Nanostructured catalysts (Fe3+-doped TiO2 and bentonite clay-based Fe nanocomposite (Fe-B)) have been developed for the discoloration and mineralization of a non-biodegradable azo dye, Orange II. The Fe3+-doped TiO2 nanocatalysts synthesized by the sol-gel method and the Fe-B nanocatalyst by the pillaring method were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), X-ray reflective fluorescence (XRF), and the BET method. Their photocatalytic activities for the discoloration and mineralization of a nonbiodegradable azo dye Orange II were evaluated. The results indicate that the concentration of Fe3+ dopant does not influence the crystal structure of the nanocatalysts, but significantly affect their photocatalytic activity. The best efficiency for both discoloration and mineralization of 0.2 mM Orange II was obtained by the 0.05 at.% Fe3+-doped TiO2 nanocatalyst. The nanostructured Fe-B catalyst exhibits good catalytic activity in the discoloration and mineralization of Orange II in the presence of UVC light (254 nm) and H2O2, at an initial solution pH of 6.60, with negligible leaching of Fe ions from the nanocatalyst. This result has demonstrated that it is feasible to use the Fe-B nanocatalyst as a heterogeneous photo-Fenton catalyst for practical industrial wastewater treatment, without the need for pre-adjustment of solution pH and removal of Fe3+ ions after the reaction. (C) 2004 Elsevier B.V. All rights reserved.