Chromium (III) coordination capacity of chitosan.

Polycationic chitosan has a strong coordination to heavy metal ions due to its multifunctional hydroxyl and amino groups. However, due to the fast and facile dissolution of chitosan in acidic medium, it is difficult to measure the exact adsorption amount or coordination capacity accurately. In this work, a simple method of lyophilization plus ethanol-washing was employed to separate and purify chitosan/Cr(III) complex for further determining the coordination capacity. Meanwhile, the coordination structure of Bridge-chitosan-N(OH)3(H2O) and morphology of regenerated fibrillar sponge of CS/Cr(III) were further certified. The coordination capacity of Cr(III) on chitosan increased with the rising concentration of Cr(III) ions till the maximum coordination capacity was reached up to 355.03 mg/g. The mechanisms and characteristic parameters of the adsorption process were fit using two-parameter isotherm models which revealed the following order (based on the coefficient of determination) of Langmuir > Halsey > Freundlich > Temkin > Dubinin-Radushkevich. A proposed coordination formula of CS/Cr (III) might be a good certificate for the homogeneous chemical combination nature of Cr(III) on the monolayer surface of chitosan in a molecular scale.