Highly crosslinked ionic β-cyclodextrin polymers and their interaction with heavy metals

A new aqueous insoluble ionic beta-cyclodextrin polymer (PYR) has been synthesized and a potentiometric study of the binary Cu(II)-PYR system is performed to calculate the complexation constants (as log beta in heterogeneous medium). The mathematical processing of the pH-metric data gave the formation constants of Cu(II) complexes and the related species distributions. The model is compatible with the presence of five complex species in the range of pH 2.5-7. Stoichiometry indicates the probable involvement of the alcoholate functionalities of the ligand in the complexation. The capacity of the polymer with respect to metal ions retention is evaluated for both Cu(II) and Cd(II) (chosen as target probes). The possibility to recover the sorbed Cd(II) is also tested by using acidic pH solutions. A complete recovery is obtained and the stability of the polymer is verified over ten steps of retention and desorption. To understand the complexation mechanism involved, two other cyclodextrin-based polymers are synthesized which are characterized by the presence of naphthalic dicarboxylic and carbonate groups as spacers. Their interactions with Cu(II) or Cd(II) are studied. Since the beta-cyclodextrin polycarbonate polymer does not have acidic groups on the spacer, it is interesting to compare metal ions retention between this material, which does not present a real cation exchange site, and PYR.