abstract: Engineered nanomaterials (ENMs) are added to numerous consumer products to enhance their effectiveness, whether it be for environmental remediation, mechanical properties, or as dietary supplements. Uses of ENMs include adding to enhance products, carbon for strength or dielectric properties, silver for antimicrobial properties, zinc oxide for UV sun-blocking properties, titanium dioxide for photocatalysis, or silica for desiccant properties. However, concerns arise from ENM functional properties that can impact the environment and a lack of regulation regarding ENMs leads to potential public exposure to ENMs and results in ill-informed public or manufacturer perceptions of ENMs. My dissertation evaluates the environmental, human health, and societal impacts of using ENMs, with a focus on ionic silver and nanosilver, in consumer and industrial products. Reproducible experiments served as functional assays to assess ENM distributions among various environmental matrices. Functional assay results were visualized using radar plots and aid in a framework to estimate likely ENM disposition in the environment. To assess beneficial uses of ENMs, bromide ion removal from drinking waters to limit disinfection by-product formation was studied. Silver-enabled graphene oxide materials were capable of removing bromide from water, and exhibited less competition from background solutes (e.g. natural organic matter) when compared against solely ionic silver addition to water for bromide removal. To assess complex interactions of ENMs with the microbiome, batch experiments were performed using fecal samples spiked with ionic silver or commercial dietary silver nanoparticles. Dietary nanosilver and ionic silver exposures to the fecal microbiome for 24 hours reduce short chain fatty acid (SCFA) production and changes the relative abundance of the microbiota. To understand the social perceptions of ENMS, statistically rigorous surveys were conducted to assess related perceptions related to the use of ENMs in drinking water treatment devices the general public and, separately, industrial manufacturers. These stakeholders are influenced by costs and efficiency of the technologies, consumer concerns of the safety of technologies, and environmental health and safety of the technologies. This dissertation represents novel research that took an interdisciplinary approach, spanning from wet-lab engineering bench scale testing to social science survey assessments to better understand the environmental, human health, and societal impacts of using ENMs such as nanosilver and ionic silver in industrial processes and consumer products. / Dissertation/Thesis / Doctoral Dissertation Civil, Environmental and Sustainable Engineering 2020

Thesis (Ph. D. (Physics)) -- University of Limpopo, 2016. / Single and double doped nanometric powders of Single and double doped nanometric powders of titanium dioxide (TiO2) were synthesised by the sol-gel process using titanium isopropoxide (TTIP) as the precursor. For comparison, an undoped sample was also prepared. The metal dopants, Ag and Cu, were used at doping levels of 5% molar weight. The samples were dried at 100°C in air and post annealing was done at 300°C, 600°C, 900°C and 1100°C. Structural characterisation of the samples was carried out by X-ray Diffraction (XRD), Raman Spectroscopy, Scanning Electron Microscopy (SEM) and Energy dispersive X-ray Spectrometry (EDS) techniques. Most samples annealed at the 300°C temperature (and lower) revealed the predominantly-anatase phase, while those annealed at 900°C and above were rutile-only. The double-doped powder that was annealed at 300°C was found to be constituted by anatase and brookite phases (with the dopants incorporated into the TiO2 matrix), and the one annealed at 600°C was a mixture of brookite and rutile. The results suggest that multiple doping of titania may favour a two-phase structure at lower temperatures than singly-doped powders. The co-existence of brookite with anatase is believed to be responsible for the enhancement of anatase to rutile transformation in the double-doped sample. UV-visible (UV-vis) and Photoluminescence (PL) measurements were also carried out to study the optical properties of the TiO2 nanoparticles. This revealed the active PL band at around 440 nm. By narrowing the band gap, the double-doped powders that exhibited the brookite phase, again showed improved visible light photo absorption over the other samples, with a significant shift of the absorption edge to shorter wavelengths. Further, PL spectra revealed a change in PL intensity with phase change, as well as the presence of exciton energy levels at the base of the conduction band. The changes in the electrical conductivities of representative anatase and rutile TiO2 nanopowders upon exposure to water-vapour, ammonia (NH3) and hydrogen (H2) were also investigated. Sensing measurements for water-vapour was done at room temperature for various humidity levels ranging from 5.4% RH to 88.4% RH. The detection of NH3 and H2 gases were carried out at temperatures extending from room temperature to 350°C and over concentration ranges of 25 sccm to 500 sccm and 15 v sccm to 200 sccm respectively. The gas-sensing results show that the sol-gel fabricated TiO2 nanoparticles (particularly in anatase form), has excellent fast and stable dynamic responses to humidity, NH3 and H2. They feature good sensitivities, even at a low operating temperatures. However, acceptor behaviour, for which there was a conductivity switch from n-type to p-type, was recorded for the Ag-doped rutile powders at operating temperatures of 300ºC and 350ºC. Overall, the double-doped sample annealed at 300ºC was deemed the most promising candidate for gassensing. (TiO2) were synthesised by the sol-gel process using titanium isopropoxide (TTIP) as the precursor. For comparison, an undoped sample was also prepared. The metal dopants, Ag and Cu, were used at doping levels of 5% molar weight. The samples were dried at 100°C in air and post annealing was done at 300°C, 600°C, 900°C and 1100°C. Structural characterisation of the samples was carried out by X-ray Diffraction (XRD), Raman Spectroscopy, Scanning Electron Microscopy (SEM) and Energy dispersive X-ray Spectrometry (EDS) techniques. Most samples annealed at the 300°C temperature (and lower) revealed the predominantly-anatase phase, while those annealed at 900°C and above were rutile-only. The double-doped powder that was annealed at 300°C was found to be constituted by anatase and brookite phases (with the dopants incorporated into the TiO2 matrix), and the one annealed at 600°C was a mixture of brookite and rutile. The results suggest that multiple doping of titania may favour a two-phase structure at lower temperatures than singly-doped powders. The co-existence of brookite with anatase is believed to be responsible for the enhancement of anatase to rutile transformation in the double-doped sample. UV-visible (UV-vis) and Photoluminescence (PL) measurements were also carried out to study the optical properties of the TiO2 nanoparticles. This revealed the active PL band at around 440 nm. By narrowing the band gap, the double-doped powders that exhibited the brookite phase, again showed improved visible light photo absorption over the other samples, with a significant shift of the absorption edge to shorter wavelengths. Further, PL spectra revealed a change in PL intensity with phase change, as well as the presence of exciton energy levels at the base of the conduction band. The changes in the electrical conductivities of representative anatase and rutile TiO2 nanopowders upon exposure to water-vapour, ammonia (NH3) and hydrogen (H2) were also investigated. Sensing measurements for water-vapour was done at room temperature for various humidity levels ranging from 5.4% RH to 88.4% RH. The detection of NH3 and H2 gases were carried out at temperatures extending from room temperature to 350°C and over concentration ranges of 25 sccm to 500 sccm and 15 v sccm to 200 sccm respectively. The gas-sensing results show that the sol-gel fabricated TiO2 nanoparticles (particularly in anatase form), has excellent fast and stable dynamic responses to humidity, NH3 and H2. They feature good sensitivities, even at a low operating temperatures. However, acceptor behaviour, for which there was a conductivity switch from n-type to p-type, was recorded for the Ag-doped rutile powders at operating temperatures of 300ºC and 350ºC. Overall, the double-doped sample annealed at 300ºC was deemed the most promising candidate for gassensing.

