Author ORCID Identifier

https://orcid.org/0000-0002-5037-7717

Date Available

5-18-2024

Year of Publication

2022

Degree Name

Doctor of Philosophy (PhD)

Document Type

Doctoral Dissertation

College

Arts and Sciences

Department/School/Program

Chemistry

First Advisor

Dr. Marcelo I. Guzman

Abstract

Natural and anthropogenic processes are emitting organic and inorganic pollutants, such as phenolic compounds, carbon dioxide (CO2), etc. in the atmosphere, which are increasing with time. In addition, to meet the energy demand of world’s growing population using nonrenewable fossil fuels are causing its depletion. Therefore, development of new technologies that can minimize atmospheric pollution and contribute to energy demand is imperative. Many methods or technologies have been developed for addressing those issues so far including advanced oxidation process, anaerobic biological treatments, and photocatalytic process. Among them, heterogenous semiconductor photocatalysis possesses clean and low-cost methodology and can simultaneously solve the problems of energy and environmental contamination. In this thesis, photocatalytic catechol (model pollutant) degradation with Degussa P25, a mixture of anatase and rutile phase of titanium dioxide (TiO2) and CO2 reduction with potassium and gallium-doped iron oxide (α-Fe2O3) are reported.

The research uses Degussa P25 to study the degradation of catechol at air-solid interface because of low cost, stability, and abundant sources of TiO2. Catechol forms a chelate with TiO2 and shows absorption band in visible range through ligand-to-metal charge-transfer (LMCT) transition. The photocatalytic activity of catechol degradation on TiO2 surface are reported irradiating at λcut-off ≥ 320 nm, 400 nm, and 515 nm. The generation of reactive oxygen species (hydroxyl radical, superoxide anion radical, singlet oxygen) and redox pairs has been studied with scavengers. The chemical fates of scavengers and selectivity are also reported. Finally, the apparent quantum efficiency (AQE) for catechol loss and CO2 and carbon monoxide (CO) growths are determined.

The amount of CO2 in the atmosphere can be minimized by reducing it to useful fuels photocatalytically. Potassium-doped iron oxide materials of varying potassium compositions (100 Fe:x K, 0 ≤ x ≤ 5) and calcination temperatures (400 °C, 500 °C, 600 °C, 700 °C, and 800 °C) are synthesized using incipient wetness impregnation method. The structure, composition, and properties of the catalysts are investigated by X-ray diffraction, thermal analysis and multiple spectroscopies, including: DRUV-vis, FTIR, Raman, ICP-AES, XPS and UPS, TEM with EDS and SAED. UV-visible light (λcut-off ≥ 295 nm) excites the catalysts in presence of pure CO2 or air (400 ppm CO2), both under a saturated water vapor atmosphere. The AQE for the CO(g) production shows maximum for 100 Fe:1 K. The surface-doped potassium photocatalyst enhances the photocatalytic efficiency by creating a more negative conduction band than the CO2/CO reduction potential. The role of potassium and nitrate has been explored. We also synthesize gallium-doped iron oxide using precipitation method with varying gallium compositions (100 Fe:x Ga, 0 x 5). The photocatalytic experiment similar to that of potassium-doped catalysts are performed. The material, 100 Fe:2 Ga shows greater reactivity creating a great scope for future studies.

The studies of pollutant degradation and CO2 reduction with TiO2 and α-Fe2O3, respectively at air-solid interface provides a pathway to minimize the atmospheric pollution and contribute to the energy. They create a path to study more for other applications in air purification, water splitting, fuel production, etc. and development of efficient semiconductor photocatalyst.

Digital Object Identifier (DOI)

https://doi.org/10.13023/etd.2022.164

Funding Information

The study was supported by a Faculty Early Career Development Program (CAREER) award from the National Science Foundation (CHE-1255290) to Dr. Marcelo I. Guzman in 2013, a National Science Foundation Grant (award 1903744) to Dr. Marcelo I. Guzman in 2019, a Research Challenge Trust Fund Fellowship from the Department of Chemistry, University of Kentucky to Md Ariful Hoque in 2020.

Available for download on Saturday, May 18, 2024

Share

COinS