Coconut Shell Biochar-Derived Graphene Oxide for Ciprofloxacin Removal from Pharmaceutical Wastewater: Synthesis, Characterization, Optimization and Regeneration

Abstract

Pharmaceutical contaminants, particularly ciprofloxacin, persist in aquatic environments due to their chemical stability and low biodegradability, posing ecological and public health risks. This study reports the synthesis of graphene oxide from coconut shell biochar (CS-GO) as a sustainable and cost-effective adsorbent for ciprofloxacin removal from pharmaceutical wastewater. CS-GO was prepared via a modified Hummers’ method and characterised using Fourier Transform Infrared Spectroscopy (FT-IR), Scanning Electron Microscopy with energy-dispersive X-ray analysis (SEM-EDX), and X-ray Diffraction (XRD), revealing a heterogeneous, porous-looking surface morphology, abundant oxygen-containing functional groups, and crystalline features favourable for adsorption. Batch adsorption experiments were designed and optimised using Response Surface Methodology–Central Composite Design (RSM-CCD) to evaluate the effects of adsorbent dosage, contact time, temperature, pH, and initial ciprofloxacin concentration. Under optimised conditions (0.926 g CS-GO, 28.5 min, 28 °C, pH 7.4, 59.652 mg/L ciprofloxacin), a maximum removal efficiency of 95.4% was achieved. Adsorption followed the Langmuir isotherm (R² = 0.9475), indicating monolayer coverage on a homogeneous surface, with a maximum adsorption capacity of 1.5555 mg g⁻¹. Desorption and reusability studies demonstrated that CS-GO retained over 90% of its adsorption capacity after five cycles, confirming its structural stability and regeneration potential. Post-treatment physicochemical analysis revealed substantial reductions in ciprofloxacin concentration and other pollutants, with water quality approaching regulatory standards. These findings highlight the potential of CS-GO as a low-cost, eco-friendly, and effective adsorbent for pharmaceutical wastewater remediation, contributing to circular economy practices through the valorisation of agricultural waste.