Adsorption Of Electrolyte Ions Research Articles

Synthesis and characterization of graphene hollow spheres for application in supercapacitors

We have successfully assembled graphene nanosheets into spherical shells using polystyrene spheres as templates. Compared with stacked planar graphene, the as-prepared graphene spherical shells have more free space in between the spheres, which results in a larger accessible surface area for adsorption of electrolyte ions in supercapacitors. Electrochemical tests show that the graphene hollow spheres exhibit a high specific capacitance of 273 F g−1 and excellent electrochemical stability.

Double layered nanostructured composite coatings with bioactive silicate glass and polymethylmetacrylate for biomimetic implant applications

We studied the corrosion behaviour of bioactive glass–polymer nanostructured coatings of titanium implants for prostheses. The layers were deposited by MAPLE on titanium substrates of biomedical use. The potentiodynamic polarization investigations showed that the obtained samples exhibited a higher corrosion resistance as compared to bare titanium. The behaviour of coatings in contact with physiological fluids was studied in vitro by electrochemical impedance spectroscopy. The initial bioactive glass–polymer coating proved to be a good insulator. After immersion in simulated body fluid the bioactive glass dissolution and the adsorption of electrolyte ions were initiated causing the formation of an outer bioapatite protective layer. A simple cell circuit proved sufficient to describe unimmersed, short (7 days) and/or long (42 days) time immersed samples at room temperature, while after 14, 21, 28 or 35 immersion days, the use of a double cell circuit was mandatory. This was indicative for the formation of a double nanostructure consisting of an inner barrier (mainly polymer) and an outer porous (bioapatite) film with potential beneficial effects for osseointegration capacity of the Ti implants.

Adsorption of alkali metal cations and halide anions on metal oxides: prediction of Hofmeister series using 1-pK triple layer model

Adsorption of electrolyte ions on metal oxides significantly affects the interfacial charge distribution. The general procedure for the prediction of surface charge on oxides in salt solutions was given by Sverjensky for the 2-pK Triple Layer Model (2-pK TLM) (Sverjensky, Geochim. Cosmochim. Acta 69:225–257, 2005). Based on his parameters values and by assuming parameters transferability (Piasecki, J. Colloid Interface Sci. 302:389–395, 2006) we have predicted the adsorption constants for three monovalent ions (Rb+, F−, Br−) for eight oxides within the framework of the 1-pK Triple Layer Model (1-pK TLM). The obtained parameters values along with the previously reported ones (Piasecki, J. Colloid Interface Sci. 302:389–395, 2006) allowed us to compare the adsorption affinities of alkali metal cations and halide anions, and construct the following Hofmeister series for the cations (Cs+≈ Rb+≈ K+< Na+< Li+) and for the anions (F−≫ Cl−≈ Br−< I−) for investigated oxides. The same lyotropic series was predicted by the 2-pK TLM. It indicates that Hofmeister series is invariable during parameter transfer between surface complexation models.

Electrolyte ion effects on Cd 2+ binding at Al 2O 3 surface: Specific synergism versus bulk effects

Cd 2+ binding on γ-Al 2O 3 was studied in the presence of the common electrolyte ions Mg 2+, SO 2− 4, and NO − 3 at high and low concentrations. Direct measurements were performed for Cd 2+ as well as for electrolyte ion adsorption as a function of pH. The experimental data reveal that Cd 2+ binding on γ-Al 2O 3 is modulated by the electrolyte ions in a complex manner. At high electrolyte concentration, Cd 2+ uptake by γ-Al 2O 3 is inhibited. Theoretical analysis by a surface complexation model shows that this effect can be attributed partially to bulk, ionic strength, and effect of the electrolyte, but the most significant inhibition is due to direct competition between Mg 2+ and Cd 2+ ions for the SO − surface sites of γ-Al 2O 3. At low concentration of electrolyte ions, Cd 2+ uptake by γ-Al 2O 3 can be enhanced due to synergistic co-adsorption of Cd 2+ and electrolyte anions, particularly SO 2− 4 and to a lesser extent NO − 3. The theoretical analysis shows that this co-adsorption is due to formation of ternary surface species ( SOH 2SO 4Cd) and ( SOH 2NO 3Cd) which enhance Cd-uptake at pH values well below the point of zero charge of the γ-Al 2O 3.

