title: Assessment of the roles of reactive oxygen species in the UV and visible light photocatalytic degradation of cyanotoxins and water taste and odor compounds using C-TiO2.
abstract: Visible light (VIS) photocatalysis has large potential as a sustainable water treatment process, however the reaction pathways and degradation processes of organic pollutants are not yet clearly defined. The presence of cyanobacteria cause water quality problems since several genera can produce potent cyanotoxins, harmful to human health. In addition, cyanobacteria produce taste and odor compounds, which pose serious aesthetic problems in drinking water. Although photocatalytic degradation of cyanotoxins and taste and odor compounds have been reported under UV-A light in the presence of TiO2, limited studies have been reported on their degradation pathways by VIS photocatalysis of these problematic compounds. The main objectives of this work were to study the VIS photocatalytic degradation process, define the reactive oxygen species (ROS) involved and elucidate the reaction mechanisms. We report carbon doped TiO2 (C-TiO2) under VIS leads to the slow degradation of cyanotoxins, microcystin-LR (MC-LR) and cylindrospermopsin (CYN), while taste and odor compounds, geosmin and 2-methylisoborneol, were not appreciably degraded. Further studies were carried-out employing several specific radical scavengers (potassium bromide, isopropyl alcohol, sodium azide, superoxide dismutase and catalase) and probes (coumarin) to assess the role of different ROS (hydroxyl radical OH, singlet oxygen (1)O2, superoxide radical anion [Formula: see text] ) in the degradation processes. Reaction pathways of MC-LR and CYN were defined through identification and monitoring of intermediates using liquid chromatography tandem mass spectrometry (LC-MS/MS) for VIS in comparison with UV-A photocatalytic treatment. The effects of scavengers and probes on the degradation process under VIS, as well as the differences in product distributions under VIS and UV-A, suggested that the main species in VIS photocatalysis is [Formula: see text] , with OH and (1)O2 playing minor roles in the degradation.
authors.affiliation: Laboratory of Catalytic - Photocatalytic Processes and Environmental Analysis, Institute of Nanoscience & Nanotechnology, National Center for Scientific Research "Demokritos", Patriarchou Grigoriou & Neapoleos, 15310, Agia Paraskevi, Athens, Greece.
authors.forename: Theodora
authors.initials: T
authors.lastname: Fotiou
authors.affiliation: Laboratory of Catalytic - Photocatalytic Processes and Environmental Analysis, Institute of Nanoscience & Nanotechnology, National Center for Scientific Research "Demokritos", Patriarchou Grigoriou & Neapoleos, 15310, Agia Paraskevi, Athens, Greece.
authors.forename: Theodoros M
authors.initials: TM
authors.lastname: Triantis
authors.affiliation: Water Quality Department, Athens Water Supply and Sewerage Company (EYDAP SA), Oropou 156, 11146, Galatsi, Athens, Greece.
authors.forename: Triantafyllos
authors.initials: T
authors.lastname: Kaloudis
authors.affiliation: Department Chemistry and Biochemistry, Florida International University, Miami, FL, 33199, USA.
authors.forename: Kevin E
authors.initials: KE
authors.lastname: O'Shea
authors.affiliation: Environmental Engineering and Science Program, Department of Biomedical, Chemical and Environmental Engineering (DBCEE), University of Cincinnati, Cincinnati, OH, 45221-0012, USA.
authors.forename: Dionysios D
authors.initials: DD
authors.lastname: Dionysiou
authors.affiliation: Laboratory of Catalytic - Photocatalytic Processes and Environmental Analysis, Institute of Nanoscience & Nanotechnology, National Center for Scientific Research "Demokritos", Patriarchou Grigoriou & Neapoleos, 15310, Agia Paraskevi, Athens, Greece. Electronic address: a.hiskia@inn.demokritos.gr.
authors.forename: Anastasia
authors.initials: A
authors.lastname: Hiskia
mesh_terms: D000470:Alkaloids; D001427:Bacterial Toxins / Q000737:chemistry*; D001892:Camphanes / Q000737:chemistry; D002384:Catalysis; D000458:Cyanobacteria; D000087522:Cyanobacteria Toxins; D016166:Free Radical Scavengers / Q000737:chemistry; D008027:Light; D008387:Marine Toxins; D052998:Microcystins / Q000737:chemistry; D009284:Naphthols / Q000737:chemistry; D009812:Odorants; D010782:Photolysis; D017382:Reactive Oxygen Species / Q000737:chemistry*; D013649:Taste; D014025:Titanium / Q000737:chemistry*; D014466:Ultraviolet Rays; D014498:Uracil / Q000031:analogs & derivatives / Q000737:chemistry; D014874:Water Pollutants, Chemical / Q000737:chemistry*; D018508:Water Purification / Q000379:methods*
chemical_list: D000470:Alkaloids; D001427:Bacterial Toxins; D001892:Camphanes; D000087522:Cyanobacteria Toxins; D016166:Free Radical Scavengers; D008387:Marine Toxins; D052998:Microcystins; D009284:Naphthols; D017382:Reactive Oxygen Species; D014874:Water Pollutants, Chemical; C009495:titanium dioxide; C005536:2-methylisoborneol; C089595:cylindrospermopsin; D014498:Uracil; D014025:Titanium; C057862:cyanoginosin LR; C001278:geosmin
keywords: Cyanotoxins; Intermediate products; Reactive oxygen species; Titanium dioxide; Visible light photocatalysis