Valorization of Spent Coffee Grounds into Hydrothermal Biochar for Sustainable Ciprofloxacin Removal from Water: Mechanistic and Thermodynamic Insights
摘要
This study investigates the potential of using spent coffee grounds (SCG) as a sustainable biomass feedstock for the production of coffee ground activated carbon (CGAC) biochar via a hydrothermal method. The resulting biochar exhibited a highly porous, graphite-like structure with a specific surface area of 51.2 m2. g−1, making it a promising material for environmental remediation. The adsorption capacity of CGAC for ciprofloxacin (CIP), a widely used antibiotic contaminant in aqueous environments, was systematically evaluated through static adsorption experiments. Factors such as equilibrium adsorption time, pH, and material-to-solution ratio were optimized, with the optimal pH for CIP removal determined to be 6.5 and the ideal material-to-solution ratio established at 1.5 g. L−1. Adsorption isotherm analysis indicated that CIP adsorption followed multiple models, including Langmuir, Freundlich, and Redlich-Peterson, with a maximum adsorption capacity of 112 mg. g−1 according to the Langmuir model. The adsorption of CIP onto CGAC followed the pseudo-second-order (PSO) kinetic model, with an average reaction rate constant of 0.0167 L·mg⁻1·min⁻1. The values for the free energy change (∆G°) ranged from -3.85 to -0.685 kJ·mol⁻1 as the temperature increased from 303 to 323 K, indicating that the CIP adsorption process on CGAC was spontaneous. The negative value of ∆H° (-51.58 kJ·mol⁻1) indicates that the adsorption process of CIP onto CGAC was exothermic. The results highlight the feasibility of utilizing CGAC biochar, derived from low-cost and abundant biomass waste (SCG), as an effective, eco-friendly adsorbent for antibiotic removal. This study not only demonstrates the potential of SCG as a valuable resource in the biorefinery process but also contributes to advancing sustainable methods for wastewater treatment and environmental protection.