Abstract: Chitosan-citric acid complex was prepared by acylation reaction between chitosan and citric acid, and its weightaverage molar mass and water solubility were determined. Then, the structural characterization was investigated by Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), thermogravimetric analysis (TGA), X-ray diffraction (XRD) and nuclear magnetic resonance (NMR) to validate the occurrence of acylation reaction. In addition, we explored the adsorption efficiency of chitosan and its complex for cadmium ions and their scavenging capacity against hydroxyl and 2,2-diphenyl-1-picrylhydrazyl (DPPH) free radicals. Results indicated that compared with chitosan, the weightaverage molar mass and water solubility of chitosan-citric acid complex significantly increased. At the same time, structural characterization directly or indirectly proved that citric acid was successfully introduced into chitosan via acylation reaction and the structure differences resulted in differences in the properties of chitosan and its complex. In addition, the adsorption efficiency for cadmium ions and free radical scavenging capacity of chitosan-citric acid complex were better than those of chitosan. This research can provide some evidence for the practical application of chitosan and its derivatives.

Key words: chitosan, chitosan-citric acid complex, structural properties, functional properties