Synthesis and application of fatty acid-modified chitosan for heavy metal remediation from waste water

A novel modified chitosan was synthesized using palmitic acid to selectively remove Cd(II), As(III), and Pb(II) from water samples. Chitosan was dissolved in acetic acid solution and N, N'-dicyclohexylcarbodiimide was used crosslinking agent, to further functionalize with palmitic acid to introduce O-donor sites in the chitosan chain. These sites entrap metal ions forming covalent bonds leading to removal of heavy metal ions. The product was characterized using Fourier transform-infrared spectroscopy (FTIR), scanning electron microscopy (SEM), elemental analysis, X-ray diffraction (XRD), energy-dispersive X-ray spectroscopy, and proton nuclear magnetic resonance. The introduction of palmitic acid into the chitosan chain did not only alter its original structure and crystallinity, as evidenced by XRD and SEM data, but enhanced stability and increased the affinity toward heavy metal ions. The adsorption processes were extensively examined under optimized conditions, and results revealed the maximum absorptivity values of 40.98, 21.8, and 47.6 mg/g for Cd(II), As(III), and Pb(II), respectively, indicating high adsorption capacity. The kinetic study suggested a pseudo-second-order reaction, and the Langmuir isotherm model demonstrated the best fit. The limits of detection for Cd, As, and Pb were 2.9, 4.3, and 15.1 ppb, while the limits of quantification were 9.07, 13.23, and 45.77 ppb, respectively. The desorption studies showed the regeneration and reusability of the adsorbent up to four cycles.