Unexpected effect of magnetic nanoparticles on the performance of aqueous removal of toxic Cr(VI) using modified biopolymer chitosan

Abstract

Modified biopolymer chitosan namely 2-hydroxy-1-naphthaldehyde chitosan (CTS-Nap) has been synthesized for the removal of toxic chromium from aqueous solutions. In an attempt to enhance the adsorption capacity of toxic chromium on the prepared modified biopolymer, magnetic Fe₃O₄ nanoparticles have been loaded on the modified adsorbent to form the magnetite adsorbent (Fe₃O₄@CTS-Nap). The adsorption mechanism of both adsorbents is explored by batch experiments, FT-IR, SEM, TEM, XRD, VSM, and EDS. The optimum adsorption is achieved at pH 1.5 for CTS-Nap and 1.0 for Fe₃O₄@CTS-Nap. Pseudo second order illustrated the best description for the adsorption process with correlation coefficient R² = 0.999 and the film diffusion or chemisorption is the rate-limiting step. The equilibrium data is analyzed using five isotherm models, the experimental data agreed well with the Freundlich model with a maximum adsorption capacity of 78.12 mg g-1 and 57.14 mg g-1 for CTS-Nap and Fe₃O₄@CTS-Nap, respectively. However, this unexpected result revealed that the presence of magnetic nanoparticles does not always enhance the adsorption process and many other factors could control the adsorption process. Generally, these outcomes revealed that the unmagnetite modified adsorbent CTS-Nap have practical greater influence on wastewater treatment management rather than the magnetic modified chitosan Fe₃O₄@CTS-Nap.

Keywords: Bio-nanocomposites; Cr(VI); Magnetic modified chitosan.