Noble Metal Nanoparticles for Surface/Gas-phase Reactions

• Author / Creator

  Rao, Chengcheng

• The climate crisis has rendered the utilization of clean and renewable solar energy for chemical transformations extremely important. Plasmonic nanostructures can provide tunable optical and electronic properties that can drive chemical reactions, realizing the conversion of light energy into chemical energy. The last decade has witnessed the development of a new research field emerging from the combination of plasmonics and surface chemistry. This thesis describes a straightforward method to fabricate plasmonic stamps that are harnessed to drive surface chemistry on silicon.
  An introduction to the plasmonics and hydrosilylation on silicon surfaces is provided first, followed by an overview of the proposed mechanisms for plasmon-driven reactions and the recent advances of plasmon-driven reactivity for surface functionalization. Hydrosilylation triggered by metallic nanoparticles, such as Pd, Pt, and Au nanoparticles embedded in soft PDMS stamps, is reviewed in detail.
  The plasmonic stamps were prepared by sputtering gold films on flexible PDMS, followed by thermal annealing to dewet the gold to form gold nanoparticles. By changing the film thickness of the sputtered gold, the approximate size and shape of these gold nanoparticles can be changed, leading to a shift in the optical absorbance maximum of the plasmonic stamp from 535 to 625 nm. By applying the plasmonic stamp to a Si(111)–H surface using a long-chain alkene as the ink, illumination with green light results in covalent attachment of linear alkyl groups to the surface. Of the dewetted gold films on PDMS used to make the plasmonic stamps, the thinnest three (5.0, 7.0, and 9.2 nm) resulted in the most effective plasmonic stamps for hydrosilylation. Because the electric field generated by the LSPR would be very local, hydrosilylation on the silicon surface should take place within only close proximity of the gold particles on the plasmonic stamps. These results underline the central role played by the LSPR in driving the hydrosilylation on silicon surfaces, mediated with plasmonic stamps. By using these highly reproducible PDMS stamps, studies of the reaction kinetics for plasmon-induced hydrosilylation on silicon substrates were carried out. Through variation of the doping levels, critical insights were gleaned, and a relationship between reaction rates and built-in electrical fields of metal-insulator-semiconductor junctions was determined, along with a set of physical models and corresponding formulae. This work provides important insights into the reactivity of plasmonic structures in close proximity to a semiconductor, which is a common and important architecture used as a platform for photochemistry, light-promoted catalysis, and photonics in general. We reveal the intricate interplay between the electronics of the semiconductor proximal to the electric field induced by the localized surface plasmons, and how the resulting charge carriers can be used to drive chemical reactivity.
  Additionally, results from a secondary project are reported in Chapter 4. Pd-Pt/ZrO2 catalysts with three different nanostructures were designed, synthesized, and their catalytic performance and lifetimes were evaluated for wet methane combustion, which pointed to advantages and limitations of yolk-shell nanostructures. Finally, the thesis concludes with a summary of each chapter and directions for future studies.

• Subjects / Keywords

  • Hydrosilylation
  • Metal nanoparticles
  • Surface plasmon

• Graduation date

  Fall 2020

• Type of Item

  Thesis

• Degree

  Doctor of Philosophy

• DOI

  https://doi.org/10.7939/r3-6pb5-k317

• License

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