A brief overview of work carried out by this group on thick (> 1 mu m), optically clear, robust titania films prepared by a sol-gel method, as well as new results regarding these films, are described. Such films are very active as photocatalysts and able to destroy stearic acid with a quantum yield of 0.32%. The activity of such films is largely unaffected by annealing temperatures below 760 degrees C, but is drastically reduced above this temperature. The drop in photocatalyst activity of such films as a function of annealing temperature appears to correlate well with the change in porosity of the films and suggests that the latter parameter is very important in deciding the overall activity of such films. The importance of porosity in semiconductor photocatalysed cold combustion may be due to the effect it has on access of oxygen to the active sites, rather like the effect the position of a fire grate (open or closed) has on the rate of burning, i.e., hot combustion, that takes place in a fireplace

An overview of the recent investigations into the direct, lateral and remote oxidation of carbon-containing materials is given. The overview begins with the pioneering work of Fujishima and his co-workers involving the remote bleaching of methylene blue by UV-irradiation of titania in the gas phase. The further research of these workers conducted on the remote photocatalytic destruction of various polymers and dyes is then discussed briefly. The notable work of Paz and his co-workers on the lateral, but not remote, oxidation of octadecyltrichlorosilane (OTS) by photoeteched titania films is then examined. The striking observations associated with the lateral oxidation of soot by UV-irradiated thin titania films, reported by Choi and his colleagues, are reported. Finally, the results of our most recent work on soot covered titania films in which the direct, lateral and remote oxidation of soot by UV-irradiated thick titania films could be observed visually is discussed. The most likely agent responsible for these photocatalytic oxidation processes is considered and a suitable candidate, hydroxyl radicals, suggested

Novel Ag on TiO 2 films are generated by semiconductor photocatalysis and characterised by UV/Vis spectroscopy, SEM, AFM as well as assessed for SERS activity. The nature and thickness of the photodeposited Ag, and thus the degree of SERS activity, is controlled by the time of exposure of the TiO 2 film to UV light. All such films exhibit the optical characteristic (λmax ≅ 390 nm) of small (<20nm) Ag particles, although this feature becomes less prominent the thicker the film. The films comprise quite large (>40nm) Ag islands that grow and merge with increasing levels of Ag photodeposition.Tested with a benzotriazole dye probe, the films are SERS active; exhibiting a similar activity as that of 6nm thick vapour-deposited films. The Ag/TiO 2 films exhibit a lower residual standard deviation (ca. 25%) compared with Ag vapour-deposited films (ca. 45%), which is, however, still unacceptable for quantitative work. The sample-to-sample variance could be reduced significantly (<7%) by spinning the film during the SERS measurement. The Ag/TiO 2 films are mechanically robust and resistant to removal and damage by scratching, unlike the Ag vapour-deposited films. The Ag/TiO 2 films also exhibit no obvious loss of SERS activity when stored in the dark under otherwise ambient conditions. The possible extension of this simple, effective, method of producing Ag films for SERS, to metals other than Ag, and to semiconductors other than TiO 2 , is briefly discussed.

An anthraquinone dye, Remazol brilliant blue R, RBBR, is used to create an indicator which can function as: (i) a UV dosimeter, (ii) an O2 indicator and (iii) a 'Consume within' indicator, CWI, for fresh, refrigerated foods. The dye is encapsulated in an ink containing a polymer, glycerol and a UVactivated semiconductor photocatalyst, titanium dioxide. When cast as a film, the dye is readily reduced by the TiO2 photocatalyst nanoparticles, thereby changing the colour of the film from blue to yellow, via a transitional green colour. The RBBR indicator is appropriately formulated, and covered with a film of Sellotape, which acts as an O2 barrier, so as to act as a sunburn warning indicator for people with skin type II. In the absence of the layer of Sellotape the RBBR indicator is used as an, albeit slow, sensor for measuring ambient levels of O2. Finally, by keeping the Sellotape layer, a UV-activated, yellow-coloured, RBBR indicator film is found to take ca. 42 h at 5 O C in ambient air to attain a green colour, and, on this basis, it is demonstrated as a possible CWI for refrigerated fresh foods.