Visible-Light-Induced and Long-Lived Charge Separation in a Transparent Nanostructured Semiconductor Membrane Modified by an Adsorbed Electron Donor and Electron Acceptor

Abstract

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.

Hydrogen generation from photoelectrochemical water splitting based on nanomaterials

“…Fitzmaurice and coworkers reported the studies of charge separation in a nanostructured TiO 2 membrane sensitized with Ru complexes [53]. The long-lived charge separation observed was an important finding that suggests that water splitting is practically feasible on nanostructured TiO 2 material.…”

Packing of ruthenium sensitizer molecules on mostly exposed faces of nanocrystalline TiO2: crystal structure of (NBu4+)2[Ru(H2tctterpy)(NCS)3]2−·0.5 DMSO

“…2) are the same within the accuracy of experimental error (Table 2). On the contrary, the conformations of all the NBu 4 cations are essentially different and, from the standpoint of packing (as space-filling bodies), they should be considered as different types of molecule.…”

Electron Transfer from Photoexcited TiO2 to Chelating Alizarin Molecules: Reversible Photochromic Effect in Alizarin@TiO2 under UV Irradiation

“…This feature is attributed to electron accumulation in the TiO 2 nanoparticles after oxidation of the solvent, and also disappears on addition of a reducible species. [26,27] However, control experiments performed with an aqueous colloid consisting of naked TiO 2 nanoparticles in the presence of 70 mm of an SED does not lead to electron accumulation. It is apparent that either holes (created in the presence of existing electrons) recombine faster than they can be scavenged, or some other acceptor in solution, probably H + , is being reduced.…”