Slow Adsorption Process Research Articles

On the charge stoichiometry upon adsorption of a cationic polyelectrolyte on cellulosic materials

Adsorption isotherms and adsorption Stoichiometry of a low-molecular-weight ( M w = 5.9·10 3) cationic polyelectrolyte, 3.6-ionene (Polybrene), on cellulosic fibers were studied. The charge density of the fibers was varied by means of carboxymethylation. In order to study the effects of increased accessibility to the charges within the fiber cell wall, part of the fiber material was treated in a high-pressure homogenizer to produce a microfibrillated cellulose ( MFC ). It is shown that the adsorption isotherms are of the high-affinity type with a pronounced plateau level. The charge of the polymer adsorbed at this plateau level provide a relatively good measure of the charge (in meq g −1) on both the fibers and the MFC, except for the unsubstituted fiber sample. By measuring simultaneously the adsorption of polymer and the amount of released counterions it was also shown that there is an almost 1:1 Stoichiometry between the charges on the polyelectrolyte and the charges on the fibers. However, the Stoichiometry drops rapidly when the amount of adsorbed polymer charges exceed the number of charges on the cellulosic fibers. Finally, the deviation from a 1:1 relation between the total charge on the cellulosic material and the adsorbed polymer charges for the unsubstituted fibers is also shown to be caused by a slow adsorption process.

On the charge stoichiometry upon adsorption of a cationic polyelectrolyte on cellulosic materials

Adsorption isotherms and adsorption stoichiometry of a low-molecular-weight ( M w = 5.9·10 3) cationic polyelectrolyte, 3.6-ionene (Polybrene), on cellulosic fibers were studied. The charge density of the fibers was varied by means of carboxymethylation. In order to study the effects of increased accessibility to the charges within the fiber cell wall, part of the fiber material was treated in a high-pressure homogenizer to produce a microfibrillated cellulose (MFC). It is shown that the adsorption isotherms are of the high-affinity type with a pronounced plateau level. The charge of the polymer adsorbed at this plateau level provide a relatively good measure of the charge (in meq g −1) on both the fibers and the MFC, except for the unsubstituted fiber sample. By measuring simultaneously the adsorption of polymer and the amount of released counterions it was also shown that there is an almost 1:1 stoichiometry between the charges on the polyelectrolyte and the charges on the fibers. However, the stoichiometry drops rapidly when the amount of adsorbed polymer charges exceed the number of charges on the cellulosic fibers. Finally, the deviation from a 1:1 relation between the total charge on the cellulosic material and the adsorbed polymer charges for the unsubstituted fibers is also shown to be caused by a slow adsorption process.

Radiotracer studies of chemisorption on copper-based catalysts. Part 1.—The adsorption of carbon monoxide and carbon dioxide on copper/zinc oxide/alumina and related catalysts

The adsorption of 14CO and 14CO2 on a hydrogen-reduced Cu/ZnO/Al2O3, a Cu/Al2O3 and a ZnO catalyst at 293 K is reported. With each adsorbate evidence for both a strongly and a weakly absorbed state has been detected on the copper component of the catalyst. Both a relatively rapid and a very slow adsorption of CO2 on each of the adsorbates have been detected. Adsorption of CO in the presence of preadsorbed CO2 and vice versa shows that the presence of one gas does not completely prevent the adsorption of the other. The adsorptive capacity of the Cu/ZnO/Al2O3 for CO is approximately twice that for CO2, although a larger fraction of the latter is strongly adsorbed and will displace some preadsorbed CO from the copper surface. Evidence for the dissociative adsorption of some of the CO2 to COads and surface oxygen, as well as the formation of surface carbonate by reaction of CO2 with catalyst oxygen, has been obtained. It is proposed that this latter process is responsible for the very slow CO2 adsorption process. Whilst CO2 is adsorbed on each of the components of the Cu/ZnO/Al2O3 catalyst, adsorption of CO is severely limited on the zinc oxide component and does not occur on the alumina. The results are interpreted in terms of a model in which at least three types of adsorption site exist on the copper surface. The role of residual oxygen on the surface, following hydrogen reduction, in the adsorption of CO2 is also discussed.

Studies on the Gas-Liquid Interface by Surface Potential Measurements III. The Surface Aging of the Solutions of the Long-chain Dibasic Acids

Abstract The surface aging of the solutions of some ω,ω′-dicarboxylic acids was investigated by measuring the surface tension and surface potential, in a function of time. Only the slow adsorption process was studied in the present experiment. Adipic, suberic, and azelaic acid reached readily an equilibrium. Sebacic acid showed considerable surface aging. The mechanism of adsorption was assumed in the light of kinetic molecular theory, and the free energy of activation for adsorption was calculated. We obtained the free activation energy, 17.5-17.9 Kcal. for suberic acid, 18.0-18.5 Kcal. for azelaic acid and 13.8 Kcal. or more than this for sebacic acid. Free energy of activation for adsorption was increased to some extent with the surface concentration of already adsorbed solute molecules and consequently, for a certain solution, with the surface age.