The Binding of Monovalent Electrolyte Ions on α-Alumina. I. Electroacoustic Studies at High Electrolyte Concentrations

Abstract

An electroacoustic technique has been used to monitor the binding of various monovalent inorganic ions on α-alumina at different pHs, nondilute solids, and moderate to high (0.01−1.0 mol dm-3) electrolyte concentrations. The ζ potential versus pH data show that NaNO3, KNO3, CsNO3, KBr, KCl, and KI are indifferent electrolytes for the α-alumina surface. However, LiNO3 causes a significant change in the isoelectric point of α-alumina, indicating that Li+ adsorbs in a specific manner to the surface over the range of concentrations investigated. At high (1.0 mol dm-3) electrolyte concentrations, the monovalent cations bind to the negative α-alumina surface in the order Li+ > Na+ > K+ ≈ Cs+. By contrast, the Br-, Cl-, I-, and NO3 - anions adsorb to an almost identical extent over the entire range of concentrations and pH conditions investigated. The cation binding sequence is consistent with the water “structure making−structure breaking” model first proposed by Gierst et al. and Bérubé and de Bruyn, which is based on the hydration enthalpies of the ions and the heat of immersion of the colloidal substrate. The comparable anion adsorption behavior is believed to arise because of the similar and/or low hydration enthalpies of the anions, which lead to a similar anion−surface interaction in each case.

Concentration and chemical-state profiles at heterogeneous interfaces with sub-nm accuracy from standing-wave ambient-pressure photoemission

“…Previous studies have demonstrated preferential adsorption of Na þ over Cs þ ions on haematite and other metal oxide surfaces [27][28][29][30][31] . The ionic adsorption sequence: (refs 30,31).…”

On the Temperature Dependence of Intrinsic Surface Protonation Equilibrium Constants: An Extension of the Revised MUSIC Model

“…Recent experimental measurements at high concentrations of various electrolytes (0.1 to 3 M) instead show that pH iep values increase with ionic strength for TiO 2 (anatase form), and ZrO 2 (55), as well as to a lesser extent with α-Al 2 O 3 (56). This is indicative of a stronger interaction of the electrolyte cation with these surfaces relative to the electrolyte anion.…”

Zeta Potentials and Yield Stresses of Silica Suspensions in Concentrated Monovalent Electrolytes: Isoelectric Point Shift and Additional Attraction

“…(20) and (21)). Another objective is to determine the effect of large quantities of adsorbed ions on the rheological behavior (yield stress) of silica and determine whether there is any correlation with the measured zeta potentials.…”

“…The vane is immersed in the suspension, and the torque is measured as a function of time as the tool is rotated at a slow constant rate (0.04 revolutions per minute). The torque response is monitored as a function of time and is simply related to the shear yield stress as detailed elsewhere (34)(35)(36).…”

“…Electrophoretic mobility measurements generally indicate that the magnitude of the negative zeta potential at high pH increases as the Hofmeister series (Cs + < K + < Na + < Li + ) (5,13,14) with Cs + producing lower magnitude negative zeta potentials than Li + . On the other hand, the inverse Hofmeister series is observed for both ion adsorption (18,19) and zeta potential measurements (20,21) for materials such as alumina, hematite, and zirconia, which have high isoelectric points.…”