Interactions of metal ions with chitosan-based sorbents: a review

Abstract

Metal cations can be adsorbed by chelation on amine groups of chitosan in near neutral solutions. In the case of metal anions, the sorption proceeds by electrostatic attraction on protonated amine groups in acidic solutions. However, the presence of ligands and the pH strongly control sorption performance (sorption isotherm) and the uptake mechanism (changing the speciation of the metal may result in turning the chelation mechanism into the electrostatic attraction mechanism). Several examples are discussed with precious metals (Pd, Pt), oxo-anions (Mo, V) and heavy metals (Cu, Ag). Sorption performance (equilibrium uptake but also kinetics) is also strictly controlled by other structural parameters of the polymer (degree of deacetylation, crystallinity for example) that control swelling and diffusion properties of chitosan. The identification of the limiting steps of the sorption process helps in designing new derivatives of chitosan. Diffusion properties may be improved by physical modification of chitosan (manufacturing gel beads, decreasing crystallinity). Selectivity can be enhanced by chemical modification (grafting, for example, sulfur compounds). Several examples are discussed to demonstrate the versatility of the material. This versatility allows the polymer to be used under different forms (from water soluble form, to solid form, gels, fibers, hollow fibers ...) for polymer-enhanced ultrafiltration and sorption processes. These interactions of metal ions with chitosan can be used for the decontamination of effluents, for the recovery of valuable metals but also for the development of new materials or new processes involving metal-loaded chitosan. Several examples are cited in the design of new sorbing materials, the development of chitosan-supported catalysts, the manufacturing of new materials for opto-electronic applications or agriculture (plant disease treatment ...).

Interaction of carboxymethylchitosan and heavy metals in cement media

“…The same solution with an excess of metal (Zn as a model) showed a different scattering profile in which a signal responsible for the 99.8% of the polymer agglomerate mass has a larger radius (1.107 nm) and a significantly decreased diffusion coefficient (2.22·10 -6 cm 2 s -1 ). This finding supports the hypothesis of a foldedlike structure being formed between the CMCH and Zn [29,30].…”

Sorption Efficiency of Chitosan Nanofibers toward Metal Ions at Low Concentrations

“…In addition, the pH of the medium and the presence of ligands can change the speciation of the metal ion in a way that may result in turning the chelation mechanism into the electrostatic attraction mechanism. 57 As reported previously in this work, the extent of metal sorption was studied at pH of 6.0. At such pH, the deprotonation of amino and hydroxyl groups is not plausible, and as a result, the metal ions seem to be fixed mainly by coordination to amine groups.…”

Adsorption of Silver (I) From Aqueous Solution Using Chitosan/Montmorillonite Composite Beads

“…Among these natural materials, chitosan has been proved to be a suitable biopolymer for the removal of metal ions from aqueous solution [18][19][20][21] . Chitosan is chemically identical to cellulose except that the hydroxyl groups in the cellulose molecule are substituted with amino groups in chitosan.…”