Studies on the adsorption of arsenic on calix[6]arene

p ‐ tert ‐butyl calix[6]arene (PTC6) was synthesized and characterized by solid‐ and liquid‐state NMR and LC‐MS techniques. The adsorption of arsenite and arsenate on calix[6]arene under different pH conditions and adsorbate doses was studied. The maximum adsorption of arsenic species on calix[6]arene was observed around neutral pH and the adsorption density of As (III) was higher than that of As (V). The adsorption of neutral H 3 AsO 3 and negatively charged H 2 AsO   4 −molecules on calix[6]arene was attributed to the condensation reaction between hydroxyl groups of PTC6 and arsenic species. The complexation of arsenite with phenolic oxygen was confirmed by solid‐state 13 C NMR CP‐MAS. Exo attack mechanism was proposed to describe the interaction of arsenous and arsenic acid molecules with PTC6. The specific interaction between calix[6]arene and arsenic species was further substantiated by zeta‐potential ( ζ ‐potential) measurements and free energy of adsorption. The free energy of adsorption ( $\Delta G_{{\rm ads}}^{\rm o} $ ) estimated from Stern–Grahame equation was found to be 25 kJ/mole for As (III) and 19 kJ/mole for As (V). Copyright © 2010 John Wiley & Sons, Ltd.