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University of Cincinnati

1. Zhang, Geshan. The Degradation of Cyanotoxins by using Polymorphic Titanium Dioxide Based Catalysts.

Degree: PhD, Engineering and Applied Science: Environmental Science, 2014, University of Cincinnati

Cyanotoxins, a family of emerging contaminants, have become a great public and environmental concern due to their extremely high toxicity and widespread presence of cyanotoxin-producing bacteria in aquatic systems. Cyanotoxins and cyanobacteria have been included in the Drinking Water Contaminant Candidate List (CCL 1 and 2) by U.S. Environment Protection Agency (EPA). Cylindrospermopsin (CYN) and microcystin-LR (MC-LR) are two of most commonly found cyanotoxins and have been listed in the newest CCL 3, along with anatoxin-a. TiO2 photocatalysis is one of the effective technologies for cyanotoxins treatment. This dissertation explored the potential of polymorphic TiO2 based photocatalysts for the degradation of cyanotoxins as well as the corresponding reaction mechanisms. The photocatalytic destruction of CYN was investigated using a novel polymorphic TiO2 photocatalyst (PM- TiO2, containing anatase, brookite, and rutile phases) under UV-Vis irradiation. The PM-TiO2 was characterized using several characterization techniques. The impacts of operation parameters, such as photocatalyst loading, pH and presence of natural organic matter, on the treatment efficiency were also examined in this work. The finding of this work can provide fundamental information for the properties of PM-TiO2 and its environmental applications for CYN treatment. The reaction byproducts of CYN during the TiO2 photocatalysis process were further studied using mass spectrometry. Since hydroxyl radical (•OH) is considered to be the main reactive agent of TiO2 photocatalysis, the reaction pathways were proposed based on hydroxyl radical chemistry and detected reaction byproducts. Hydroxylation, sulfate elimination and ring opening reactions on the hydroxymethyl uracil moiety and tricyclic guanidine moiety were proposed to be the main reaction mechanisms of photocatalytic reaction. Besides, detoxification studies based on the cytotoxicity of CYN proved the effective toxicity removal of CYN-contaminated water during TiO2 photocatalysis process.Moreover, the mechanistic effects of basic pH and carbonate ion on the TiO2 photocatalytic degradation of CYN were investigated based on the different reaction kinetics and byproducts observed in the systems. We found high pH can inhibit sulfate elimination, although the main reaction mechanism is still based on •OH. When carbonate ion was in the system, it can compete with CYN and react with •OH to form carbonate radical (CO3•-), which can also induce CYN degradation but through different mechanisms. The second order rate constant of CO3•- with CYN was estimated in the work. This part of the study can further support the complete assessment of CYN removal using photocatalysis process.Motivated from the dependence of normal TiO2 photocatalyst on the UV light, visible light-sensitized S, N and C co-doped polymorphic titanium dioxide photocatalysts were synthesized through a modified sol-gel method followed by calcination, using thiourea as the precursor for the dopants. The photocatalyst were optimized by… Advisors/Committee Members: Dionysiou, Dionysios (Committee Chair).

Subjects/Keywords: Environmental Science; Cylindrospermopsin; Microcystin-LR; Photocatalytic degradation; Polymorphic TiO2; Reaction byproduct; Reaction pathway

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APA · Chicago · MLA · Vancouver · CSE | Export to Zotero / EndNote / Reference Manager

APA (6th Edition):

Zhang, G. (2014). The Degradation of Cyanotoxins by using Polymorphic Titanium Dioxide Based Catalysts. (Doctoral Dissertation). University of Cincinnati. Retrieved from http://rave.ohiolink.edu/etdc/view?acc_num=ucin1406810827

Chicago Manual of Style (16th Edition):

Zhang, Geshan. “The Degradation of Cyanotoxins by using Polymorphic Titanium Dioxide Based Catalysts.” 2014. Doctoral Dissertation, University of Cincinnati. Accessed November 22, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1406810827.

MLA Handbook (7th Edition):

Zhang, Geshan. “The Degradation of Cyanotoxins by using Polymorphic Titanium Dioxide Based Catalysts.” 2014. Web. 22 Nov 2019.

Vancouver:

Zhang G. The Degradation of Cyanotoxins by using Polymorphic Titanium Dioxide Based Catalysts. [Internet] [Doctoral dissertation]. University of Cincinnati; 2014. [cited 2019 Nov 22]. Available from: http://rave.ohiolink.edu/etdc/view?acc_num=ucin1406810827.

Council of Science Editors:

Zhang G. The Degradation of Cyanotoxins by using Polymorphic Titanium Dioxide Based Catalysts. [Doctoral Dissertation]. University of Cincinnati; 2014. Available from: http://rave.ohiolink.edu/etdc/view?acc_num=ucin1406810827

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