Abstract
Solar energy, as an environmentally friendly and sustainable source of energy, is believed to be the future of mankind. To effectively utilize solar energy, photocatalysis, which converts solar energy into chemical energy, has garnered significant attention over the past years.Semiconductor photocatalysis is used in a wide range of applications, such as the treatment of water, pollutants, and industrial waste gases. In this thesis, density functional theory (DFT) calculations are conducted to investigate the oxidation mechanism of formaldehyde on several surfaces of TiO2. In addition, some key properties are analyzed to achieve a better understanding at a theoretical level.
Chapter 1 provides a literature review and general introduction to the topic of the thesis, while Chapter 2 gives a brief overview of the methods utilized in this study.
In Chapter 3, we conducted density functional theory (DFT) calculations with Hubbard-type corrections and the HSE06 function to investigate the photocatalytic oxidation of
formaldehyde on a rutile TiO2 (110) surface. Through this study, we discovered a two-step dehydrogenation oxidation process for formaldehyde on the surface. During the reaction, a bridge adsorption structure, Dioxymethylene (DOM), was obtained. In addition, we simulated different surface-trapping sites and analyzed their hole-trapping capacity (HTC). The most stable photogenerated radical was determined. Based on our results, The role of water molecules in photocatalysis is revealed.
In Chapter 4, we explore the mechanism of photocatalytic formaldehyde oxidation on TiO2 (101) anatase using the DFT+U combined HSE functional method for calculations.
DOM also occurs during we simulate formaldehyde adsorption. The stepped surface structure of anatase enables two DOM adsorption structures through the binding of C atoms of formaldehyde to different lattice oxygen atoms. Two reaction pathways were determined and the favored two-step dehydrogenation oxidation mechanism is revealed, which is different from that on a rutile surface. By comparing the mechanisms on two surfaces. Some properties have been demonstrated. These findings provide a new perspective for the study of photocatalytic dehydrogenation and oxidation processes of organic compounds on TiO2.
During the study of the formaldehyde oxidation process, we found that the reaction was constrained by the concentration of the surface-reach holes. To enhance hole transfer to surface locations, we delved into the hole transfer process. In Chapter 5, we employed density of states (DOS) calculations to determine the energy levels of specific atoms. This allowed us to examine the relationship between energy level alterations and structural distortion. Based on these findings, we proposed a correlation between energy levels and bond vibrations, as well as a mechanism for the transfer of holes from the bulk to the surface site.
Thesis is embargoed until 31 December 2026.
| Date of Award | Dec 2023 |
|---|---|
| Original language | English |
| Awarding Institution |
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| Supervisor | Peijun Hu (Supervisor) & Meilan Huang (Supervisor) |
Keywords
- Photocatalysis
- computational chemistry
- density functional theory