EXPERIMENTAL-DETERMINATION OF THE ELECTRON-DONOR AND ACCEPTOR NUMBERS OF OXIDES BY ZETAMETRY IN ORGANIC MEDIA

A method allowing the experimental determination of the electron acceptor number and electron donor number (AN and DN respectively) of mineral oxides, namely TiO2 and Al2O3, in organic media by zetametry is described. The donor-acceptor concept approach to molecular interactions shows that the total donor-acceptor interaction energy (Delta H) between 1 mol of solid single particles and the organic liquid molecules is given by Delta H = (DNS - DNL) (AN(S) - AN(L)) where the subscript L denotes the liquid and subscript S denotes the solid. In zetametry, the electrically charged particles are submitted to a constant electric field V. The particle charge Q can therefore be considered to be proportional to the donor-acceptor interactions between the liquid and the solid, thus leading to the relationship (DNS - DNL) (AN(S) - AN(L)) = kQVN(p) where k is the proportionality constant, QV is the electrical energy of one particle and N-p is the number of particles per mole of solid. Now, the electric charge is known from zetametry as Q = 4 pi epsilon(0) epsilon alpha zeta where epsilon(0) is the permittivity of vacuum, epsilon is the permittivity of the liquid, alpha is the particle radius, zeta is the zeta potential and N-p is easily calculated knowing the specific surface area of the solid. Finally, we obtain the following relationship: (DNS - DNL) (AN(S) - AN(L)) = k(1) epsilon alpha zeta where k(1) = 4 pi epsilon(0)VkN(p) is the proportionality constant including the conversion factor of energy units. In this relationship, AN(L), DNL and epsilon are known quantities, alpha and zeta can be determined experimentally, and AN(S), DNS and k(1) are unknown values. However, AN(S), DNS and k(1) are solutions of the system composed of n equations established using n different organic lest liquids. The values of AN(S) and DNS determined for TiO2 and Al2O3 oxides by zetametry agree very well with those obtained by inverse gas chromatography.