Magnetic EDTA-modified chitosan/SiO2/Fe3O4 adsorbent: Preparation, characterization, and application in heavy metal adsorption

The aim of this study was to develop a novel magnetic EDTA-modified chitosan/SiO2/Fe3O4 adsorbent (EDCMS) for removal of heavy metals ions from aqueous solution. EDCMS was prepared by surface modification of chitosan/SiO2/Fe3O4 (CMS) with EDTA using water-soluble carbodiimide as the cross-linker in buffer solution. Both EDCMS and CMS were characterized and their adsorption properties for removal of heavy metal ions under varied experimental conditions were also investigated. The results revealed that EDCMS had better tolerance to low pH and exhibited much higher removal efficiency for the metal ions in comparison with CMS. Moreover, the adsorption kinetics for EDCMS and CMS followed the mechanism of the pseudo-second order kinetic model, and their equilibrium data were fitted with the Langmuir isothermal model well. The maximum adsorption capacities of CMS were found to be 0.495, 0.045, 0.040 mmol g−1 for Cu(II), Pb(II) and Cd(II) ions at pH 5.0 (25 °C), respectively, which showed the selective adsorption of Cu(II) ions, and the values of EDCMS were 0.699, 0.596, 0.563 mmol g−1 for Cu(II), Pb(II), and Cd(II) ions under the same conditions, respectively, which were much higher than that of CMS. The adsorption process of EDCMS and CMS was endothermic, and further recycle experiments showed there was about 25% loss in the adsorption capacity of EDCMS for heavy metal ions after 12 times reuse. All the results demonstrate that EDCMS is a potential recyclable adsorbent for hazardous metal ions in waste water.