Influence of anions on the adsorption kinetics of salicylate onto α-alumina in aqueous medium

The adsorption kinetics of salicylate on alpha-alumina surfaces were studied at 25 degrees C and pH 6 in the presence of 0.05 mM concentration of different anions (Cl-, Br-, I-, SCN-, HCOO-, CH3COO-, S2O32-, CO32-, and SO42-) as a function of time. The experimental data were significantly better fitted to a pseudo-second-order kinetics equation of nonlinear form in the entire time duration and are in excellent agreement with corresponding estimated values. Considering adsorption data for salicylate in the presence of Cl- as the face value, all the monovalent anions (Br-, I-, SCN-, HCOO-, CH3COO-) promote the adsorption of salicylate onto alpha-alumina surfaces while the divalent anions (S2O32-, CO32-, and SO42-) have the reverse effect under similar conditions. DRIFT spectra of alpha-alumina treated with salicylate reveal that the symmetric peak vs(-COO-) is shifted by similar to 40 cm(-1) to a lower wavelength region, which implies that salicylate forms an inner-sphere complex with alpha-alumina surface in the presence of both mono- and divalent anions. (C) 2007 Elsevier Inc. All rights reserved.