Innovative chitosan/graphene oxide composites: A thermodynamic and calorimetric approach to pharmaceutical waste removal from water

The study explores the adsorption behavior of pharmaceutical molecules, including the antiepileptic drug Levetiracetam (LEV), Ketorolac Tromethamine (KT), and Mefenamic Acid (MA), using bioadsorbents based on chitosan and graphene derivatives. Chitosan, derived from crab shell chitin, was blended with graphene oxide (GO) and reduced graphene oxide (rGO) at varying concentrations (0.05 % and 0.5 %) to assess its impact on adsorption performance and material properties. Composites containing 0.5 % GO and rGO demonstrated the highest adsorption capacities, achieving maximum values of 30.85mg/g for KT on rGO and 29.74mg/g on GO. Adsorption equilibrium was rapidly attained, typically within 10 min to a few hours, and the process conformed to a pseudo-second-order kinetic model. Adsorption isotherms were best described by the Sips model, suggesting increased capacity with rising temperature, consistent with results from immersion calorimetry. Optimal adsorption occurred at a pH of 5.5 and a temperature of 60 °C. Comprehensive characterization using N2 and CO2 adsorption isotherms, FTIR, Raman spectroscopy, and pHpzc measurements validated the physical and chemical properties of the adsorbents. Thermodynamic analyses revealed spontaneous and exothermic adsorption interactions, with enthalpy values indicative of physical adsorption mechanisms. These findings underscore the potential of these chitosan-based bioadsorbents for the efficient removal of pharmaceutical molecules, demonstrating their applicability in environmental remediation and water purification technologies.