published_or_final_version / abstract / Physics / Doctoral / Doctor of Philosophy

Nanomaterials have gained much attention as in energy storage application for its unique electrical properties. Many research groups have developed various methods to fabricate nanomaterials for various applications. However, there exists much possibilities of developing cost-effective methods for nanomaterial fabrication. No one has studied using natural organic compound A as solution base for wet process nanomaterial synthesis. In this study, a new method of fabricating two-dimensional structure nanomaterials is proposed. This method is applicable for multiple metal elements such as copper oxide, copper hydroxide, and iron oxide. The two dimensional structure nanomaterials have prestige properties because of their large surface aspect ratio. The organic compound A is also found useful for silver nanoparticle synthesis. The growth mechanism of copper nanowires is also studied using other synthesis method. The IR absorption property for 2D materials as well as copper nanorod are tested, and the 2D copper sheets perform light absorption properties characterized by UV-VIS. The organic compound A used in this study is under provisional patent process.

Dye-sensitized solar cells (DSSC) have drawn much attention due to their higher versatility and lower production cost compared to inorganic photovoltaics. The top performers of DSSC have achieved power conversion efficiency over 10%, which is comparable to amorphous silicon solar cells. In this work, new photosensitizers and nanostructure for improving the photovoltaic performance of DSSC were developed and evaluated. Two series of cyclometalated ruthenium(II) complex photosensitizer were presented and their photosensitizing properties in DSSC were studied. Eight cyclometalated ruthenium(II) terpyridine complexes with three carboxylic acid groups on the terpyridine ligand were synthesized. Series A (M1 to M4) consist of C,N,N’ ligands substituted with phenyl group whereas series B (M5 to M8) consist of C,N,N’ ligands substituted with m-fluorophenyl group. All of the complexes exhibited broad aborption spectra covering the whole visible spectrum. The complexes in series B generally showed better photovoltaic performance than those in series A in the DSSCs. DSSC fabricated from M7 achieved the highest Voc, Jsc and power conversion efficiency among other DSSC, which were 0.56 V, 7.30 mAcm-2 and 2.63 % respectively. Truxene-core donor--acceptor dyes were presented and their photosensitizing properties in DSSC were studied. Eight dyes with either one donor two acceptors system (T2, B2, T2R and B2R) or two donor one acceptor system (T1, B1, T1R and B1R) were synthesized. Dyes with two acceptors have high molar extinction coefficients originated from the charge-transfer transition band, which are almost two times higher than those with only one accceptors. Both the enhanced absorption and better anchoring geometry on TiO2 contribute to the better photovoltaic performance of the two acceptors dyes in the DSSCs. Devices fabricated from B2 and volatile solvent electrolyte exhibited the best photovoltaic performance among the truxene-core dyes. The Voc, Jsc, FF and power conversion efficiency of the device were 0.59 V, 9.69 mAcm-2, 0.63 and 3.62 % respectively. Dyes based on cyanoacrylic acid anchoring groups (T1, T2, B1 and B2) were found to perform better than those based on rhodanine-3-acetic acid dyes (T1R, T2R, B1R and B2R) in both donor--acceptor configurations. ITO nanorod/TiO2 nanoparticle composite films with the three different types of ITO nanorod with different length (150 nm, 600 nm and 1.5 μm) were fabricated on FTO glass substrate. The transmittance and sheet resistance of the ITO nanorod array on the FTO glass substrate were found decreased with increasing the length of the ITO nanorod. When the ITO nanorod/TiO2 nanoparticle composite films were applied as the anode in DSSCs, the device fabricated from 600 nm ITO nanorod with TiO2 ‘double layer‘ film showed enhanced photocurrent generation. The improved photocurrent generation is suggested to be due to an improved charge collection efficiency at the ITO nanorod back electrode. / published_or_final_version / Chemistry / Doctoral / Doctor of Philosophy

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published_or_final_version / abstract / Chemistry / Doctoral / Doctor of Philosophy

