 250 to 500 kg·m^–3.     

Photophysics and photochemistry of colloidal poly (p-phenylinevinylene) (PPV) polymer

The photophysical and photochemical behaviour of colloidal PPV polymers has been investigated by emission and photoelectrochemical studies. Emission studies indicated an increased conjugation length for PPV polymers on going from solution to the solid state. The quenching of the emission of PPV polymer by iodine can be used to probe the hole transfer by PPV–iodide complex with subsequent formation of I^*−. To elucidate the role of hole trapping in the process of photo-generation charge separation in various PPV/OTE electrodes, various electrolytes have been used. The values of photon-to-photocurrent conversion efficiency (IPCE) were evaluated from the short circuit photocurrent measurements at different excitation wavelengths. The close match between the IPCE and the absorption spectra shows that the photosensitization mechanism is operative in extending the photocurrent response of OTE/PPV into the visible. The maximum IPCE observed in the present experiments was 1.5% in the wavelength region of 425 nm which commensurates well with the reported values [M. Jonforsen, I. Ahmad, T. Johansson, J. Larsson, L.S. Roman, M. Svensson, O. Inganas, M.R. Andersson, Synth. Met. 119 (2001) 185]. From the photoelectrochemical response of an OTE/PPV electrode to visible light irradiation, the generation of photovoltage and photocurrent was prompt and was reproducible under several on–off cycles of illumination. Optimization of redox couple, electrolyte and film thickness is essential for improving the performance of PPV-based photoelectrochemical cells.     

Transport Properties of Nonelectrolyte Liquid Mixtures. XI. Mutual Diffusion Coefficients for Toluene+n-Hexane and Toluene+Acetonitrile at Temperatures from 273 to 348 K and at Pressures up to 25 MPa

Mutual diffusion coefficients,D ₁₂, have been measured at pressures up to 25 MPa using the chromatographic peak broadening technique (Taylor dispersion method) forxtoluene+(1–x)n-hexane in the temperature range 298 to 348 K and forxtoluene+(1–x) acetonitrile in the temperature range 273 to 348 K. The estimated uncertainty is ±4%. Both systems show negative deviations from straight-line behavior. The fractional decrease inD ₁₂is about 0.8% per MPa. Hard-sphere theory is applied under limiting conditions where one of the components is present in a trace amount. It is shown that the diffusion coefficients can be estimated by the Dullien method from a knowledge of the viscosity and density under the same conditions.     

Measurement of Diffusion in Ternary Liquid Mixtures by Light Scattering Technique and Comparison with Taylor Dispersion Data

Results of diffusion coefficient measurements by dynamic light scattering (DLS) in the ternary liquid systems, glycerol–acetone–water (GAW), and cyclohexane–methanol–toluene (CMT), are reported. Data for the GAW system are compared with Taylor dispersion (TD) measurements in overlapping concentration regions close to the critical solution point at 298.15 K. A fit of the intensity autocorrelation function (ACF) could be used to predict values and explain the physical character of the corresponding diffusion coefficients. In the vicinity of the critical solution point, the DLS measurements reveal two and more hydrodynamic relaxation modes with well separated characteristic relaxation times. From the ACF, at least two effective diffusivities, D ₁ and D ₂, can be experimentally determined. Theoretical predictions reveal that they may result from pure mass diffusion and pure thermal diffusion transport processes. A possible physical meaning of the modes D ₁ and D ₂ in the ternary liquid mixtures is discussed. When we compare the transport modes from DLS with the Taylor dispersion results, only the slowest mode represents mass diffusion, and this mode agrees very well with one of the eigenvalues of Fick’s diffusion matrix. There is no relation between the mass diffusion mode from DLS and any one of the four diffusion coefficients obtained by TD.     

