Year: 2014
Type: article
Abstract: 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.TiO 2 photocatalysis is one of the effective technologies for cyanotoxins treatment.This dissertation explored the potential of polymorphic TiO 2 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 TiO 2 photocatalyst (PM-TiO 2 , containing anatase, brookite, and rutile phases) under UV-Vis irradiation.The PM-TiO 2 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-TiO 2 and its environmental applications for CYN treatment.The reaction byproducts of CYN during the TiO 2 photocatalysis process were further studied using mass spectrometry.Since hydroxyl radical ( • OH) is considered to be the main reactive agent of TiO 2 photocatalysis, the reaction pathways were proposed based ABSTRACT ii 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 TiO 2 photocatalysis process.Moreover, the mechanistic effects of basic pH and carbonate ion on the TiO 2 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 (CO 3 •-), which can also induce CYN degradation but through different mechanisms.The second order rate constant of CO 3 •-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 TiO 2 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 adjusting the calcination temperature and adding sequence of doping precursor.Detailed characterization was applied on the synthesized catalysts.Moreover, the photocatalytic destruction of MC-LR using the catalysts was investigated under visible light.This work can be considered as a promising demonstration for the application of such visible light-ABSTRACT iii sensitized polymorphic TiO 2 in the treatment of cyanotoxins in water.
Author: Geshan Zhang
Institution: University of Cincinnati
Language: English
Field: Energy
Domain: Physical Sciences
Open Access status: green
Awards: G7944148144, G8320831949
OpenAlex ID: W2564982913