Abstract
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.
Highlights
A large number of studies have been published on the use of TiO2 as a photocatalyst for the decomposition of organic compounds or molecules [1,2,3,4,5]
In a set of experiments, pure and doped-titania coatings were deposited by directly sputtering oxide powder targets
The as-deposited coatings were analyzed by scanning electron microscopy (SEM—Zeiss Supra 40), energy dispersive X-ray spectroscopy (EDX—Edax Trident), and micro-Raman spectroscopy (Renishaw Invia, 514 nm laser)
Summary
A large number of studies have been published on the use of TiO2 as a photocatalyst for the decomposition of organic compounds or molecules [1,2,3,4,5]. This generates electron-hole pairs that can migrate to the surface of the titania and promote oxidation/reduction reactions, creating radical species, which can degrade pollutant organic compounds [7,8,9]. The coatings were deposited by mid-frequency pulsed magnetron sputtering directly from blended oxide powder targets [14] This approach has been demonstrated by the present authors as an efficient way of screening candidate materials and identifying optimum compositions for multi-component coatings. It provides an economic way of testing dopant materials before employing a full size ‘solid’ sputtering target [14] and has been shown to produce surfaces with photocatalytic activities very close to similar coatings produced by conventional reactive sputtering techniques [15]
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