MCM-41 materials were modified with Cr, Fe, Co and Ti and characterized by ICP, XRD, N-2 adsorption, UV-Vis DRS and TPR. Their photo-catalytic activity was evaluated for the degradation of Acid Orange 7 (AO7) in aqueous suspensions irradiated by artificial UV-Vis and visible light. The results showed that the Cr-modified catalysts exhibited the highest activity under visible light. The presence of Cr6+ highly dispersed on the internal surface of the MCM-41 structure would have a significant influence on the photo-activity. Thus, the lack of a notable increment in the activity when the Cr loading was duplicated is probably due to the increased presence of inactive Cr3+ species. Upon the TiO2 loading, an increase in the degradation was not observed. It is suggested that the Cr3+ species, as Cr2O3 clusters and/or alpha-Cr2O3 nano-particles, could avoid the desired heterojunction between Cr6+ and titania species. (C) 2011 Elsevier B.V. All rights reserved.