Synthesis, characterization, and highly acid-resistant properties of crosslinking β-chitosan with polyamines for heavy metal ion adsorption

Abstract

This study primarily used β-chitosan as the main reactant and benzaldehyde as the protecting group to convert the amine groups on location C2 of chitosan into Schiff bases. Grafting and crosslinking of epichlorohydrin and triethylenetetramine with chitosan was conducted and the structural changes were analyzed with Fourier transform infrared spectroscopy (FTIR), UV-visible spectroscopy (UV-Vis), thermogravimetric analysis (TGA), elemental analyses (EA), differential scanning calorimeter (DSC), X-ray powder diffraction (XRD), nuclear magnetic resonance (NMR), and scanning electron microscope (SEM) to prove the successful modification to form crosslinked β-chitosan. Lastly, this study compared the heavy metal ion (such as Cu²⁺ and Ag⁺) adsorption capacities of chitosan before and after the graft modification. The capacity of modified chitosan for adsorbing copper ions improved in acid environments with pH of 2 to 6. The capacity increased from 67.76 mg g⁻¹ to 117.60 mg g⁻¹ when the pH value was 6. In addition, the capacity of adsorbing silver ions was higher than that of adsorbing copper ions and it enhanced from 116.80 mg g⁻¹ to 151.20 mg g⁻¹ when the pH level was 6. Furthermore, the modified crosslinked β-chitosan had an excellent acid-resistant property.