Adsorption of aromatic compounds on activated carbons from lignin:: Equilibrium and thermodynamic study

The adsorption processes of several aromatic chemicals onto activated carbons (ACs) from aqueous solutions have been studied. The activated carbons were prepared from eucalyptus kraft lignin with CO2 at 1073 K activation temperature. The surface properties of the ACs play a significant role when these materials are used for adsorption from liquid phases. The physicochemical properties and the surface chemical structure of the ACs were studied by means of N-2 adsorption experiments, elemental analysis, XPS, and TPD. The XPS and TPD spectra of ACs suggest the presence of aromatic rings and oxygenated functional groups in the surface material. Benzene, nitrobenzene, aniline, p-nitroaniline, toluene, and p-nitrotoluene as aromatic adsorbates have been used in the present study. Adsorption isotherms data were fitted to the Freundlich and Fritz-SchlUnder equations. We have developed the thermodynamic study from the equilibrium data. The values of Delta H, Delta G, and Delta S were calculated, and these indicate that the process is exothermic in nature in all the examined cases.