Highly efficient removal of perchlorate and phosphate by tailored cationic metal-organic frameworks based on sulfonic ligand linking with Cu-4,4′-bipyridyl chains

Abstract

Abstract Perchlorate (ClO 4 − ) had caused great impacts to human health via inhibiting the uptake of iodide by the thyroid gland and its removal was strongly affected by co-existing anions in aqueous solution. The adsorptive features of perchlorate, co-existing anions and their removal mechanisms on two different metal-organic frameworks (MOFs) are compared in this paper. Two MOFs (i.e., α , β -ethanebbbdisulfonic-Cu-(4,4′-bipy) 2 and sulfamic-Cu-(4,4′-bipy) 2 ) were synthesized to remove ClO 4 − and co-existing anions from aqueous solution. It was found that MOFs can effectively remove PO 4 3− and ClO 4 − . The adsorption reactions of PO 4 3− and ClO 4 − by MOFs were exothermic and spontaneous, as confirmed by the thermodynamic analysis. The sorption rates of the anionic pollutants followed the pseudo first-order reaction. The sorption isotherms followed the Langmuir model with K L values of 0.0083, 0.0257, 0.2133 and 0.0448 for ClO 4 − , PO 4 3− , ClO 4 − (PO 4 3− ), PO 4 3− (ClO 4 − ), respectively. A certain amount of perchlorate and phosphate were adsorbed by MOFs under the pH range of 2 to 10. However, as long as pH increased up to 12, the absorption capability decreased remarkably due to the crystal structure of materials being collapsed in an alkaline environment. For the absorption of anions by MOFs, Gibbs’ free energy of may be attributed to the effects of adsorption. Sulfonic acid groups interlaminated in MOFs were exchanged by tetrahedral oxoanions, contributing to ion-exchange adsorption. The findings in this study help develop novel methods for perchlorate and phosphate removal from aqueous solution.