Valorizing Macadamia Nut Waste into Activated Carbon for Paracetamol Adsorption: Kinetic, Isotherm, and Mechanistic Investigations

Abstract

The efficacy of activated carbon derived from macadamia nuts (ACM) in removing paracetamol from aqueous solutions was evaluated. The adsorbent was characterized by Fourier transform infrared spectroscopy, point-of-zero-charge analysis, and thermogravimetric analysis/derivative thermogravimetry. Adsorption kinetics followed the pseudo-second-order model ( R 2 = 0.990–0.992), indicating that the adsorption rate is governed by strong interaction-based mechanisms. Equilibrium isotherms indicated endothermic adsorption, with a maximum capacity of 76 mg/g. The Toth model provided the best fit to the equilibrium data ( R 2 = 0.999), suggesting adsorption occurs on a heterogeneous surface. The adsorption mechanism likely involves π–π interactions and hydrogen bonding, with minimal electrostatic contributions at natural pH. ACM shows promise as a sustainable adsorbent for paracetamol removal; however, further research on regeneration, reusability, and life-cycle assessment is needed to confirm its sustainability.