Influence of electrolyte ion adsorption on the derivative of potentiometric titration curve of oxide suspension – theoretical analysis

The theory based on the 1-pK triple layer model of the oxide/electrolyte interface is used to obtain the derivative of a proton adsorption isotherm. The present approach is much more rigorous and complex from a physical point of view compared to our previous paper [J. Phys. Chem. B. 106 (2002) 13280]. In the present work we take into account adsorption of inert electrolyte ions. Also, the present approach takes into consideration the local surface heterogeneity. The aim of this work is not to propose new surface model, but to develop a theoretical basis for obtaining of proton affinity distribution from the derivatives of a potentiometric titration curve. We demonstrate how including of electrolyte ion adsorption influences on the shape and behavior of the local derivatives of potentiometric titration curves. The influence of the other parameters is also thoroughly investigated. It was found that complete description of the derivative of surface charging curve requires a high number of parameters. Therefore, it is difficult to adopt the obtained peaks for unambiguous decomposition of experimental derivative of a titration curve onto the parts coming from different patches of the surface.

Prevention of gallium arsenide photocorrosion by an epoxy adhesion layer

Coating of gallium arsenide with an adhesion layer of commercial epoxy prevented its photocorrosion. A two-component room temperature curing adhesive paste (Araldite 2014) has been selected. When GaAs/Araldite was employed as an anode in a three-electrode photoelectrochemical cell the photogenerated current density decreased significantly due to epoxy coating. However, depositing of few monolayers of Pt on GaAs surface prior to epoxy adhesion increased the photogenerated current density about four times. Moreover, impregnation of the epoxy film with gold enhanced the photogenerated current density significantly. The room temperature electrical conductivity of the epoxy films increased from 10 −8 to 10 −4 Ω −1 cm −1 due to gold impregnation. Enhancement of the photocurrent due to gold impregnation is attributed due to better conduction of the photogenerated holes into the electrolyte, also due to activating the adsorption of electrolyte ions. Several parameters are studied with the objective of determining the stability of epoxy films: these are continuous current–voltage ( I– E) scans, prolonged illumination, weight changes and surface topography by scanning electron microscopy. All investigations have proven that the epoxy film was quite stable under anodic potentials and illumination in aqueous solutions.

The influence of surface potential on quantities measuring for metal oxide/electrolyte solution interface: theoretical study based on 1-pK and 2-pK surface charging models

Two models of oxide surface charging, 1-pK and 2-pK, and the basic Stern model of electric double layer were applied in order to calculate surface potential. The potential was calculated by means of exact equations developed for these models, simplified equations, which neglected electrolyte ion adsorption, and the Nernst equation. The potentials obtained in this way were used to calculate: surface charge, electrokinetic potential, isotherms of electrolyte ion adsorption, temperature dependence of surface potential, and the molar heat of proton adsorption. The calculated values were compared with experimental data for the system γ-Al2O3/NaCl. It was found that, except for surface charge, the calculated quantities were very sensitive to the surface potential. The best results were obtained when this potential was calculated by means of exact equations taking into account electrolyte ion adsorption. The analysis presented shows clearly that evaluation of the theoretical models on the basis of only one kind of experimental data is questionable. However, it is common practice.