Influence of clay mineral structure and surfactant nature on the adsorption capacity of surfactants by clays

Adsorption of three surfactants of different nature, Triton X-100 (TX100) (non-ionic), sodium dodecylsulphate (SDS) (anionic) and octadecyltrimethylammonium bromide (ODTMA) (cationic) by four layered (montmorillonite, illite, muscovite and kaolinite) and two non-layered (sepiolite and palygorskite) clay minerals was studied. The objective was to improve the understanding of surfactant behaviour in soils for the possible use of these compounds in remediation technologies of contaminated soils by toxic organic compounds. Adsorption isotherms were obtained using surfactant concentrations higher and lower than the critical micelle concentration (cmc). These isotherms showed different adsorption stages of the surfactants by the clay minerals, and were classified in different subgroups of the L-, S- or H-types. An increase in the adsorption of SDS and ODTMA by all clay minerals is observed up to the cmc of the surfactant in the equilibrium solution is reached. However, there was further TX100 adsorption when the equilibrium concentration was well above the cmc. Adsorption constants from Langmuir and Freundlich equations (TX100 and ODTMA) or Freundlich equation (SDS) were used to compare adsorption of different surfactants by clay minerals studied. These constants indicated the surfactant adsorption by clay minerals followed this order ODTMA>TX100>SDS. The adsorption of TX100 and ODTMA was higher by montmorillonite and illite, and the adsorption of SDS was found to be higher by kaolinite and sepiolite. Results obtained show the influence of clay mineral structure and surfactant nature on the adsorption capacity of surfactants by clays, and they indicate the interest to consider the soil mineralogical composition when one surfactant have to be selected in order to establish more efficient strategies for the remediation of soils and water contaminated by toxic organic pollutants.     

Transport properties of nonelectrolyte liquid mixtures. X. Limiting mutual diffusion coefficients of fluorinated benzenes inn-hexane

Mutual diffusion coefficients.D ₁₂. have been measured for benzene, seven fluorinated benzenes. and octafluorotoluene diffusing inn-hexane at trace concentration in the temperature range 213.2–333.2 K by the chromatographic peak-broadening, technique with an estimated accuracy of ±2.5% These results are compared with the predictions of rough hard-sphere theory (RHS). The results are reproducible to within ±10% with the translational rotational coupling factor equal to the value for the solvent. The activation energy of diffusionE _D, computed from Arrhenius plots. is almost constant for these solutes.     

Infinite-Dilution Binary Diffusion Coefficients of 2-Propanone, 2-Butanone, 2-Pentanone, and 3-Pentanone in CO2 by the Taylor Dispersion Technique from 308.15 to 328.15 K in the Pressure Range from 8 to 35 MPa

Infinite-dilution binary diffusion coefficients of 2-propanone, 2-butanone, 2-pentanone, and 3-pentanone in carbon dioxide were measured by the Taylor dispersion method at temperatures from 308.15 to 328.15 K and pressures from 7.60 to 34.57 MPa. The D₁₂ values were obtained from the response curves by the method of fitting in the time domain. The accuracy in the fitting error was examined for each measurement. The measured D₁₂ data were found to be well correlated by the Schmidt number correlation, with AAD%=3.74% for all solutes.     

亚甲基蓝分光光度法测定污染源废气中的硫化氢

本文根据作者的实际工作经验,着重讨论了亚甲基蓝分光光度法测定污染源废气中硫化氢时应注意的一些问题,并提出解决办法。     

Measurement of the Diffusion Coefficient of Miscible Fluids Using Both Interferometry and Wiener's Method

Measurements of the diffusion coefficient of two miscible liquids are reported. The liquids are various combinations of pure silicone oils and those to which small amounts of solvents are added to control the difference in density between the fluids. The liquids were placed in a quartz cell such that the interface is initially horizontal. As the fluids diffuse, the profile of the index of refraction near the interface is time dependent and is related to the local concentration of the diffusing fluids. The concentration gradient profile was measured by a shearing interferometer incorporating a Wollaston prism, as well as Wiener's method. In the latter technique, a 45° light sheet was passed through the test cell, and the local deflection of the light beam was measured. The average diffusion coefficient was obtained by analysis of the measured concentration gradient profile, assuming that the diffusion process is one-dimensional and is characterized by a constant value of the diffusion coefficient.     

Mutual diffusivity of a mixture of n-hexane and nitrobenzene near its consolute point

It is demonstrated that the Taylor dispersion method can be used to measure the mutual diffusivity of liquid mixtures near a critical mixing point. For this purpose we have measured the mutual diffusivity of a liquid mixture of n-hexane and nitrobenzene at the critical composition at temperatures from 16 K down to 1 K above the critical temperature. The results are in agreement with the theoretically predicted behavior of the diffusivity near a critical point of mixing.     

