Fruit waste to wealth: Adsorption isotherm, kinetics, and thermodynamic studies of methylene blue removal using activated carbon derived from jackfruit peel (Artocarpus heterophyllus)

Jackfruit peels, an abundant agricultural byproduct and a sustainable precursor, were successfully transformed into low-cost activated carbons for the removal of methylene blue (MB) from aqueous solutions. Activated carbons (AC) were prepared using NaOH, H 2 SO 4 , and HCl as activating agents and characterized by Fourier Transform Infrared (FTIR) spectroscopy, Electron Microscopy (SEM), and CHNS Analysis. Batch adsorption experiments were performed to evaluate the effects of adsorbent dosage, pH, contact time, initial MB concentration, and temperature. The NaOH-activated carbon (ACN) exhibited the highest MB removal efficiency (99.99%) and reached equilibrium within 10 min. Under optimal conditions (pH 8.0, 0.06 g dosage, 50 mg/L, 60 min), the ACN adsorbent demonstrated a maximum experimental adsorption capacity of 147.1 mg/g. The Langmuir isotherm analysis yielded a predicted monolayer capacity ( q max ) of 149.3 mg/g, demonstrating an exceptional fit (R² = 0.998), suggesting that adsorption occurred through a favourable monolayer mechanism. The strong agreement between experimental and estimated capacities further supports that electrostatic interactions were predominant in the adsorption process. Kinetic analysis indicated a pseudo-second-order model fit ( R 2 = 1.000), confirming a strong adsorbate-adsorbent interaction. Thermodynamic studies revealed that the adsorption was spontane°us (ΔG°< 0), and exothermic in nature. Overall, this work highlights jackfruit peel-derived activated carbon as a cost-effective, eco-friendly adsorbent for dye wastewater treatment, thereby promoting the value-added utilization of agricultural waste for environmental sustainability.