Graduation Year

2015

Document Type

Dissertation

Degree

Ph.D.

Degree Name

Doctor of Philosophy (Ph.D.)

Department

Chemical Engineering

Degree Granting Department

Chemical and Biomedical Engineering

Major Professor

D. Yogi Goswami, Ph.D.

Co-Major Professor

John Kuhn, Ph.D.

Committee Member

John Kuhn, Ph.D.

Committee Member

Babu Joseph, Ph.D.

Committee Member

Elias Stefanakos, Ph.D.

Committee Member

Manoj K. Ram, Ph.D.

Committee Member

Sarina Ergas, Ph.D.

Keywords

Optimization, Phenol, Photocatalysis, Titanium, Zinc oxide

Abstract

Growing demand and shortages of potable water sources due to industrialization have become a great concern worldwide. Various approaches and solutions have been adopted to provide cleaner and quality water. In a preliminary study, a method of treating wastewater was investigated in which algae were used to remove nutrients (nitrogen and phosphorous) from wastewater and then the algae were harvested for use as a biofuel. The results from this investigation are included in the Appendix B. Employing traditional oxidants, such as hydrogen peroxide, chlorine, and ozone, for treatment of recalcitrant organic compounds have achieved less promising results. However, photocatalysis, an advanced oxidation process (AOP), which is a low-cost and high-efficiency technique, has been widely recognized as a promising approach for water purification and elimination of organic constituents in wastewater. Photocatalysis is the increase in the rate of a chemical reaction by employing a catalyst in the presence of photons. Generally, for a high performance photocatalyst, light of appropriate wavelength is used to activate a catalyst in close contact with contaminants, thereby modifying the rate of the reaction. The presence of these contaminants could pose potential health and environmental concerns, especially in a controlled environment such as on a space station or during long-term manned missions. Thus, the development of energy efficient and "green" technologies to reduce or eliminate organic constituents in wastewater has important potential applications.

This research investigated the supported semiconductor photocatalysts (TiO2 and ZnO), particularly ZnO nanorods and nanowires, their synthesis methods, properties and corresponding effectiveness in photocatalysis. The effect of transition metal co-catalysts on the photocatalytic properties of TiO2 was investigated. Although TiO2 is the most extensively studied photocatalyst for water decontamination, ZnO, as presented in this work, could be a substitute because of its lower cost, relative energy bandgap and higher visible light photoactivity. Both photocatalysts were doped and screened for the decomposition of model contaminates, rhodamine B (RhB), phenol and methyl orange, under ultraviolet and/or visible light irradiation. In the photodegradation of RhB, TiO2/Ru 1% showed a superior photocatalytic activity relative to P25-TiO2 under broad-band irradiation, while doped ZnO-Ag resulted in better photodegradation of methyl orange, compared to P25-TiO2, under visible light irradiation.

The morphology and estimated chemical composition of photocatalysts were determined by energy dispersive spectroscopy (EDS) and scanning electron microscopy (SEM). Brunhauer, Emmett and Teller (BET) analysis was utilized to measure mass-specific surface area(s). A X-ray diffraction (XRD) study was carried out to confirm the identity of photocatalyst phase(s) present. The cause of low photocatalytic activity under an inert atmosphere, the simple effective fabrication technique of doped ZnO nanowires over TiO2 and properties of the photocatalyst are also discussed.

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