Valorization of Coconut Husk for Mitigating Antimicrobial Resistance: Mechanistic Insights into Ciprofloxacin Removal from Water

Antibiotic residues such as ciprofloxacin in aquatic systems contribute to antimicrobial resistance and environmental contamination. Conventional treatment processes are often insufficient for removing pharmaceutical contaminants. In this study, activated carbon synthesized from coconut husk using orthophosphoric acid was evaluated for ciprofloxacin adsorption through equilibrium, kinetic, and thermodynamic analyses. The adsorption capacities were 42.34 mg/g for commercial activated carbon (AC) and 36.72 mg/g for synthesized coconut husk activated carbon (CHAC), at an initial ciprofloxacin concentration of 50 mg/L, achieving 85% and 73% removal, respectively. The experimental data obtained were analyzed using five isotherm models (Langmuir, Freundlich, Temkin, Dubinin–Radushkevich, and Sips). The Sips isotherm better describes AC sorption data than the Freundlich isotherm model for the CHAC, indicating heterogeneous surface coverage. The kinetic model investigation showed a better fit with the Elovich model for AC and the pseudo-second-order model for CHAC, as indicated by higher R2 values and lower sum-of-squares errors. Thermodynamic parameters indicated spontaneous and exothermic processes, while SEM analysis confirmed surface porosity and heterogeneity. The results demonstrate that the chemically activated coconut husk is an efficient, low-cost, and sustainable material for mitigating pharmaceutical contamination and addressing antimicrobial resistance in water systems.