ABSTRACT
I. Introduction 351 II. Theoretical Treatment 352
A. Single-step adsorption/desorption models 352 B. Multistep adsorption/desorption models 357
III. Experimental Methods 363 A. Pressure-jump method 363 B. Electric field-jump method 368 C. Concentration-jump method 370
IV. Adsorption/Desorption of Cations and Anions on Metal Oxides 371 A. Adsorption /desorption of potential determining ions 371 B. Adsorption/desorption of anions 372 C. Adsorption/desorption of metal ions 380 D. Intercalation of ions into the interlamellar layer 385
V. Adsorption/Desorption of Metal Ions, Amino Acids, and Charged Proteins on Ion-Exchange Sephadex A. Proton association/dissociation of functional groups on
ion-exchange sephadex 388 B. Adsorption/desorption of alkali metal ions 391 C. Adsorption/desorption of amino acids 394 D. Adsorption/desorption of charged proteins 395
VI. Conclusion and Further Problems 399 References 400
I. INTRODUCTION
The rate of adsorption of a substance to a particle surface is usually measured by a period ical batch experiment. After a constant amount of sample is withdrawn from a large vol ume of suspension each time, the amount of the substance adsorbed on the particle is determined [1,2]. Since it takes, at least, several minutes for a series of the above pro cedures, a fast adsorption process cannot be followed by such a batch method. Fortunately, particles such as metal oxide have functional groups like the amphoteric surface hydroxyl groups [3]. When the particle surface becomes positive or negative
because of an association /dissociation of the functional groups, the adsorptions of various substances onto particles often occur as ionic reactions. Then a concentration change of ion, which is caused by the adsorption, can be immediately followed by a change in the conductivity. Even a small conductivity change can be measured sensitively with a Wheatstone bridge circuit. Fast reactions in the suspensions are now observed by the pressure-jump, electric field-jump, and concentration-jump methods with conductometric detection. These methods have been developed on the basis of the principle of chemical relaxation [4]: a small perturbation, applied to a certain chemical equilibrium by a change of pressure, temperature, or concentration, causes a shift to a new equilibrium state. This shift can be measured as a chemical relaxation with suitable detections. In Section III, the relaxation methods will be explained. These methods are applied to measure the adsorption/desorptions of various ions on metal oxides and ion-exchange Sephadexes. The reaction mechanisms are introduced in Sections IV and V.
