The Physical Chemistry of Electrolytic Solutions.

Binary mutual diffusion coefficients measured by the Taylor dispersion method in two different laboratories (University of Naples, Federico II, Italy, and University of Coimbra, Portugal) are reported for aqueous solutions of lactose, sucrose, glucose, and fructose at various concentrations (0001 to 01) mol·dm-3 and temperatures (29815 to 32815) K The hydrodynamic radius and activation energy for the diffusion of aqueous sugars are calculated from those results In addition, the measured diffusion coefficients are used with the Hartley equation to estimate activity coefficients for aqueous lactose, sucrose, glucose, and fructose

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Binary Mutual Diffusion Coefficients of Aqueous Solutions of Sucrose, Lactose, Glucose, and Fructose in the Temperature Range from (298.15 to 328.15) K

Nanolaminate membranes made of two-dimensional materials such as graphene oxide are promising candidates for molecular sieving via size-limited diffusion in the two-dimensional capillaries, but high hydrophilicity makes these membranes unstable in water. Here, we report a nanolaminate membrane based on covalently functionalized molybdenum disulfide (MoS2) nanosheets. The functionalized MoS2 membranes demonstrate >90% and similar to 87% rejection for micropollutants and NaCl, respectively, when operating under reverse osmotic conditions. The sieving performance and water flux of the functionalized MoS2 membranes are attributed both to control of the capillary widths of the nanolaminates and to control of the surface chemistry of the nanosheets. We identify small hydrophobic functional groups, such as the methyl group, as the most promising for water purification. Methyl- functionalized nanosheets show high water permeation rates as confirmed by our molecular dynamic simulations, while maintaining high NaCl rejection. Control of the surface chemistry and the interlayer spacing therefore offers opportunities to tune the selectivity of the membranes while enhancing their stability

/pdf/enhanced-sieving-from-exfoliated-mos-2-membranes-via-17w9zh45ti.pdf

Enhanced sieving from exfoliated MoS 2 membranes via covalent functionalization

Theory is presented for cyclic voltammetry at a hemispherical electrode under conditions where the electric field is nonzero and migration is significant to mass transport. The nonlinear set of differential equations formed by combining the Nernst−Planck equation and the Poisson equation are solved numerically, subject to a zero-field approximation at the electrode surface. The effects on the observed voltammetry of the electrode size, scan rate, diffusion coefficient of electroactive and supporting species, and quantity of supporting electrolyte are noted. Comparison is drawn with experimental voltammetry for the aqueous system [Ru(NH3)6]3+/2+ at a Pt macroelectrode with varying levels of supporting electrolyte KCl. The approximations concerned are shown to be applicable where the ratio of supporting (background) electrolyte to bulk concentration of electroactive species (support ratio) exceeds 30, and general advice is given concerning the quantity of supporting electrolyte required for quantitatively d...

How Much Supporting Electrolyte Is Required to Make a Cyclic Voltammetry Experiment Quantitatively “Diffusional”? A Theoretical and Experimental Investigation

[1] A review of heat and solute transport in sediments demonstrates that the use of heat as a tracer has not been experimentally evaluated under the same experimental conditions as those used for the evaluation of solute as a tracer. Furthermore, there appears to be disagreement in the earth science literature over the significance of the thermal dispersivity term. To help resolve this disagreement, detailed experimentation with typical groundwater flow velocities (Darcy range, Re < 2.5) was conducted in a specifically designed hydraulic tank containing well-sorted saturated sand. The experiment enabled, for the first time, the precise monitoring of heat and solute tracer movement from a point source in separate runs under identical solid matrix and steady state flow conditions. Experimental results demonstrate that heat transport with natural groundwater flow velocities can reach a transition zone between conduction and convection (0.5 < Pet < 2.5). The thermal dispersion behavior can be described by using a thermal dispersivity coefficient and the square of the thermal front velocity. We propose an empirical formulation for thermal dispersion with Darcy flow in natural porous media and clarify the disagreement regarding its significance. Finally, it was observed that Darcy velocities independently derived from heat and solute experimentation show a systematic discrepancy of up to 20%, and that experimental thermal dispersion results contain significant scatter.

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/2011WR011038

Experimental investigation of the thermal dispersivity term and its significance in the heat transport equation for flow in sediments

https://estudogeral.sib.uc.pt/bitstream/10316/5282/1/filef165a90a02bd4844afe291aad5da3cf4.pdf

Diffusion coefficients in aqueous solutions of potassium chloride at high and low concentrations

Diffusion coefficients of paracetamol in aqueous solutions

Mutual diffusion coefficients of L-glutamic acid and monosodium L-glutamate in aqueous solutions at T = 298.15 K

Differential diffusion coeficients of beryllium sulfate in water at 298 K and at different concentrations have been measured using a conductimetric cell. The results are discussed on the basis of the OnsagerFuoss theory. The results were interpreted with success, using the developments introduced by Pika1 in the above theory. The cell uses an open-ended capillary method, and a conductimetric technique is used to follow the diffusion process by measuring the resistance of a solution inside the capillaries at recorded times.

https://estudogeral.sib.uc.pt/bitstream/10316/10483/1/Diffusion%20Coefficients%20in%20Aqueous%20Solutions.pdf

Diffusion Coefficients in Aqueous Solutions of Beryllium Sulfate at 298 K

Although aspartic acid is a non-essential amino acid, its importance is crucial for a major metabolic pathway and it is present in different types of foods. This highlights the need of a better knowledge of its transport properties. A Taylor dispersion technique has been used for measuring mutual diffusion coefficients of binary aqueous solutions of l-aspartic acid, an associated electrolyte, and the corresponding salt sodium l-aspartate, which behaves as a non-associated electrolyte, at 298.15 K and concentrations ranging from (0.001 to 0.100) mol·dm−3. Thermodynamic factors for the diffusion of aspartic acid and sodium aspartate have been estimated on the basis of the Onsager–Fuoss equation. Furthermore, experimental diffusion coefficients of aspartic acid are compared with those computed by the modified Onsager–Fuoss equation, applied for partially dissociated electrolytes.

Luis M.P. Verissimo

Papers

Diffusion coefficients in aqueous solutions of potassium chloride at high and low concentrations

Diffusion coefficients of paracetamol in aqueous solutions

Mutual diffusion coefficients of L-glutamic acid and monosodium L-glutamate in aqueous solutions at T = 298.15 K

Diffusion Coefficients in Aqueous Solutions of Beryllium Sulfate at 298 K

Binary Diffusion Coefficients for Aqueous Solutions of l-Aspartic Acid and Its Respective Monosodium Salt