The focus of this solicitation was to develop concepts for a photosynthetic biorefinery, in which micro-organisms are employed in the conversion of sunlight and carbon dioxide (CO2) to produce biofuel and bioproduct species. A systems approach is needed, and the system should be scalable. Life cycle analysis should be a tool used to evaluate various approaches. These components have been organized in an alternative manner in a project awarded jointly by the NSF Emerging Frontiers in Research and Innovation Division and the Catalysis and Biocatalysis Program of the CBET Division to the team of scientists and engineers of Professors Steven McIntosh, Bryan W. Berger, Robert Skibbens and Christopher J. Kiely of Lehigh University, Bethlehem, PA, and Ivan V. Korendovych of Syracuse University, Syracuse, NY.
The investigative team proposes to create a novel bio-synthesized enzyme-quantum dot hybrid photocatalyst for the direct production of methanol fuel from sunlight, water, and carbon dioxide. The key components of this system include (1) quantum dots (QDs) as electron donors and (2) CO2-reducing enzymes for continuous conversion of CO2 and water to MeOH. Absorption of photons by QDs will generate electron-hole exciton pairs. The hole will be harnessed for water splitting to form protons, while the electron will be utilized as the energy source for the enzymatic CO2 reduction steps. This enzymatic process consumes the protons formed from water splitting, completing the catalytic cycle. Combining these two components (QDs and enzymes) in the proposed continuous flow process will create a cost-effective technology for the large-scale production of renewable liquid fuels.
QDs will be synthesized using a unique bacterial system that facilitates precise control over particle size and corresponding wavelength range of the harvested light. In contrast to conventional, batch QD chemical synthesis, in which high temperatures, pressures and toxic solvents are required, the team approach allows for direct, extracellular production of water-soluble QDs directly from culture supernatants, with a target of reducing the cost of these materials by two orders of magnitude by removing the need for complex and expensive chemical processing steps, which is critical for achieving a cost-effective and scalable solution for direct liquid fuel production. A yeast-based system will be engineered to continuously generate the three enzymes that sequentially catalyze the reduction of carbon dioxide to methanol. Using a protein engineering approach, the PIs will modify these enzymes to self-assemble into a heterotrimeric complex on the surface of the quantum dot. These self-assembling enzyme catalysts overcome the current requirements for expensive precious metal based photocatalysts. Furthermore, the integrated enzyme-QD catalyst will achieve high selectivity for desired liquid fuel products by eliminating non-selective side reactions occurring with precious metal catalysts.
Broader Impacts: Both scalable photocatalytic MeOH production and low cost QD fabrication offer significant long term impact on society and the US economy. A low cost, green fuel, produced continuously at commercial scale from carbon dioxide, sunlight, and water has obvious potential. The application of QD technology in information technology, lighting, and medicine is currently limited by the high cost of these specialized, crystalline nanomaterials. Reducing their production cost has the potential to foster new domestic industries. Likewise, the modular nature of the enzyme-QD hybrid nanocatalyst platform opens up new opportunities for scalable synthesis of other high-value chemical products from CO2 and sunlight.
