A. V. Volkova

Colloido-chemical characteristics of porous glasses with different compositions in KNO3 solutions. 1. Structural and electrokinetic characteristics of membranes

The structural (specific surface area, liquid-filtration coefficient, average pore radius, volume porosity, and structural-resistance coefficient) and electrokinetic (counterion transport numbers, specific electrical conductivity, and electrokinetic potential) characteristics of porous glasses with different compositions have been determined in potassium nitrate solutions with concentrations of 10−3–10−1 M. All the membranes under investigation have been shown to exhibit the dependences of efficiency coefficients and counterion transport numbers on electrolyte concentration and pore size that are predicted by the theory of an electrical double layer. It has been established that, at a constant electrolyte concentration, the absolute values of electrokinetic potential increase with the average pore radius because of variations in the slipping-plane position.

Colloido-chemical characteristics of nanoporous glasses with different compositions in solutions of simple and organic electrolytes. 1. Structural and transport characteristics of membranes

The regularities of variations in the structural (bulk porosity, structural resistance coefficient, and average pore radius) and transport (specific electrical conductivity and ion transport numbers) characteristics of nanoporous glass membranes with different compositions have been studied as depending on their preparation conditions and the type of electrolyte (sodium, potassium, ammonium, tetramethylammonium, and tetraethylammonium chlorides). An additional alkaline treatment of the porous glasses, which increases the average pore radius and modifies the morphology of pore channels, leads to variations in the electrotransport characteristics of the glasses. In solutions containing inorganic counterions, the dependences of the transport characteristics of the porous glasses on the solution concentration and pore size have a classic character. The high specificity of tetraalkylammonium ions in relation to the surface gives rise to a region of negative values of the specific surface conductivity and complex dependences of efficiency coefficients and transport numbers on electrolyte concentration and pore channel size. The duration of the thermal treatment of initial sodium-borosilicate glass containing small amounts of phosphorus oxide and fluoride ions, as well as the conditions of its leaching, has almost no effect on the properties of the membranes in tetraethylammonium chloride solutions.

Colloido-chemical characteristics of porous glasses with different compositions in KNO3 solutions. 2. Electrosurface characteristics of porous glass particles

The surface charge and electrophoretic mobility of particles of porous glasses with different compositions have been studied in potassium nitrate solutions with concentrations of 10−3–10−2 M. It has been shown that the surface charge in KNO3 solutions virtually coincides with the charge in KCl solutions and has negative values in the studied pH range of 4–9. The concentrations and mobilities of ions in glass pores, Donnan potentials, and the convection component of electrical conductivity have been calculated within the framework of a homogeneous model. Electrokinetic potentials of the glasses under investigation have been calculated with regard to the effect of the electrolytic conductivity of the porous particles and electroosmotic transport in the pore space on the electrophoretic mobility.

Colloido-chemical characteristics of nanoporous glasses with different compositions in solutions of simple and organic electrolytes. 2. Equilibrium electrochemical characteristics of membranes

The regularities of variations in the electrokinetic potential and surface charge of nanoporous glass membranes with different compositions have been studied as depending on the type of an electrolyte (sodium, potassium, ammonium, tetramethylammonium, and tetraethylammonium chlorides) and the structure of pore space. It has been shown that, in solutions containing specifically sorbed organic counterions, the range of positive values of electrokinetic potential arises due to the superequivalent absorption of counterions in the Stern layer. It has been found that the influence of the specific adsorption of counterions on the electrokinetic potential of porous glasses increases with the amount of secondary silica in the pore space. The effects of the counterion specificity, pore channel sizes, and composition of a porous glass on the value of the surface charge have been analyzed. The absolute value of the surface charge has been shown to significantly increase in the presence of organic counterions in comparison with inorganic ions throughout the examined range of background electrolyte concentrations.

Highly Efficient Photodegradation of Organic Pollutants Assisted by Sonoluminescence

The mechanism of the photodegradation of azo dyes via ultrasonication is studied using a combination of the high‐performance liquid chromatography and UV–vis spectroscopy with detailed analysis of the kinetics. Based on the kinetics studies of the sonodegradation, it was proposed that the degradation of azo dyes was a multistage process that involved: (1) the direct attack of azo bonds and phenyl rings of dyes by the sonochemically formed reactive oxygen species; (2) the activation of semiconductor particles by the light emitted during cavitation and the triggering of the photocatalytic pathways of dye degradation and (3) increase of the adsorption capacity of the semiconductor particles due to the sonomechanically induced interparticle collisions. The detailed kinetics study can help in following an effective process up‐scaling. It was demonstrated that extremely short pulses of light flashes in a cavitated mixture activated the surface of photocatalysts and significantly enhanced dye degradation processes.

