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The preparation and characterization of thick (9 microns), clear, mechanically robust and photocatalytically active films of nanocrystalline anatase titania are described. XRD and SEM analysis show the films comprise 13 nm particles of anatase TiO2. Thin (54 nm) films of the 'paste' TiO2, along with sol-gel titania films made by a more traditional route are also prepared and characterised. All titania films mediate the photocatalytic destruction of stearic acid with a quantum yield of 0.0016 +/- 0.0003, using either 365 nm (i.e. BLB) or 254 nm (germicidal) light. P25 TiO2 films also appear to mediate the same process with a similar formal quantum efficiency. Of all the films tested, the thick paste TiO2 films are the most ideally suited for use with near UV light, for reasons which are discussed. All the titania films tested exhibit photoinduced superhydrophilicity.

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

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.