title: Colorimetric Detection of an Airborne Remote Photocatalytic Reaction Using a Stratified Ag Nanoparticle Sheet.
abstract: Photocatalysts are practically used for decomposition of harmful and fouling organic compounds. Among the photocatalytic reactions, remote oxidation via airborne species is a relatively slow process, so that a sensitive technique for its detection has been awaiting. Here, we investigated an airborne remote photocatalytic reaction of a TiO2 photocatalyst modified with Pt nanoparticles as co-catalysts via the color change caused by a decomposition of a multilayered silver nanoparticle sheet. The silver nanoparticle sheet fabricated by the Langmuir-Schaefer method on a gold substrate exhibits a unique multicolor depending upon the number of layers. The color originates from multiple light trapping in the stratified sheets that has a metamaterial characteristic along with an intra- and interlayer coupling of localized surface plasmon resonance (LSPR). The stepwise decomposition of the sheets was confirmed by the colorimetric data, which exhibited not only a monotonic decrease but also a maximized absorption of light when the film thickness reached the optimal thickness for light trapping or when the oxidation of the Ag core started. Scanning electron microscopy (SEM), atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), and surface plasmon resonance (SPR) spectroscopy data provided a complete view of the decomposition process of this inorganic-organic nanocomposite film, and simulation by the transfer-matrix method explained a simultaneous plasmonic response rationally. The influence of the humidity and gas flow rate on the airborne remote photocatalytic reaction kinetics was examined by this colorimetric detection method, and it suggests that H2O in air plays an essential role in the reaction.
authors.forename: Ryo
authors.initials: R
authors.lastname: Degawa
authors.forename: Pangpang
authors.initials: P
authors.lastname: Wang
authors.affiliation: Department of Electrical and Electronic Engineering, National Institute of Technology, Oita College , Oita 870-0152, Japan.
authors.forename: Daisuke
authors.initials: D
authors.lastname: Tanaka
authors.affiliation: Institute of Industrial Science, The University of Tokyo , Komaba, Meguro-ku, Tokyo 153-8505, Japan.
authors.forename: Susie
authors.initials: S
authors.lastname: Park
authors.affiliation: Institute of Industrial Science, The University of Tokyo , Komaba, Meguro-ku, Tokyo 153-8505, Japan.
authors.forename: Nobuyuki
authors.initials: N
authors.lastname: Sakai
authors.affiliation: Institute of Industrial Science, The University of Tokyo , Komaba, Meguro-ku, Tokyo 153-8505, Japan.
authors.forename: Tetsu
authors.initials: T
authors.lastname: Tatsuma
authors.forename: Koichi
authors.initials: K
authors.lastname: Okamoto
authors.forename: Kaoru
authors.initials: K
authors.lastname: Tamada