High-Strength Physically Multi-Cross-Linked Chitosan Hydrogels and Aerogels for Removing Heavy-Metal Ions

With the goal of improving the mechanical strength of chitosan hydrogels, gallic acid modified carboxymethyl chitosan/iron ion (GA-CMCS/FeIII) complex hydrogels were initially prepared via noncovalent interactions and metal coordination. 1H NMR, 13C NMR, and Fourier trantsform infrared spectra analysis confirmed the covalent reactions between CMCS and GA. The formation of GA-CMCS hydrogel occurred through electrostatic interactions, hydrogen bonds, and hydrophobic interactions. GA-CMCS/FeIII hydrogel (380 kPa) exhibited higher compressive strength than GA-CMCS hydrogel (315 kPa). In addition, GA-CMCS/FeIII aerogel displayed satisfactory mechanical strength (1.59 MPa) and high-efficiency adsorption capacities up to 97.15 mg/g for Pb2+, 99.75 mg/g for Cd2+, and 98.50 mg/g for Cu2+, respectively. In addition, both of the GA-CMCS and GA-CMCS/FeIII aerogel adsorbents exhibited satisfactory recyclability. The design of GA-CMCS and GA-CMCS/FeIII hydrogels and aerogels offers a new opportunity for the construction of physically multi-cross-linked systems with excellent mechanical properties.