Removal of ciprofloxacin from water by graphene oxide-like carbon nanosheets derived from onion peel

The widespread presence of ciprofloxacin (CIP) in aquatic environments poses significant risks to public health and ecosystems due to its role in promoting antibiotic resistance. Addressing this challenge, we developed graphene oxide-like carbon nanosheets (CNSs) from onion peel waste as a low-cost and sustainable adsorbent for efficient CIP removal from water, where the cost savings originate from free raw materials and an energy-efficient synthesis, thereby valorizing waste and reducing pollutants as key sustainability indicators. The CNSs, synthesized via pyrolysis and ultrasonic exfoliation, exhibited abundant oxygen-containing functional groups and a negatively charged surface (zeta potential: -20.9 mV), with TEM confirming nanosheet structure. Under optimized conditions (pH 7, 0.4 g L^-1 adsorbent dosage), the CNSs achieved 90% CIP removal (q_max= 51.28 mg g^-1), with adsorption following pseudo-second-order kinetics and the Freundlich isotherm. Reusability tests showed 50% efficiency retention after five cycles. Thermodynamic analysis confirmed the process was spontaneous and exothermic (ΔG° = -7.19 to -6.38 kJ mol^-1, ΔH° = -15.26 kJ mol^-1). Density functional theory calculations revealed hydrogen bonding between CIP's amine groups and CNS hydroxyls as the primary adsorption mechanism, with strong binding energies (-87.0 kJ mol^-1). This work highlights the potential of agricultural waste-derived nanomaterials as eco-friendly and high-performance solutions for pharmaceutical wastewater remediation, offering a dual benefit of waste valorization and environmental protection.