Recent interest in environmentally friendly alternatives to chromate-based corrosion inhibitors has led to the development of a range of novel coating formulations. The work described in this thesis has been aimed at investigating the mechanism of self-healing and active corrosion protection of the new coatings by searching for active components that have migrated from the coating to a controlled defect. The use of glow discharge optical emission spectroscopy (GDOES) has been investigated as a tool for both the generation of a reproducible controlled defect and for elemental depth profiling of the coatings and corroded substrates. Conclusions drawn from the elemental depth profiles have been validated by a range of characterisation techniques including optical microscopy, scanning electron microscopy, energy-dispersive X-ray spectroscopy (EDX) and electrochemical techniques. The work has focused particularly on a comparison of hybrid coatings doped with inhibitors encapsulated in nano-containers, as compared with the direct addition of inhibitor species to the coating matrix. The work also investigates the effects of inhibitor addition to sol-gel coatings or primer systems or both, highlighting possible synergistic effects of mixed inhibitor systems (for example, sol-gel coating doped with strontium aluminium polyphosphate (SAPP)) supporting primers doped with benzotriazol (BZT) or mercaptobenzothiazol (MBT). The various coatings have also been studied in the absence of inhibitor species to assess the effectiveness of the coatings as barriers between the substrate and the corrosive environment. This aspect of the study has highlighted minor inhibitive effects of some of the reagents used in the coating formulations and a major inhibitive effect of the nano-containers. The work therefore concludes with recommendations for a possible coating formulation combining the most beneficial elements of the various coatings investigated.

Magister Scientiae (Medical Bioscience) - MSc(MBS) / The aim of this study is to be the first to ascertain the effects of silver nanoparticles on testosterone production. The Ag NPs used for this study have the following characteristics; purity ≥ 99.5%; 66.7 % of particles have a diameter between 20-40 nm in aqueous solution. Three month old male Balb/C mice were sacrificed and testicular cell cultures were prepared. The cells were subsequently treated with various concentrations of Ag NPs (with or without luteinizing hormone (LH)-treatment) and incubated for 4 hours. Testosterone secretion in the culture supernantant was then determined using a testosterone ELISA kit. Ag NPs (at 20 μg/ml) significantly (p < 0.001) decreased LH-stimulated testosterone production as compared to the control. This study showed that Ag NPs adversely affect testosterone synthesis in vitro and can therefore pose a risk for male reproduction.

This thesis presents an integrated study of nanocatalysts for heterogenous catalytic and electrochemical processes using pure ruthenium (Ru) with mixed-phase and platinum-based nanomaterials synthesized by continuous-flow chemistry. There are three major challenges to the application of nanomaterials in heterogenous catalytic reactions and electrocatalytic processes in acidic solution. These challenges are the following: (i) controlling the size, shape and crystallography of nanoparticles to give the best catalytic properties, (ii) scaling these nanoparticles up to a commercial quantity (kg per day) and (iii) making stable nanoparticles that can be used catalytically without degrading in acidic electrolytes. Some crucial limitations of these nanostructured materials in energy conversion and storage applications were overcome by continuous-flow chemistry. By using a continuous-flow reactor, the creation of scalable nanoparticle systems was achieved and their functionality was modified to control the nanoparticles’ physical and chemical characteristics. The nanoparticles were also tested for long-term stability, to make sure these nanoparticles were feasible under realistic working conditions. These nanoparticles are (1) shape- and crystallography-controlled ruthenium (Ru) nanoparticles, (2) size-controlled platinum-metal (Pt-M= nickel (Ni) & copper (Cu)) nanooctahedra (while maintaining morphology) and (3) core-shell platinum@ruthenium (Pt@Ru) nanoparticles where an ultrathin ruthenium shell was templated onto the platinum core. Thus, a complete experimental validation of the formation of a scalable amount of these nanoparticles and their catalytic activity and stability towards the oxygen evolution reaction (OER) in acid medium, hydrolysis of ammonia borane (AB) along with plausible explanations were provided.