abstract: A Fundamental study of bulk, layered, and monolayers bromide lead perovskites structural, optical, and electrical properties have been studied as thickness changes. X-Ray Diffraction (XRD) and Raman spectroscopy measures the structural parameter showing how the difference in the thicknesses changes the crystal structures through observing changes in average lattice constant, atomic spacing, and lattice vibrations. Optical and electrical properties have also been studied mainly focusing on the thickness effect on different properties where the Photoluminescence (PL) and exciton binding energies show energy shift as thickness of the material changes. Temperature dependent PL has shown different characteristics when comparing methylammonium lead bromide (MAPbBr3) to butylammonium lead bromide (BA2PbBr4) and comparing the two layered n=1 materials butylammonium lead bromide (BA2PbBr4) to butylammonium lead iodide (BA2PbI4). Time-resolved spectroscopy displays different lifetimes as thickness of bromide-based perovskite changes. Finally, thickness dependence (starting from monolayers) Kelvin Probe Force Microscopy (KPFM) of the layered materials BA2PbBr4, Butylammonium(methylammonium)lead bromide (BA2MAPb2Br7), and molybdenum sulfide (MoS2) were studied showing an exponential relation between the thickness of the materials and their surface potentials. / Dissertation/Thesis / Masters Thesis Electrical Engineering 2019

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<p dir="ltr">Deoxyribonucleic acid or DNA is an essential component in cells and organisms for genetic information storage and transduction. The base paring chemistry offers excellent programmability and structural predictability. This gives rise to the field of DNA nanotechnology, which uses DNA to design nanostructures and nanomachines with unprecedented designability and controllability. With the development of DNA nanotechnology, numerous chemical tools have been introduced for designing complex molecular mechanisms with DNA molecules. Various nanostructures of arbitrary shapes have been demonstrated, which shows the immense potential of DNA-based engineering. Dynamic nanodevices and their programmable actuations have also been successfully realized using DNA strand displacement and/or enzymatic reactions.</p><p dir="ltr">With controllable interactions with various biomolecules, it is possible to implement DNA in synthetic biological systems to program their behaviors. Two systems with programmed behaviors are introduced in this dissertation. The first system is a lipid-based protocell that can perform programmed migration with DNA-based mechanisms. This model system extracts chemical energy from fuel strands via enzymatic reaction and converts it into autonomous translocation on a surface. A mechanistic model is proposed to understand the migration dynamics. Furthermore, a path-tracking behavior between synthetic vesicles is demonstrated, which mimics cellular chemotaxis for the first time.</p><p dir="ltr">The second synthetic biological system explored is DNA origami structures capable of programmable auxetic reconfiguration. Auxetic materials are artificial systems with a negative Poisson’s ratio, which show great promise in various applications including space engineering and flexible/wearable electronics. With DNA-based sliding mechanisms, the proposed auxetic architecture can switch between two conformations with different Poisson’s ratios. The proposed strategy may be applied to designing adaptive materials or biochemical sensors with mechanical responses. The DNA-programmed behaviors demonstrated in this dissertation show unprecedented versatility and programmability, thus opening new opportunities for using molecular mechanisms to control synthetic biological systems with complex functions in diverse areas including biology, biomedicine, and material sciences.</p>

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