Carbon nanomaterials have a great potential in environmental studies; they are considered as superior adsorbents of pollutants due to their physical and chemical properties. Functionalization and dimension play an important role in many functions of these nanomaterials including adsorption. In this research, adsorption process was achieved with one‐dimension nanomaterials: single walled and multiwalled carbon nanotubes were used as received and after oxidation treatment also two‐dimensional nanomaterials were used: graphene oxide and reduced graphene oxide. Carbon nanotubes were modified by hydrogen peroxide under microwave irradiation. The reduction of graphene oxide was achieved by using ascorbic acid. R² values obtained with the pseudo‐second‐order model are higher than 0.99. The results demonstrate that Freundlich isotherm provides the best fit for the equilibrium data (R² > 0.94). R_L values are between 0 and 1; this represents favorable adsorption between carbon nanomaterials and phenol. The adsorption process occurs by π‐π interactions and hydrogen bonding and not by electrostatic interactions. The results indicate that the adsorption of phenol on carbon nanomaterials depends on the adsorbents’ surface area, and it is negatively influenced by the presence of oxygenated groups.