Date of Award
Spring 2023
Document Type
Dissertation
Degree Name
Doctor of Philosophy (PhD)
Department
Chemistry
First Advisor
Brudvig, Gary
Abstract
Solar energy is an incredibly abundant, renewable resource with the ability to meet our growing energy needs, but its diffuseness and intermittency has limited its potential. Taking note from photosynthesis in nature, we can design artificial systems that carry out similar processes in order to store solar energy in the form of chemical bonds as “solar fuels.” Molecular and materials approaches can be combined in heterogenized molecular WS-DSPECs where small molecules are attached to metal oxide surfaces to carry out water oxidation and fuel forming reactions. In this dissertation, small molecule surface attachment is investigated using the silatrane anchor to enhance the synthetic ease, long-term stability, and control over the design of these systems to improve their viability. Chapter 1 serves as an introduction to the WS-DSPEC and describes the associated design principles for heterogenized molecular systems. The photoanode, where water oxidation must occur, is discussed in more detail to highlight the harsh conditions that impede long-term stability. Several common moieties for molecular surface attachment are reviewed, noting their shortcomings in the areas of hydrolytic stability, loading control, synthetic ease, or charge transfer dynamics. The silatrane is presented as a promising option to address some of these limitations. In Chapter 2, the robust nature of the silatrane anchoring group is utilized to enable surface coupling for dye formation directly on a TiO2 surface. This is done through modification of the classical diazo coupling reaction. Aniline is anchored on TiO2 through a silatrane anchoring group and the amine is reacted with several activated aromatics, including 2-naphthol, aniline and phenol. These simple model complexes are used to demonstrate the wide substrate scope of this reaction. The strong silyl ether surface bonds are crucial here to survive the alkaline conditions needed for the coupling step, performed at pH 10 in aqueous solution, which would lead to desorption of most other surface anchors. In Chapter 3, protocols are presented to understand, enhance, and control the surface loading of the silatrane anchor. A new and improved method for estimating surface coverage is described and it was determined that loading with previously reported binding procedures is very low. Notably, we were able to increase the loading of a model arylsilatrane by 145% through use of a benzoic acid additive. This enhancement is attributed to aromatic stacking between the aromatic additive and the arylsilatrane. The role of the TEOA protecting group was also investigated and it was found to block surface sites where additional silatrane could otherwise bind. Removal of TEOA and re-loading was found to increase surface coverage significantly beyond re-loading without such removal. In Chapter 4, STEM imaging is investigated to determine its suitability for studying small molecules anchored onto TiO2 surfaces. We were interested in seeing if the TEOA removal method could be used to pattern the electrode surface, positioning the second loaded molecule in direct proximity to the first. This requires resolution at the atomic level, achievable with STEM and widely demonstrated for materials applications. Methods were developed and adapted to account for the fragility of our anchored small molecules and the increased background signal of TiO2 compared with typical carbon-based supports used for small molecules. The most promising method involved ALD of TiO2 directly onto a TEM grid and subsequent small molecule loading. Some sample damage and decomposition were observed, but significant progress was made to establish a protocol that achieved successful resolution of elemental markers in anchored small molecules on TiO2.
Recommended Citation
Troiano, Jennifer L., "Investigations of the Silatrane Anchoring Group for Solar Fuel Applications" (2023). Yale Graduate School of Arts and Sciences Dissertations. 1050.
https://elischolar.library.yale.edu/gsas_dissertations/1050
