Hot Carrier Assisted Plasmonic Photocatalysis

  • Author / Creator
    Manuel, Ajay P.
  • Plasmonic photocatalysis has drawn immense interest due to the innovative possibilities it provides in harnessing photonic energies across the full width of the solar spectrum to drive chemical reactions. Plasmonic noble metal nanoparticles are excellent light absorbers and their ability to focus light into small volumes have led to their use in a variety of applications from bio-molecular sensing, surface catalytic reactions, and as light concentrators for solar energy cells.

    These abilities are enabled by the excitation of localized surface plasmon resonances, the coherent oscillations of conduction electrons, within metal nanoparticles. Metals such as gold and silver are particularly popular due to their resonances in the visible region of the electromagnetic spectrum. Utilizing solar energy to drive catalytic chemical reactions is often touted as an environmentally friendly alternative. There has been a tremendous amount of research dedicated to design metal nanostructures, modulate their resonance frequencies, and provide for systems that can enhance electromagnetic fields over the full width of the solar spectrum. The incorporation of metal nanoparticles that can absorb visible light with green semiconductor photocatalysts to form composite plasmonic photocatalytic systems that are far more efficient than their individual counterparts has been a major objective of the field. Nevertheless, there remains much to be learned and understood of the physical processes involving the dynamics of high-energy charge carriers or hot carriers that facilitate the catalytic potential of these unique systems.

    This thesis begins by providing a comprehensive overview of the rich history of the field alongside the latest developments and issues for advanced research in hot carrier mediated plasmonic photocatalysis. In-depth discussions on the constituent components of a plasmonic system including the optical properties of noble metal nanoparticles, and the current landscape of noble metal-semiconductor heterojunction photocatalysis are considered. Further insights are provided via electromagnetic finite-difference time-domain simulations that have been extensively performed to guide various experiments and optimize relevant systems. With an incentive toward understanding the deeper fundamental roles of hot carrier phenomena and the relevant charge carrier dynamics in metal nanoparticles to facilitate plasmonic photocatalysis, we begin by examining monometallic silver nanoislands. This is followed by the study of gold nanoislands organized in a bimetallic heterostructure involving a plasmonic gold core and a catalytic platinum shell.

    Research into the monometallic and bimetallic nanostructures provides for a comparative study on overcoming the chemical inertness of noble metals by incorporating them alongside another metal that is catalytic in nature. Facile and highly reproducible fabrication techniques involving physical vapor deposition methods are identified and exclusively utilized to build these monometallic and bimetallic nanoisland structures. Primary characterization techniques including ultraviolet-visible spectroscopy, and Raman spectroscopy are utilized to identify the plasmonic potential of these structures. Photocatalytic tests involving surface catalytic reactions with aromatic thiols, surface enhanced Raman spectroscopy, dye degradation, and Raman thermometry provide greater insights into the hot carrier dynamics within these systems. These efforts are extensively supplemented by knowledge from theoretical collaborations in other projects, involving electromagnetic simulations, on the optical characteristics of diverse plasmon-enhanced photocatalytic substrates including nanotubes, nanocubes, nanodimples, nanofractals as well as other exotic nanoparticle morphologies including nanoprisms, nanorods, nanoshells, and trimetallic heterostructures.

    We conclude by discussing future directions of research that can be pursued building on what we have learned thus far on physical vapor deposition-based nanostructure fabrication, and plasmonic charge-carrier dynamics in monometallic and bimetallic heterostructures. Critical remarks on the limitations of existing systems and their optimization as potential plasmonic platforms in diverse photocatalytic applications are also provided.

  • Subjects / Keywords
  • Graduation date
    Fall 2021
  • Type of Item
  • Degree
    Doctor of Philosophy
  • DOI
  • License
    This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.