The combinatorial atmospheric pressure chemical vapour deposition (cAPCVD) of a gradating substitutional/interstitial N-doped anatase TiO2 thin-film; UVA and visible light photocatalytic activities

Combinatorial atmospheric pressure chemical vapour deposition (cAPCVD) was used to synthesise a film with gradating substitutional (N-s) and interstitial (N-i) nitrogen dopant concentrations across an anatase TiO2 thin-film. A transition from predominantly N-s-doped, to N-s/N-i mixtures, to purely N-i-doped titania was observed by X-ray photoelectron spectroscopy (XPS) analysis of positions across the film. We believe this to be the first time that such a gradient from N-i to N-s-doping has been achieved by a CVD process in a single film. The film was characterized by X-ray diffraction, Raman, and atomic force microscopy. Film thicknesses and bandgap energies were calculated from Swanepoel and Tauc plot manipulations of transmittance spectra. The photocatalytic activity to UVA (365 nm = 1.75 mW cm(-2)) light was assessed by monitoring colour changes in digital images of an even layer of intelligent ink deposited by an aerosol-spray method and by UV-visible spectroscopic assessment of the degradation of an aqueous methylene blue dye. The photo-activity to visible light (indoor white light source) was assessed by monitoring the degradation of a stearic acid over-layer. This allowed for the systematic investigation on the effect of N-s and/or N-i-doping in anatase TiO2 and the dopant concentration on the thin-film's photocatalytic activity. The results indicated that N-s-doping of anatase titania causes detriment to the film's photocatalytic activity to UVA-light. It was also found that purely N-i-doped anatase made a marginally more active visible light photocatalyst than predominantly N-s-doping. The differences were related to increased recombination effects in N-s-doped systems versus N-i-doped systems. Films synthesized by the cAPCVD route analysed in conjunction with mapping analysis tools provide a shortcut to identifying numerous phases and compositions and their functional property relationships on a single film, offering a rapid method for analysis of phase-space. (C) 2010 Elsevier B.V. All rights reserved.