Pyridine-Functionalized Chitosan for Arsenic and Antimony Removal: Adsorption Kinetics and Thermodynamics

Heavy metal contamination in wastewater remains a critical environmental concern. This study investigates the adsorption performance of pyridine-functionalized chitosan (CS-PY) for the removal of arsenic (As) and antimony (Sb) from aqueous solutions. Batch experiments were conducted using unmodified chitosan (CS) and CS-PY under varying conditions, including initial metal ion concentration, pH, contact time, temperature, and the presence of coexisting anions. Kinetic and equilibrium analyses indicated that adsorption followed the pseudo-second-order and Langmuir isotherm models. CS-PY exhibited significantly enhanced adsorption capacities of 32.49 mg/g for As and 48.31 mg/g for Sb, compared to 21.02 mg/g and 31.12 mg/g for CS, respectively. Thermodynamic studies confirmed that the adsorption process is spontaneous, endothermic, and primarily governed by physisorption, with Gibbs free energy (ΔG°) values ranging from -2.476 to -3.186 kJ/mol for As and -3.945 to -5.071 kJ/mol for Sb, and enthalpy changes (ΔH°) of 4.832 kJ/mol for As and 7.345 kJ/mol for Sb. The presence of common competing anions (NO₃⁻, Cl⁻, and SO₄²⁻) had minimal impact on adsorption efficiency, demonstrating the strong selectivity of CS-PY. These findings establish CS-PY as a highly effective adsorbent for As and Sb removal, offering a promising solution for water purification.