The use of activated carbon for the removal of favipiravir from aqueous solutions: Isotherm, kinetic and thermodynamic studies

Abstract

This study investigates the removal of the antiviral drug favipiravir (FPR) from aqueous solutions using activated carbon through batch adsorption experiments. The effects of initial concentration, pH, adsorbent dosage, contact time, and temperature on adsorption performance were systematically evaluated. The highest FPR removal efficiency (91.93%) was achieved at an initial concentration of 30 mg/L, an adsorbent dose of 0.30 g/L, a contact time of 120 min, a temperature of 20 °C, and pH 3.0. Adsorption kinetics were analyzed using pseudo-first-order and pseudo-second-order models. The pseudo-second-order model provided the best fit (R² = 0.9999), indicating that the adsorption process was predominantly governed by surface interactions. Equilibrium data were evaluated using Langmuir and Freundlich isotherm models. The Langmuir model showed superior agreement with the experimental data (R² = 0.9982), suggesting monolayer adsorption on a homogeneous surface. Thermodynamic analysis performed at 20, 35, and 50 °C revealed negative ΔG° (-8.873 kJ mol^-1) and ΔH° (-29.61 kJ mol^-1) values, confirming that the adsorption process was spontaneous and exothermic. The negative ΔS° value (-70.77 J mol^-1 K^-1) indicated decreased randomness at the solid–liquid interface. These findings demonstrate the potential of activated carbon as an effective adsorbent for the removal of favipiravir from water.

KEY WORDS: Favipiravir, Activated carbon, Batch adsorption, Water treatment, Adsorption kinetics, Thermodynamics

Bull. Chem. Soc. Ethiop. 2026, 40(10), 2081-2095.                                               

DOI: https://dx.doi.org/10.4314/bcse.v40i10.3