Adsorption of Cu(II) ions from aqueous solution using pyridine-2,6-dicarboxylic acid crosslinked chitosan as a green biopolymer adsorbent.

In this study, crosslinked chitosan (CCS) has been synthesized by anchoring a bifunctional ligand, namely pyridine-2,6-dicarboxylic acid (PDC) with chitosan through ion exchange. The functionalized biopolymer has been characterized using different instrumental analyses including elemental (CHN), spectroscopic (UV-visible, NMR, powder XRD, and FTIR), thermal analyses (TGA and DSC), surface and morphological (BET and SEM) analyses. The PDC-CCS was utilized for the recovery of Cu(II) from water contaminated with Cu. The adsorption limit/capacity of PDC-CCS has been examined for solution pH, temperature, Cu(II) ion concentration, and the contact time of the adsorbent. An extreme adsorption limit of 2186 mmol·g has been found for the PDC-CCS. Equilibrium was quickly attained within 60 min from the start of adsorption. Also, it was discovered that the adsorption limit/capacity exceedingly relies upon temperature and pH. On testing the experimental data with the two most popular adsorption models (fundamentally, Freundlich and Langmuir), we found that Cu(II) ion adsorption suit both models. Similarly, the experimental adsorption kinetics is in reality, second-order. Thermodynamic studies also revealed that the adsorption process was spontaneous and enthalpy driven. DFT calculations suggest that the main adsorption mechanism is by chelation through charge transfer from the adsorbent to the Cu(II) ions in solution.