Isolated iron(III)-oxo clusters were synthesized onto TiO2 using atomic layer deposition. The FexOy/TiO2 nanocomposites have unique properties that enable not only absorption of visible light, but efficient photocatalysis as demonstrated by methylene blue degradation. The localization of photogenerated electrons in core TiO2 nanocrystallites upon visible light excitation demonstrates coupling of conduction band of mixed oxides. The redox properties of photogenerated charges in nanocomposites were studied using in situ electron paramagnetic resonance spectroscopy.