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Title: Structure-activity relationships in organic photocatalysts for hydrogen production from water
Author: Aitchison, Catherine
ISNI:       0000 0005 0288 0897
Awarding Body: University of Liverpool
Current Institution: University of Liverpool
Date of Award: 2020
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Hydrogen produced from water by photocatalysis has the potential to be a cheap, sustainable and low-carbon 'solar fuel'. Conjugated organic semiconductors are particularly interesting as photocatalysts as material properties can be tuned through easy modification of chemical structure. However, the relationships between specific material properties and photocatalytic activity are not yet well defined, posing a challenge to the design of new photocatalysts and the development of existing ones. The most widely studied organic semiconductors for solar fuel production are organic-solvent-insoluble bulk polymers with a low degree of order. The inability to process such materials after synthesis means that i) characterisation and ii) optimisation of secondary and tertiary structures are not facile. In this work, alternative conjugated organic materials are investigated as photocatalysts for hydrogen production from water. In each, a degree of control can be exerted during or post synthesis to give a desired or quantifiable material structure. First, a series of polymers synthesised by emulsion polymerisation were studied. The optimised microstructure of these materials, in comparison to bulk analogues synthesised in precipitation polymerisations, lead to increased photocatalytic activity with EQEs of up to 20% at 420 nm. The ability to generate polymers from the same monomers but with different particle size also allowed the relationship between catalyst surface area and catalytic activity to be investigated. Next, a series of oligomers were tested for photocatalytic hydrogen evolution. The welldefined chemical structure, conformation and packing of these oligomers was used to determine how properties such as chain length and backbone twisting affect photophysical properties and photocatalytic activity of the materials. Finally, a hydrogen-bonded organic framework and related materials were studied. By comparing the activity of the same molecule in ordered and amorphous phases it was shown unambiguously that crystal packing can have orders of magnitude effect on photocatalytic activity. The high activity of some of the oligomers and this hydrogen-bonded framework indicates that molecular materials can be as active for photocatalytic hydrogen production as polymers, significantly expanding the scope of organic semiconductors that should be considered for further study.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral