Facile synthesis of a MOF-derived magnetic CoAl-LDH@chitosan composite for Pb (II) and Cr (VI) adsorption

A novel sorbent [email protected]/Fe3O4 was synthesized in this learning for the elimination of Pb (II) and Cr (VI) from water using Co-Al layered double hydroxides (LDHs) as precursors, combined with cross-linked compounds of magnetically interspersed chitosan (CS) and cystamine. The successful synthesis of the adsorbent [email protected]/Fe3O4 was demonstrated by SEM, FTIR, XRD and XPS characterization. The maximum adsorption capacities of [email protected]/Fe3O4 at 25 °C were 558.84 and 710.79 mg/g for Pb (II) (pH = 6) and Cr (VI) (pH = 4), respectively. The sorption kinetics prove that the sorption is chemisorption and the rate-limiting step is exterior dispersion. The adsorption isotherms indicate that the sorption process is an irreversible process with positive synergistic effects at multiple sites. Thermodynamic studies show that Pb (II)/Cr (VI) sorption is spontaneous and irreversible in the process. Further, [email protected]/Fe3O4 also possesses a good selectivity and reusability (5 cycles) for Pb (II) and Cr (VI). The DFT calculations revealed that -SH and –NH2 on the adsorbent surface have a stronger affinity for Pb (II) and Cr (VI).