A comprehensive study on the adsorption of ciprofloxacin using chitosan: Spectroscopic, DFT, kinetic, isotherm, thermodynamic, and reusability insights

Pharmaceutical contamination in water resources poses considerable threats to health and the ecosystem. This study investigated ciprofloxacin (CPF) adsorption onto chitosan, analyzing the impacts of interaction time, pH, adsorbent dosage, CPF concentration, ionic strength, and temperature. CPF adsorption was validated using XRD, XPS, FTIR, FE-SEM, EDX, and density functional theory (DFT). The best pH for CPF adsorption onto chitosan was 6.50. The pseudo-second-order kinetic model demonstrated the best fit ( R 2 = 0.996–0.999), while the Langmuir isotherm model ( R 2 = 0.997–0.999) showed the most consistent fit with the equilibrium adsorption isotherm data. The maximum CPF uptake capacity of chitosan was obtained to be 20.83 μmol/g at 30°C. Thermodynamic investigation showed that CPF uptake onto chitosan occurs through a spontaneous, exothermic physisorption mechanism, confirmed by interaction energy ( E int : -5.561 kJ/mol) from DFT, activation energy ( E a : 18.29 kJ/mol), and additional thermodynamic parameters (Δ G ⧧ , Δ H ⧧ , Δ S ⧧ , Δ G , Δ H , and Δ S ). Within 180 min, 92% of CPF was liberated from the CPF-loaded chitosan at pH ≥ 12, and chitosan maintained 67.18% of its CPF adsorption ability after five reuse cycles. This study integrates DFT with experimental methods to clarify CPF-chitosan interactions, offering a promising approach for developing sustainable materials for CPF removal from aqueous solutions. • Interaction of chitosan and CPF confirmed by spectroscopy, microscopy, and DFT. • Chitosan showed strong CPF removal with a q max of 20.83 μmol/g at 30°C. • Adsorption followed pseudo-second-order kinetics and the Langmuir isotherm. • Adsorption was exothermic, spontaneous, and driven by physisorption. • CPF desorbed in NaOH, confirming the reusability of chitosan for water treatment.