Graduation Year

2021

Document Type

Dissertation

Degree

Ph.D.

Degree Name

Doctor of Philosophy (Ph.D.)

Degree Granting Department

Chemical Engineering

Major Professor

D. Yogi Goswami, Ph.D.

Committee Member

John N. Kuhn, Ph.D.

Committee Member

Venkat R. Bhethanabotla, Ph.D.

Committee Member

Elias K. Stefanakos, Ph.D.

Committee Member

George R. Philippidis, Ph.D.

Keywords

Finite Difference Time Domain, Silver Nanoparticles, Titanium Dioxide, Zinc Oxide

Abstract

Plasmonic nanomaterials have become a strong contender for improving the efficiency of photocatalytic degradation of air pollutants. This study demonstrates an easy and scalable fabrication method, employing electron beam evaporation and rapid thermal annealing, for producing plasmonic photocatalysts. Samples were made by either coating silver on, or layering silica-protected (i.e., silica-coated) or unprotected (i.e., uncoated) silver beneath, the photocatalyst (either zinc oxide or titanium dioxide). Stability and catalytic performance for gas-phase toluene degradation was assessed by monitoring total volatile organic compound (TVOC) concentration versus ultraviolet-A (UV-A) illumination time in a recirculating batch reactor (plate-type flow-through). Samples were characterized using a variety of spectroscopic methods, electron microscopy, and X-ray diffraction. Finite difference time domain (FDTD) simulations demonstrate that the UV-A light-induced electric fields around silica-protected and unprotected silver nanoparticles extend significantly beyond the nanoparticle surfaces, allowing contact between the fields and the photocatalyst, and justifying the catalyst design. Experimental results, and analysis of reaction kinetics, show that silver-coated photocatalysts and layered photocatalysts with unprotected silver exhibit initially high TVOC degradation rates, but suffer from deactivation, attributed to silver oxidation. Layered photocatalysts with silica-protected silver exhibited improved stability versus unprotected samples and improved performance over titanium dioxide. The results of this study demonstrate that a silica layer can help slow down fouling of silica nanoparticles, and that silica-coated silver nanoparticles not only help speed up reaction rate overall but also appear to speed up release of adventitious hydrocarbons from the photocatalyst surface during the initial phase of a reaction. The layered fabrication approach developed and employed in this study for application to gas-phase photocatalysis may enable plasmonic photocatalysis by offering a simple, scalable fabrication method more reliable than the more prevalent colloidal synthesis.

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