The zero point of charge of alpha-alumina

Surface acid–base properties and hydration/dehydration mechanisms of aluminum (hydr)oxides

“…After that the surface oxygen ions' coordination environment of Al ions changed into (Al,O 6 ) octahedra and tended to form oxygen bridges between surface aluminum ions, leading to higher acidity at the surface binding sites. The three surface states of alumina, i.e., physically adsorbed water, chemically adsorbed water, and oxygen bridges at the surface of aluminum (hydr)oxide may be depicted as (6) The surface hydration of α-Al 2 O 3 may be regarded as a reversible process of gibbsite dehydration. At the last stage of the hydration the gibbsite surface may form, and that is the case reported.…”

“…On the hydroxylated surface of aluminum oxides, the surface hydroxyl groups may ionize as Brønsted acid or base sites in appropriate circumstances. The nature of surface sites determines the ability to bind protons, and then the con-centration of these sites macroscopically presents acid-base properties [5,6]. The surface charge, which is due to the protonation/deprotonation reaction of surface sites, is mainly a function of pH and the ionic strength of the aqueous solution, and consequently potentiometric titration techniques are the most commonly used method to evaluate the surface acid-base properties [7][8][9][10][11].…”

Effect of Saturating Cation, pH, and Aluminum and Iron Oxide on the Flocculation of Kaolinite and Montmorillonite

“…It is reasonable that less salt is required to flocculate the materials when they have lower charge density. Similarly, Yopps and Fuerstenau (1964) reported that coagulation was most rapid near the PZC. In the CaC12 solutions, the CCC minima shifted to higher pHs.…”

Physicochemical Fate of Sulfate in Soils

“…In the case of oxides such as Al, the potential determining role of H + and 0H~ involves a charge transfer across the Al-water interface by equilibration with Al 3+ or 0 2~ in the lattice. 41 This involves protonation or deprotonation as follows: The proportion of aquo and hydroxo and ol groups, and consequently the charge, is determined by the equilibrium pH. The formation and composition of colloidally dispersed hydrous oxides and precipitates may be explained on the basis of olation, oxolation, and anion penetration.…”