Abstract
Bi2O3 nanocone films functionalized with an overlayer of TiO2 were deposited by d.c. reactive magnetron sputtering. The aforementioned nanocone structures were formed via a vapour-liquid-solid (VLS) growth, starting from a catalytic bismuth seed layer. The resultant nanocones exhibit an improved surface area, measured by atomic force microscopy, when compared to non-VLS deposition of the same metal oxide. X-ray diffraction texture analysis enabled the determination of the crystallographic β-phase of Bi2O3. A very thin TiO2 overlayer (6 nm thick), undoped and doped with nitrogen, was deposited onto the nanocones template, in order to functionalize these structures with a photocatalytic, self-cleaning, cap material. N-doped TiO2 overlayers increased the selective absorption of visible light due to nitrogen doping in the anatase cell, thus, resulting in a concomitant increase in the overall photocatalytic efficiency.
Highlights
Photocatalytic materials are commonly used in the industry for water and air de-pollution systems [1,2]
An opportunity has arisen in recent years to enhance the absorption of visible light in TiO2 [1,14,15]
Reactive oxygen gas was introduced with a partial pressure of 0.14 Pa for the Bi2 O3 layer, while maintaining all other deposition process parameters constant (Table 1)
Summary
Photocatalytic materials are commonly used in the industry for water and air de-pollution systems [1,2]. In the majority of cases, these photocatalytic processes involve the illumination of a semiconductor material with ultraviolet (UV) light [3,4] From this activation, hydroxyl radicals with a high oxidation potential are created from the inherent oxidation-reduction mechanisms on the photocatalyst surface [5], which lead to the mineralisation of adsorbed pollutants. Anionic doping of TiO2 has proven to have a positive effect on the absorption of visible light, in particular, substitutional of oxygen atoms in the anatase cell for nitrogen atoms [6,16,17] This anionic doping is efficient as long as the O 2p and N 2p orbitals overlap in the valence band, in order to inhibit the formation of defect levels inside the gap, which are active recombination centres.
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