title: Sequential Process Combination of Photocatalytic Oxidation and Dark Reduction for the Removal of Organic Pollutants and Cr(VI) using Ag/TiO2.
abstract: We investigated a sequential photocatalysis-dark reaction, wherein organic pollutants were degraded on Ag/TiO2under UV irradiation and the dark reduction of hexavalent chromium (Cr(VI)) was subsequently followed. The photocatalytic oxidation of 4-chlorophenol (4-CP), a test organic substrate, induced the generation of degradation intermediates and the storage of electrons in Ag/TiO2which were then utilized for reducing Cr(VI) in the postirradiation period. The dark reduction efficiency of Cr(VI) was much higher with Ag/TiO2(87%), compared with bare TiO2(27%) and Pt/TiO2(22%). The Cr(VI) removal by Ag/TiO2(87%) was contributed by adsorption (31%), chemical reduction by intermediates of 4-CP degradation (26%), and reduction by electrons stored in Ag (30%). When formic acid, humic acid or ethanol was used as an alternative organic substrate, the electron storage effect was also observed. The postirradiation removal of Cr(VI) on Ag/TiO2continued for hours, which is consistent with the observation that a residual potential persisted on the Ag/TiO2electrode in the dark whereas little residual potential was observed on bare TiO2and Pt/TiO2electrodes. The stored electrons in Ag/TiO2and their transfer to Cr(VI) were also indicated by the UV-visible absorption spectral change. Moreover, the electrons stored in the preirradiated Ag/TiO2reacted with O2with showing a sign of low-level OH radical generation in the dark period.
authors.affiliation: Department of Chemical Engineering and Division of Environmental Science and Engineering, Pohang University of Science and Technology (POSTECH) , Pohang, Korea 37673.
authors.forename: Yeoseon
authors.initials: Y
authors.lastname: Choi
authors.affiliation: Department of Chemical Engineering and Division of Environmental Science and Engineering, Pohang University of Science and Technology (POSTECH) , Pohang, Korea 37673.
authors.forename: Min Seok
authors.initials: MS
authors.lastname: Koo
authors.affiliation: Department of Chemical Engineering and Division of Environmental Science and Engineering, Pohang University of Science and Technology (POSTECH) , Pohang, Korea 37673.
authors.forename: Alok D
authors.initials: AD
authors.lastname: Bokare
authors.affiliation: Department of Chemical Engineering and Division of Environmental Science and Engineering, Pohang University of Science and Technology (POSTECH) , Pohang, Korea 37673.
authors.forename: Dong-Hyo
authors.initials: DH
authors.lastname: Kim
authors.affiliation: Laboratory "Photoactive Nanocomposite Materials" Saint-Petersburg State University, Saint-Petersburg, Russia and "Photocatalysis and Nanotechnology", Institut fuer Technische Chemie, Gottfried Wilhelm Leibniz Universitaet Hannover , Hannover, Germany.
authors.forename: Detlef W
authors.initials: DW
authors.lastname: Bahnemann
authors.affiliation: Department of Chemical Engineering and Division of Environmental Science and Engineering, Pohang University of Science and Technology (POSTECH) , Pohang, Korea 37673.
authors.forename: Wonyong
authors.identifier: 0000-0003-1801-9386
authors.initials: W
authors.lastname: Choi
mesh_terms: D000327:Adsorption; D002384:Catalysis; D002857:Chromium; D004785:Environmental Pollutants / Q000737:chemistry / Q000528:radiation effects; D006812:Humic Substances; D010084:Oxidation-Reduction; D014025:Titanium; D014466:Ultraviolet Rays
chemical_list: D004785:Environmental Pollutants; D006812:Humic Substances; D002857:Chromium; D014025:Titanium