title: The effect of basic pH and carbonate ion on the mechanism of photocatalytic destruction of cylindrospermopsin.
abstract: This study investigated the mechanistic effects of basic pH and the presence of high carbonate concentration on the TiO2 photocatalytic degradation of the cyanobacterial toxin cylindrospermopsin (CYN). High-performance liquid chromatography combined with quadrupole time-of-flight electrospray ionization tandem mass spectrometry (LC/Q-TOF-ESI-MS) was employed for the identification of reaction byproducts. The reaction pathways were proposed based on the identified degradation byproducts and radical chemistry. In high pH system (pH = 10.5) similar reaction byproducts as those in neutral pH system were identified. However, high pH appeared to inhibit sulfate elimination with less sulfate elimination byproducts detected. In the presence of carbonate in the photocatalytic process, hydroxyl radical reaction would be largely inhibited since carbonate ion would react with hydroxyl radical to form carbonate radical. The second order rate constant of carbonate radical with CYN was estimated to be 1.4 × 10(8) M(-1)s(-1), which is much smaller than that of hydroxyl radical. However, the more significant abundance of carbonate radical in the reaction solution strongly contributed to the transformation of CYN. Carbonate radical has higher reaction selectivity than hydroxyl radical and hence, played a different role in the photocatalytic reaction. It would promote the formation of byproduct m/z 420.12 which has not been identified in the other two studied photocatalytic systems. Besides, the presence of carbonate ion may hinder the removal of toxicity originated from uracil moiety due to the low reaction activity of carbonate radical with uracil moiety in CYN molecule. This work would further support the application of photocatalytic technologies for CYN treatment and provide fundamental information for the complete assessment of CYN removal by using TiO2 photocatalysis process.
authors.affiliation: Environmental Engineering and Science Program, University of Cincinnati, Cincinnati, OH 45221, United States.
authors.forename: Geshan
authors.initials: G
authors.lastname: Zhang
authors.affiliation: Environmental Engineering and Science Program, University of Cincinnati, Cincinnati, OH 45221, United States.
authors.forename: Xuexiang
authors.initials: X
authors.lastname: He
authors.affiliation: College of Pharmacy, Sangolli Rayanna Nagar, Dharwad 580002, India.
authors.forename: Mallikarjuna N
authors.initials: MN
authors.lastname: Nadagouda
authors.affiliation: Department of Chemistry and Biochemistry, Florida International University, Miami, FL 33199, United States.
authors.forename: Kevin
authors.initials: K
authors.lastname: E O'Shea
authors.affiliation: Environmental Engineering and Science Program, University of Cincinnati, Cincinnati, OH 45221, United States. Electronic address: dionysios.d.dionysiou@uc.edu.
authors.forename: Dionysios D
authors.initials: DD
authors.lastname: Dionysiou
mesh_terms: D000470:Alkaloids; D001427:Bacterial Toxins; D002254:Carbonates / Q000032:analysis*; D002851:Chromatography, High Pressure Liquid; D000087522:Cyanobacteria Toxins; D006863:Hydrogen-Ion Concentration; D010782:Photolysis; D053719:Tandem Mass Spectrometry; D014025:Titanium / Q000737:chemistry*; D014498:Uracil / Q000031:analogs & derivatives* / Q000737:chemistry; D014865:Waste Disposal, Fluid; D014874:Water Pollutants, Chemical / Q000737:chemistry*
chemical_list: D000470:Alkaloids; D001427:Bacterial Toxins; D002254:Carbonates; D000087522:Cyanobacteria Toxins; D014874:Water Pollutants, Chemical; C009495:titanium dioxide; C089595:cylindrospermopsin; D014498:Uracil; D014025:Titanium
keywords: Basic pH; Byproduct; Carbonate radical; Cylindrospermopsin; Reaction pathway; Titanium dioxide photocatalytic degradation