Abstract Orange II decomposition was studied on a variety of iron/carbon supported catalysts and control studies of the supports alone (carbon), and iron/alumina (non-active support). Variables tested included the impact of UV radiation, inclusion of hydrogen peroxide, catalyst treatment methods (oven treated and plasma torch treated) and type of the support. Results obtained for Orange II degradation indicated that active sites on carbon are more active for the catalytic decomposition of Orange II molecules, than metal sites. Oven-treated iron catalysts showed higher OII removal than catalysts prepared by plasma torch due to the fact that iron blocks carbon catalytic sites. XRD experiment on the non-active support allowed concluding that the oxidation state of Fe on the catalyst is not the main factor in the photocatalytic degradation of Orange II.