Diffusion transport of aqueous solutions of alkali metal chlorides in porous glass membranes

The diffusion coefficients of lithium, sodium, potassium, and cesium chlorides in aqueous solutions in their passage through silica membranes with the pore radius r _p = 4.5–70 nm are determined over a wide range of solution concentrations. The membrane transport of the salts is discussed in terms of the structuring of the water boundary layers near the silica surface and their disruption by cations.     

Specific features of the diffusion of potassium dichromate aqueous solutions in porous glass membranes

The diffusion coefficients of 0.1 M aqueous solution of potassium dichromate (pH 2–8) in a series of glass membranes with the prevailing pore radii from 4.5 to 70 nm were determined. Characteristic features of variation of the diffusion coefficient were correlated with the calculated content of chromium(VI) anionic species over a wide interval of pH of the solution.     

A glass formation study of aqueous tetraalkylammonium nitrate solutions

The glass-forming composition regions of aqueous tetraalkylammonium nitrate solutions (alkyl = ethyl and n-propyl) were determined by a simple DTA method with a cooling rate of about 600 K-min^–1. The glass transition temperatures T_g of these solutions vary in a different manner from those for simple inorganic salt solutions such as aqueous LiCl, MgCl₂,and AlCl₃ solutions. Liquid-liquid immiscibilities are observed in these solutions at low temperatures.     

Diffusion in polyacrylic acid aqueous solutions

The four diffusion coefficients for the ternary system polyacrylic acid (mol. weight 5000)-polyacrylic acid (mol. weight 115000)-water have been measured at 25°C and at one average polyelectrolytes concentration. The experimental values of main and cross terms have been briefly discussed. The large cross term D ₁₂ in the system with water as solvent shows that, contrary to intuition, different molecular weight species do interact with each other.     

Dimensional and concentration dependences of diffusion of aqueous alkaline-earth metal nitrate solutions in porous-glass membranes

Diffusion coefficients characterizing penetration of aqueous solutions of magnesium, calcium, strontium, and barium nitrates across porous-glass membranes with predominant pore radii of 4.5–70 nm were determined. A decrease in the pore radii of the membranes is accompanied in all cases by an exponential fall of the diffusion mobility. A reversal of the diffusion mobility series was observed for membranes with pore radii of 4.5 and 70 nm on the background of the general tendency toward a concentration-related rise in the diffusion coefficients.     

Diffusion coefficients of paracetamol in aqueous solutions

Binary mutual diffusion coefficients measured by the Taylor dispersion method, for aqueous solutions of paracetamol (PA) at concentrations from (0.001 to 0.050) mol·dm⁻³ at T = 298.15 K, are reported. From the Nernst–Hartley equation and our experimental results, the limiting diffusion coefficient of this drug and its thermodynamic factors are estimated, thereby contributing in this way to a better understanding of the structure of such systems and of their thermodynamic behaviour in aqueous solution at different concentrations.     

Diffusion of cyclodextrins in aqueous polymer solutions

Diffusion of α and β cyclodextrin (α-CD and β-CD, respectively) has been studied in aqueous solutions of poly(methacrylic acid), sodium poly(styrene sulfonate), having three different degrees of sulfonation (DS), and copoly(styrene-methacrylic acid) containing three different amounts of styrene. N-Acetylglucosamine and raffinose were included as reference diffusants. It was found that a decrease of the diffusion coefficients of the CD's in these polymer solutions is characteristically dependent on the polymer concentration, DS, Styrene content, and the degree of neutralization. The results were interpreted by assuming a 1:1 complex formation between CD and an appropriate residue in the polymer. The complex diffusion behavior of CD in the copolymer solutions suggested that the ability of the polymer residue to form complexes with the CD is lost when the polymer chain dimensions are reduced with decreasing neutralization.     

