Hybrid Catalyst System Combining Hot Electron-Generating Quantum Dots and Molecular Catalyst for Efficient Photocatalytic CO2 Reduction
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Photocatalysis utilizes energy from the sun to achieve a sustainable route to producing high-value fuels and chemicals from low-value or environmentally harmful molecules. In this project, new combinations of photocatalysts will be investigated to upgrade carbon dioxide (CO2) to molecules that can be used to make fuels or chemicals. The new catalytic materials will help pave a path to the Nation''s future energy security while decreasing the environmental impact of carbon emissions. The project also includes plans for education and outreach at all levels, ranging from training graduate and undergraduate students in energy-related technologies to promoting interest in STEM-related areas amongst K-12 students. The novelty of the proposed hybrid systems lies in the combination of specifically doped quantum dot (QD) photosensitizers with molecular, transition metal-based catalysts. The ability of doped QDs to generate hot electrons upon irradiation will allow for long-range hot electron photosensitization and efficient electron transfer to molecular CO2 reduction catalysts without the need for direct linkage between the sensitizer and catalyst. In the new hybrid systems, manganese and copper dual-doped quantum dots will produce energetic hot electrons under weak visible light, which will perform efficient long-range (e.g., 10 nm) sensitization to molecular catalysts in solution. The large increase of the sensitization volume and energetically more favorable and unidirectional hot electron transfer to the molecular catalyst are expected to enhance the overall catalytic CO2 reduction efficiency of the hybrid catalyst system, while keeping the convenience and flexibility of uncoupled hybrid catalyst system in construction and regeneration. To quantify the rates of key processes at each stage of the entire photocatalytic reduction process and to optimize their efficiency through structural variations of the sensitizer and hybrid system, several objectives will be pursued: (1) structural control of the doped quantum dot sensitizer for maximum hot electron generation efficiency, (2) quantitative measurements of hot electron sensitization efficiency to molecular rhenium- and nickel-based molecular catalysts, and (3) assessment of the overall catalytic efficiency in the reactor at varying reaction conditions. Comparative evaluation of the overall efficiency of the hybrid catalysts designed here with that of the existing hybrid architectures will lead to the identification of the optimum structure of the hot electron-sensitized hybrid catalyst system. With respect to education, new multimedia materials will be used to complement instrumental training in undergraduate laboratories and graduate classes and in workshops on instrumentation/data acquisition/processing. Outreach will involve new hands-on experiments that are related to the synthesis of plasmonic nanocrystals and simple optical experiments that can be safely performed by middle or high school classes as a part of their science curriculum. Additionally, the Texas-wide Texas Sized Crystal Contest is being organized which will allow large numbers of high school students and teachers to experience the fascinating world of crystalline solids. This award reflects NSF''s statutory mission and has been deemed worthy of support through evaluation using the Foundation''s intellectual merit and broader impacts review criteria.