1pK and 2pK Protonation Models in the Theoretical Description of Simple Ion Adsorption at the Oxide/Electrolyte Interface: The Analysis of Temperature Dependence of Potentiometric Titration Curves

Two models of oxide surface charging (1pK and 2pK) were used to describe the potentiometric titration curves measured by Blesa et al. ( J. Colloid Interface Sci. 101, 410 (1984)) at three temperatures and at three concentrations of electrolyte. Rudzinski et al. ( Langmuir 13, 483 (1997)) have applied the 2pK Triple Layer Model to analyze the above system earlier. Two calculation procedures based on the 1pK Basic Stern Model were developed to described Blesa's data. Since the experimental curves have the CIP (common intersection point) it was assumed that heat of electrolyte ion adsorption was equal to zero. We assumed two different values of the double layer innermost capacitance on both sides of PZC (point of zero charge), which was followed from asymmetry of surface charge curves relative to PZC. Moreover, it was necessary to take into consideration the dependence of capacitance on ionic strength and temperature. The quality of fit given by two models was comparable. Since the 1pK BSM is simpler than the 2pK TLM and includes not so many best-fit parameters it seems to be a better choice in this case. Discussion of the results obtained by other authors concerning the subject under consideration is also presented.

Role of electrophoretic mobility of protein on its retention by an ultrafiltration membrane: Comparison to chromatography mechanisms

Lysozyme and lactoferrin, two globular proteins, were first studied separately in order to elaborate a strategy for the improvement of their separation by ultrafiltration (UF) with zirconia-based membranes of different charge sign and pore radius. The electrophoretic mobility ( μ) at fixed pH and variable ionic strength was used for the characterisation of both proteins and zirconia particles, similar to the active layer of the membrane during the UF run. Specific adsorption of phosphate ions was shown for both proteins resulting in new isoelectric points. The occurrence of electrostatic exclusion mechanism in addition to the molecular sieving in UF of charged solutes was shown for: • Low molecular weight solute: multivalent citrate at pH 6 was specifically adsorbed on zirconia and its transmission through the membrane (defined as the ratio of the concentration in the permeate to that of the feed solution) was reduced in the range 0.001–0.01 mol l −1 of citrate concentration • Proteins: their transmissions increase when the ionic strength increases (ion-exchange is not the relevant mechanism because transmission is irrespective of the initial charge of the membrane compared with the protein charge). A model based on convection, diffusion and electrophoretic migration mechanisms (CDE model) was proposed to take into account this behaviour. The CDE model predicts the possible existence of a depleted sub-layer of the charged protein in the concentration polarisation layer, located in the close vicinity of the membrane surface. A strategy for the separation of two proteins in mixed solution was proposed by varying both the physico–chemical environment in the feed solution (pH, ionic strength, chemical nature of the electrolyte) and the membrane pore radius. Maximum selectivity was obtained when the target protein (to be transmitted in the permeate side) is close to being uncharged due to specific adsorption of electrolyte ions. Ultrafiltration selectivity is enhanced with membrane of large pore radius, which provides high transmission of the target protein and efficient electrostatic exclusion of the solute to be retained in the retentate side. This UF approach corresponds roughly to the separation of one uncharged and one charged protein from a mixed solution by size exclusion chromatography of the uncharged protein combined with electrostatic exclusion of the charged protein due to packing of similar charge.

