Aqueous systems experimental results

Bhanushali, D., Kloos, S., and Bhattacharyya, D. (2002) Solute transport in solvent resistant nano filtration membranes for non-aqueous systems Experimental results and the role of solute-solvent coupling. Journal of Membrane Science 208, 343-359. 

A., Blesade, M.A., and Bahnemann, D. (2009) Adsorption of oxalate on anatase (100) and rutile (110) surfaces in aqueous systems experimental results vs. theoretical predictions. Phys. Chem. 

A series of bottle point erqreriments was conducted to assess the wettability of these materials. The solid materials were equilibrated with an aqueous lO MNaCl solution for at least 24 hours. PCE, dyed red to inqrrove visualization, was then added to the soil/aqueous phase slurry and the mixture was shaken. No surface active agents were added to these systems. Experimental results indicate a range of wetting conditions (Figure 4). The quartz sand system serves as a water-wet standard (bottle 1). The Ann Aibor II soil and Utica shale also exhibit water-wet behavior (bottles 2 and 3). In these three bottles, PCE is present as a distinct phase and does not coat the soil particles. In contrast, the Garfield oil shale and Waynesburg coal (bottles 4 and 5) systems appear organic-wet. In these systems, only the clear aqueous phase is visible above the soil and PCE coats the surfaces of diese natural materials. 

The calculation of diffusion coefficients from equations based on some models describing the movement of matter in electrolyte solutions, in the end, a process contributing to the knowledge of their stmcture, provided we have accurate experimental data to test these equations. Thus, to understand the behavior of transport process of these aqueous systems, experimental mutual diffusion coefficients have been compared with those estimated using several equations, resulting from different models. 

Only the obvious studies of aqueous plutonium photochemistry have been completed, and the results are summarized below. The course of discussion will follow the particular photochemical reactions that have been observed, beginning with the higher oxidation states. This discussion will consider primarily those studies of aqueous plutonium In perchloric acid media but will include one reaction in nitric acid media. Aqueous systems other than perchlorate may affect particular plutonium states by redox reactions and complex formation and could obscure photochemical changes. Detailed experimental studies of plutonium photochemistry in other aqueous systems should also be conducted. 

Lead sulfide films have been prepared by various deposition processes like vacuum evaporation and chemical bath deposition. Electrochemical preparation techniques have been used in a few instances. Pourbaix diagrams for all three aqueous lead-chalcogen Pb-S, Pb-Se, and Pb-Te systems, along with experimental results and cited discussion on the chemical etching and electrolytic polishing of lead chalcogenide crystals and films, have been presented by Robozerov et al. [201]. 

It is important to propose molecular and theoretical models to describe the forces, energy, structure and dynamics of water near mineral surfaces. Our understanding of experimental results concerning hydration forces, the hydrophobic effect, swelling, reaction kinetics and adsorption mechanisms in aqueous colloidal systems is rapidly advancing as a result of recent Monte Carlo (MC) and molecular dynamics (MO) models for water properties near model surfaces. This paper reviews the basic MC and MD simulation techniques, compares and contrasts the merits and limitations of various models for water-water interactions and surface-water interactions, and proposes an interaction potential model which would be useful in simulating water near hydrophilic surfaces. In addition, results from selected MC and MD simulations of water near hydrophobic surfaces are discussed in relation to experimental results, to theories of the double layer, and to structural forces in interfacial systems. 

NH4NH2C00, DNH4HC03.NH3. D(NH4)2C03,NH3,and DNH4NH C00,NH3 as adjustable parameters. Experimental data and calculated results are shown in Figure 2. The average percent deviation of calculated versus measured partial pressure is 11% for CO2 and 3.9% for NH3. The same system and the same least squares objective function have been studied by Beutier and Renon (9J. Their results, on the same basis, were 16% for C02 and 5% for NH3. Edwards, et al. (10) also studied vapor-liquid equilibrium of a NH3 C02 aqueous system at 373.15°K. 

The comparison between measured and calculated results for vapor-liquid equilibria in aqueous systems of weak electrolytes confirms the applicability of van Krevelen 1s method for moderate temperatures and concentrations. The comparison also indicates that the procedure of Edwards, Maurer, Newman and Prausnitz yields reliable results also at temperatures around 100 °C therefore, it may be expected that it is also useful at higher temperatures where experimental material, necessary for checking that procedure, is not available... 

