In this paper two commercial activated carbons, granular and pelletized, were impregnated with aqueous solutions of phosphoric acid (H3PO4), or potassium hydroxide (KOH) in 60% w/w concentrations under moderate temperature conditions (18 °C). It was observed that the impregnation with phosphoric acid increases the adsorption of 2,4-dinitrophenol regarding the starting activated carbon. The adpsorption was determined from isotherms in aqueous solution of phenol and 2,4-dinitrophenol, and experimental data were adjusted to the Freundlich, Langmuir, Toth and Prausnitz-Radke models. Langmuir was the model that best fitted for phenol adsorption, and Toth was the model that best fitted the for 2,4-dinitrophenol adsorption. The results showed that the impregnation