The results presented in this thesis demonstrate the first synthesis of several nanostructured transition metal oxides and lithium containing transition metal oxides. Their uses in lithium-ion batteries and/or as magnetic materials have been investigated. The first example of two and three dimensional mesoporous Fe₂O₃ has been prepared by using the soft templating (surfactant) method. The materials have amorphous walls and exhibit superparamagnetic behaviour. By using a hard template route, a mesoporous α-Fe₂O₃ with highly crystalline walls has been synthesized. Its unique magnetic behaviour, distinct from bulk α-Fe₂O₃, nanoparticulate α-Fe₂O₃, and mesoporous Fe₂O₃ with disordered walls, has been demonstrated. The hard template method was also used to prepare nanowire and mesoporous Co₃O₄, β-MnO₂ and MnO₃ with crystalline walls. Their electrochemical properties as electrodes in Li-ion batteries have been investigated. Mesoporous β-MnO₂ can accommodate 0.9 Li/Mn in stark contrast to bulk β-MnO₂ which cannot accommodate Li. To prepare mesoporous materials which cannot be obtained directly by the hard template method, a post-templating route has been developed. Mesoporous Fe₃O₄, γ-Fe₂O₃, and Mn3O4 with ordered mesostructures and highly crystalline walls have been obtained by post-synthesis reduction/oxidation treatments. All the materials show unique magnetic properties compared with nanoparticulate and bulk materials. Also, the first example of lithium containing mesoporous material, LT-LiCoO₂, was synthesized by first preparing mesoporous Co₃O₄, then reacting this with LiOH to form LT-LiCoO₂, with retention of the ordered nanostructure. The nanostructured LT-LiCoO₂ compounds demonstrate superior performance compared with normal or nanoparticulate LT-LiCoO₂, when used as intercalation electrodes in lithium batteries. Finally, monodispersed Mn₃O₄ nanoparticles (diameter ~ 8 nm) with a core-shell structure (a highly crystalline Mn₃O₄ core encased in a thin MnO₂ shell) have been prepared for the first time. Ordered three-dimensional arrays form by spontaneous self-assembly. Magnetic measurements demonstrated that the self-assembled three-dimensional arrays exhibit spin-glass behaviour, rather than the anticipated superparamagnetic behaviour for isolated nanoparticles. Such behaviour is interpreted as arising from strong interactions between the core (crystallized Mn₃O₄) and shell (MnO₂).

M.Sc. (Nanoscience) / Please refer to full text to view abstract

The work presented in this dissertation is a composite of experiments in the growth of gold nanoparticles with specific optical properties of interest. The goal is to synthesize these gold nanoparticles using soybean extract for not only shape control, but for propensity as a biocompatible delivery system. The optical properties of these nanoparticles has found great application in coloring glass during the Roman empire and, over the centuries, has grown into its own research field in applications of nanoparticulate materials. Many of the current functions include use in biological systems as biosensors and therapeutic applications, thus making biocompatibility a necessity. Current use of cetyltrimethylammonium bromide leads to rod-shaped gold nanoparticles, however, the stability of these gold nanoparticles does not endure for extended periods of time in aqueous media. In my research, two important components were found to be necessary for stable, anisotropic growth of gold nanoparticles. In the first experiments, it was found that bromide played a key role in shape control. Bromide exchange on the gold atoms led to specific packing of the growing crystals, allowing for two-dimensional growth of gold nanoparticles. It was also discerned that soybean lecithin contained ligands that blocked specific gold facets leading to prismatic gold nanoparticle growth. These gold nanoprisms give a near infrared plasmon absorption similar to that of rod-shaped gold nanoparticles. These gold nanoprisms are discovered to be extremely stable in aqueous media and remain soluble for extended periods of time, far longer than that of gold nanoparticles grown using cetyltrimethylammonium bromide. Since soy lecithin has a plethora of compounds present, it became necessary to discover which compound was responsible for the shape control of the gold nanoprisms in order to optimize the synthesis and allow for a maximum yield of the gold nanoprisms. Many of these components were identified by high performance liquid chromatography and liquid chromatography-mass spectrometry. However, re-spike of these components into growth solutions did not enhance the growth of gold nanoprisms. Upon separating the shapes of the gold nanoparticles using gel electrophoresis, addition of KCN to the separated gold nanoparticles allowed us to extract the culpable ligands for shape control. Analysis of these ligands by mass spectrometry elucidated the identity of PA and upon re-spike of the PA into a growth solution of PC95, the growth of a near-infrared plasmon absorption was seen. The stability of these gold nanoparticles was tested with and without the addition of decane thiol and it was concluded that addition of the thiol allowed for improved stability of the gold nanoparticles towards cyanide. It was determined that at a concentration of 2 μM decanethiol, spherical gold nanoparticles remained stable to cyanide at the expense of the prismatic gold nanoparticles. However, at 5 μM decanethiol, both spherical and prismatic gold nanoparticles retained stability to cyanide in aqueous conditions.

published_or_final_version / abstract / Physics / Master / Master of Philosophy