Correlation between the photocatalysed oxidation of methylene blue in solution and the reduction of resazurin in a photocatalyst activity indicator ink (Rz Paii)

Assessment of Activity of 'Transparent and Clear' and 'Opaque and Highly Coloured' Photocatalytic Samples using a Fluorescent Photocatalytic Activity Indicator Ink, FPaii.

The photocatalytic activity of self-cleaning glass is assessed using a resazurin (Rz) photocatalyst activity indicator ink, i.e. Rz paii, via both the rate of change in the colour of the ink (blue to pink), R(Abs), and the rate of change in the fluorescence intensity, R(Fl), (λ(excitation) = 593 nm; λ(emission) = 639 nm) of the ink. In both cases the kinetics are zero order. Additional work with a range of glass samples of different photocatalytic activity reveal R(Abs) is directly related to R(Fl), thereby showing that the latter, like the former, can be used to provide a measure of the photocatalytic activity of the sample under test. The measured value of R(Fl) is found to be the same for 5 pieces of, otherwise identical, selfcleaning glass with: black, red, blue, yellow and no coloured tape stuck to their backs, which demonstrates that R(Fl) measurements can be used to measure photocatalytic activity under conditions of high colour and opacity under which R(Abs) cannot be measured. The relevance of this novel, fluorescence-based paii to the assessment of the activity of highly coloured, opaque photocatalytic samples, such as paints and tiles, is discussed briefly.

Multifunctional anthraquinone-based sensors: UV, O2and time

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 UV-activated 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 °C in ambient air to attain a green colour, and, on this basis, it is demonstrated as a possible CWI for refrigerated fresh foods.

Continuous flow gas phase photoreforming of methanol at elevated reaction temperatures sensitised by Pt/TiO2

Gas phase photoreforming of methanol using a Pt/TiO2 photocatalyst has been performed under flow conditions at elevated temperatures. Comparing the activity of the reforming process as a function of temperature under dark and irradiated conditions shows a significant enhancement in the rate of H2 production using the photo-assisted conditions at temperatures between 100-140 °C. At higher temperatures, the effect of irradiation is small with the process dominated by the thermal process. Deactivation of the catalyst was observed under irradiation but the catalyst was easily regenerated using an oxygen treatment at 120 °C. Diffuse Reflectance Infra-red Fourier Transform Spectroscopy (DRIFTS) showed that the activity of the catalyst could be correlated with the presence of the photogenerated trapped electrons. In addition, lower amounts of CO adsorbed on Pt, compared to those observed in the dark reaction, were found for the UV-irradiated systems. It is proposed that CO and adsorbed intermediates, such as formate, can act as inhibitors in the photoreforming process and this is further supported by the observation that, before and after the regeneration process in O2, the CO and surface adsorbed organic intermediate products are removed and the activity is recovered.