Empty fruit bunch hydrochars to adsorb malachite green from water - equilibrium, kinetic and thermodynamic

Abstract

Four empty fruit bunch hydrochars namely HC, HC-Acr, HC-APS, and HC-Acr-APS, were synthesized through one-step hydrothermal carbonization in the presence of acrylic acid (Acr) and/or ammonium persulphate (APS). This study aims to combine HTC with free radical graft copolymerization to produce hydrochar with enhanced functional groups and adsorption capabilities. The FTIR results show that the modified hydrochars contain more functional groups as compared to the unmodified hydrochar. The HC-Acr-APS demonstrates the highest MG capacity ( q m = 72.86 mg/g). The kinetic data obeyed the pseudo-second order model ( q e = 19.61 mg/g, k 2 = 0.02 g/mg.h), while isotherm demonstrates a good fit with the Freundlich model. The positive enthalpy change ( Δ H = 26.06 kJ/mol) indicates an endothermic adsorption process, while the positive entropy change ( Δ S = 77.15 J / mol . K ) suggests increased molecular randomness during adsorption. The Gibbs free energy change ( Δ G ) is also assessed, indicating the thermodynamic favorability of the adsorption process. This study offers valuable insights into the potential of surface-modified EFB hydrochar as an efficient adsorbent for MG removal, providing a sustainable solution for environmental challenges.