Date of Award

Summer 2021

Level of Access Assigned by Author

Open-Access Thesis

Degree Name

Doctor of Philosophy (PhD)

Department

Chemistry

Advisor

Aria Amirbahman

Second Committee Member

Carl P. Tripp

Third Committee Member

Scott Collins

Additional Committee Members

Brian G. Frederick

Douglas W. Bousfield

Abstract

Ultraviolet (UV) radiation application in water and wastewater treatment has become a common approach for inactivation of protozoa and other pathogenic microorganisms. However, degradation of most organic compounds, such as taste and odor products prevalent in surface waters, has not been proven effective with direct UV photolysis. Advanced oxidation processes (AOPs) that involve efficient photocatalysts like TiO2 show an advantage over direct UV photolysis providing fast reaction rates and non-selective oxidation of contaminants. However, the real-world application of TiO2 in water and wastewater treatment is limited due to difficulties in separating the suspended nanosized particles following treatment, the relatively high charge carrier recombination effect, and the low absorption of visible light due to the wide bandgap of TiO2. This study has developed two different TiO2-based photocatalysts that address these limitations. In the first study, an AEROXIDE® P25 TiO2 powder-modified immobilized catalyst was developed using a glass substrate to degrade common algal taste and odor compounds 2-methylisoborneol (MIB) and geosmin (GSM) under UV-A (350 nm) irradiation. Attachment of the photocatalyst particles on the substrate was improved by incorporating a TiO2-SiO2 sol-gel mixture as the binder and optimizing the Si concentration of the catalyst film to achieve superior robustness while maintaining a high photocatalytic activity. Catalyst films with a surface Ti:Si ratio ≈ 7 showed similar degradations rates but better robustness compared to immobilized P25 films. In the second study, a bismuth-titanate heterostructure composite containing a Bi2O3/Bi4Ti3O12/TiO2 mixture that showed visible light activity and a better charge carrier separation was developed. Heterostructure composition was optimized by incorporating the nonionic surfactant Tween-80 and varying the Bi concentration to achieve efficient photodegradation of phenol under visible light (420 nm) illumination. The catalyst with a Bi2O3:TiO2:Bi4Ti3O12 ratio = 1:7:15 showed the highest photocatalytic activity. The UV active P25-modified TiO2-SiO2 film and visible light active bismuth-titanate heterostructure composite catalysts developed in this study showed promising efficacy with respect to photocatalytic degradation of organic pollutants. Future studies may consider a combination of the P25 modified TiO2-SiO2 catalyst film and bismuth-titanate heterostructure composite to extend the catalyst activity to a wide spectrum of electromagnetic energy. Further, pilot-scale application of these photocatalysts can assess their efficacy in drinking water treatment facilities.

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