Sorption of Pb(II) on carboxymethyl chitosan-conjugated magnetite nanoparticles: application of sorbent dosage-dependent isotherms

Carboxymethyl chitosan (CMCS)-conjugated magnetite (Fe₃O₄) nanoparticles (MNPs), which are denoted as CMCS-MNPs, were synthesized by covalently binding CMCS onto the surface of the MNPs via carbodiimide activation in a paraffin-acetic acid medium. The CMCS-MNPs exhibited a high level of CMCS binding (∼24.7 wt.%) and a spherical morphology with a mean diameter of 15 nm. In particular, they showed good water dispersity and a strong magnetic response. The sorption of Pb(II) on the CMCS-MNPs in aqueous solutions at different sorbent dosages (C _s), pH, electrolyte (NaNO₃) concentrations (C _NaNO3), and temperatures (T) was investigated. The CMCS-MNPs showed high sorption capacity for Pb(II). The equilibrium amount increased with increasing pH but decreased with increasing C _NaNO3 or T. In addition, a significant C _s-effect was observed in the sorption equilibria. Two C _s-dependent models, the Langmuir-SCA and Freundlich-SCA isotherms that were derived from a surface component activity (SCA) model, could describe the C _s-effect observed. The changes in pH, C _NaNO3, and T have no obvious influence on the C _s-effect. In addition, the changes in the thermodynamic parameters, ∆G°, ∆H°, and ∆S°, for sorption were estimated, showing that the sorption process is spontaneous and exothermic.