Electrokinetic Properties of Aluminum Oxide Nanodispersions in NaCl Solutions

Using a Zetasizer Nano analyzer, electrophoretic mobility and particle sizes are studied as depending on the pH (3–11) and concentration (10−3–10−1 M) of NaCl background solutions for two samples of aluminum oxide, namely, γ-oxide of the Degussa brand and a sample synthesized by aluminum chloride hydrolysis. The values of the electrokinetic ζ potential are calculated through the Smoluchowski equation and with allowance for the effect of the polarization of electrical double layer on the electrophoretic mobility within the framework of the Overbeek-Boes-Wiersema model (ζW). It is established that, in the region of the isoelectric point (IEP), at (pH-pHIEP) = ±1.5, the |ζW|-pH dependences are linear and their slopes are almost equal for both aluminum oxide samples. The difference between the positions of IEPs for γ-oxide and synthesized oxide sample may be related to different degrees of their surface hydration.

Photometric study of the kinetics of TiO2 hydrosol coagulation in electrolyte solutions

The aggregative stability of TiO2 sols in aqueous solutions of NaCl, KCl, BaCl2, and LaCl3 is studied by photometry at pH 3.2 and natural values of pH (5.0–5.6). Dramatic effects of coion type and charge on the aggregation kinetics and characteristics of resulting aggregates are revealed.

Colloid chemical characteristics of nanoporous glasses with different compositions in solutions of simple and organic electrolytes. 3. Calculation of electrochemical characteristics of membranes in terms of a homogeneous model

The electrosurface characteristics of nanoporous glass membranes–ion concentrations in pores with taking into account the specificity of counterions, electrokinetically mobile charge, the convective component of pore solution electrical conductivity, electroosmotic mobility of a liquid in the field of streaming potential and ion mobilities in pore space–were calculated within the homogeneous model. The effects of the type of counterion (sodium, potassium, ammonium, tetramethylammonium, and tetraethylammonium ions), solution concentration, glass composition, and pore size on the equilibrium and transport characteristics of membrane systems have been analyzed. A method for the determining of electrolyte activity coefficients in the membranes has been proposed.

Synergetic effect of sodium polystyrene sulfonate and guanidine hydrochloride on the surface properties of lysozyme solutions

A study of the dilational surface viscoelastic properties of mixed solutions of lysozyme and denaturing agents with different chemical natures allows us to characterize the changes of protein tertiary structure in the surface layer upon adsorption at the liquid–gas interface. We show that guanidine hydrochloride (GuHCl) and urea influence the dynamic surface properties of lysozyme solutions less than the properties of previously studied solutions of bovine serum albumin and β-lactoglobulin. Although the addition of sodium polystyrene sulfonate (PSS) changes the kinetic dependencies of the surface properties and leads to the formation of large aggregates in the bulk phase, the dependencies of the dynamic surface elasticity on the surface pressure almost coincide with the results for pure lysozyme solutions thereby indicating the preservation of the adsorption layer structure. At the same time, the simultaneous addition of PSS and GuHCl to lysozyme solutions results in a strong synergistic effect: the kinetic dependency of the dynamic surface elasticity becomes non-monotonical and similar to that for solutions of amphiphilic polymers and non-globular proteins. The local maximum of this dependency indicates the destruction of the protein globular structure and formation of the distal region of the surface layer. The simultaneous addition of PSS and urea to lysozyme solutions does not lead to a similar effect. These results confirm different mechanisms of protein denaturation under the influence of urea and GuHCl, and the important role of electrostatic interactions in the latter case.

Aggregation stability of a positively charged γ-Al2O3 sol prepared from an air-dry nanopowder

Photometric data on the aggregation stability of Al2O3 hydrosols prepared from Aeroxide Alu C nanopowder in NaCl solutions at pH 4.5 and 5.5 have been discussed within the framework of the generalized Derjaguin-Landau-Verwey-Overbeek theory. Analysis of the pair interaction potentials in an ensemble of particles of a sol primordially containing both primary nanoparticles and their aggregates has led to the conclusion that the coagulation proceeds via the barrierless mechanism in the secondary potential minimum.