Cross-linked polymer nanocapsules (PC) encapsulating an iron tris(bipyridine) complex, Fe(bPY)(3)(2+)@PC, have been synthesized by a ship-in-a-bottle method. This was used as a photosensitizer for the decomposition of organic pollutant in water under visible light irradiation with molecular oxygen. The Fe(bpy)(3)(2+)@PC promotes efficient decomposition of organic pollutant, whereas noticapsulated Fe(bpy)(3)(2+) is inactive. The enhanced sensitization activity of Fe(bpy)(3)(2+) within PC is due to the interaction with the PC wall. This lengthens the lifetime of the excited state Fe(bpy)(3)(2+) and promotes efficient production of hydroxyl radicals. The sensitization activity of Fe(bPY)(3)(2+)@PC depends on the thickness of the PC wall. The Fe(bPY)(3)(2+)@PC with an appropriate PC wall thickness allows accumulation of pollutant within the PC and, hence, promotes efficient decomposition of pollutant. (C) 2009 Elsevier B.V. All rights reserved.