Amino-functionalized grafted cross-linked chitosan beads for the efficient adsorption of Pb2+ and Cu2+ ions in a synthetic media: equilibrium, kinetic, thermodynamic, and desorption study

Abstract

Chitosan enhancement is essential for establishing an improved adsorbent and binding toxic heavy metal ion. In this investigation, chitosan powder was converted to chitosan beads (CH) for effortless handling and easy penetration into binding sites. The beads were cross-linked with glutaraldehyde, which made them insoluble in acidic media. The cross-linked beads (CCH) were then further grafted with an amino-functionalized solution (5-amino-1,10-phenanthroline) to provide more binding sites. The three sets of chitosan derivatives produced were characterized by Fourier Transform Infrared (FTIR), Scanning Electron Microscope (SEM), Thermogravimetric (TGA), X-ray diffraction (XRD), and BET analysis. The grafted cross-linked chitosan beads (GCCH) were applied in adsorption studies to remove Pb²⁺ and Cu²⁺ ions from the synthetic solutions. The equilibrium experiment data were explained using the Langmuir and Freundlich models, while the kinetics data were studied using pseudo-first- and pseudo-second-order kinetic models. A thermodynamic study was carried out, and the parameters from the study, such as Gibb’s free energy change (∆G^O), enthalpy change (∆H^O), and entropy change (∆H^O), were obtained. The Langmuir model reasonably described the equilibrium data well, with a correlation coefficient (R²) of 0.99 for both metal ions and a maximum binding capacity of 376 mg/g and 348 mg/g for Pb²⁺ and Cu²⁺ ions, respectively. The pseudo-second-order kinetic model gave the line of best fit with an R² value of 0.97. The results from the thermodynamic study showed that binding Pb²⁺ and Cu²⁺ ions onto the adsorbent is endothermic and spontaneous. The spent adsorbent was regenerated with five successive cycles. The study thoroughly covers equilibrium, kinetics, thermodynamics, and desorption, providing insights into adsorption mechanisms. The modified chitosan beads offer increased selectivity, stability, and reusability, making the adsorbent a potential material for heavy metal removal. This method improves adsorption performance while advancing sustainable water treatment.