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/Fe^III) 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/Fe^III hydrogel (380 kPa) exhibited higher compressive strength than GA-CMCS hydrogel (315 kPa). In addition, GA-CMCS/Fe^III 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/Fe^III aerogel adsorbents exhibited satisfactory recyclability. The design of GA-CMCS and GA-CMCS/Fe^III hydrogels and aerogels offers a new opportunity for the construction of physically multi-cross-linked systems with excellent mechanical properties.