Analytica Chimica Acta 663 (2010) 69–76 Contents lists available at ScienceDirect Analytica Chimica Acta journal homepage: www.elsevier.com/locate/aca A comprehensive aerosol spray method for the rapid photocatalytic grid area analysis of semiconductor photocatalyst thin films Andreas Kafizas a , Andrew Mills b , Ivan P. Parkin a,∗ a Department of Chemistry, University College London, 20 Gordon Street, London WC1H 0AJ, UK b Department of Pure and Applied Chemistry, University of Strathclyde Glasgow, 16 Richmond Street, Glasgow G1 1XQ, UK article info Article history: Received 28 October 2009 Received in revised form 5 January 2010 Accepted 8 January 2010 Available online 18 January 2010 Keywords: Photocatalysis area Thin film Aerosol Mapping method Rapid abstract Indicator inks, previously shown to be capable of rapidly assessing photocatalytic activity via a novel photo-reductive mechanism, were simply applied via an aerosol spray onto commercially available pieces of Activ TM self-cleaning glass. Ink layers could be applied with high evenness of spread, with as little deviation as 5% upon UV–visible spectroscopic assessment of 25 equally distributed positions over a 10 cm × 10 cm glass cut. The inks were comprised of either a resazurin (Rz) or dichloroindophenol (DCIP) redox dye with a glycerol sacrificial electron donor in an aqueous hydroxyethyl cellulose (HEC) polymer media. The photo-reduction reaction under UVA light of a single spot was monitored by UV–vis spec- troscopy and digital images attained from a flat-bed scanner in tandem for both inks. The photo-reduction of Rz ink underwent a two-step kinetic process, whereby the blue redox dye was initially reduced to a pink intermediate resorufin (Rf) and subsequently reduced to a bleached form of the dye. In contrast, a simple one-step kinetic process was observed for the reduction of the light blue redox dye DCIP to its bleached intermediates. Changes in red–green–blue colour extracted from digital images of the inks were inversely proportional to the changes seen at corresponding wavelengths via UV–visible absorption spectroscopy and wholly indicative of the reaction kinetics. The photocatalytic activity areas of cuts of Activ TM glass, 10 cm × 10 cm in size, were assessed using both Rz and DCIP indicator inks evenly sprayed over the films; firstly using UVA lamp light to activate the underlying Activ TM film (1.75 mW cm -2 ) and secondly under solar conditions (2.06 ± 0.14 mW cm -2 ). The photo-reduction reactions were monitored solely by flat- bed digital scanning. Red–green–blue values of a generated 14 × 14 grid (196 positions) that covered the entire area of each film image were extracted using a custom-built program entitled RGB Extractor(C). A homogenous degradation over the 196 positions analysed for both Rz (Red colour deviation = 19% UVA, 8% Solar; Green colour deviation = 17% UVA, 12% Solar) and DCIP (Red colour deviation = 22% UVA, 16% Solar) inks was seen in both UVA and solar experiments, demonstrating the consistency of the self- cleaning titania layer on Activ TM . The method presented provides a good solution for the high-throughput photocatalytic screening of a number of homogenous photocatalytically active materials simultaneously or numerous positions on a single film; both useful in assessing the homogeneity of a film or determining the best combination of reaction components to produce the optimum performance photocatalytic film. © 2010 Elsevier B.V. All rights reserved. 1. Introduction Anatase titanium dioxide (TiO 2 ) has become the foremost semiconductor material for semiconductor photocatalysis (SPC) applications due to its biological and chemical inertness, mechani- cal robustness to copious photocatalytic cycles, physical durability, relatively low cost and high activity [1]. When titania is irradiated with UV-light (typically  ≤ 388 nm), an electron is promoted from the semiconductor’s valence band to its conduction band, thereby simultaneously creating a hole in the valence band. Although this ∗ Corresponding author. Tel.: +44 020 7679 4669; fax: +44 020 7679 7463. E-mail address: i.p.parkin@ucl.ac.uk (I.P. Parkin). electron–hole pair is formed within the bulk, it is capable of migrat- ing to the surface where the photogenerated electrons can reduce atmospheric O 2 to superoxide O 2 - , which can be subsequently further reduced to H 2 O. Photogenerated holes can oxidise surface- bound hydroxyl groups to highly reactive hydroxyl radical species. These radicals, in turn, are capable of oxidising a range of organic pollutants into mineral acids and CO 2 . A summary of this process is shown below: Organic pollutant + O 2 Semiconductor -→ h ≥ E bg CO 2 + H 2 O + Mineral acids (1) where E bg is the band-gap energy of the semiconductor; typically ca. 3.0 eV for anatase TiO 2 . 0003-2670/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.aca.2010.01.022