Nanogel and super-paramagnetic nanocomposite of thiacalix[4]arene functionalized chitosan: synthesis, characterization and heavy metal sorption

Nowadays, development of materials based on biopolymers in sorption process for removal of heavy metal ions from wastewater has been considered by many researchers. In this research, the nanogel of chitosan-gthiacalix[4]arene (CS-g-TC4A) was synthesized from chitosan-azide and monopropargyl thiacalix[4]arene via click reaction. Firstly, Fe3O4-contained chitosan was synthesized via co-precipitation of Fe(II) and Fe(III) salts in the presence of chitosan. Then, magnetic chitosan grafted thiacalix[4]arene (Fe3O4-contained CS-g-TC4A) super-paramagnetic nanocomposites were prepared via click reaction of freshly prepared magnetic chitosan-azide with monopropargyl thiacalix[4]arene. The structure and surface morphology, thermal and magnetic properties of the nanogel and nanocomposite were characterized by Fourier transform infrared (FTIR), X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), thermal gravimetric analysis (TGA), atomic force microscopy (AFM) and vibrating sample magnetometer (VSM), respectively. The trend of heavy metal sorption in the CS-g-TC4A nanogel and Fe3O4-containing CS-g-TC4A super-paramagnetic nanocomposites is in the order of Pb(II) > Cd(II) > Co(II) > Ni(II) > Cu(II) > Cr(III) and Pb(II) > Cd(II) > Cu(II) > Ni(II) > Co(II) > Cr(III), respectively, in aqueous solutions at pH 7. The experimental data for all the cations were analyzed by isotherms and kinetics equations. The results of adsorption isotherm of cations on CS-g-TC4A nanogel and Fe3O4-contained CS-g-TC4A super-paramagnetic nanocomposite were fitted well with the Freundlich and Langmuir models, respectively. The maximal adsorption capacities of Pb(II), Cd(II), Co(II), Ni(II), Cu(II), Cr(III) by CS-g-TC4A nanogel and Fe3O4-contained CS-g-TC4A super-paramagnetic nanocomposite, as calculated from the Langmuir model, were 23.25, 16.20, 14.08, 13.88, 12.37, 11.11; and 23.28, 20.08, 15.89, 16.12,17.85, 14.92 mg/g, respectively. The kinetic study was in best agreement with pseudo-first-order model for both adsorbents.