Author : Mollie Rose Waller
Publisher :
ISBN 13 : 9781267663276
Total Pages : pages
Book Rating : 4.6/5 (632 download)
Book Synopsis Investigation of Metal and Metal Oxide Nanomaterials for Solar Energy Conversion by : Mollie Rose Waller
Download or read book Investigation of Metal and Metal Oxide Nanomaterials for Solar Energy Conversion written by Mollie Rose Waller and published by . This book was released on 2012 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Power harnessed from the sun has the capacity to meet the energy demands of the entire planet. Here we present research in the areas of solar energy conversion accomplished by photochemical water splitting, to produce renewable chemical fuels, and by photovoltaics, to generate electrical power. The entire discussion takes place within the context of nanochemistry. Investigation of the novel properties developed by materials when they become very small offers us new insight into the field of chemistry and provides us with unique ways of improving existing solar energy conversion technologies. Nanocrystalline tungsten trioxide, nano-WO3, is presented as a new photocatalyst for water oxidation in the presence of a sacrificial electron acceptor. The monoclinic structure of the nanomaterial is analyzed by powder X-ray diffraction and electron microscopy. Optical spectroscopy data is consistent with quantum confinement in nano-WO3. Comparison of the nanomaterial with the bulk phase, via surface photovoltage spectroscopy and electrochemical analysis, demonstrates that the principle photochemical and photophysical properties of tungsten trioxide are conserved upon nanoscaling. These results indicate that nano-WO3 has potential as a functional replacement for bulk WO3 in applications incorporating nanomaterials, such as ultrathin solar cells. The effects of nanosheet size and defect concentration are investigated for the known photocatalyst calcium niobate, TBA[Ca2Nb3O10]. The dimensions of the nanosheets, and the edge defect concentration, are controlled by ultrasonication and analyzed by optical and vibrational spectroscopy and high-resolution electron microscopy. The rate of photochemical hydrogen evolution from water, in the presence of a sacrificial electron donor, is shown to decrease linearly with sheet size. Surface photovoltage spectroscopy indicates a correlation between nanosheet size and charge carrier concentration that is consistent with photocatalytic activity being limited by charge recombination in edge defect sites. TBA[Ca2Nb3O10] nanosheets have previously been shown to photocatalytically split water into hydrogen and surface-bound peroxides. Peroxide formation is a result of incomplete water oxidation and eventually leads to deactivation of the catalyst. We present here the functionalization of the nanosheets with metal oxide nanoparticles as potential water oxidation co-catalysts, in an attempt to promote complete water splitting. The functionalized materials are well characterized using electron microscopy and optical, infrared, and Raman spectroscopies. However, a reduction in photocatalytic activity is observed following functionalization that can be explained in terms of competitive light absorption, electron-hole recombination, and electron trapping within the metal oxides. Finally, we present studies performed during the development of a one-pot synthesis for titanium dioxide nanospheres coated with silver shells (Ag@TiO2). Nanoscale silver demonstrates surface plasmon resonance (SPR) upon light absorption, and the incorporation of SPR exhibiting core–shell particles is reported to increase the efficiency of photovoltaic devices. Here we use photogenerated electrons within TiO2 to reduce silver onto the material surface as nanoseeds. The effects of silver concentration, reaction temperature, and photodeposition time on seed morphology and dispersion are presented, following analysis by electron microscopy. An electroless plating method utilizing acetaldehyde to chemically reduce additional silver is explored as a technique for shell formation following surface seeding. However, optical spectroscopy data indicates that seeds continue discrete growth, rather than merging into a shell. Ultimately, consistent silver seeding could not be achieved and shell formation was unsuccessful. The results of these studies are consistent with the conclusion that silver nucleation is limited by the photogeneration of electrons in TiO2, active site chemistry, and the inherent weakness of the Ag-TiO2 interaction.
