pH-dependent surface charging of metal oxides

Aqueous dispersions of metal oxide particles are of great practical interest due to their wide-ranging industrial applications and everyday uses under the conditions required. The latter involves the broad variability of pH and dissolved materials among them electrolytes which have definite role in charge neutralization in the vicinity of particle surface. In this work, the pH-dependent surface charging of metal oxides due to the specific adsorption of H+/OH- in the presence of indifferent and specific ions, and other simultaneous processes at solid/water interface such as hydration of surface, dissociation of surface sites, dissolution of solid matrix, then hydrolysis of dissolved ions are discussed. The governing role of solid particles will be showed by means of characteristic examples of aluminum, iron, titanium and zinc oxides, which have significant differences in chemical properties considering e.g., their pH-dependent dissolution and the speciation of dissolved ions.