Plasmonic photochemistry on the nanoscale

Over the past decade, nanomaterials have been the subject of enormous interest. These materials are notable for their tunable properties that exist when material's size is confined and show potential for use in wide-ranging industrial, biomedical, and electronic applications. The purpose of this thesis is to discuss some of the photochemistry that occurs on the nanoscale; especially those photochemical reactions that are adjustable by plasmonic metal nanoparticles.;The first application involves using gold nanocages for azo-dye degradation. Azo-dyes are frequently used in the textile industry and are toxic and carcinogenic. These dyes are typically released through waste water and thus are a threat to the surrounding ecosystem. The most challenging problem for removal of these pollutants is that azo-dyes are not compatible with traditional environmental treatment processes. A new nanoreactor, gold nanocages with unique hollow interiors, is developed to overcome this obstacle. The inner layer of a gold nanocage is silver and the outer surface is gold. When a gold nanocage is purged with oxygen gas, the silver atoms can be easily transformed to silver oxide. The band gap of silver oxide is 2.5-3.1 eV and it is therefore an analog of other metal oxide materials, allowing it to absorb the energy from light and produce radicals to perform photodegradation of azo-dyes. The photocatalyic efficiency of these hollow gold nanocages is better than that of solid catalysts because the surface-to-volume ratios is higher in gold nanocages and also because of the increased likelihood of the azo-dyes contacting hydroxyl radicals since the reactants can be confined within the cages.;The second application is to use the photothermal effect for catalysis. The photothermal effect is when plasmonic metal nanoparticles rapidly convert absorbed light energy into heat and the heat from the metal lattice dissipates into the surrounding environment by phonon-phonon relaxation. Therefore, plasmonic metal nanoparticles can be regarded as a thermal agent. This characteristic is most often applied to cancer therapy. This is the first time that photothermal effect has been utilized to enhance the catalysis of the electron transfer reaction between hexacyanoferrate and thiosulfate. Two different types of plasmonic gold nanoparticles were prepared: gold nanospheres with a surface plasmon resonance band at 527 nm and gold nanocages with a surface plasmon resonance band at 796 nm. Two continuous wavelength laser were used, 514 and 808 nm, to irradiate the gold nanospheres and the gold nanocages, respectively. The gold nanoparticles served not only as a catalyst but also as a heating source to increase the reaction solution temperature. The properties of gold nanoparticles remained the same even after extended exposure to the laser. This technique can be used for accelerating thermal or photochemical reactions and may have the potential to heat reactions via solar energy.;The last application involves applying the plasmonic field of silver nanoparticles to bacteriorhodopsin, which is a photosynthetic system and a future candidate for use as alternative energy. Bacteriorhodopsin (bR) can transfer light energy into electrochemical energy by utilizing a proton gradient. However, the photocurrent density values reported so far are around 0.2--40 pA cm-2 in thin film systems, which also require an external bias. In this thesis work, a non-thin film (solution) based electrochemical cell was successfully built up which did not require any external bias. The cell design used commercially available indium tin oxide glass as optical windows and electrodes. Small amounts of bR suspensions were utilized as the photovoltaic medium to generate the proton gradient between two half-cells separated by a molecular porous membrane. The maximum photocurrent density was 1.5 nA/cm3, which is orders of magnitude higher than previous reports. To achieve an even higher photocurrent, metallic nanoparticles were prepared and incorporated into bR. Silver nanoparticles whose surface plasmon resonance overlaps well with the longest-lived intermediate of the bR photocycle (M412) show a significant enhancement of photocurrent generation. The plasmonic field of silver nanoparticles can effectively increase the flux of blue photons and the bypassed photocycle is formed due to this enhanced blue light effect. (Abstract shortened by UMI.)...