The heat of dissolution of uranyl nitrate in aqueous nitrate solutions

Conclusions A model has been suggested to explain the observed relationship between the measured heats of dissolution of uranyl nitrate in aqueous nitrate solutions and the concentration of the salting-out agent. The model describes the change in the structure of water in the solution with change in its concentration. On the one hand, a destruction of the water structure by ions occurs, which is weakened with increase in the distance from the ion, and leads to such irregularity in the distribution of water molecules in the solution that the mean number of molecules of water in unit volume is increased with increase in the distance from the ions. In experiments on the heat of dissolution this increase leads to increased hydration of the uranyl cation and reduction in the endothermicity of the dissolution with increase in the concentration of the solution. On the other hand, an interaction occurs between the ions of the salting-out agent and the water molecules in the solution, leading to the opposite result: There is an increase in the mean number of water molecules of the solution in unit volume in the direction of these ions. In experiments on the heat of dissolution this is revealed in the dehydration of the uranyl cation, and correspondingly in an increase in the endothermicity of the dissolution with increase in the concentration of the solution. The proposed model is in harmony with data on vapor pressure above the solutions (the relationship between the activity coefficient of the water and the concentration of the solution).Translated from Zhurnal Strukturnoi Khimii. Vol. 3, No. 2, pp. 143–150, March–April. 1962     

Preparation of magnesium hydroxide from nitrate aqueous solution

Nucleation of Mg(OH)₂ was investigated by measuring the electrical conductivity and pH of the Mg(NO₃)₂ reaction solution to which ammonia containing different amounts of NH₄NO₃ was added. NH₄NO₃ increases solubility and slows down precipitation of Mg(OH)₂ in the system. Data are presented on the influence of NH₄NO₃ on the solubility of Mg(OH)₂ at 25°C. The phenomena observed can be explained by the solvation effect of nitrate ions brought to the system with the addition of ammonium nitrate, which was proved by NMR spectroscopy. When the mass fraction of NH₄NO₃ exceeds 15 %, homogeneous nucleation does not proceed. It was found that seeding of the system with Mg(OH)₂ crystals only influenced the rate of Mg(OH)₂ crystallisation, not the size and shape of the crystals. Primary crystals are smaller than 0.1 μm. The large difference in the surface energy of individual crystal planes leads to oriented agglomeration. This process is accelerated in a pressure reactor at 130°C. The resulting polycrystals are hexagonal plates 0.2 μm thin with a diameter of 1–2 μm. Under variable reaction conditions, agglomerates as big as 30 μm can be prepared.     

Radiolysis of aqueous solutions of gadolinium nitrate

The specific effect due to Gd³⁺ ion on the radiolysis of aqueous nitrate solutions was determined by measurement of H₂, H₂O₂ and NO ₂ ^– radiolytic yields produced by gamma-irradiation of aerated and deaerated solutions of gadolinium, sodium and calcium nitrates in the concentration range of 10^–5 to 0.3M. Important O₂ consumption in aerated and O₂ evolution in deaerated Gd(NO₃)₂ solutions was found by radiolysis in comparison with the inert cations nitrates. In the former the Gd³⁺ ion generates an O₂ transporter producing an increase in the H₂O₂ yield and a decrease in the NO ₂ ^– yield, while in the latter it enhances the H₂ and NO ₂ ^– production with respect to the same nitrate concentration of the Na⁺ solutions.     

Study of magnesium nitrate behavior in sodium nitrate solutions at 25°C

Solubility in the system KNO₃-Mg(NO₃)₂-H₂O at 25°C was studied by the isothermal method. Crystallization of potassium nitrate from aqueous solutions was studied. Coefficients of the removal of magnesium nitrate admixture were calculated.     

Diffusion coefficients of iodide in high temperature aqueous solutions

The diffusion coefficients of iodide in water solutions containing NaHSO₄ as supporting electrolyte have been measured between 102 and 215 °C using a high-temperature wall-tube cell. The temperature behavior of the diffusion coefficients is well described by the Arrhenius law and the activation energy for the mass transport is 17 kJ mol⁻¹. The results are compared to those calculated from the iodide conductivity at infinite dilution and to recent results from other authors. The solvation and speciation of the iodide ion in aqueous solutions at high temperature are analyzed.     

Short-range forces between glass surfaces in aqueous solutions

We found that the force between glass surfaces measured with an atomic force microscope (AFM) has universal character in the short range, less than approximately 1 nm or about 3-4 water molecules, independent of solution conditions, that is, electrolyte ion size, charge and concentration and pH. Our results suggest that the excess DLVO force, obtained by subtracting the DLVO theory with a charge regulation model from the AFM force data, essentially does not change with the electrolytes Na, Ca, and Al, in the range of concentration from 10(-6) to 10(-2) M and the range of pH from 3.1 to 7.9. Single force curves for a glass-silica system in a 10-4 M aqueous NaCl solution at pH approximately 5.1 show oscillations with a period of about 0.25 nm, roughly the diameter of a water molecule. We postulate that the excess force between glass surfaces arises from a surface-induced solvent effect, from the creation of a hydrogen-bonding network at the surface level, rather than from a solvent-induced surface steric hindrance.     

