Experimental determination of the electron donor and acceptor numbers of oxides by zetametry in organic media

Abstract

A method allowing the experimental determination of the electron acceptor number and electron donor number ( AN and DN respectively) of mineral oxides, namely TiO 2 and Al2O 3, in organic media by zetametry is described. The donor—acceptor concept approach to molecular interactions shows that the total donor—acceptor interaction energy (Δ H) between 1 mol of solid single particles and the organic liquid molecules is given by Δ H = ( DN s − DN L) ( 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 ( DN s − DN L) ( 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 = 4πϵ 0ϵ aζ where ϵ 0 is the permittivity of vacuum, ϵ is the permittivity of the liquid, a is the particle radius, ζ is the zeta potential and N p is easily calculated knowing the specific surface area of the solid. Finally, we obtain the following relationship: ( DN s − DN L) ( AN s − AN L) = k 1ϵ aζ where k 1 = 4πϵ 0 VkN p is the proportionality constant including the conversion factor of energy units. In this relationship, AN L, DN L and ϵ are known quantities, a and ζ can be determined experimentally, and AN s, DN s and k 1 are unknown values. However, AN s, DN s and k 1 are solutions of the system composed of n equations established using n different organic test liquids. The values of AN s and DN s determined for TiO 2 and Al 2O 1 oxides by zetametry agree very well with those obtained by inverse gas chromatography.