This proposal is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5).
Prof. Stephen Cronin at the University of Southern California is supported by the Division of Chemical, Bioengineering, Environmental, and Transport Systems in the Engineering Directorate (with co-funding from the Division of Chemistry in the Directorate for Mathematics and Physical Sciences) to develop an understanding of the effect of plasmon resonance on catalytic performance. Two main postulates will be explored: (i) the effect of plasmon-induced electric field on chemical activity, and (ii) the effect of plasmon-induced heating on catalysis.
Approach: The PI will produce arrays of metal nanostructures on top of and embedded in both active (e.g., TiO2) and non-active supports. Irradiating these plasmonic/catalytic nanostructures with a laser at their plasmon resonance frequency will generate immense plasmonic charge and high temperatures needed to drive the catalytic process. The plasmon-induced charge is orders of magnitude larger than that created by standard optical absorption and therefore has the potential to dramatically improve the efficiency of these catalytic processes. Also, the local heating of the nanoparticles generates large temperature gradients, which in turn create new pathways by allowing different chemical processes to occur side by side.
The catalytic activity of these samples will be studied in an automated micro-reactor system that rapidly evaluates catalytic nanostructures and permits thousands of experimental conditions to be tested on a single chip. The system measures in situ diagnostics of the reaction byproducts using mass spectrometry and Raman spectroscopy, allowing direct correlation between structural properties and catalytic performance. High throughput screening of various catalytic and geometric configurations will enable us to investigate several fundamental questions about the enhanced catalytic mechanism.
Fundamental Questions Addressed in this Proposal: - Is the catalytic enhancement heat mediated, electric field mediated, or otherwise? - What is the role/importance of the large temperature gradients created by nanoplasmonic heating? - How does the bandgap energy and doping level affect the catalytic activity? - What is the critical thickness of the metal oxide film that enables the plasmon-induced charge to diffuse to the catalytic surface? - How does surface binding of reactants, byproducts, and free radicals affect the catalytic activity and selectivity? - What is the theoretical optimum enhancement in catalytic activity achievable through surface plasmon resonant excitation?
The intellectual merit is to expand the understanding and applicability of plasmonic processes into the field of chemistry. By systematically addressing these fundamental questions, the PI will be able to identify which particular aspects of the plasmon enhancement will be most useful and which chemical reactions will benefit most from it. The area of plasmon assisted catalysis is rich with new and interesting phenomena that remain poorly understood. Plasmonic excitation opens up additional degrees of freedom in the search for new chemical pathways, for example, for the production of tricyclic ozone. The systematic studies put forth in this proposal will likely provide an understanding of unexplored catalytic phenomena and introduce novel concepts that are widely applicable to the larger scientific community.
Broader Impacts: The outreach program to Los Angeles area high school teachers will expose underrepresented students to the results and, more importantly, the excitement of this proposed research and other cutting-edge research at universities in the Los Angeles area. In this effort, the PI will develop a long-term, working relationship between USC and its neighboring high schools. Research projects for undergraduate students will introduce them to the creative and intuitive nature of scientific research, thereby giving them the confidence and inspiration to pursue careers in science and engineering. The novel curriculum, which integrates creativity into a new nanoscience course, will produce skilled and knowledgeable students able to address the next generation of challenges in nanotechnology. The general scheme of incorporating in-class brainstorming sessions into traditionally technical curriculum can be applied to a wide range of subjects in the physical sciences and engineering.
The importance of catalysis in modern industrial chemistry cannot be overstated, impacting nearly every aspect of our economy. The successful completion of this proposed work will lead to a number of future studies with scientific and industrial relevance. The improved catalytic processes investigated herein may be applicable to other fields of science and engineering to enhance various important chemical and electrochemical phenomena. Alternatively, these plasmonic nanoparticles can be incorporated onto a chip to drive endothermic reactions with sunlight for energy storage. The localized nature of plasmonic heating and electric field enhancement is ideal for creating an integrated fuel source for hydrogen and methane fuel cells, without having to heat up the entire device. In the face of the global energy crisis, this work will provide new inroads in the critical search for novel and efficient chemical processes.
