The adsorption of tetraethylammonium ions at a mercury electrode from perchlorate solutions

The adsorption of tetraethylammonium ions at the mercury-perchlorate solution interphase has been studied. Solutions at constant perchloric acid activity have been prepared and the use of several perchloric acid activities allows us to calculate the simultaneous adsorption of both ions: tetraethylammonium and perchlorate. An interphase model is described to explain co-adsorption of both ions.     

The problem of the irreversibility of the adsoprtion of halides on platinum

The problem of the irreversibility of the adsorption of Cl^? ions on platinum has been studied by a tracer method described previously. The mobility of adsorbed Cl^? ions has been observed in the following experiments: in the exchange of adsorbed labelled Cl^? with nonlabelled dissolved Cl^? ions; in the desorption caused by the rinsing of the electrode; in the displacement of adsorbed Cl^? ions by Br^? and I^? ions; in the simultaneous adsorption of Cl^? ions and other halide ions. In the light of these results the views based on the assumption of irreversibility have been criticized.     

Sur les indicateurs d'absorption. iv

A new adsorption indicator. Red acid 6B, has been described for argentometric titrations of the halide ions.The great usefulness of the indicator lies in its being applicable for the very diluted solutions of the ions I^-.     

Preparation of graphene oxide and its application in Ni<Superscript>2+</Superscript> removal

Graphene oxide (GO) has been prepared by the modified Hummers method using graphite as starting material. The product was studied by the X-ray diffraction (XRD), Raman spectroscopic, transmission electron microscopic (TEM), and scanning electron microscopic (SEM) analyses. Adsorption capacity of GO for heavy metal ions was studied for the example of the Ni²⁺ ions and the adsorption kinetics and adsorption isotherm were determined. It was shown that the adsorption equilibrium curves are adequately described by the Langmuir equation.     

Adsorption of neodymium ions on activated charcoal from aqeous solutions

Summary A commercial activated charcoal has been tested as an adsorbent for the removal of neodymium ions from aqueous solutions. The adsorption behavior of neodymium ions on activated charcoal from aqueous solutions has been studied as a function of shaking time, neodymium ions concentration and concentration of different acids. Results reveal that the adsorption equilibrium is attained within 30 minutes, and diffusion of neodymium ions into the pores of activated charcoal controls the adsorption process. The adsorption process follows the first order kinetics. The Langmuir isotherm equation was obeyed well in the whole range of concentration studied. The influence of different cations and anions on the adsorption of neodymium ion from aqueous solutions have also been investigated. Approximately 98% of neodymium ions adsorbed onto activated charcoal could be recovered with 40 ml of 3M HNO₃ solutions.     

Study of adsorption of tetraethylammonium ions on Bi single crystal planes from solutions in ethanol

The adsorption of tetraethylammonium (TEA⁺) ions on the (001) and planes of the bismuth single crystal from solutions in ethanol has been investigated by impedance measurement method. The experimental data were obtained in 0.02 M mixed-electrolyte solutions and the calculations performed with electrode potential as the independent electrical variable. The Gibbs energy of adsorption of TEA⁺ ions has been calculated using the simple virial adsorption isotherm, and it was found that the adsorption of TEA⁺ cations is weaker than the adsorption of halide anions. The electrosorption valency evaluated has a nearly constant value in the potential region studied. It was concluded that the formed effective surface dipole is significantly screened by the solvent molecules and the metal electron gas. The analysis of the impedance spectra was performed by fitting the experimental data to the various equivalent circuits. It was found that the behaviour of TEA⁺ ions at Bi(hkl)∣ethanol interface can be described with the equivalent circuit, corresponding to the classical Frumkin–Melik-Gaikazyan model. The results obtained indicate that only weak interaction between TEA⁺ ions and bismuth surface takes place, and there is no remarkable partial charge transfer from the adsorbed ions to the Bi surface atoms.     

