Immersion enthalpies of five samples of activated carbon obtained from diverse lignocellulosic materials are determined, each with different burn off, around 20%, in aqueous solutions of phenol and 4-nitrophenol of 100 mg. L (-1). The values of immersion enthalpy relate with the solutes adsorbed quantity, with the immersion enthalpy in NaOH solutions and the pH in the point of charge zero, pH (PZC). The activated carbons obtained have a basic character with pH values at the point of zero charge, pH (PZC), that vary from 7