Aquatic surface chemistry: Edited by Werner Stumm. Wiley, New York. 1987. $69.95 (ISBN 0471822951)

Removal of arsenic from groundwater by granular titanium dioxide adsorbent.

Phosphorus removal from aqueous solution using iron coated natural and engineered sorbents.

Adsorption of phosphate ions on novel inorganic ion exchangers

Phosphate removal from aqueous solution using iron oxides: Adsorption, desorption and regeneration characteristics.

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

The problem of the distinction between the so-called free charge and the thermodynamic (total) charge of electrodes was discussed in the light of the relevant IUPAC definitions calling attention to the strict relationships existing between charge and mass balances during the formation of a double layer at electrodes or/and particles. It is demonstrated that the origins of controversial views concerning partial charge transfer and electrosorption valency, notions widely used nowadays in the electrochemical literature, could be ascribed to confusion of the free and thermodynamic charges. Although there are, even if sporadic, evidences and theoretical considerations in the literature proving that electrosorption valency as usually defined is an extrathermodynamic and self-contradictory concept, it is widely used by many authors for the interpretation of electrosorption phenomena. One of the most important aims of the present work was to demonstrate that independent of the thermodynamic considerations, the concept of electrosorption valency cannot be reconciled with elementary laws of electrochemistry. On the basis of analysis of real processes occurring in the interfacial layer of electrodes it was urged to avoid the treatment of some double-layer phenomena in terms of electrosorption valency in order to eliminate far-reaching misinterpretations leading to serious contradictions.

Double-layer phenomena in electrochemistry: controversial views on some fundamental notions related to electrified interfaces.

The specific adsorption of radiolabeled sulfate ions from perchlorate supporting electrolyte onto TiO2 powder (anatase) has been investigated. The pH and concentration dependence of the adsorption was determined. Langmuir-like adsorption behavior similar to that on other oxides was found. From the pH dependence it follows that the protonation of the surface should precede the specific anion adsorption. The results obtained are compared with those reported for TiO2 bulk electrodes.

Investigation of the specific adsorption of sulfate ions on powdered TiO2.

The pH dependence of adsorption of 14C-labeled benzoic and oxalic acids on γ-Al2O3 and hematite was studied in acid medium in the presence of 0.5 mol dm−3 NaClO4 supporting electrolyte. It was found that the adsorption of the organic species starts at pH values where the protonation of the oxide surface takes place. In the case of benzoic acid the extent of adsorption with decreasing pH goes through a sharp maximum at a pH value not far from the pK (4.2) of the acid, while in the case of oxalic acid only a small decrease can be observed at very low pH values (pH<1). In indirect radiotracer studies using 35S-labeled sulfate ions it was shown that the competitive adsorption of formic, malonic, maleic, and oxalic acids with sulfate ions depends on pH and the effect of the organic acid on the anion adsorption becomes pronounced at pH values about and above the pK of the acid. On the basis of these observations and considerations concerning the dissociation of the organic acids studied it is assumed that the specific adsorption of the anionic form of the acids takes place. It is, however, emphasized that the negative charge of the anions, consequently the electrostatic forces, do not play significant role in the adsorption.

Specific adsorption of simple organic acids on metal(hydr)oxides: A radiotracer approach

The specific adsorption of radiolabeled anions (sulfate, chloride) from perchlorate supporting electrolyte on γ-Al 2 O 3 powder has been investigated. It was demonstrated that a measurable adsorption occurs only at pH values under pH 6. The adsorption capacity of a given amount of γ-Al 2 O 3 powder tends to a limiting value with decreasing pH. A Langmuir-like adsorption isotherm describes the concentration dependence of the adsorption of sulfate species. It was found that the experimental results are very similar to those obtained in the case of hematite.

G. Horányi

Papers

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

Double-layer phenomena in electrochemistry: controversial views on some fundamental notions related to electrified interfaces.

Investigation of the specific adsorption of sulfate ions on powdered TiO2.

Specific adsorption of simple organic acids on metal(hydr)oxides: A radiotracer approach

Application of the Radiotracer Technique for the Study of the Specific Anion Adsorption on Al2O3 in Acidic Medium