Synthesis, Characterization, Swelling, and Metal Uptake Studies of Aryl Cross-Linked Chitosan Hydrogels

Today, many chemical modifications are being made to increase the utilization of chitosan and to make the best use of it. In this study, four novel cross-linked chitosan derivatives in the form of hydrogel (CS-L1 CS-L2, CS-L3, and CS-L4) were prepared by the condensation of chitosan with anisole-based phenolic and nonphenolic aromatic dicarbonyls. Structural analyses were performed by elemental analysis (C, H, N), scanning electron microscopy, Fourier transform infrared, ¹³C-CP/MAS (cross-polarization, magic angle spinning) nuclear magnetic resonance, powder X-ray diffraction, and thermogravimetric analysis techniques. Metal ion uptake capacities were studied for selected transition-metal cations in aqueous medium. The amount of metal ions was determined by microwave plasma-atomic emission spectroscopy. In addition, the swelling behaviors were investigated at different temperatures (25 and 37 °C) and at different pH values (3, 7, and 10). The order of the selectivity of cross-linked chitosan derivatives toward metal ions was found to be Cu­(II) > Cd­(II) > Fe­(II) > Co­(II) > Ni­(II). The results showed that the derivatives exhibited the property of hydrogel and suggest that they could be applied in many areas such as metal removing, water removing, and biological applications.