title: Applying zeta potential measurements to characterize the adsorption on montmorillonite of organic cations as monomers, micelles, or polymers.
abstract: A systematic study was carried out to characterize the adsorption of organic cations as monomers, micelles, or polymers on montmorillonite by monitoring zeta potential (ξ) as a function of cation loading on the clay. In general, the clay's ξ became less negative as cation loading increased. A fairly good linear correlation between adsorption of organic cations on the clay, up to the cation exchange capacity (CEC) of the clay, and ξ potential of the composites was fitted. However, when the adsorption of the larger cation exceeded the CEC, a nonlinear increase in ξ was measured. The degree of this increase corresponds to the cation size and affinity to the clay (in the order surfactant<dye dimer<micelle). In contrast to the organic cations, ξ reached zero at polycation loadings that were significantly lower than the CEC. The zeta-adsorption plot of the polycations reached a well-defined plateau which correlates to the zeta potential of the polycations. The effect of electrolytes on ξ of the crude clay was monitored, and as expected, the extent of the effect increased with valency (Na(+)<Ca(2+)<Al(3+)) and with intrinsic cation radius (Na(+)<Cs(+)); however, an unexpected anion effect was observed.
authors.affiliation: The Robert H. Smith Faculty of Agriculture, Food, and Environment, The Hebrew University of Jerusalem, Rehovot 76100, Israel.
authors.forename: Dikla
authors.initials: D
authors.lastname: Zadaka
authors.forename: Adi
authors.initials: A
authors.lastname: Radian
authors.forename: Yael G
authors.initials: YG
authors.lastname: Mishael
mesh_terms: D000327:Adsorption; D001546:Bentonite / Q000737:chemistry*; D002412:Cations / Q000737:chemistry; D005840:Gentian Violet / Q000737:chemistry*; D008823:Micelles; D010316:Particle Size; D011108:Polymers / Q000737:chemistry*; D000644:Quaternary Ammonium Compounds / Q000737:chemistry*; D013499:Surface Properties
chemical_list: D002412:Cations; D008823:Micelles; D011108:Polymers; D000644:Quaternary Ammonium Compounds; D001546:Bentonite; D005840:Gentian Violet