The use of prepared activated carbon as adsorbent for the removal of orange G from aqueous solution

Abstract This work is devoted to the study of the adsorption properties of a food waste “coffee grounds” activated carbon (AC) for the uptake of acid dye orange G (OG). ACs were previously prepared from chemical activation of pyrolysed coffee ground by KOH (1 g of KOH/1 g of biomass). The AC characterization shows that it has essentially microporous structure with a specific surface area of 1455 m 2  g −1 and acid-basic functional surface character. Many aspects of the kinetics and isotherms for the dye removal indicate that the equilibriums were achieved in 3 h. Three models are attempted to fit the kinetic data i.e. pseudo-first order, pseudo-second order and intra-particle diffusion models. An evaluation of the correlation coefficients (R 2 ) and adsorbed amount per mass unit of adsorbent (Q e ) at equilibrium indicates that orange G adsorption on AC is well fitted by the pseudo-second order model (R 2  = 0.998). The experimental adsorption equilibrium data are described by the Langmuir, Freundlich, Temkin, Dubinin-Radushkevich and Redlich-Peterson isotherm models. The Langmuir and Redlich-Peterson models are judged to be the closest for the description of the experimental data based on the coefficients (R 2  ≈ 0.999). Non-linear regression was also used to evaluate the isotherms models. The thermal effect on the adsorption is studied and the thermodynamic parameters: enthalpy (∆H°), entropy (∆S°) and free energy (∆G°) are determined. The adsorption of orange G is thermodynamically spontaneous (∆G°   0).