Study of molybdate ion sorption on chitosan gel beads by different spectrometric analyses

Molybdate ion uptake both by raw chitosan and by glutaraldehyde cross-linked chitosan beads was investigated. This study focused on the identification of sorption mechanisms by means of several analytical procedures such as infra-red and reflectance spectrophotometries and CP-MAS 13C NMR analyses. Although the amine functions of glucosamine residues remain the major sites of interaction with the metal species, other functional groups can also be involved. It is certainly the case with carbonyl functions provided by the glutaraldehyde structure in cross-linked sorbents. Due to the large size of the polynuclear hydrolysed molybdate species, the sorption may involve several monomer units, resulting in additional linkages between the polymer chains. This behaviour can be confirmed by the chemical shifts of the carbon atoms observed by CP-MAS 13C NMR on raw chitosan beads, showing that the carbon atoms supporting the amino sites are not the only atoms affected by molybdate ion sorption. Moreover, cross-linking promotes a partial reduction of molybdenum species in the presence of some unreacted aldehyde groups.