Improving the Ca(II) adsorption of chitosan via physical and chemical modifications and charactering the structures of the calcified complexes

Abstract

Chitosan (CS) has limited capacity for Ca(II)-adsorption abilities. Here, glutaraldehyde cross-linked chitosan (GLA-CTS) and maltose chitosan (MAL-CTS) were obtained by physical and chemical modifications to improve the adsorption of Ca2+. By comparing the adsorption kinetics and isotherm, the adsorption capabilities of GLA-CTS and MAL-CTS reached 112.27 ± 2.63 and 240.38 ± 31.88 mg/g in the presence of concentrations of 3000 mg/L Ca2+, which were about 2.1 and 4.6 times than CS. The structures of the resulting calcified complexes were profiled by SEM, XPS, FT-IR, and 13C NMR. Unlike the folds and spherical particles observed in CS-Ca(II) and GLA-CTS-Ca(II), the surface morphology of MAL-CTS-Ca(II) presented as flat-membrane-structures. In XPS assays, the peaks of Ca in GLA-CTS-Ca(II) and MAL-CTS-Ca(II) were significantly higher than that of CS-Ca(II), and the percentages of Ca atoms on the surfaces were 1.67 and 1.95 times higher respectively. Structural analyses were indicated from the FT-IR and 13C NMR results, the –NH2, –NHCOCH3 and –OH groups were all involved in the adsorption to Ca2+, and the worked groups were changed when calcium contents increased. Accordingly, possible structures of Ca(II)-complexes and the adsorption mechanisms were initially proposed. These two chitosan derivatives with evidently improved Ca(II)-adsorption are favorable for developing applications based chitosan.