Exploring the favorable ion-exchange ability of phthalylated cellulose biopolymer using thermodynamic data

A phthalylated ion-exchange biopolymer was obtained by adding cellulose to molten phthalic anhydride in a quasi solvent-free procedure. Through this route 2.99 ± 0.07 mmol g−1 of pendant groups containing ester and carboxylic acid moieties were incorporated into the polymeric structure that was characterized by elemental analysis, solid-state carbon nuclear magnetic resonance (CP/MAS), infrared spectroscopy, X-ray diffraction, and thermogravimetry. The chemically modified polysaccharide is able to exchange cations from aqueous solution as demonstrated by batchwise methodology. The data were adjusted to a modified Langmuir equation to give 2.43 ± 0.12 and 2.26 ± 0.11 mmol g−1 for divalent cobalt and nickel cations, respectively. The net thermal effects obtained from calorimetric titration measurements were also adjusted to a modified Langmuir equation, and the enthalpy of the interaction was calculated to give endothermic values of 2.11 ± 0.28 and 2.50 ± 0.31 kJ mol−1 for these cations, respectively. The spontaneity of this ion-exchange process is reflected in negative Gibbs energy and with a contribution of positive entropic values. This set of thermodynamic data at the solid–liquid interface suggests a favorable ion-exchange process for this anchored biopolymer for cation exchange from the environment.

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