Two-Dimensional Coordination Polymers with “X”-Shaped Cavities as Adsorbents of Oxoanion Pollutants and Toxic Dyes

Abstract

The role of cationic and neutral two-dimensional (2D) coordination polymers (CPs) in the efficient capture of inorganic pollutants (chromate and dichromate) and toxic dyes has been explored. Two cationic CPs with Ag(I) salts of BF4– and ClO4– anions and one neutral CP with Cd(NO3)2 of bis(pyridylcarboxamide) ligands have been structurally characterized, and it was found that all of them have isostructural 2D CPs. The sorption of chromate/dichromate by CPs via anion exchange mechanism was shown to depend not only on the nature of the network but also on the nature of the anion present in the as-synthesized host. Among three CPs, the BF4– containing Ag(I) CP exhibited a better ability of sorbing chromate and dichromate from very dilute solution of sorbates (10–4 M). On the other hand, neutral Cd(II) CP containing NO3– ion were found to have a better ability to sorb chromate/dichromate from somewhat concentrated (10–1 M) solutions. Further, BF4– and NO3– containing CPs exhibit selective sorption of chromate from the solution containing mixture of CrO42–, NO3–, SO42–, and BF4– in equimolar concentrations. The structure of chromate sorbed material was determined with the help of the as-synthesized Cd(II) CP of chromate. Further, Ag(I) CP containing BF4– ion and Cd(II) CP containing NO3– ion have shown the ability for selective dye sorption and luminescence based detection of dichromate ions, respectively.