Diffusion and formation energies of adatoms and vacancies on magnesium surfaces

This paper reports classical molecular statics calculations of magnesium {0 0 0 1}, , , and surfaces, specifically formation energies of defects (adatoms and surface vacancies) and flat surfaces and diffusion energy barriers of the defects. The formation energies show that the surface is thermodynamically more favorable than , and surfaces; in contrast, literature reports have often ignored the surface. The diffusion energy barriers of both adatoms and surface vacancies show strong diffusion anisotropy on , , and surfaces. Based on this anisotropy, the ratio of diffusion distances (of either adatoms or surface vacancies) along two orthogonal directions on is 37–55 at room temperature. Using the results of formation energies and diffusion energy barriers we develop a more complete understanding of surface orientations in Mg nanoblades synthesized by physical vapor deposition [F. Tang, T. Parker, H.-F. Li, G.-C. Wang, T.-M. Lu, J. Nanosci. Nanotechnol. 7 (2007) 3239]. In contrast to previous reports, we postulate that the side surfaces of Mg nanoblades are because (a) they have the second lowest surface formation energy and (b) the ratio of diffusion distances on them agrees with the experimental value of approximately 50.     

Linear and non-linear regression analysis for the sorption kinetics of methylene blue onto activated carbon

Batch kinetic experiments were carried out for the sorption of methylene blue onto activated carbon. The experimental kinetics were fitted to the pseudo first-order and pseudo second-order kinetics by linear and a non-linear method. The five different types of Ho pseudo second-order expression have been discussed. A comparison of linear least-squares method and a trial and error non-linear method of estimating the pseudo second-order rate kinetic parameters were examined. The sorption process was found to follow a both pseudo first-order kinetic and pseudo second-order kinetic model. Present investigation showed that it is inappropriate to use a type 1 and type pseudo second-order expressions as proposed by Ho and Blanachard et al. respectively for predicting the kinetic rate constants and the initial sorption rate for the studied system. Three correct possible alternate linear expressions (type 2 to type 4) to better predict the initial sorption rate and kinetic rate constants for the studied system (methylene blue/activated carbon) was proposed. Linear method was found to check only the hypothesis instead of verifying the kinetic model. Non-linear regression method was found to be the more appropriate method to determine the rate kinetic parameters.     

液态金属扩散系数的测量方法与理论研究的进展

介绍了液态金属扩散系数的测量方法和理论研究,对比了各种实验方法的优缺点,分析了理论计算对实测结果的偏差原因,并指出了存在的问题和发展方向.     

Silver and gold nanocluster catalyzed reduction of methylene blue by arsine in micellar medium

Arsenic can be determined in parts-per-million (ppm) level by absorbance measurement. This method is based on the quantitative colour bleaching of the dye, methylene blue by arsine catalyzed by nanoparticles in micellar medium. The arsine has been generated in situ from sodium arsenate by NaBH₄ reduction. The absorbance measurement was carried out at the λ_max of the dye at 660 nm. The calibration graph set-up for three linear dynamic ranges (LDR) are 0-8.63 ppm, 0-1.11 ppm and 0-0.11 ppm and limit of detections (LODs) are 1.3, 0.53 and 0.03 ppm, respectively. This method is simple, sensitive and easy to carry out. It is free from phosphate and silicate interference and applicable to real sample analysis.     

Cloud point extraction for the determination of copper, nickel and cobalt ions in environmental samples by flame atomic absorption spectrometry

A cloud point extraction procedure was presented for the preconcentration of copper, nickel and cobalt ions in various samples. After complexation with methyl-2-pyridylketone oxime (MPKO) in basic medium, analyte ions are quantitatively extracted to the phase rich in Triton X-114 following centrifugation. 1.0 mol L⁻¹ HNO₃ nitric acid in methanol was added to the surfactant-rich phase prior to its analysis by flame atomic absorption spectrometry (FAAS). The adopted concentrations for MPKO, Triton X-114 and HNO₃, bath temperature, centrifuge rate and time were optimized. Detection limits (3 SDb/m) of 1.6, 2.1 and 1.9 ng mL⁻¹ for Cu²⁺, Co²⁺ and Ni²⁺ along with preconcentration factors of 30 and for these ions and enrichment factor of 65, 58 and 67 for Cu²⁺, Ni²⁺ and Co²⁺, respectively. The high efficiency of cloud point extraction to carry out the determination of analytes in complex matrices was demonstrated. The proposed procedure was applied to the analysis of biological, natural and wastewater, soil and blood samples.