Adsorption of strontium ions from aqueous solution on Pakistani coal

Summary The adsorption of strontium ions from aqueous solution on a Pakistani coal powder has been studied as a function of shaking time, amount of adsorbent, pH, and strontium ion concentration. Conditions for the maximum adsorption of strontium ions have been established. Results reveal that the diffusion of strontium ions into the pores of coal powder occurs during the adsorption process and intra-particle diffusion controls the kinetics of the process. The Langmuir and D-R adsorption equations are valid over the entire range of studied concentration. The influence of different anions on the adsorption of strontium ions was also studied.     

On the theory of adsorption kinetics of ionic sufactants at fluid interfaces 4. Deceleration of the adsorption rate due to non-equilibrium distribution of adsorbed ions in the diffuse layer

An approximate analytical solution is obtained for the adsorption kinetics equation derived earlier. On the basis of these relations the importance of the consideration of a non-equilibrium diffuse layer has been shown. To describe the retarded adsorption kinetics the distribution of adsorbed ions in the diffuse layer section of multivalent surfactant ions has been taken into account. The rate of adsorption calculated for a non-ionic surfactant is compared with the adsorption rate for monovalent and bivalent ionic surfactants, respectively.     

Kinetics of metal ions adsorption at heterogeneous solid/solution interfaces: A theoretical treatment based on statistical rate theory

The statistical rate theory combined with a two-component competitive adsorption model is applied to describe the effect of pH on the kinetics of metal ions adsorption at energetically heterogeneous solid/solution interfaces. The surface heterogeneity has been represented by both Gaussian-like and rectangular functions of the adsorption energy distribution. A concept of effective heterogeneity parameters is found to represent very well the combined effects of surface energetic heterogeneity and of the electrostatic lateral interactions in the adsorbed phase, described by using the mean field approximation. The applicability of our approach is demonstrated by a quantitative analysis of two sets of experimental data reported in literature. Our theoretical expressions have been able to successfully correlate kinetic and equilibrium data in both these cases.     

Some peculiarities in the specific adsorption of phosphate ions on hematite and gamma-Al2O3 as reflected by radiotracer studies

The specific adsorption of radiolabeled phosphate ions from perchlorate supporting electrolyte onto gamma-Al2O3 and hematite powder has been investigated. The pH dependence of the adsorption of phosphate species was compared with that of sulfate ions. It was demonstrated that in contrast to the behavior of sulfate ions the pH dependence of phosphate ions goes through a maximum. On the other hand, it was found that the reversible adsorption of phosphate ions is accompanied by the formation of strongly chemisorbed species. Results obtained from a study of the competitive adsorption of sulfate and phosphate ions at various pH values are reported and interpreted. An attempt is made to correlate the experimental findings with the models for anion adsorption reported in the literature.     

Ternary surface complexes in silica-Ni2+ ions-2,2′-dipyridyl systems

The adsorption of complexes of nickel ions with an organic base (2,2′-dipyridyl) at an interface between silica and an aqueous electrolyte solution has been considered in terms of the theory of complexation. It has been shown that, on the silica surface, ternary complexes are formed, in which nickel ions are bonded to silanol groups. The equilibrium constants of the reactions of ternary surface complex formation have been calculated from the adsorption curves describing the pH dependences of nickel ion and dipyridyl adsorption.     

Effect of background electrolytes and pH on the adsorption of Cu(II)/EDTA onto TiO2

