| My dissertation includes three major applications of plasmon-enhanced photocatalysis: plasmonic enhancement of photocatalytic decomposition of methyl orange under visible light, photocatalytic conversion of CO2 to hydrocarbon fuels via plasmon-enhanced absorption and metallic interband transitions, and plasmon resonant enhancement of dye sensitized solar cells.;In Chapter One, metal nanoparticle enhanced photocatalysis is reviewed. This chapter starts with a brief introduction of the surface plasmon resonance phenomenon and basic principles of photocatalytic reactions, including degradation of organic wastes, water splitting, and reduction of CO2. This is followed by a summary of a recent burst of papers in this field. A particular emphasis is given to the factors limiting photocatalytic conversion efficiencies and the plasmon enhancement mechanisms by which surface plasmon resonance of noble metal nanoparticles can influence the photocatalytic activity of nearby semiconductors.;In Chapter Two, the application of plasmon resonant enhancement to increase the photocatalytic decomposition of methyl orange under visible light is demonstrated. A 9-fold improvement in the photocatalytic decomposition rate of methyl orange is observed using a photocatalyst consisting of strongly plasmonic Au nanoparticles deposited on top of strongly catalytic TiO2.;In Chapter Three, a systematic study of the mechanisms of Au nanoparticle/TiO 2-catalyzed photoreduction of CO2 and water vapor is carried out over a wide range of wavelengths. When the photon energy matches the plasmon resonance of the Au nanoparticles (free carrier absorption), which is in the visible range (532 nm), a 24-fold enhancement in the photocatalytic activity is observed because of the intense local electromagnetic fields created by the surface plasmons of the Au nanoparticles as discussed in Chapter Two. When the photon energy is high enough to excite d band electronic transitions in the Au, in the UV range (254 nm), a different mechanism occurs resulting in the production of additional reaction products, including C2H 6, CH3OH, and HCHO. T.;In Chapter Four, the application of plasmonic enhancement to improve the efficiency of dye sensitized solar cells (DSSCs) is explored. By comparing the performance of DSSCs with and without Au nanoparticles, a 2.4-fold enhancement in the photoconversion efficiency is demonstrated. Enhancement in the photocurrent extends over the wavelength range from 460 nm to 730 nm. The underlying mechanism of enhancement is investigated by comparing samples with different geometries, including nanoparticles deposited on top of and embedded in the TiO2 electrode, as well as samples with the light absorbing dye molecule deposited on top of and underneath the Au nanoparticles.;In Chapter Five, the effect of doping in photocatalysis is explored. TiO2 is doped by ion implantation, plasma ion implantation (PII), and annealing in H2, CH4. The p- or n-type carriers of these H, C, and N-doped TiO2 films are measured using hot-probe measurements. The p- or n-type carriers then are correlated with the photocatalytic performance, which is measured in the photocatalytic water splitting system. This study serves to establish the validity of the plasmonic enhancement mechanism proposed in the previous chapters. In Chapter Six, the photocatalytic activities of several other semiconductors, including Fe2O3, GaN, Nb-doped SrTiO3, spray pyrolysis TiO2, and thermally oxidized TiO2 are investigated. This study serves to evaluate alternative semiconductor photocatalysts with potentially higher photocatalytic efficiencies. (Abstract shortened by UMI.). |
