title: Chromate enhanced visible light driven TiO₂ photocatalytic mechanism on Acid Orange 7 photodegradation.
abstract: When hexavalent chromium (Cr(VI)) is added to a TiO2 photocatalytic reaction, the decolorization and mineralization efficiencies of azo dyes Acid Orange 7 (AO7) are enhanced even though the mechanism is unclear. This study used 5,5-dimethyl-l-pyrroline-N-oxide (DMPO) as the scavenger and the analysis of Electron Spin Resonance (ESR) to investigate this enhancement effect by observing the hydroxyl radical (OH) generation of the Cr(VI)/TiO2 system under UV and visible light (Vis) irradiation. With Cr(VI), the decolorization efficiencies were approximately 95% and 62% under UV and Vis, and those efficiencies were 25% less in the absence of Cr(VI). The phenomena of the DMPO-OH signals during the ESR analysis under Vis 405 and 550 nm irradiation were obviously the enhancement effects of Cr(VI) in aerobic conditions. In anoxic conditions, the catalytic effects of Cr(VI) could not be achieved due to the lack of a redox reaction between Cr(VI) and the adsorbed oxygen at the oxygen vacancy sites on the TiO2 surfaces. The results suggest that by introducing the agents of redox reactions such as chromate ions, we could lower the photoenergy of TiO2 needed and allow Vis irradiation to activate photocatalysis.
authors.affiliation: Graduate School of Engineering Science and Technology, National Yunlin University of Science and Technology (YunTech), Douliou, Yunlin, Taiwan.
authors.forename: Yeoung-Sheng
authors.initials: YS
authors.lastname: Wang
authors.affiliation: Graduate School of Engineering Science and Technology, National Yunlin University of Science and Technology (YunTech), Douliou, Yunlin, Taiwan.
authors.forename: Jyun-Hong
authors.initials: JH
authors.lastname: Shen
authors.affiliation: Department of Safety, Health and Environmental Engineering, National Yunlin University of Science and Technology (YunTech), Douliou, Yunlin, Taiwan. Electronic address: horngjj@gmail.com.
authors.forename: Jao-Jia
authors.initials: JJ
authors.lastname: Horng
mesh_terms: D001391:Azo Compounds / Q000737:chemistry*; D001557:Benzenesulfonates / Q000737:chemistry*; D002384:Catalysis; D002857:Chromium / Q000737:chemistry*; D004396:Coloring Agents / Q000737:chemistry*; D003497:Cyclic N-Oxides / Q000737:chemistry; D004578:Electron Spin Resonance Spectroscopy; D017665:Hydroxyl Radical / Q000737:chemistry; D008027:Light; D010782:Photolysis; D014025:Titanium / Q000737:chemistry* / Q000528:radiation effects; D014874:Water Pollutants, Chemical / Q000737:chemistry*; D018508:Water Purification
chemical_list: D001391:Azo Compounds; D001557:Benzenesulfonates; D004396:Coloring Agents; D003497:Cyclic N-Oxides; D014874:Water Pollutants, Chemical; D002857:Chromium; C009495:titanium dioxide; C074702:chromium hexavalent ion; D017665:Hydroxyl Radical; C069977:2,2-dimethyl-5-hydroxy-1-pyrrolidinyloxy; D014025:Titanium; C014722:2-naphthol orange
keywords: Electron spin resonance; Hexavalent chromium; Hydroxyl radical; TiO(2)