Visible-light-induced and long-lived charge separation in a transparent nanostructured semiconductor membrane modified by an adsorbed electron donor and electron acceptor

The preparation of transparent nanostructured TiO2 (anatase) membranes is described. Detailed characterization shows these membranes to be 50 μm thick nanoporous-nanocrystalline structures with associated values for porosity and surface roughness of 50% and 5000, respectively. Modification of these membranes by coadsorption of a ruthenium complex, bis[(4,4′-dicarboxy-2,2′-bipyridine)(4,4′-dimethyl-2,2′- bipyridine)-ruthenium(II)] dichloride (I), and of a viologen, 1-ethyl-1′-[(4-carboxy-3-hydroxyphenyl)methyl]-4,4′-bipyridinium perchlorate (II), is also described. Detailed studies show that visible-light-induced electron transfer by electronically excited I to the conduction band of the nanostructured TiO2 membrane is followed by membrane mediated electron transfer to coadsorbed II. Detailed studies also show that, as a consequence of the rectifying properties of the semiconducting membrane, charge separation is long-lived. The possible significance of these findings for the development of a practical water splitting device is considered.