Nitrogen-doped graphene-based materials were prepared by the modified Hummers method using natural graphite as primary precursor, followed by chemical and thermal reduction processes, and finally ball milled with urea or melamine. The graphene-based materials were characterized at different stages of their synthesis by different techniques (including temperature programmed desorption and X-ray photoelectron spectroscopy) and then tested as metal-free catalysts in the degradation of oxalic acid and phenol by two different oxidation processes: catalytic wet air oxidation (temperature between 413 and 433 K, and 7 bar of O-2) and catalytic ozonation (room temperature and atmospheric pressure). The melamine treated sample was always found to be more active due to the presence of nitrogen groups and adequate surface area available. (C) 2014 Elsevier B.V. All rights reserved.