Crosslinked chitosan-glutaraldehyde/ZrO2 nanocomposite for ciprofloxacin adsorption: Isotherm, kinetics, thermodynamic, and mechanistic investigation

The widespread occurrencee of pharmaceutical contaminants, particularly antibiotics, in aquatic environments has become a major environmental concern due to their persistence and potential to promote antimicrobial resistance. In this study, a glutaraldehyde-crosslinked chitosan-ZrO₂ (CTS-ZrO₂) nanocomposite was synthesised and evaluated as an adsorbent for the removal of ciprofloxacin (CIP) from aqueous solution. The synthesised adsorbent was characterised using Fourier Transform Infrared (FTIR) spectroscopy, Scanning Electron Microscopy (SEM), Energy Dispersive X-ray (EDX) analysis, Thermogravimetric Analysis (TGA), and Brunauer–Emmett–Teller (BET) surface area analysis. The reported adsorption results are based on the average of three independent experiments. The optimum adsorption conditions were pH 7, an adsorbent dosage of 2.0 g/L, and a temperature of 298 K. Equilibrium data were best described by the Langmuir isotherm model, with a maximum adsorption capacity of 36.10 mg g⁻¹ , while the adsorption kinetics followed the pseudo-second-order model. Thermodynamic analysis indicated that the adsorption process was spontaneous and exothermic, with negative values of ΔG°, ΔH°, and ΔS°. The combined adsorption of CIP, kinetics, thermodynamics, reusability and characterisation results suggest that ciprofloxacin adsorption onto CTS-ZrO₂ occurs predominantly through electrostatic attraction, hydrogen bonding, n–π interactions, and pore filling. These findings demonstrate that the CTS-ZrO₂ nanocomposite is a promising highly efficient, and reusable adsorbent with strong potential for the removal of ciprofloxacin and related pharmaceutical contaminants from wastewater.