The Effect of Oxidative Modification of Activated Carbon on Adsorption of Aromatic Compounds from Aqueous Solutions

Activated carbon F-400 was modified by using different oxidation agents: nitric acid, sulfuric acid, and ozone. The influence of the type of carbon surface groups on adsorption effectiveness towards selected aromatic compounds was analyzed. The commercial carbon F-400 was deashed and modified, and the obtained materials were characterized by using different techniques to determine their textural, thermal, morphological, and surface properties: low-temperature adsorption/desorption isotherms of nitrogen, scanning electron microscopy (SEM), Boehm titration, and Fourier transform infrared spectroscopy (FTIR). The adsorption properties towards four aromatic compounds, i.e., toluene, 4-nitrotoluene, nitrobenzene, and 4-nitrobenzoic acid, were evaluated based on isotherm measurements. Adsorption equilibrium data were analyzed by applying the generalized Langmuir isotherm. The influence of carbon surface groups and adsorbate functional groups in interaction mechanisms was discussed. It was found there was a strong effect of oxidation on adsorption efficiency. The adsorption capacity of modified activated carbon F-400 strongly depends on the type of oxidant used, e.g., in the case of toluene, the use of ozone as an oxidant gives a sorption capacity of 5.51 mmol/g, and of nitric acid-4.20 mmol/g.