The scope of this work was to control the surface functional groups of nanoporous carbons (NPs) by oxidizing agents (nitric acid and hydrogen peroxide) treatments and to investigate the relation between carboxyl group and ammonia removal efficiency. The NPs were directly prepared from a cation exchange resin by the carbonization of a mixture with Ni acetate at 900 degrees C. N-2/-196 degrees C adsorption, Boehm's titrations, and X-ray photoelectron spectroscopy (XPS) analyzes were employed to confirm the physicochemical properties of NPs. The ammonia removal efficiency was confirmed by temperature programmed desorption (TPD) technique. In the result, the oxygen content of NPs increased after various treatments and the highest content of carboxyl group formation appeared at a 2:3 volume ratio of HNO3/H2O2. It was also found that the oxidation treatment led to an increase in ammonia removal efficiency of NPs, mainly due to an increase of acid oxygen functional groups (such as carboxyl) on NPs surfaces. Crown Copyright (C) 2012 Published by Elsevier B.V. All rights reserved.