Adsorption of copper cations at chitosan samples prepared by lyophilic drying

Supramolecular structures of copper complexes with chitosan were studied by spectroscopic methods to understand better the adsorption of metal cations by polysaccharides. Sublimation drying of chitosan was found to influence the adsorption of copper cations by the resulting polymer adsorbents with supramolecular structures. The conditions for preliminary drying of the water-swollen adsorbents (in particular, chitosan) are decisive for the relative positions of chains and the arrangement of adsorption amino sites. According to spectroscopic data, copper cations form various complexes with amino groups, depending on the supramolecular structure of chitosan. Sublimation drying of chitosan substantially enhances the adsorption of metal cations. The sorption capacities of chitosan samples prepared by sublimation drying, reprecipitation with soda and sublimation drying, and air drying were 5.1, 4.0, and 1.8 mmol/g, respectively. The resulting adsorption isotherms were described by the Dubinin-Radushkevich equation for a wide range of surface coverages. This made it possible to calculate the effective adsorption energies of the systems studied.