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

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

published_or_final_version / abstract / Physics / Master / Master of Philosophy

Thesis (Ph.D)--Materials Science and Engineering, Georgia Institute of Technology, 2008. / Committee Chair: Wang, Zhong Lin; Committee Member: Degertekin, F. Levent; Committee Member: Liu, Meilin; Committee Member: Snyder, Robert L.; Committee Member: Tannenbaum, Rina. Part of the SMARTech Electronic Thesis and Dissertation Collection.

D.Phil. / The work that is presented in this thesis describes the numerous detailed investigations that were conducted with a custom-made horizontally aligned, water-cooled, gas-filled DC arc-discharge reactor. A focus of the investigations was the establishment of the effects of high purity graphite electrodes in ultra-high purity (UHP) He, H2 or mixtures thereof, in the absence of a metal catalyst on the reaction. These studies showed that higher yields of MWCNTs were formed in reactions between graphite electrodes in H2 than in He. Additionally, a range of gaseous hydrocarbons were formed in H2 that were not formed in He. After the initial parameters were established, investigations examined the effects on the products that were formed by the addition of high purity Cu to graphite. The data from these studies revealed that H2 played a pivotal role in the reactions and that metallic copper nanoparticles were the active catalysts. In particular, they showed that when the Cu/C mole ratio and particle size ranges were fixed (i.e. 0.20 and < 150 μm respectively), then branched CNTs were exclusively found in a collar deposited around the cathode, with bamboo-shaped CNTs formed in the reaction chamber. Characterisation of these products revealed that the Cu nanoparticles were probably molten during the reactions and thus a growth model was proposed in which it was suggested that dehydrogenation reactions of gaseous hydrocarbon species on the surfaces of unsupported molten copper nanoparticles led to the formation of either bamboo-shaped or branched CNTs.

Thesis (Master of Applied Sciences in Chemistry)--Cape Peninsula University of Technology, 2018. / Biosensors have been on the forefront to provide clinical diagnosis tools for various diseases. Proper selection of biomarkers as well as chemical electrode modification is key in the fabrication of electrochemical biosensors. Hence, electrode modified with nanomaterials devices to improve electroanalytical applications. These nanomaterials were functionalized to improve conductivity, accelerate signal transduction and amplify biorecognition events. Thus, resulting in novel sensing platforms that are highly sensitive and selective towards the target analyte. In this study, gold nanorods (Au NRs) capped with CTAB, zeolitic imidazole framework were synthesised using the seed mediated and hydrothermal method respectively. Composites of gold nanorods with cysteine, ZIF-8 or both were also synthesised. All synthesised materials were characterized using ultraviolet–visible (UV-Vis) spectroscopy, Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), X-Ray diffraction (XRD) and cyclic voltammetry (CV) techniques. The obtained results confirmed the synthesis of the nanomaterials and composites. Identification of the ideal platform for fabrication of a transducer with the best electrochemical response was determined by studying the combinations of the synthesised nanomaterials and composites. The studied parameters were surface coverage, conductivity, rate of electron transfer constant. Cysteine-Au NRs composites platforms, had exceptional properties hence its synthesis optimisation of was undertaken. The effect of CTAB, reaction time, volume and concentration ratio of Au:Cysteine, temperature and pH on the composite properties were assessed. However, this composite’s electrochemical properties decreased when bioconjugated with the antibodies. Hence, the choice of Au NRs CTAB functionalised ZIF-8 (CTABAu/ZIF-8) as the transducer for biosensor applications due to a more favourable biocompatibility. Biosensor fabrication was done by drop coating glassy carbon electrode with the CTABAu/ZIF-8 forming a transducer followed by immobilisation of the antibody (Ab) using a covalent attachment method with glutaraldehyde (GA) as a cross linker. The target analyte, epidermal growth factor (EGF) was interacted with the Ab binding sites via electrostatic forces. All the fabrication steps were optimized for biosensor components, immobilization technique (drop coating and immersion), concentration and incubation time of linker and bioreceptor, as well as the synthesis of the CTABAu-ZIF-8 composites where in situ and ex situ techniques were compared together with the effect of the concentration ratio of Au: ZIF-8. There was also an analysis of optimum pH. Optimum conditions were found to be immersion in 3 % GA and 2 μg/ml Ab, with incubation times of 8, 10 and 5 minutes for GA, Ab and EGF respectively at a pH of 6. The following electroanalytical techniques: cyclic voltammetry (CV), differential pulse voltammetry (DPV) and square wave voltammetry (SWV) were utilised for EGF detection. The DPV showed better reproducibility, higher currents and better resolution hence; it was the method of choice. The technique’s optimisation involved assessments of the effect of step potential, starting potential and pulse amplitude. The optimum response for pulse amplitude, step potential and starting potential were 60 mV, 20 mV and 0.5 V respectively. The biosensor analytical parameters were linear towards EGF in the concentration range from 2 to 100 nM with a detection limit of 0.58 nM. Reproducibility and repeatability tests were acceptable, and the biosensor had a stability over 80 % within 15 days. There was no interference observed in the presence of glucose and creatine. The EGF biosensor was successfully applied in urine and saliva analysis, obtaining 67.5 and 3.12 nM respectively. This biosensor’s positive outcome strongly suggests its potential as a diagnosis tool for early detection of kidney disease as it was able to detect EGF concentration within physiological levels of EGF in normal kidney function.