Date of Award

Summer 8-23-2019

Level of Access Assigned by Author

Open-Access Thesis

Degree Name

Master of Science (MS)

Department

Ecology and Environmental Sciences

Advisor

Scott D. Collins

Second Committee Member

Robert D. Pike

Third Committee Member

Matthew P. Brichacek

Additional Committee Members

Sofian M. Kanan

Abstract

The focus of this thesis is to investigate the structural modification and characterization potential of common photocatalysts that have various uses for environmental remediation purposes. Pollution involving organic chemicals is one of the most common scenarios found in communities throughout the country. Efforts to rid contaminated drinking water supplies of these chemicals include physical and chemical filters, which have limited ability and efficacy. This lack of efficient filtration services has led to an increased demand for more effective treatment methods. Chemical species that react in the presence of light are known as photocatalysts and have been used in previous studies involving chemical reduction of pollutant species. Photocatalytic semiconductors have been investigated for their photochemical responses and ability to mineralize organic pollutants into unreactive species such as carbon dioxide. These photochemical responses have shown favorable in water treatment applications that utilize high energy irradiation sources. Previous studies have indicated complexes that contain bismuth were more efficient at photochemical reduction of organic pollutants as opposed to titanium centered species.

In this study, well known photocatalytic complexes were modified through the addition of d-block metallic species. Complexes comprised of primarily Bi(III) centers where synthesized due to their ubiquitous presence in enviornmental remediation efforts. Concerns over the long-term environmental presence of these catalysts led to the development of complexes such as the ones listed in this study that remain environmentally benign. Mechanistic investigations of catalysis pathways revealed the distribution of electrons was facilitated through single electron transfer (SET) mechanisms. Oxidation-reduction reactions involving molecules of the surrounding medium generated free radical species that facilitated the hydrolyzation of the target pollutants. Novel findings in this study include the “electron trap” effect of photophysically active d-block elements in the presence of a known catalyst. The modified compounds of TiO2 and BiOCl have demonstrated remarkable efficacy and durability in photocatalytic applications yet continue to encounter serious drawbacks in continual wastewater treatment efforts.

Several investigations were conducted throughout this study that determined the effectiveness of novel compounds in photocatalytic applications. To measure how these complexes react in the presence of various excitation sources, photoluminescence studies were performed to determine energetic pathways. Photodegradation experiments were conducted in aqueous solutions using both visible and ultraviolet irradiation sources. X-ray diffraction measurements on single crystal and powder samples were performed to corroborate the photophysical observations and physical structure. Transmission electron microscopy was used to measure photocatalyst size and morphology. Several visible light experiments were conducted throughout this study and only one compound, a halogenobismuth species, produced sufficient degradation results. The primary motivation for these studies were industrial drawbacks that led to the synthesis and design of photophysically active complexes which permitted solar utilization of ultraviolet and visible light. The addition of d10 metallic ions permitted increased proliferation of charge transfer mechanisms and formation of reactive radical species, which are the primary contenders in degradation through photocatalysis. These increased charge transfer mechanisms equate to sustain photodegradation and mineralization of organic species present. Our findings throughout this study enhance the experimental and mechanistic understandings of these metallic photocatalytic species in the use of environmental and wastewater treatment efforts.

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