| Popis: |
Spin-coating was used to produce a multitude of mesoporous titanium dioxide thin films, using \ud stearic acid as a model organic pollutant to assess their activity. Spin speeds between 500 and \ud 8000 rpm were used to produce films of TiO2, meso-TiO2 and Cu-doped meso-TiO2. Layering films \ud was explored to determine its effect on the activity of the resulting surface coatings. An optimum \ud was reached at four layers, after which subsequent layers proved detrimental to the activity. The \ud activity of films with 0.1 to 5 wt% copper-doping was assessed, finding copper-doping above 1 \ud wt% proved to be detrimental to the activity of the photocatalysts. The 0.5 and 0.1 wt% samples \ud proved to be more active than undoped meso-TiO2 films. Photocatalytic testing using a solid layer \ud of stearic acid spin-coated directly on top of the photocatalyst film allowed for an effective \ud mechanistic study. It was possible to decompose stearic acid on the surface in air, nitrogen, and \ud under vacuum, revealing the Mars-van Krevelen mechanism by which the reactions on the surface \ud progress. Accurate film depth measurements using optical profilometry exposed the non�Newtonian behaviour of the fluid used to produce the films. Comparing the spin speed, film \ud depth, kinetics, and activity of the films showed that the spin-coating process has a greater impact \ud than merely the film thickness. The critical shear rate of the fluids used to produce these films\ud coincided with a change in the kinetics of the decomposition of stearic acid over the \ud photocatalysts. The 5 wt% copper-doped meso-TiO2 samples showed a clear increase in bandgap \ud energy with increasing spin speed, beyond any changes in film depth. The photocatalysts also \ud proved to be effective at decomposing polystyrene. Increasing the spin-speed improved the \ud selectivity towards the phenyl ring, showing that these materials could be easily tailored to \ud specific needs. |
