Adsorption of 1-(2-thiazolylazo)-2-naphthol on amberlite XAD-7 and silica gel: Isotherms and kinetic studies

Abstract

The reagent 1-(2-thiazolylazo)-2-naphtol (TAN) has been extensively used in solid-phase extraction without a critical evaluation of the adsorption process. In this work, the adsorption of TAN onto XAD-7 and silica gel has been investigated and the experimental equilibrium data were fitted to the Langmuir, Freundlich and Dubinin-Radushkevich models. These models provided good fits for both adsorbents and their respective parameters KL, KF and KD-R were calculated. For the same TAN concentration range, the minimum time of contact for adsorption and the maximum amount of TAN adsorbed per gram were lower in XAD-7 (35 min and 4.05 × 10?3 g g?1) than in silica gel (210 min and 1.81 × 10?2 g g?1). The evaluation of the mean sorption energy characterized the adsorption as physical and the surfaces for both adsorbents as energetically heterogeneous. The experimental data for both systems showed an excellent adjustment to the pseudo-second order model. Excellent agreements between qmax,calc and qmax,exp were found in all cases and the kinetic constant value confirmed the different minimum time to reach maximum adsorption of TAN onto XAD-7 and silica gel. By considering the adsorption capacity and the force of the interaction, silica gel can be pointed out as the best support for adsorption of TAN. © 2014 Sociedade Brasileira de Química.