Restricted Geometry Conditions Promoted by AlOOH Nanoparticles: Variable Strength and Character of AlOOH-Cluster/Charged Ligand Interactions As a Consequence of Changes in the Solvent

Abstract

AlOOH nanoparticles have been used to study the strength and character of the binding of the persulphate ion (S2O82−), at pH = 5.4, to them. The strength of the binding has been studied using a kinetic approach which consists of the study of the oxidation kinetics of a metal cation complex ([Ru(NH3)5pz]2+ (pz = pyrazine)) by S2O82− at different NaCl concentrations. When the ionic strength increases, the strength of the binding decreases, as a consequence of the partial neutralization of the charge on the AlOOH surface which, at pH = 5.4, is positively charged. The increase of the ionic strength also produces a change in the character of the binding, which changes from anticooperative to noncooperative when the ionic strength increases. The nonelectrostatic and electrostatic components of the free energy of binding are determined. The nonelectrostatic component of the free energy of binding is almost zero. On the other hand, the values of the differences of electrostatic potential at the AlOOH/solutions interface have been obtained from the electrostatic component.