Cu(II)/EDTA adsorption onto TiO2 has been studied with a variation of pH, ionic strength, and type of background electrolytes. Cu(II) adsorption onto TiO2 increased as ionic strength increased when NaClO4 was used as a background electrolyte. This can be explained by the increase of exp(-FPsi/RT) as a part of the electrostatic correction within a surface complexation model. Model predictions described experimental adsorption trends. Types of background anions (ClO4, Cl, NO2, NO3, SO3, and PO4) did not affect adsorption trends and adsorption amounts of Cu(II) onto TiO2. However, different trends were observed with various types of background ions used as ionic strength in EDTA and Cu(II)-EDTA adsorption. EDTA adsorption was decreased by using Na2SO3 and Na3PO4 as background ions, while NaClO4, NaCl, NaNO2, and NaNO3 showed negligible interference on the EDTA adsorption, which matched well with model predictions. The presence Na2SO3 and Na3PO4 also interfered with Cu(II)-EDTA adsorption, to a somewhat greater extent compared to EDTA adsorption, especially at lower pH. This interference was also noted in Cu(II)-EDTA adsorption with a variation of Cu(II)-EDTA concentration at constant ionic strength (3 x 10(-3) M) by using Na2SO3 and Na3PO4, especially at lower ratios of Cu(II)-EDTA to Na2SO3 and Na3PO4. These results suggest that the ratio of Cu(II)-EDTA to Na2SO3 and Na3PO4 is an important factor for the controlling of competition between these background ions and Cu(II)-EDTA onto TiO2. Model prediction generally matched well with experimental adsorption using NaClO4, NaCl, NaNO2, and NaNO3 as backgrounds ions, while a severe deviation was observed in the presence of Na2SO3 and Na3PO4. These results suggest that the mobility of copper ions as Cu(II)-EDTA can be increased from polluted area in the presence of multivalent background ions, especially as the ratio of adsorbates/background ions decreased.     

Experimental isotherms of HCl on H2O ice under stratospheric conditions: connections between bulk and interfacial thermodynamics

The adsorption of HCl on the surface of H(2)O ice has been measured at temperatures and pressures relevant to the upper troposphere and lower stratosphere. The measured HCl surface coverage is found to be at least 100 times lower than currently assumed in models of chlorine catalyzed ozone destruction in cold regions of the upper atmosphere. Measurements were conducted in a closed system by simultaneous application of surface spectroscopy and gas phase mass spectrometry to fully characterize vapor/solid equilibrium. Surface adsorption is clearly distinguished from bulk liquid or solid phases. From 180 to 200 K, submonolayer adsorption of HCl is well described by a Bragg-Williams modified Langmuir model which includes the dissociation of HCl into H(+) and Cl(-) ions. Furthermore, adsorption is consistent with two distinct states on the ice substrate, one in which the ions only weakly adsorb on separate sites, and another where the ions adsorb as an H(+)-Cl(-) pair on a single site with adsorption energy comparable to the bulk trihydrate. The number of substrate H(2)O molecules per adsorption site is also consistent with the stoichiometry of bulk hydrates under these conditions. The ionic states exist in equilibrium, and the total adsorption energy is a function of the relative population of both states. These observations and model provide a quantitative connection between the thermodynamics of the bulk and interfacial phases of HCl/H(2)O, and represent a consistent physicochemical model of the equilibrium system.     

Electrophoretic Mobility Study of the Adsorption of Alkyl Xanthate Ions on Galena and Sphalerite

The adsorption of ethyl and amyl xanthate ions on galena and sphalerite fines has been studied using electrophoretic light-scattering (ELS) measurements. It was performed on galena and sphalerite (<2&mgr;m) in aqueous solution at different potassium ethyl xanthate (PEX) and potassium amyl xanthate (PAX) concentrations. It has been observed that the presence of PEX or PAX caused the isoelectric points (IEP) of galena and sphalerite fines to shift and the electrophoretic mobility to reverse in sign, indicating that the xanthate ions chemisorbed on galena and sphalerite surfaces. This adsorption markedly broadened the electrophoretic mobility distribution of the mineral fines, suggesting that the populations of the particles have quite different adsorption densities of xanthate ions, and therefore the particle hydrophobicity was different. This phenomenon might be attributable to the effect of the hemimicelle adsorption of the xanthate ions on the minerals, the nonuniform distribution of active sites and their degree of activity, the effect of particle size and shape, etc. The nonuniform adsorption has been found to increase with increasing PEX or PAX concentration, reaching a maximum at a medium concentration followed by a decline. Also, experimental results have demonstrated that the nonuniform adsorption of the xanthate ions is much stronger on sphalerite than on galena, which may explain why sphalerite has a worse flotation response than galena when alkyl xanthates are used as collectors in flotation systems. Copyright 2001 Academic Press.     