Drug dissociation constants are experimentally determined by manual or automated potentiometric titration or by spectrophotometric methods.40 Current methods allow determination of pXa values with drug concentrations as low as 10 to 100 pM. For highly insoluble compounds (concentration <1 to 10 pM), the Yesuda-Shedlovsky method41 is commonly used where organic cosolvents (i.e., methanol) are employed to improve solubility. The method takes three or more titrations at different cosolvent concentrations, and the result is then extrapolated to pure aqueous system. The dissociation constant can also be determined with less accuracy from the pH-solubility profile using the following modification of Henderson-Hasselbach equation ... 

The most commercially important mechanism of all is the kinetics of solute transfer from an aqueous to a reverse micelle phase. The kinetics of extraction of metal ions have not received the same research attention as the extraction capacity of W/O microemulsions. As the mechanism of extraction of metal ions is chemical, the effect of creating a microemulsion in an organic phase that contains the reactant can be measured experimentally. Results indicate that, as in the case of extraction equilibrium, the rate of extraction may increase substantially by the presence of the microemulsion as compared with the conventional system [20,38,44] or decrease it to... 

With particular reference to reverse osmosis systems involving cellulose acetate membranes and aqueous solutions, the membrane material has both polar and nonpolar character, and the solvent, of course, is polar. When these two components of the reverse osmosis system are kept constant, preferential sorption at the membrane-solution interface, and, in turn, solute separation in reverse osmosis, may be expected to be controlled by the chemical nature of the solute. If the latter can be expressed by appropriate quantitative physicochemical parameters representing polar-, steric-, nonpolar-, and/or ionic-character of the solutes, then one can expect unique correlations to exist between such parameters and reverse osmosis data on solute separations for each membrane. Experimental results confirm that such is indeed the case (18). 

The hydrolysis of pesticides which are sorbed to sterilized natural sediments has been investigated in aqueous systems at acid, neutral and alkaline pH s. The results show that the rate constants of pH independent ("neutral") hydrolyses are the same within experimental uncertainties as the corresponding rate constants for dissolved aqueous phase pesticides. Base-catalyzed rates, on the other hand, are substantially retarded by sorption and acid-catalyzed rates are substantially enhanced. A large body of evidence will be presented which substantiates these conclusions for a variety of pesticide types sorbed to several well-characterized sediments. The significance of our results for the evaluation of the effects of sorption on the degradation of pesticides in waste treatment systems and natural water bodies will also be discussed. 

Again it seems not necessary to discuss the considerations of the chemical versus electrochemical reaction mechanism. It is clear from the extremely negative standard potential of silicon, from Eqs. (2) and (6), that the Si electrode is in all aqueous solutions a dual redox system, characterized by its OCP, which is the resultant of an anodic Si dissolution current and a simultaneous reduction of oxidizing species in solution. The oxidation of silicon gives four electrons that are consumed in the reduction reaction. Experimental results show clearly that the steady value of the OCP is narrowly dependent on the redox potential of the solution components. In solutions containing only HF, alternatively alkaline species, the oxidizing component is simply the proton H+ or the H2O molecule respectively. 

Let us recall the micellar aqueous system, as this procedure is actually the basic one. The chemistry is based on fatty acids, that build micelles in higher pH ranges and vesicles at pH c. 8.0-8.5 (Hargreaves and Deamer, 1978a). The interest in fatty acids lies also in the fact that they are considered possible candidates for the first prebiotic membranes, as will be seen later on. The experimental apparatus is particularly simple, also a reminder of a possible prebiotic situation the water-insoluble ethyl caprylate is overlaid on an aqueous alkaline solution, so that at the macroscopic interphase there is an hydrolysis reaction that produces caprylate ions. The reaction is very slow, as shown in Figure 7.15, but eventually the critical micelle concentration (cmc) is reached in solution, and thus the first caprylate micelles are formed. Aqueous micelles can actually be seen as lipophylic spherical surfaces, to which the lipophylic ethyl caprylate (EC) avidly binds. The efficient molecular dispersion of EC on the micellar surface speeds up its hydrolysis, (a kind of physical micellar catalysis) and caprylate ions are rapidly formed. This results in the formation of more micelles. However, more micelles determine more binding of the water-insoluble EC, with the formation of more and more micelles a typical autocatalytic behavior. The increase in micelle population was directly monitored by fluorescence quenching techniques, as already used in the case of the... 

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