Synthesis of magnetic graphene quantum dots-chitosan nanocomposite: an efficient adsorbent for removal of Pb2+ from aqueous solution

This study describes the use of a ternary composite of Fe3O4, chitosan and graphene quantum dots (Fe3O4/GQDs-Chit) as an efficient magnetic adsorbent for the removal of Pb2+ from aqueous solutions. A number of methods were employed to describe the prepared adsorbent including scanning and transmission electron microscopy, vibrating sample magnetometer, Fourier-transform infrared spectroscopy and X-ray diffraction. Removal experiments were conducted in a batch system to optimize adsorbent amount, initial Pb2+ concentration, solution pH, and contact time. To explore the equilibrium isotherm and calculate the isotherm constants, Langmuir and Freundlich adsorption models were used. Accordingly, the Fe3O4/GQDs-Chit were successful in removing Pb2+ up to 117.65 mg g(-1) from water, with good agreement to Langmuir isotherm model (R-2 = 0.9957). The adsorption kinetic was well fitted (R-2 > 0.9940) with pseudo-second-order model indicating chemical adsorption as the rate-limiting step in the adsorption process. Furthermore, thermodynamic parameters revealed that the adsorption of Pb2+ on the Fe3O4/GQDs-Chit was exothermic and spontaneous. As evidenced by regeneration experiments, Fe3O4/GQDs-Chit were a highly stable and reproducible adsorbent, which can function as an efficient adsorbent in water treatment.