Formation and Photocatalytic Properties of Nanocomposite Films Containing Both Tetracobalt Dawson-Derived Sandwich Polyanions and Tetracationic Porphyrins

Films based on electrostatic interactions between tetracationic zinc porphyrins, ZnOEP(py)(4)(4+) or ZnTMePyP4+, and the tetracobalt Dawson-derived sandwich polyanion alpha beta beta alpha-[Co-4( H2O)(2)(P2W15O56)(2)](16-) are formed by the so-called layer-by-layer method. These films have been characterized by UV-visible absorption spectroscopy, atomic force microscopy and electrochemistry. The composition of the film was measured by X-ray photoelectron spectrum (XPS). The XPS data confirm the presence of the expected elements. The photocatalytic properties of these films have been also studied for the reduction of silver and gold ions. Indeed, in these systems, porphyrins can be excited by visible light and then play the role of photosensitizers able to give electrons to POM known to be good catalysts. Silver nanowires and gold nanosheets have been obtained.