Amoxicillin adsorption onto oil palm trunk-derived activated carbon: synthesis optimization, modelling of mass transfer and ultrasonic regeneration

Abstract

BACKGROUND

Antibiotics such as amoxicillin (AMC) can persist in the environment due to their stable molecular structures. This study aimed to (i) optimize the synthesis of oil palm trunk-based activated carbon (OPTAC) for AMC removal, (ii) model the adsorption process using the mass transfer model (MTM) and (iii) evaluate OPTAC regeneration through ultrasonic washing. OPTAC was synthesized using potassium hydroxide activation followed by carbon dioxide treatment.

RESULTS

Response surface methodology (RSM) identified optimal synthesis conditions at 343 W, 12.87 min and an impregnation ratio of 2.00 g g⁻¹. Under these conditions, the predicted AMC uptake was 146.44 mg g⁻¹ (actual: 154.15 mg g⁻¹; 5.00% error), and the predicted OPTAC yield was 42.78% (actual: 41.19%; 3.86% error). The AMC–OPTAC adsorption followed the Freundlich isotherm, with a Langmuir capacity (Q_m) of 238.67 mg g⁻¹. Kinetic analysis revealed that the pseudo-first-order model best described the system. MTM analysis yielded an average mass transfer constant (k_m) of 0.23 mg m L⁻¹ h⁻¹, rate constant (k_MTM) of 0.00051 h⁻¹ and estimated surface area (a_MTM) of 611.34 m² g⁻¹, closely matching the measured mesopore surface area (647.82 m² g⁻¹; 5.63% error). Thermodynamic analysis confirmed physisorption as the dominant mechanism, with spontaneous and endothermic behavior. In regeneration studies, ultrasonic washing outperformed microwave reactivation, maintaining AMC removal efficiency and OPTAC yield above 50% for five cycles, compared to three with microwave treatment.

CONCLUSIONS

RSM successfully optimized AMC removal and OPTAC yield, while the MTM effectively predicted the active surface area involved in the adsorption process. © 2025 Society of Chemical Industry (SCI).