Functionalized aminophosphonate chitosan-magnetic nanocomposites for Cd(II) removal from aqueous solutions: Performance and mechanisms of sorption

Functionalized magnetic nanocomposites have recently retained a great attention for metal recovery from aqueous solutions. In this work, two magnetic-chitosan nanocomposites are synthesized by grafting alpha-amino-phosphonate functions (i.e., methyl- and phenyl-aminophosphonate, Me-MCS and Ph-MCS, respectively) using a facile two-steps process. The physicochemical properties of these nanocomposites are characterized including nano-structure characterization (TEM), magnetic properties (VSM), crystallinity (XRD), and chemical characterization (elemental CHNP analysis, FTIR, XPS and TGA). FTIR and XPS analyses confirm the contribution of amine and phosphonic groups in the binding of cadmium ions. These materials are extensively investigated for Cd(II) removal: maximum sorption capacities reach 118.1 mg g(-1) for Me-MCS and 193.5 mg g(-1) for Ph-MCS, at the optimum pH (in the range pH 6-7); and the sorption isotherms are fitted by the Langmuir model. Small-size particles allow achieving fast uptake (within 2 h of contact); and kinetic profiles are appropriately modeled by the PSORE (pseudo-second order rate equation) and the Crank equation (for resistance to intraparticle diffusion). Cadmium sorption is exothermic. The metal is efficiently desorbed using 0.5 M acidified thiourea solution and the sorbent can be recycled for a minimum of five cycles (loss in sorption and desorption performances around 20% at the fifth cycle). In multi-component solutions the two sorbents show some differences in selectivity profiles, which can be roughly correlated with the hard/soft characteristics of reactive groups and the softness properties of heavy metal ions. The sorbents are successfully used for Cd(II) removal from a water sample obtained from Al-Burullus Lake (Kafr-El-Sheikh Governorate, Egypt).