The use of titanium dioxide to catalyse the breakdown of water-borne pathogens under UV (and sometimes visible) light is well-documented, and is known  to be particularly effective in the anatase crystalline phase. TiO2 has been shown  to yield optimum photocatalytic performance in the form of fine anatase nanoparticles, which can also be altered by doping , such as with sulphur. This is thought to alter the band gap of the compound, potentially offering the compound photocatalytic activity in the visible range, which could prove highly favourable in industrial applications.
Nanoparticles, while displaying superior photocatalytic efficiency, have the disadvantage of remaining loose in the water treatment systems after use. One known solution to this problem is to grow the TiO2 on a titanium substrate by Plasma Electrolytic Oxidation (PEO) , a process involving the immersion of the substrate in a conductive electrolyte and the application of an electrical potential to it, which causes a porous oxide-based layer to form on the surface. Although typically less effective a photocatalyst than the nanoparticle form, this arrangement has the considerable benefit of giving a versatile and robust substrate for the TiO2, keeping the water free from the nanoparticle powder and allowing flexible engineering solutions to the problem of catalyst geometry within the treatment system.
This project primarily aims to optimise the photocatalytic effectiveness of PEO-processed titanium for use in this application by investigating the links between the coating composition and microstructure and the rate of photodegradation of a standard dye. The coating will be manipulated by altering first the processing parameters and coating conditions, then the electrolyte composition, maximising anatase content and exploring the addition of nanoparticles and dopants into the electrolyte.
The resulting PEO-processed samples will be tested for photocatalytic efficiency by addition into a UV water treatment system, provided by atg UV Technology, and measuring how exposure to the different coatings affects the rate of degradation of Methlyene Blue dye. The system, shown below (Fig. 1), comprises a medium pressure mercury lamp, reactor and transformer (supplied by atg UV Technology) a dye reservoir, a circulation pump and a cooling coil immersed in a cooling reservoir.
Fig. 1 - UV Degradation Testing set-up
1. Choi, H.S., Elias; Dionysiou, Dionysios D., Photocatalytic TiO2 films and membranes for the development of efficient wastewater treatment and reuse systems. Desalination, 2007. 202(1-3): p. 199-206.
2. Zhang, Z.W., C-C; Zakaria, R; Ying, J Y, Role of Particle Size in Nanocrystalline TiO2-Based Photocatalysts. Journal of Physical Chemistry B, 1998. 102(52): p. 10871-10878.
3. Chaudhuri, R.G.P., S, Visible light induced photocatalytic activity of sulfur doped hollow TiO2 nanoparticles, synthesized via a novel route. Dalton Transactions, 2013. 43(14): p. 5526-5534.
4. Mirelman, L.K., J.A. Curran, and T.W. Clyne, The Production of Anatase-rich Photoactive Coatings by Plasma Electrolytic Oxidation. Surface and Coatings Technology, 2012. 207: p. 66-71.