The adsorption properties of a modified activated carbon with various oxygen- and/or nitrogen-containing surface groups toward copper ions was studied. Previously de-ashed and chemically modified commercial activated carbon D-43/1 (Carbo-Tech, Essen, Germany) was used. The chemical properties of the modified carbon surface were estimated by standard neutralization titration with HCl, NaOH, and NaOC2H5. The adsorption of CU2+ ions on three modified activated carbons from aqueous CuSO4 solution of various pH was measured. The carbon samples with adsorbed CU2+ ions were analyzed by spectroscopic methods (X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy). In addition, an electrochemical measurement (cyclic voltammetry) was performed using powdered activated carbon electrodes. While the modification procedures employed alter the surface only slightly, they strongly influence the surface chemical structure. Basic groups are predominant in the heat-treated samples; acidic functional groups are predominant in the oxidized sample. Both the copper cation adsorption studies and the spectral and electrochemical measurements show that adsorbed ions interact with the carbon surface in different ways. The number of adsorbed ions depends on the nature and quantity of surface acid-base functionalities and on the pH equilibrium in the aqueous solution. The possible mechanisms of interactions between metal ions and carbon surface functionalities are summarized and discussed.