The photocatalytic behavior of titania coatings is largely determined by their crystalline structure. Depending on deposition conditions, though, titania may form amorphous, brookite, anatase or rutile structures, with anatase or anatase/rutile mixed phase structures showing the highest levels of activity. Anatase is activated by UV light and, consequently, there is a great deal of interest in doping titania films to both increase activity and extend it into the visible range. In this study, titania and doped titania coatings have been deposited from blended oxide powder targets. This highly versatile and economical technique allows dopant levels to be readily varied. Using this technique, titania coatings doped with W, Nb and ZnFe2O4 have been deposited onto glass substrates by pulsed magnetron sputtering. The as-deposited coatings were analyzed by scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX) and micro-Raman spectroscopy. Selected coatings were then annealed at temperatures in the range of 400–700 °C and re-analyzed. Structural transformation of the titania coatings was initiated in the 500–600 °C range, with the coatings annealed at 700 °C having predominantly anatase structures. The photocatalytic activity of the coatings was assessed through measurements of the degradation of organic dyes, such as methyl orange, under the influence of UV and fluorescent light sources. It was found that, after annealing, coatings with photo-active surfaces were produced and that activity varied with dopant content. Activity levels under fluorescent light irradiation were up to 60% of the activity measured under UV irradiation.
References
[1]
Gloss, D.; Frach, P.; Zywitzki, O.; Klinkenberg, S.; Gottfried, C. Photocatalytic titanium dioxide thin films prepared by reactive pulse magnetron sputtering at low temperature. Surf. Coat. Technol. 2005, 200, 967–971, doi:10.1016/j.surfcoat.2005.01.018.
[2]
Salvador, P. Sub-bandgap photoresponse of n-TiO2 electrodes: Transient photocurrent-time behaviour. Surf. Sci. 1987, 192, 36–46, doi:10.1016/S0039-6028(87)81160-3.
[3]
Mahdjoub, N.; Allen, N.; Kelly, P.; Vishnyakov, V.; Photochem, J. SEM and Raman study of thermally treated TiO2 anatase nanopowders: Influence of calcination on photocatalytic activity. J. Photochem. Photobiol. Chem. 2010, 211, 59–64, doi:10.1016/j.jphotochem.2010.02.002.
[4]
Fujishima, A.; Honda, K. Electrochemical photolysis of water at a semiconductor electrode. Nature 1972, 238, 37–38, doi:10.1038/238037a0.
[5]
Allen, N.S.; Edge, M.; Verran, J.; Stratton, J.; Maltby, J.; Bygott, C. Photocatalytic titania based surfaces: Environmental benefits. Polym. Degrad. Stab. 2008, 93, 1632–1646, doi:10.1016/j.polymdegradstab.2008.04.015.
[6]
Mills, A.; Le Hunte, S. An overview of semiconductor photocatalysis. J. Photochem. Photobiol. Chem. 1997, 108, 1–35, doi:10.1016/S1010-6030(97)00118-4.
[7]
Tavares, C.J.; Marques, S.; Lanceros-Mendez, S.; Sencadas, V.; Teixeira, V.; Carneiro, J.O.; Martins, A.J.; Fernandes, A.J. Strain analysis of photocatalytic TiO2 thin films on polymer substrates. Thin Solid Films 2008, 516, 1434–1438, doi:10.1016/j.tsf.2007.03.134.
[8]
Yates, H.M.; Brook, L.A.; Ditta, I.B.; Evans, P.; Foster, H.A.; Sheel, D.W.; Steele, A. Photo-induced self-cleaning and biocidal behaviour of titania and copper oxide multilayers. J. Photochem. Photobiol. Chem. 2008, 197, 197–205, doi:10.1016/j.jphotochem.2007.12.023.
[9]
Zhang, W.; Li, Y.; Zhu, S.; Wang, F. Fe-doped photocatalytic TiO2 film prepared by pulsed DC reactive magnetron sputtering. J. Vac. Sci. Technol. A Vac. Surf. Films 2003, 21, 1877–1882, doi:10.1116/1.1615973.
[10]
Wade, J. An investigation of TiO2-ZnFe2O4 nanocomposites for visible light photocatalysis. Master’s Thesis, University of South Florida, Tampa, FL, USA, 24 March 2005.
[11]
Zhao, L.; Jiang, Q.; Lian, J. Visible-light photocatalytic activity of nitrogen-doped TiO2 thin film prepared by pulsed laser deposition. Appl. Surf. Sci. 2008, 254, 4620–4625, doi:10.1016/j.apsusc.2008.01.069.
[12]
Rampaul, A.; Parkin, I.P.; O’Neill, S.A.; De Souza, J.; Mills, A.; Elliot, N. Titania and tungsten doped titania thin films on glass; active photocatalysts. Polyhedron 2003, 22, 35–44, doi:10.1016/S0277-5387(02)01333-5.
[13]
Park, S.E.; Joo, H.; Kang, J.W. Effect of impurities in TiO2 thin films on trichloroethylene conversion. Sol. Energy Mater. Sol. Cells 2004, 83, 39–53, doi:10.1016/j.solmat.2004.02.012.
[14]
Kelly, P.J.; Zhou, Y. Zinc oxide-based transparent conductive oxide films prepared by pulsed magnetron sputtering from powder targets: Process features and film properties. J. Vac. Sci. Technol. A Vac. Surf. Films 2006, 24, 1782–1789, doi:10.1116/1.2218857.
[15]
Farahani, N.P.; Kelly, J.; West, G.; Ratova, M.; Hill, C.; Vishnyakov, V. Photocatalytic activity of reactively sputtered and directly sputtered titania coatings. Thin Solid Films 2011, 520, 1464–1469, doi:10.1016/j.tsf.2011.09.059.
[16]
Kelly, P.J.; Onifade, A.A.; Zhou, Y.; Clarke, G.C.B.; Audronis, M.J.; Bradley, W. The influence of pulse frequency and duty on the deposition rate in pulsed magnetron sputtering. Plasma Process. Polym. 2007, 4, 246–252, doi:10.1002/ppap.200600159.
[17]
Mills, A.; McGrady, M. A study of new photocatalyst indicator inks. J. Photochem. Photobiol. A Chem. 2008, 193, 228–236, doi:10.1016/j.jphotochem.2007.06.029.
[18]
Evans, P.; Mantke, S.; Mills, A.; Robinson, A.; Sheel, D.W. A comparative study of three techniques for determining photocatalytic activity. J. Photochem. Photobiol. A Chem. 2007, 188, 387–391, doi:10.1016/j.jphotochem.2006.12.040.