Synthesis and radioiodination of new dipeptide coupled with biologically active pyridine moiety

The adsorption of uranium (VI), cesium and strontium ions from aqueous solutions onto a commercial activated carbon obtained by physical activation of coconut shell has been studied in batch systems. In particular the adsorption of uranium, studied as a function of contact time and metal ion concentration, followed pseudo-first-order kinetics. Equilibrium adsorption data were fitted by Langmuir and Freundlich isotherm models and the maximum adsorption capacity of the activated carbon resulted to be 55.32 mg/g. The study showed that the considered activated carbon could be successfully used for uranium adsorption from aqueous solutions. Feasibility of cesium and strontium adsorption onto the same activated carbon has been also investigated. Results showed that no affinities with both of these ions exist.     

Dynamic instability at liquid/vapor interface far from equilibrium

Attempt has been made to elucidate the mechanism of electric potential oscillations at oil-aqueous solution interface involving adsorption at oil-vapor interface on a semi-theoretical basis. The mechanism stipulates adsorption of ammonia, amines and pheromones at the liquid-vapor interface followed by transfer of ions through membrane-aqueous solution interface and subsequent interaction of ammonium (amine) ions and carbocations from pheromones with diffusing halide ions from the bulk. Relationship of the above mechanism with sensing mechanism of smell by olfactory nerves has also been pointed out.     

Electrical double layer and adsorption of iodide ions at the Bi | acetonitrile interface

The adsorption of I^? ions on the Bi(111) single crystal plane from solutions in acetonitrile has been investigated by impedance measurement method. The ionic charge due to the specific adsorption has been obtained using the mixed electrolyte method applied for both electrode charge and electrode potential as the independent electrical variables. The Gibbs energy of ions adsorption has been calculated using the virial adsorption isotherm. It was found that under comparable conditions the results obtained at constant electrode potential and at constant electrode charge are coincident and the Gibbs energy of I^? anion adsorption increases in the sequence of solvents: methanol < ethanol < propylene carbonate < acetonitrile. The electrosorption valency has been calculated and it was found that this parameter increases in the sequence propylene carbonate < ethanol < methanol < acetonitrile.     

Studies on the adsorption behaviour of trace amounts of cerium on manganese dioxide from aqueous solutions in the presence of complexing agents

Adsorption behaviour of trace amounts of cerium on manganese dioxide has been studied as a function of pH (1–10) in the presence of EDTA, oxalate, citrate, tartrate, cyanide and thiocyanate ions. The influence of their concentration on the adsorption has also been investigated. Maximum adsorption of cerium has been noticed at pH6. Under specific conditions, adsorption of other metal ions has been measured for comparison. Low distribution coefficients are obtained for Cs(I) and Hg(II) in the presence of oxalate, and for Cr(III) in the presence of thiocyanate ions. Based on these data, separation of cesium, chromium and mercury from rare earths and cerium scavenging in natural water or in waste water treatment can be achieved.     

Ion-exchange studies of <Superscript>110m</Superscript>Ag(I) using synthetic inorganic ion-exchanger

In the present investigation, the selective adsorption of silver on synthetic inorganic ion exchanger, zinc(II) ferrocyanide, has been established by batch method, under specific conditions, using ^110mAg as a tracer. The efficiency of adsorption has been determined by γ-ray spectrometry and was found to be greater than 96%. The Ag(I) uptake by the exchanger has also been evaluated. The selectivity of the method was checked by studying the adsorption of Ag(I) in the presence of a number of foreign ions using their corresponding tracers. The interfering ions were removed by washing the ion-exchanger with appropriate reagents, so that it could be applied for the determination of trace amount of Ag(I) in complex matrices, containing trace amount of other metal ions.