STUDYING CATALYSIS OF METAL NANOSTRUCTURES USING SINGLE MOLECULE FLUORESCENCE MICROSCOPY
This dissertation focuses on studying the heterogeneous catalysis using single molecule fluorescence microscopy. We utilize its advantages in high-temporal, high-spatial resolution and correlate the catalytic activity with surface plasmon and catalytic communication. In Chapter 2 and 3 of this thesis, I report a direct visualization of the activity enhancement at nanoscale gaps between two plasmonic nanoparticles (Au nanorod or Ag nanoparticle), using single-molecule super-resolution catalysis imaging in correlation with electron microscopy. Surface plasmon enhanced catalysis is promising in harvesting light to drive chemical reactions that were otherwise inefficient or to bias the reaction pathways toward more desirable products. Catalytic hotspots at plasmonic hotspots is long predicted, but experimentally observing it has been challenging, even though it is crucial for understanding the enhancement mechanism. Here, I define the correlations of the enhancement with the nanostructure geometry and local electric field enhancement, and show that the enhancement scales quadratically with the local actual light intensity, reflecting the involvement of plasmon-excitation induced hot electrons in the catalytic enhancement mechanism. This study demonstrates a methodology of applying correlated super-resolution microscopy and electron microscopy to study plasmonic nanocatalysts at the sub-particle level. The results reveal the intimate relation between the activity increase of metal nanocatalysts and local surface plasmon enhancement, demonstrating a long-predicted but hard-to-observe phenomenon in plasmon-enhanced catalysis. In Chapter 4 and 5 of this thesis, I report both intraparticle and interparticle catalytic communication by analyzing the correlation between temporally subsequent reactions occurring at different locations within and among single nanocatalysts, resolved spatiotemporally using single-molecule fluorescence localization microscopy. This catalytic communication phenomenon, a first-of-its-kind discovery, occurs in three Pd or Au based nanocatalysts and in three distinct catalytic reactions including a photo-induced disproportionation reaction, an oxidative deacetylation reaction, and a reductive deoxygenation reaction. As the catalytic communications are phenomenologically similar and conceptually analogous to synergism in enzymes, which are nature’s most efficient catalysts, I envision that exploration of their generality and utility may bring new theoretical framework in understanding nanocatalysis.
Physical chemistry; Materials Science; Nanotechnology
Hines, Melissa A.; Robinson, Richard Douglas
Chemistry and Chemical Biology
Ph. D., Chemistry and Chemical Biology
Doctor of Philosophy
dissertation or thesis