The adsorption of the metallic ions Cd(II) and Pb(II) onto the surface of the mesoporous activated carbon CMK-3 is presented. The carbon was synthesized from a SBA-15 template by the method of nanocasting and oxidized in an aqueous solution with nitric acid (HNO3). The effect of temperature and oxidation time was studied. The presence of the functional groups, formed during the oxidation, onto the carbon surface was confirmed by FT-IR analysis. The structural and textural properties of activated carbon were obtained by nitrogen adsorption, SEM, EDX and HTEM. The surface area of the CMK-3 is 1170 m2/g, and it contains 96.7% of carbon and 3.3% of oxygen, whereas the oxidized CMK-3-O exhibits a surface area of 944 m2/g and contains 85.2% of carbon and 14.8% of oxygen. The adsorption isotherms follow the Langmuir model and the maximum amount of adsorbed ions was 40.4 mg/g for Cd(II) and 94 mg/g for Pb(II) at pH 5 and 25 degrees C. The spatial distribution and amount of oxygen and adsorbed metal ions were determined by elemental mapping and line scanning EDX. It was confirmed that the amount of oxygen is directly related with the amount of adsorbed ions. (C) 2014 Elsevier B. V. All rights reserved.