Enhancement of basic dye adsorption uptake from aqueous solutions using chemically modified oil palm shell activated carbon

The effect of hydrochloric acid (HCl) treatment of activated carbon prepared from oil palm shell on methylene blue (MB) adsorption was investigated. The Fourier transform infrared spectroscopy (FTIR) measurements showed that the surface chemistry of the activated carbon was influenced by the acidic treatment. Adsorption equilibrium data were fitted to the Langmuir, Freundlich and Dubinin–Radushkevich isotherm models. The equilibrium data for both the untreated and HCl-treated activated carbons were best represented by the Langmuir isotherm. The adsorption capacity of HCl-treated activated carbon was 303.03 mg/g, which was 24.24% higher compared to the untreated activated carbon. The kinetic data were found to follow closely the pseudo-second-order model for both activated carbons. Various thermodynamic parameters such as standard enthalpy (ΔH°), standard entropy (ΔS°) and standard free energy (ΔG°) were evaluated. The adsorption of MB on the HCl-treated activated carbon was found to be endothermic in nature and was favoured by using a higher solution pH.