Performance of ceria/iron oxide nano-composites based on chitosan as an effective adsorbent for removal of Cr(VI) and Co(II) ions from aqueous systems

A novel chitosan/ceria/iron oxide (CS/ceria/Fe3O4) nano-composite adsorbent was synthesized for removal of Cr(VI) and Co(II) ions from aqueous systems in a batch system. The adsorbents were characterized by field emission scanning electron microscopy (FESEM), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), transmission electron microscopy (TEM), thermal gravimetric analysis (TGA), and Brunauer- Emmett-Teller (BET) analyses. The behavior of swelling kinetics was also studied. The effect of several adsorption parameters including CeO2 and Fe3O4 contents, initial pH, contact time, initial Cr(VI) and Co(II) concentration, and temperature on the adsorption capacity was studied. The double exponential model revealed a better fit with the kinetic data of Cr(VI) and Co(II) ions. The Cr(VI) and Co(II) adsorption process well fitted the Langmuir model. The maximum adsorption capacities estimated from Langmuir isotherm model were 315.4 and 260.6 mg/g for Cr(VI) and Co(II) ions, respectively. Also, thermodynamic parameters were used to distinguish the nature of Cr(VI) and Co(II) adsorption. The reusability of CS/ceria/Fe3O4 nano-composite was evaluated with stripping agents of 0.1 M NaOH and 0.1 M HNO3. Finally, the evaluation of Cr(VI)-Co(II) coexisting system confirmed that the presence of Co(II) ions played an inhibitor role on the Cr(VI) adsorption.