Efficient adsorption of Congo red by MIL-53(Fe)/chitosan composite hydrogel spheres

MIL-53(Fe)/chitosan composite hydrogel spheres were formed by chitosan (CS) coating MIL-53(Fe). The structural and physicochemical properties of the material were characterized by SEM, FTIR, XRD, TGA, BET, and Zeta potential. The adsorption properties of the adsorbents were systematically analyzed for different conditions, such as pH, contact time, adsorbent dosage, initial concentration, and temperature. The experimental data were fitted using adsorption isotherms, adsorption kinetics, and adsorption thermodynamics models. The results show that the pseudo-first-order model and Liu model are fitted to the adsorption kinetics and adsorption isotherm respectively. The adsorption capacity of CR reached the maximum value of 590.8 mg g−1 at 298 K. The adsorption efficiency of the composite material for CR was high, and when 100 mg L−1 CR solution was used, 99.97% of CR could be removed by reaching adsorption equilibrium. After three times of adsorption, the recovery was still close to 85%. The adsorption mechanism is mainly the synergistic effect of pore filling, ionic interactions, and hydrogen bonding.