Electrokinetic surface characterization of biomedical polymers — a survey

The application of streaming potential measurements in support of the development of blood compatible polymers is reviewed. Current knowledge about the relevance of interfacial charge of materials with respect to thrombogenicity of and coagulation activation by medical devices is discussed. Potentialities of streaming potential measurements for the characterization of biomedical polymers comprise the distinction between interfacial charge formation processes, the derivation of acid–base characteristics of surface functions, and the estimation of the relative contribution of known molecular surface sites to the interfacial charge density. Frequently, polymer surfaces consist of different types of surface sites. Beyond sites with Bronsted-acidic or -basic character the preferential adsorption of electrolyte ions onto indifferent surface sites may substantially contribute to the interfacial charge. Examples are given for the detection of acidic and basic properties of hemodialysis membranes of different shape made of poly(sulfone)/poly(vinylpyrrolidone) and cellulose derivates. For partially amine-modified cellulose flat membranes the percentage of basic surface sites is derived from the shift of the isoelectric point. Further, the use of streaming potential measurements is demonstrated in the optimization of surface modifications of cardiovascular implant materials by low pressure plasma treatments. The introduction of basic groups into the poly(tetrafluoroethylene) implant surfaces by ammonia plasma treatments manifests itself in the shift of the isoelectric point. A correlation between hydrophobicity and charge formation of the polymer–solution interface by preferential ion adsorption is confirmed for polymers without dissociating functions. This is based on the comparison of water contact angles for a series of poly(styrene) derivates of different hydrophobicity and the maximum zeta potential of these polymer films in potassium hydroxide solutions. Advanced applications of streaming potential measurements for the characterization of biomedical polymers are comprise the in situ characterization of protein adsorption processes onto polymer solids. This approach is demonstrated for the adsorption of the blood plasma proteins albumin and fibrinogen onto a fluorocarbon polymer substrate. The potentialities of a recently developed microslit electrokinetic setup are illustrated which permits to study simultaneously zeta potential and surface conductivity of flat polymer–liquid interfaces. Data gained by the microslit electrokinetic setup reveal the dramatic increase of the surface conductivity of a fluorocarbon polymer–solution interface caused by fibrinogen adsorption.

Interfacial Charging Phenomena of Aluminum (Hydr)oxides

The interfacial charging of Al(OH)3 (gibbsite and bayerite) and Al2O3 has been studied. For Al(OH)3 it can be shown that the very strong variation in charging behavior for different preparations is related to the relative presence of differently reacting crystal planes. The edge faces of the hexagonal gibbsite crystals are proton reactive over the whole pH range, in contrast to the 001 plane, which is mainly uncharged below pH = 10. On this 001 face only doubly coordinated surface groups are found, in contrast to the edges which also have singly coordinated surface groups. The results are fully in agreement with the predictions of the Multi site complexation (MUSIC) model. The proton adsorption, electrolyte ion adsorption, and shift of the IEP of gibbsite and aluminum oxide have been modeled simultaneously. For gibbsite, the ion pair formation of Na is larger than that of Cl, as is evidenced by modeling the experimentally observed upward shift of the IEP and charge reversal at high electrolyte concentrati...

An experimental trial for the determination of the critical coagulation concentration using the sedimentation method

A method for determining the critical coagulation concentration (Cc) from the change in the transmittance of the sol with stand time after adding a coagulating agent is discussed. Potassium nitrate was used as the coagulating agent because the specific adsorption of electrolyte ions on the particle and the hydrolysis of electrolyte ions are negligible. Apparent critical coagulation concentrations,Cca, of iron (III) hydroxide and silver iodide sols were obtained from the transmittance vs. potassium nitrate concentration curves for various stand times. The values ofCca decreased with increasing stand time. TheCca value obtained for the shortest stand time was closer toCc obtained from the initial turbidity change of the sol by applying Rayleigh's law. The Hamaker constant for the particle in water was calculated from theCca value obtained at the shortest time and the experimentally determined outer Helmholtz plane potential. The calculated Hamaker constants were comparable to the theoretical values for iron (III) hydroxide and silver iodide.

Adsorption of sodium and chloride ions at the rutile/electrolyte interface — Parameters of the electric double layer

The surface charge and the adsorption of background electrolyte ions at the rutile/water interface has been studied. On the basis of the potentiometric titration data the surface reaction equilibrium constants were calculated according to the site binding theory of the electric double layer (EDL). An attempt of estimation of surface potential at the TiO 2/electrolyte interface is presented in this paper taking into consideration the surface charge data and the site binding model of the EDL. Comparison between concentration of surface species calculated on the basis of the site binding model of the EDL and the adsorption of electrolyte ions is made.

