Adsorption and surface complexation of trimesic acid at the α-alumina–electrolyte interface

Abstract

Adsorption kinetics, adsorption isotherms and surface complexation of trimesic acid onto α-alumina surfaces were investigated. Adsorption kinetics of trimesic acid with an initial concentration of 0.5 mM onto α-alumina surfaces were carried out in batch method in presence of 0.05 mM NaCl (aq) at pH 6 and 298.15, 303.15 and 313.15 K. Adsorption isotherms were carried out at 298.15 K, pH 5–9, and 0.05 mM NaCl (aq) by varying trimesic acid concentration from 0.01 to 0.6 mM. Three kinetics equations such as pseudo-first-order, pseudo-second-order and Ho equations were used to estimate the kinetics parameters of the adsorption of trimesic acid on the α-alumina surfaces. Ho equation fits the experimental kinetics data significantly better and the estimated equilibrium concentration is in excellent agreement with the experimental value. The adsorption data were fitted to Freundlich and Langmuir adsorption model and the later best fits the adsorption isotherms. Comparison of adsorption density of trimesic acid with that of benzoic and phthalic acids follows the sequence: benzoic acid < trimesic acid < phthalic acid. The negative activation energy and the Gibbs free energy for adsorption indicate that the adsorption of trimesic acid onto α-alumina is spontaneous and facile. DRIFT spectroscopic studies reveal that trimesate forms outer-sphere complexes with the surface hydroxyl groups that are generated onto α-alumina surfaces in the pH range of the study.