Imaging UV photoactivity and photocatalysis of TiO2-films

Differently prepared thin layers of TiO2 were scanned with a UV-laser to produce images of photocurrents. The technique used a scanning optical microscope. Flame oxidized, galvanostatically oxidized, thermogravimetrically oxidized, sputtered and sol–gel prepared layers were compared by determining images of UV-induced photocurrent under otherwise identical conditions. Significant differences were found between the samples, both with respect to local distribution and intensity of photoactivity. Also within the same sample, variations in photoactivity of up to one order of magnitude were found, which partially could be traced back to characteristic features of the preparation technique. The UV-photoactivity of TiO2-layers was shown to depend on the preparation procedure and the duration of photoelectrochemical operation. The developed technique is discussed as a strategy for optimising photoactivity of TiO2-layers. For locally immobilized substances (e.g. methanol, 4-chlorophenole) within a deposited porous sodium silicate layer (water-glass), enhanced photooxidation activity could be identified as patches of increased photocurrent density. In this way the technique will allow combinatorial approaches to photooxidation and detoxification of chemicals. The described UV-imaging techniques could be developed as a useful tool for optimizing photocatalytic layers for solar detoxification and surface cleaning.