A study of composite membranes consisting of hydrargillite immobilized in a porous glass

Hydrargillite crystals were synthesized within the pores of a porous membrane (porous glass) from alumosilicate gel prepared by mixing solutions of sodium aluminate and sodium silicate diffusing from opposite sides. A study of the permeability of the composite membrane showed that virtually all the pores are sealed by the crystals grown within them. Dehydration above 200°C increases the permeability of the membrane by two orders of magnitude and subsequent rehydration does not restore the starting properties of the membrane.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 12, pp. 2842–2845, December, 1990.     

Diffusion transport of sucrose, ß-alanine and bovine serum albumin in aqueous solutions of hydroxypropyl cellulose

Diffusion of sucrose, ß-alanine and bovine serum albumin has been studied in moderately concentrated aqueous solutions of hydroxypropyl cellulose (HPC), both at 25° (good solvent conditions) and at 36° (approaching theta solvent conditions). For sucrose, the diffusion rate is almost independent of the concentration of HPC. For the two other diffusants, the diffusion rate decreases significantly when the concentration of HPC is increased; the decrease is more pronounced at 36° than at 25°. The results are discussed qualitatively in the light of recent theoretical models.     

Immobilization of invertase on porous membranes made from modified polysulfone

The activity of invertase that was immobilized within asymmetric ultrafiltration membranes was determined as a function of the immobilization mode such as adsorption, ionic interaction and covalent bonding. For these different bonding possibilities adequate membranes were prepared from chemically modified polysulfone fitted out with the corresponding substituents. The amount of enzyme was lowest for adsorption and highest for chemical fixation. In the latter case spacers were useful because substituents adjacent to the polymer backbone caused a relatively large loss of activity which can stem either from chemical reaction or from the hampered development of the appropriate conformational structure. Compared to the activity of the native invertase the fixation yielded a remarkable reduction of activity which was compensated for by the very extended stability of the bonded enzyme.     

VUV photolysis of aqueous solutions of nitrate and nitrite

Water homolyses upon vacuum-uv excitation into HO^* radicals, hydrogen atoms and with lower efficiency, hydrated electrons. These primary species induce a series of reactions partially depleting nitrate and nitrite from aqueous solutions. Depletion rates depend on the presence of dissolved oxygen and temperature. Nitrate, nitrite, peroxynitrite and N₂O were identified as reaction products after irradiation of, either, nitrite and nitrate in aqueous solutions. A reaction mechanism is proposed in accord with the experimental facts and with the evidence given in the literature, where NO₂ ^* and NO^* are key intermediates. NO₃ ^?, NO₂ ^?, NO₂ ^*, NO^* O₂NO₂ ^?, ONO₂ ^? and N₂O, seem to be interrelated by many redox reactions and reaction equilibria where pH and the availability of electrons determine their occurrence. The proposed mechanism is supported by a computer program with which the observed experimental behavior could be simulated.     

FT-IR spectroscopy of supersaturated aqueous solutions of magnesium borate

FT-IR spectra of supersaturated aqueous solution of magnesium borate, its acidized solutions with azeotropic hydrochloric acid, and its diluted solutions with water have been recorded. The FT-IR spectra of borate in solution are obtained by difference, subtracting the FT-IR spectrum of water from that of the magnesium borate supersaturated aqueous solution. All of the results showed that various polyborate anions in the supersaturated aqueous solutions exist. The bands of symmetric pulse vibration of the corresponding polyborate anions were indicated and some assignments were tentatively given.     

Amino acid hydration in aqueous magnesium and sodium sulfate solutions

We study the partial volumes of amino acids in aqueous magnesium and sodium sulfate solutions, which have a different effect on the structure of water, and calculate the structural parameters of hydrated complexes of NH ₃ ⁺ and COO^? groups: hydration numbers and water volumes inside and outside the hydration shell. The hydration numbers are given as a sum of the contributions of the interactions in the ternary (water-salt-amino acid) and binary (water-salt) systems.