At the time he made the first photographs on paper: Did Henry Fox Talbot oxidize water to oxygen with sunlight?

Abstract

Photocatalytic water oxidation to O 2 takes place at the solid/water phase boundary of an appropriately prepared thin AgCl layer in the presence of a small excess of Ag +. This water oxidation reaction shows self-sensitization: as the reaction proceeds, the sensitivity is extended from the near-UV—visible towards the red range. This means that new photo active colour centres are formed upon near UV illumination composed of reduced silver species. The quantum yield per redox equivalent for O 2 evolution upon illumination with near UV light (340–390 nm) is ∼0.8 and it is the same upon illumination with blue light (420–480 nm). In the green range it is ∼0.5. We discuss parameters controlling these reactions. Some of our observations parallel those made by Henry Fox Talbot 160 years ago when he made his first “photogenic drawings” on silver chloride containing paper. Zeolite microcrystals are investigated as hosts for supramolecular organization of clusters, complexes and molecules. They offer possibilities to design precise and reversible functionalities which have the potential to become useful in a solar energy conversion system because in favourable cases very stable materials have been obtained. The possibility to arrange zeolite microcrystals of good quality and narrow size distribution as dense monograin layers on different types of substrates allows the discovery of specific properties. In the present context, three functionalities are of special importance: intrazeolite ion transport, intrazeolite charge transport and intrazeolite excitation energy transport. All of them have been clearly demonstrated experimentally although there are still some controversies going on. The zeolite acts as a host in each case mentioned. It is not actively involved in the corresponding processes, but provides the necessary geometrical and chemical environment. Favourable conditions for finding an efficient antenna device are a high concentration of monomeric dye molecules with a large Förster energy transfer radius, high luminescence quantum yield and ideal geometrical arrangement of the chromophores, as well as an optimal size of the device. Very interesting supramolecular devices can be realized by enclosing dyes inside a microporous material such that the volume of the cages and channels is able to uptake monomers only, but not aggregates.