摘要:

The adsorption of metal ions at the stearic acid/electrolyte and nnonadccane-stearic acid mixture/electrolyte interface was investigated by means of the potentiometric titration, zeta potential and adsorption measurements. It was found that the studied colloidal suspensions exhibited an adsorption affinity towards multivalent metal ions. The adsorption of Ca2+, Cd2+and Al3+ions caused a strong decrease of surface charge density and zeta potential values in this systems. The adsorption reactions occur by way of cation exchange with protons from two surface carboxyl groups. Al high metal concentrations, in adsorption reactions there are involved also carboxyl groups from the subsurface layer. On the basis of the adsorption data, the cation surface complexation constants were calculated by Shindler's method.

ISSN:0193-2691    

DOI:10.1080/01932690008913303

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

A model for the adsorption of ionic surfactants on oppositely charged solid surfaces of uniform charge density is developed. The model is based on the assumption that, on the solid surface, adsorbed surfactant monomers, monolayered and bilayered surfactant aggregates of different sizes and specifically adsorbing ions of added electrolyte constitute a mixture of hard discs. It means that only excluded area interactions between the surface discs are taken into account. To avoid a rapid two-dimensional condensation of the adsorbed surfactant the potential energy per molecule in the surface aggregates, which is a sum of chemical and electrostatic interactions, is assumed to decrease linearly with the increasing aggregate size. The electrostatic interactions of ionic species with the charged solid surface are described in terms of the Guy-Chapman theory of the double layer formation. The appropriate equations for adsorption isotherms of surfactant and electrolyte ions are derived and used to predict the experimental adsorption isotherms of DTAB on the precipitated silica at two different salt concentrations in the aqueous solution, On the basis of the obtained results the evolution of the adsorbed phase structure and the charge of silica particles with an increasing surface coverage is discussed.

ISSN:0193-2691    

DOI:10.1080/01932690008913304

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

The equations developed by us for the surface complexation models, taking into account energetic heterogeneity of surface oxygens, are applied here to study the effects of the shape of adsorption energy distribution on the ion adsorption at the oxide/electrolyte interface. The paper presents comparison of two models: one assuming that the energetical heterogeneity of oxide surface is described by a symmetrical and next a non-symmetrical adsorption energy dispersion for the formation of various surface complexes. The comparison of these two models was based on the obvious assumption that the variances of both the symmetrical and the non-symmetrical distributions are equal. The potentiometric titration data are not sensitive enough to choose the right adsorption model. So, in addition the individual isotherms of adsorption of cation and anion, of the inert electrolyte measured radiometrically, have been taken into consideration. The symmetrical adsorption energy distribution seems to represent the features of these adsorption systems better.

ISSN:0193-2691    

DOI:10.1080/01932690008913305

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

Mechanism of adsorption of Zn(II) and Cd(II) ions at the TiO2(anatase)/electrolyte interface has been studied by different experimental techniques (potentiometric titration, microelectrophoresis and adsorption measurements of zinc and cadmium species). It was found that the point of zero charge (pzc) of anatase (pH =5.8) was shifted to the lower pH values with increasing concentrations of Zn(II) or Cd(Il) ions. The surface charge of anatase in the presence of Zn(II) and Cd(II) for pH > pHpzcwas higher than that observed for original sample in NaClO4solutions only. Due to low coverage of anatase surface with Zn(II) or Cd(II) species almost no shift of the isoelectric point (iep) or charge reversal were observed. Adsorption density vs. pH plots for both Zn(Il) or Cd(II) showed, typical for multivalent ions, presence of “adsorption edge.”

ISSN:0193-2691    

DOI:10.1080/01932690008913306

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

An influence of the molecular weight of the polymer and inorganic contaminations of zirconia on the adsorption and electrokinetic properties on ZrO2-electrolyte solution interface was studied. Two polymers were used; polyacrylic acid (PAA) and polyacrylamide (PAM). On the basis of the obtained dependencies, main factors responsible for observed changes of zeta potential and surface charge of washed and contaminated ZrO2were determined. It was showed, that the change of ionic structure in the Stem layer depends on the number and arrangements of-COOH groups in PAA and PAM macromolecules. These groups are responsible for the conformation of polymer chains near the surface and have direct influence on the amount of the adsorbed polyelectrolyte. The inorganic ions, present on the surface of the oxide, blocking some part of active sites, making them inaccessible for adsorbing by carboxylic groups polymer chains. That makes the adsorption on the contaminated oxide lower than on the washed one. From the comparison of the determined values of the diffuse layer charge and surface charge, the main factor influencing the zeta potential changes at different pH, molecular weight and polymer concentration was determined. Also was demonstrated, that the contaminations of the solid are reason for considerable shift of pHpzcin relation to pHicpof the zirconia. Thickness of the adsorption layers and free energies of the adsorption of polyacrylic acid and polyacrylamide on the surface of ZrO2were calculated.

ISSN:0193-2691    

DOI:10.1080/01932690008913307

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

The electrical properties of colloidal asphaltene/water solution interface were determined by carrying out the potentiometric titration and electrokinetic measurements. Asphaltenes in aqueous solutions exhibit typical organic colloid propertiesi.e.surface charge and electrophoretic mobility. It was considered that the surface charge at the asphaltene particles is a result of protonation and dissociation reactions of surface functional groups. On the base of the surface charge density data vs. pH the surface reaction constants were calculated by numerical method. The agreement of these values with calculated ones, on the base of ζ potential data, is noticeable.

ISSN:0193-2691    

DOI:10.1080/01932690008913308

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

ISSN:0193-2691    

DOI:10.1080/01932690008913309

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor