Pyridine and aniline adsorption from an apolar solvent: the role of the solid adsorbent

Determinations of the adsorption of aniline and pyridine at solid/liquid interfaces from n-hexane solutions have been performed. The solid adsorbents were alpha-Al2O3 and iron powders. The experimental adsorption isotherms were paired in respect of the solutes while marked differences were shown by changing the solid adsorbent. In the case of the oxide substratum,the adsorption isotherms presented a langmuirian shape with a long plateau and a final slight upward bend. Parameters describing the adsorption were obtained by processing data by both the Langmuir and the BET equations. The shape of the isotherms pertaining to the iron powders was sigmoid at low-intermediate concentrations and presented two successive plateau regions and a final upward rise. Results were analysed on the basis of the Frumkin-Fowler-Guggenheim equation. The two solid adsorbents have been analysed by XPS determinations to assess their actual surface state and degree of hydration/hydrophilicity. The features of the adsorption and the possible adsorbate orientations are discussed on the grounds both of the parameters obtained by the model elaborations and of XPS data, also in the light of literature previous results. (C) 1998 Elsevier Science S.A. All rights reserved.