Energy and environmental problems represent one of the greatest challenges facing humankind in this century. Despite tremendous efforts to develop renewable energy sources, still the majority of energy used is derived from non-renewable fossil fuels. Reducing carbon dioxide, an abundant carbon source, into value added fuels using a renewable energy input (i.e. artificial photosynthesis) would allow us to reduce our dependence on conventional fossil fuels, mitigate CO2 emissions and make our society more sustainable. Furthermore, chemical fuels produced from carbon dioxide could be readily implemented in the current energy infrastructure allowing a quick and smooth transition toward a renewable energy society. This research is aimed at solving several problems: harvesting solar electricity using semiconductor nanocrystals, synthesizing a variety of useful chemicals with nanocrystal/bacteria hybrids, and disposing of a troublesome waste product produced in very large quantities, i.e., carbon dioxide. This research is also highly cross-disciplinary as the confluence of two disparate technologies to produce a solution to a problem, i.e., materials science to produce semiconductor nanocrystals, and biotechnology to use the electrons and holes produced by the nanocrystals to general value-added chemicals. The insights gained in this study possesses the potential to supplant the reliance on petrochemical routes to chemical synthesis for fuels, fertilizers, industrial and commodity chemicals, polymers, pharmaceuticals, and more, while simultaneously providing a path towards carbon capture and reduction of atmospheric CO2 levels.
Technical Natural photosynthesis relies upon a series of light harvesting proteins, which are optically limited to an absorption peak, only capable of utilizing a relatively narrow region of the solar spectrum and are susceptible to damage by higher energy photons. In comparison, inorganic, solid-state semiconductors, which form the basis of high efficiency commercial photovoltaic cells, surpass their biological analogues, possessing an absorption band, above which all higher energy photons can be collected for chemical work. However, such inorganic light harvesting schemes are quite costly, requiring scarce elements in exceptionally high purity, and energy intensive synthesis schemes. Additionally, unlike their biological counterparts, many of the highest performing materials are fundamentally unstable, susceptible to a variety of damage and degradation pathways with no built in mechanism for self-repair. One might envision a hybrid system, in which the best of both worlds are combined for the purpose of photochemical biosynthesis: the optoelectronic properties of inorganic chemical systems, with the synthetic, self-regenerative properties of biological systems. Through such a symbiotic relationship, in which each half augments the capabilities of the other, it is possible to design a new type of biotic-abiotic hybrid biomaterial that surpasses the capabilities of their individual components.
The objective of this research is to design and explore the fundamental biotic-abiotic interfaces of a model system for inorganic-biological artificial photosynthesis of a diversity of chemical products utilizing CO2 as the sole carbon source. This model system will require several phases: 1) selection of a biological component for chemical synthesis; 2) selection of an inorganic light harvester; 3) exploration of the synergistic effects of the inorganic-biological hybrid system; and 4) detailed study of the fundamental mechanisms at the newly formed biotic-abiotic interfaces. This proposed work represents a first foray into relatively unexplored territory: the energy transduction between semiconductors and whole cell microorganisms. Of what the PI believe to be the first work of its kind is the examination of the self-photosensitization of a microorganism, in which bacteria is able to synthesize its own inorganic semiconductor light harvester, and carry out normal metabolic function through this new form of energy transduction. The proposed work will serve as a foundation for teaching and training students highly interdisciplinary skills in chemistry, physics, biology and materials engineering for renewable energy research.
