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Title: Integrating photosystem II and electroactive bacteria with three-dimensional electrodes for semi-artificial photosynthesis
Author: Fang, Xin
Awarding Body: University of Cambridge
Current Institution: University of Cambridge
Date of Award: 2019
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Artificial photosynthesis is at the forefront of strategies to tackle the global reliance on fossil fuels and shape the contour of a sustainable future fuelled by renewable resources. In this way, solar energy is harvested and stored into chemical bonds to render it viable for transport and utilisation. Yet coordinating the interwoven processes therein in an efficient and orderly fashion poses profound challenges for synthetic chemistry. Biology wields plenty of evolutionarily-optimised biosynthetic pathways that operate in concert to yield complex chemicals from simple feedstocks. This thesis aims to achieve the solar-to-chemical conversion through a semi-biological approach: biocatalytic machinery in the form of enzymes and whole cells were integrated with artificial electronics to repurpose their biochemical pathways for the production of value-added fuels and chemicals. In particular, this thesis works with three-dimensional electrodes with different materials and variable morphologies to host photosynthetic enzymes and electroactive bacteria as biocatalysts. Chapter 1 introduces the fundamentals of biocatalysis and artificial photosynthesis, and reviews the progressing efforts to integrate biocatalysts with synthetic materials for semi-artificial photosynthesis. The rationale and contents of this thesis are outlined at the end of this chapter. Chapter 2 provides the experimental details that underlie this thesis, including protocols for electrode preparation, enzyme separation, bacteria culturing and an array of analytical methodologies. Chapter 3 presents a systematic study on benchmark inverse opal-indium tin oxide (IO-ITO) electrodes for protein film-photoelectrochemistry with photosystem II. The relationships of IO-ITO electrode structure and photosystem II activity were discussed following a combination of microscopic, spectroscopic and photoelectrochemical characterisations. Chapter 4 reports an inverse opal-graphene electrode as the host for photosystem II. The enzyme activity in such carbon-based electrodes is quantified by protein-film photoelectrochemistry and further compared with that in IO-ITO counterparts. Chapter 5 tailors the structure of the IO-ITO electrode to accommodate metal-reducing bacteria Geobacter sulfurreducens and Shewanella loihica. Their colonisation and current production in electrodes arising from anaerobic respiration are studied. Chapter 6 utilises the resulting biohybrid electrodes to drive reducing reactions within and beyond their native metabolic pattern, with electrons supplied by an external circuit or ultimately outsourced to a photoanode. Chapter 7 summarises the key findings in this thesis and blueprints future directions of research in this field. The research represents an interdisciplinary approach that takes advantages of biocatalysis featuring high selectivity and efficiency in chemical transformation, and synergistically combines strengths of synthetic materials and analytic toolsets, to induce shifts in the production of high value fuels and chemicals with renewable energy sources.
Supervisor: Reisner, Erwin Sponsor: China Scholarship Council ; Cambridge Trust
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
Keywords: Photosystem II ; Three-dimensional electrode ; Geobacter ; Semi-artificial photosynthesis