Eco-friendly activated carbon derived from pomegranate peel for amoxicillin removal: batch adsorption, kinetic modeling, and thermodynamics

Activated carbon derived from waste pomegranate peels was investigated for the removal of amoxicillin (AMX) from aqueous solutions. The prepared adsorbent exhibited a high BET surface area (1307 m²/g) and a well-developed micro-mesoporous structure. Under optimal conditions (pH 2, 0.05 g, 25 °C, 50 mg/L), a maximum removal efficiency of 97% was achieved, while 87% removal was maintained at near-neutral pH (pH 6). Increasing the initial concentration reduced removal efficiency due to adsorption site saturation, whereas increasing temperature decreased adsorption, confirming the exothermic nature of the process. Kinetic studies showed that the pseudo-second-order model provided the best fit, indicating that surface-controlled interactions govern the adsorption rate. Equilibrium data were better described by the Freundlich model, suggesting heterogeneous adsorption behavior, although the Langmuir model also indicated a high monolayer adsorption capacity (qₘₐₓ = 100 mg g⁻¹). Thermodynamic parameters (ΔG° = -6.13 to - 5.16 kj/mol, ΔH° = -15.59 kj/mol, ΔS° = -32.29 J/mol K) confirmed that the adsorption process is spontaneous and exothermic. The relatively low ΔH° value indicates that adsorption is predominantly governed by physisorption mechanisms. Overall, the results demonstrate that this low-cost and sustainable adsorbent is a promising alternative for efficient antibiotic removal from water.