A functionalized asphaltene, obtained by refluxing with an acid solution. The functionalized asphaltene contains elevated levels of oxygen content due to nitration and oxidation of the refluxing process. The refluxing process also imparts organic functional groups including at least amines, nitro groups carbonyl groups, carboxylic groups and hydroxyl groups to the functionalized asphaltene, and these functional groups are attached to, thereby coating the surface of a functionalized asphaltene particle. A method for removing dye compounds from an aqueous sample with the functionalized asphaltene is also described.