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

摘要

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_3AsO_3 and negatively charged H_2AsOS_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 (z-potential) measurements and free energy of adsorption. The free energy of adsorption (ΔG _(ads)~o) estimated from Stern-Grahame equation was found to be 25 kJ/mole for As (III) and 19 kJ/mole for As (V).