A Schiff base-functionalized chitosan magnetic bio-nanocomposite for efficient removal of Pb (II) and Cd (II) ions from aqueous solutions.

The rapid industrialization and human activities in catchments have posed notable global challenges in removing of heavy metal contaminants from wastewater. Here, Schiff-bases (SB) of cyanoguanidine (CG) and salicylaldehyde (SA) were covalently grafted on a magnetic nanocomposite of chitosan to form a hybrid magnetic nanostructure (FeO@CS-CGSB). The synthesized structure was characterized using various techniques such as Fourier transform infrared spectroscopy (FT-IR), field emission scanning electron microscopy (SEM), transmission electron microscopy (TEM), powder X-ray diffraction (XRD), thermogravimetric analysis (TGA), vibrating sample magnetometry (VSM), dynamic light scattering (DLS), zeta potential, and Brunauer-Emmett-Teller surface area analysis (BET). The prepared adsorbent demonstrated strong binding capabilities and high efficiency in adsorbing Pb(II) and Cd(II) metal ions from aqueous solutions with removal efficiencies of 98 % and 97 %, respectively. The study investigated various factors such as pH, adsorbate concentration, adsorbent dosage, isotherms, kinetics, and adsorption mechanism. The heavy metal ions were adsorbed through coordination with the nitrogen and hydroxyl groups of the nanostructure, as well as electrostatic interactions. The adsorption process followed the Freundlich isotherm with a high correlation coefficient (R = 0.97, 0.96) and a pseudo-second-order kinetic model. The FeO@CS-CGSB is highly effective in removing heavy metal ions with maximum adsorption capacities of 394 mg/g for Pb(II) and 391 mg/g for Cd(II). The recycled hybrid nanostructure was dried and subjected to various adsorption-desorption tests, revealing a desorption efficiency of 98 %. In conclusion, the synthesized magnetic bio-sorbent shows great promise in effectively removing heavy metal ions from water and wastewater.