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PLASMONIC ENHANCEMENT OF CATALYSIS AND SOLAR ENERGY CONVERSION
by
Wei Hsuan Hung
A Dissertation Presented to the
FACULTY OF THE USC GRADUATE SCHOOL
UNIVERSITY OF SOUTHERN CALIFORNIA
In Partial Fulfillment of the
Requirements for the Degree
DOCTOR OF PHILOSOPHY
(MATERIALS SCIENCE)
August 2011
Copyright 2011 Wei Hsuan Hung
Object Description
| Title | Plasmonic enhancement of catalysis and solar energy conversion |
| Author | Hung, Wei Hsuan |
| Author email | weihsuah@usc.edu;wave0626@gmail.com |
| Degree | Doctor of Philosophy |
| Document type | Dissertation |
| Degree program | Materials Science |
| School | Viterbi School of Engineering |
| Date defended/completed | 2011-05-23 |
| Date submitted | 2011-06-14 |
| Date approved | 2011-06-14 |
| Restricted until | 2011-06-14 |
| Date published | 2011-06-14 |
| Advisor (committee chair) | Cronin, Stephen |
| Advisor (committee member) |
Zhou, Chongwu Goo, Edward |
| Abstract | This thesis is dedicated to exploring the potential applications of plasmonic metal nanoparticles and understanding their fundamental enhancement mechanisms. Photocatalysis and solar energy conversion are the two main topics investigated in this work. In Chapter 2, we demonstrate the growth of a variety of carbonaceous materials by plasmonic heating. When the metal nanoparticles are irradiated with a laser near their plasmon resonant frequency, a localized region at high temperature is achieved due to the ohmic losses at the plasmon resonance. In this plasmon resonant chemical vapor deposition (PRCVD) process, high temperatures are created at the surface of the plasmonic nanoparticles to trigger the dissociation of gaseous precursors, (e.g. carbon monoxide), which results in the deposition of amorphous carbon, graphitic carbon, and carbon nanotubes. The formation of iron oxide nanocrystals is also observed at the beginning of the reaction due to a trace amount of iron pentacarbonyl in the CO feed gas. The growth of iron oxide at the surface of gold nanoparticles forms a new type of composite catalyst, Au nanoparticle/Fe₂O₃, which also catalyzes the growth of carbon nanotubes through this plasmon excitation process. The real time temperature dependence and sequential growth of different carbonaceous and metal oxide materials are monitored and characterized by Raman spectroscopy and infrared spectroscopy. Additionally, pre-defined microstructure geometries of crystalline iron oxide and carbon nanotubes are demonstrated by rastering the focused laser spot during the growth process in a controlled fashion. ❧ In Chapter 3, the concentrations of gas phase reaction products are observed in real time using mass spectrometry, which is used to evaluate the performance of Au nanoparticle/Fe₂O₃ composite catalysts. This new plasmonic composite catalyst exhibits an excellent catalytic ability in the CO oxidation reaction, which exceeds that of the Au nanoparticles and Fe₂O₃ alone. This indicates that this reaction is not driven solely by thermal (plasmonic) heating of the gold nanoparticles, but relies intimately on the interaction of these two materials. This hybrid plasmonic nanoparticle catalyst and PRCVD method open up new possibilities in the local chemistry, enabling new growth pathways of materials, not possible using standard CVD methods with uniform heating. ❧ In addition to photocatalysis, we also explored plasmonic enhancement of solar energy conversion. In Chapter 4, plasmonic gold nanoparticles are incorporated into dye sensitized solar cells (DSSCs) by electron beam deposition. Increased photocurrents are observed due to the thin layer of plasmonic gold, which results in a 45% increase in the cell’s power conversion efficiency. This enhancement is attributed to the strong plasmon-induced electric field from the presence of gold nanoparticles, as indicated by electromagnetic finite-difference-time-domain (FDTD) simulations. Additionally, the photoluminescence spectra of the TPBP dye molecule rule out the mechanism of plasmon energy transfer through a Forester resonance process. Another potential application of plasmonic nanoparticles that we have explored is solar fuel production. In Chapter 5, we demonstrate an enhancement of solar methane production by the reduction of aqueous carbon dioxide (CO₂) in the visible wavelength range. The underlying enhancement mechanisms of the Au nanoparticle/TiO₂-catalyzed photoreduction of CO₂ are investigated by irradiating several different sample configurations with a wide range of wavelengths. Based on these results, we attribute the plasmonmic enhancement to the local electric field enhancement. However, several questions remain open and further studies will be required in order to obtain a deeper and more quantitative understanding of the plasmonic enhancement process. Some future directions include exploring the dependence of the doping concentration in the TiO₂, the chemical state of the catalytic surface, and how the plasmonic nanoparticles perform in co-catalyst systems (e.g., TiO₂-Fe₂O₃). Chapter 6 describes a side project carried out at the beginning of my graduate work. In this Chapter, we report a novel method for creating three-dimensional carbon nanotube structures from dense, vertically-grown carbon nanotube forests. The minimum power density for burning carbon nanotubes is also determined in this study. |
| Keyword | plasmonic; gold nanoparticles; photocatalysis; carbon nanotubes; solar energy conversion |
| Language | English |
| Part of collection | University of Southern California dissertations and theses |
| Publisher (of the original version) | University of Southern California |
| Place of publication (of the original version) | Los Angeles, California |
| Publisher (of the digital version) | University of Southern California. Libraries |
| Provenance | Electronically uploaded by the author |
| Type | texts |
| Legacy record ID | usctheses-m |
| Contributing entity | University of Southern California |
| Rights | Hung, Wei Hsuan |
| Access conditions | The author retains rights to his/her dissertation, thesis or other graduate work according to U.S. copyright law. Electronic access is being provided by the USC Libraries in agreement with the author, as the original true and official version of the work, but does not grant the reader permission to use the work if the desired use is covered by copyright. It is the author, as rights holder, who must provide use permission if such use is covered by copyright. The original signature page accompanying the original submission of the work to the USC Libraries is retained by the USC Libraries and a copy of it may be obtained by authorized requesters contacting the repository e-mail address given. |
| Repository name | University of Southern California Digital Library |
| Repository address | USC Digital Library, University of Southern California, University Park Campus MC 7002, 106 University Village, Los Angeles, California 90089-7002, USA |
| Repository email | cisadmin@usc.edu |
| Archival file | uscthesesreloadpub_Volume71/etd-HungWeiHsu-23.pdf |
Description
| Title | Page 1 |
| Contributing entity | University of Southern California |
| Full text | PLASMONIC ENHANCEMENT OF CATALYSIS AND SOLAR ENERGY CONVERSION by Wei Hsuan Hung A Dissertation Presented to the FACULTY OF THE USC GRADUATE SCHOOL UNIVERSITY OF SOUTHERN CALIFORNIA In Partial Fulfillment of the Requirements for the Degree DOCTOR OF PHILOSOPHY (MATERIALS SCIENCE) August 2011 Copyright 2011 Wei Hsuan Hung |
