We applied the hard and soft acid-base (HSAB) model (Xu and Harsh 1990a, 1990b) to bivalent cation exchange on a purified Ca-montmorillonite. As a result, a satisfactory model is proposed to describe the gradual selectivity of exchange with Ca for 4 of the 6 metals studied (Cd, Cu, Pb, Zn). The selectivity is predicted as a function of the differences of electronegativity and softness of the metals. The deviation of Ni and Co data from the predicting model is interpreted in terms of hydration (Ni and Co being the most strongly hydrated ions). The fitting parameters of the model, α and β, are related to the electronegativity and softness characteristics of the surface, respectively. Their ratio gives information on the nature of bonding. Results suggest that covalent bonding modifies electrostatic interactions, which in turn affect selectivity, with an increasing influence of covalent bondings in the order: Pb < Cd < Zn < Cu.

To balance the lack of representativity of the model for the small molar fraction (NM), we propose to associate to the HSAB model an equation describing the variation of the Vanselow selectivity coefficient as a function of the molar fraction of metal on clay.

In the present study, we report an activation and enhancement of room temperature ferromagnetism in pure ZnO and V-doped ZnO (Zn0.95V0.05O and Zn0.90V0.10O) thin films by trioctylphosphine (TOP) functionalization. X-ray diffraction patterns show a slight decrease in the intensity of the diffraction peak on TOP functionalization. Atomic force micrographs of pure and V-doped ZnO films reveal no disorder in the film surface on TOP functionalization. The chemical bond formation of TOP on ZnO film surface was examined by x-ray photoelectron spectroscopy measurements. Photoluminescence measurements of TOP-functionalized ZnO films show enhancements of UV emission and quenching of visible emission. TOP-functionalized ZnO films reveal enhanced ferromagnetic behavior as evidenced from vibrating sample magnetometer measurements.