Investigation of electrical properties of the electrical double layer on porous glasses

A series of Controlled Porosity Glasses was employed to investigate their electrical surface properties. Surface charge density and adsorption of electrolyte ions were examined, in order to link initial glass composition and physicochemical properties with its surface electrical double layer characteristics. Results prove the increase of surface boron concentration and consequently growing of negative charge and adsorption properties. Authors find it more complicated to explain characteristics of positive charge changes, which require further investigation.

Use of a three‐plane model to describe charge properties of some iron oxides and soil clays

SummaryThe pH‐dependence of surface charge density of three iron oxides and the clay fraction of five horizons of a variable‐charge soil has been studied by adsorption of potential‐determining ions (p.d.i.) and by adsorption of electrolyte ions. The general trend of results for iron oxides can be satisfactorily explained by a model which considers a three‐plane distribution of electric potential. When the model is applied to soil clays the outcome is less satisfactory and, although their charge properties seem to be largely determined by their high content of minerals with variable charge surfaces, the presence of minerals with a permanent charge (clay minerals) should be considered when explaining the particular data, even for those horizons where clay minerals are present in low proportions.

Ionenadsorption an Elektroden in wäßrigen und nichtwäßrigen Elektrolyten

AbstractAdsorption of ions on electrodes in aqueous and nonaqueous electrolytes. This article considers the practical implications of adsorption of electrolyte ions on electrodes and methods for quantitative determination of electrosorption of ions. Adsorbed ions influence the potential drop in the inner Helmholtz layer and thereby modify the rate of charge transfer for redox processes occurring at electrodes, and the chemical reactions ensuing upon charge transfer can be effectively directed by adsorbed ions. Corrosion and its inhibition as well as deposition of metal in electroplating can be influenced by surface‐active ionic additives which are adsorbed. Measurement of differential capacity provides information about the electrosorption of ions and neutral compounds. A knowledge of the zero point of the electrode metal permits clear predictions concerning ion adsorption. Anions are preferentially adsorbed at potentials on the anodic side of the zero point, and cations at potentials that are more negative than the zero point. Surface‐active neutral compounds and lyophobic ions are most strongly adsorbed in a narrow potential range around the zero point. Adsorption of weakly solvated ions on hydrophobic metals (e. g. Au, Hg) is more pronounced than the adsorption of strongly solvated ions on hydrophilic metals (e. g. Ga, Cd, Zn).

On the cataphoresis of gliadin Part II—The effect of strong electrolytes upon the mobility

Careful analyses of the cataphoretic velocity of a colloid particle suspended in an electrolyte solution have been made by Smoluchowski, by Debye and Hückel, and by Henry. No actual test of their theoretical conclusions over a sufficiently wide range of ionic strength appears yet to have been made, with the exception of some experimental work recorded by Audubert, whose results indicate good agreement for particles of radius 60 - 130 A, but not for particles of radius 2-8 μ. Unfortunately, no details are given of the measurement of the sizes of such small particles. In adopting the hypothesis of Pauli that a colloidal particle behaves like a large polyvalent ion, it is assumed that on altering the electrolyte concentration there is no change in valency of the ion when the theory of Debye-Hückel and of Henry is applied. In practice those colloids whose charge is derived mainly from adsorption of ions do not exhibit constant valency on variation of the ionic strength of the electrolyte. According to Abramson, quartz particles covered with protein behave as ions of constant valency in solutions of the same ionic strength and hydrion activity. This assumption can be valid only over a restricted range of concentrations. Thus, at high ionic strengths, the valency may be altered appreciably by the adsorption of electrolyte ions, whilst it may reasonably be anticipated that at small ionic strengths the effect of the restriction of ions inside the double layer will lead to an alteration in the effective valency of the particle. In general a Donnan equilibrium is set up wherever one ionic species is constrained in any manner from free diffusion; modification of the effective valency of the colloid ion may be expected in very dilute electrolyte solutions on this account.