Catalytic photochemical water oxidation is one of the key problems in the development of both the generation of solar fuels and renewable chemical feed stocks. One of the leading proposals is to use heterogeneous semiconductors, which, when under irradiation, generate a large enough voltage to electrolyse water molecules in situ. To the effectiveness of this process, dye sensitisers are employed to harvest more of the high intensity visible spectrum. The purpose of this thesis is to gain a better understanding of how these dyes behave in combination with selected substrates, and to examine how, with minor alterations to existing dyes, their effectiveness could be improved. Chapter I consists of a survey of various different water oxidation methods found in both nature and in the lab, to build an understanding of both homogenous and heterogeneous water oxidation pathways and how they are connected. Chapter II details the synthesis, characterisation and catalytic testing of a series of ruthenium (IV)based dyes, deriving from ethylcarboxylate-substituted picolinic acid. The investigation determined that significant shifts in the redox couples could be achieved via the simple variation of the substitution pattern of the ethylcarboxylates. What was also discovered was the reduced form of the dyes and the subsequent exchange of charge-carrying ligands for neutral aqua groups. In chapter III, DFT and TDDFT calculations were performed in order to gain a more fundamental understanding of the behaviour of these dyes at a molecular level. The results show that the complexes are reducing upon contact with water, as the experimental UV-Vis spectra match those of the reduced species rather than the original ruthenium (IV) dyes. This reduction is attributed to the complexes acting as water-oxidation agents due to the high oxidation potential of their Ru III/IV couples in comparison with that of the water oxidation reaction. Attempts to develop similar ruthenium-amide based dyes are discussed in chapter IV. What was discovered was that, while the ligands could be synthesised easily, the complexes proved to be unstable and unsuitable for the water oxidation reaction. Overall these studies show that small changes in ligand design, such as variation in anchoring position, can have pronounced effects on the characteristics of those dyes and highlight the need for systematic exploration of ruthenium based dye sensitisers if improvements to the heterogeneous water oxidation reaction are going to occur.
|Date of Award||31 Oct 2016|
- University Of Strathclyde
|Supervisor||John Reglinski (Supervisor) & Mark Spicer (Supervisor)|