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

p‐tert‐butyl calix6]arene (PTC6) was synthesized and characterized by solid‐ and liquid‐state NMR and LC‐MS techniques. The adsorption of arsenite and arsenate on calix6]arene under different pH conditions and adsorbate doses was studied. The maximum adsorption of arsenic species on calix6]arene was observed around neutral pH and the adsorption density of As (III) was higher than that of As (V). The adsorption of neutral H₃AsO₃ and negatively charged H₂AsO molecules on calix6]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 ¹³C NMR CP‐MAS. Exo attack mechanism was proposed to describe the interaction of arsenous and arsenic acid molecules with PTC6. The specific interaction between calix6]arene and arsenic species was further substantiated by zeta‐potential (ζ‐potential) measurements and free energy of adsorption. The free energy of adsorption ( ) 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.