Honeycomb porous L-cysteine bridged chitosan/Mg-Al hydrotalcite composite foam for efficient biosorption of U(VI) from aqueous solution.

The separation of U(VI) from radioactive wastewater via adsorption enables effective recovery of uranium resources while mitigating environmental pollution. In this study, L-cysteine bridged chitosan/Mg-Al hydrotalcite (CLM) composite foams were synthesized through chemical modification and freeze-drying technology for the efficient adsorption of U(VI). Among various CLM foams, CLM-2 exhibited optimal performance due to its highly developed honeycomb pores and the synergistic effects of multiple functional groups. The adsorption isotherms and kinetics conformed to the Freundlich model and the pseudo-second-order model, respectively. This indicates heterogeneous multilayer adsorption, and chemisorption significantly affects the kinetic rate of U(VI) adsorption. At pH 5.0 and 298 K, CLM-2 exhibited a maximum adsorption capacity of 262.23 mg/g for U(VI) and demonstrated high selectivity in multicomponent complex solutions. Thermodynamic calculations revealed a spontaneous and endothermic nature for U(VI) adsorption. The material characterization suggested that L-cysteine effectively bridged chitosan and MgAl hydrotalcite, enhancing the material's stability and increasing adsorption sites. The synergistic coordination of U(VI) with multiple functional groups (including amino, thiol, carboxyl, and hydroxyl groups) in CLM-2 significantly improved its adsorption performance for U(VI). CLM-2 has a honeycomb porous structure, high adsorption capacity, good stability, and easy recovery, making it a promising biosorbent for U(VI) removal.