This study aims to synthesize nanostructured hematite films using spray pyrolysis at different deposition temperatures. L-arginine was used to transform the irregular shaped nanoparticles to uniform nanospheres by chemical bath deposition at 90°C for 48 h. We also investigated the variation of L-arginine: iron precursor concentrations from 1:1 to 3:1, respectively. Likewise, hematite films doped with zinc (Zn), silver (Ag), and Zn/Ag were synthesized using spray pyrolysis. All the films were annealed at temperatures ranging from 450 to 500°C for complete hematite phase transformation. The films were used as photoanodes in photoelectrochemical (PEC) water splitting experiments. X-ray diffraction confirmed the formation of the corundum hexagonal structure of hematite with space group. Raman spectroscopy further confirmed the polycrystalline hematite symmetry with two Eg and five A1g vibrational phonon modes. UV-Vis absorption showed a variation of absorbance with bandgaps that ranged from 2.10 to 1.90 eV. Scanning electron microscopy reported the shape transformation of nanoparticles to nanospheres that ranged in size from 6 to 100 nm. The study showed that the nanostructured films synthesized at temperatures of 430 and 400°C have the highest photocurrent densities of 6 and 1.52 µAcm-2, respectively. There was an improvement of the photocurrent density from 6.4 to 10 µAcm-2 after the transformation of pristine irregularly shaped hematite nanoparticles to spherical hematite. However, on the variation of L-arginine: iron precursor concentrations, a photocurrent of 9.8 µAcm-2 was obtained for 3:1 sample. Also, an improvement of photocurrent from 17 to 89 µAcm-2 was observed for films prepared at 30 and 50 mM iron precursor concentration, respectively. In addition, there was a significant increase in the photocurrent density from 40 to 813 µAcm-2 for pristine and Zn/Ag hematite films, respectively. Ultrafast transient absorption spectroscopy was used to study the electron-hole recombination rates and lifetimes. The results indicated four lifetimes obtained from global analysis with a reduction in the electron-hole recombination rate in the femtosecond and nanosecond range, both for L-arginine/hematite and doped samples. From this study, we were able to prove that the nanostructured and doped hematite films had a longer charge carrier lifetime compared to bulk hematite. / Thesis (PhD)--University of Pretoria, 2021. / African Laser Center (ALC) National Research Foundation (NRF) Grant no. N0115/115463 (SARChI, M.D.) University of Pretoria / Physics / PhD / Restricted

Parasitic friction and material wear exist in all moving parts, causing about 20% in global energy loss annually. Machinery startup accounts for a major portion of this loss. This issue involves a boundary lubrication problem, where rubbing surfaces are inadequately covered by lubricating oils. Lubricating oil fluids rely on tribochemical reactions to establish metalorganic tribofilms that protect the contacting surfaces. The improved oil lubrication mechanism can ensure smooth operation, improving efficiency, and extending the mechanical component lifetime. In this thesis, we study tribochemical reactions resulting from various fuel and oil blends. The interactions among blended additives are given particular attention. Lubrication phenomena are simulated using a ball-on-disk linear reciprocation configuration in a standardized tribological test rig, Optimol SRV5. The tribofilm growth patterns are investigated by measuring friction and electrical contact resistance (ECR), followed by a detailed surface analysis. The proposed lubrication mechanisms are verified with experimental and numerical simulation results. Fuel lubrication studies are conducted by investigating a) lubricity loss upon the addition of multiple oxygenated compounds, b) accelerated material wear rates observed in dieselethanol fuel blends, and c) enhanced lubrication performances with carbon-based nanofluid fuels. Lubricity loss is found to correlate with: ● Extended induction periods for ECR rises, ● Reduced average electrical contact resistance values, and ● Inhibitions of protective frictional species formations (e.g., iron oxides and graphite). The developed tribochemical reaction model advances the design of friction and extremepressure modifiers using tribo-active nanomaterials. For instance, adding carbon-based nanomaterials to fuels enhances lubrication performance by serving as tribo-active materials to accelerate tribofilm formation and by replenishing damaged surfaces. In engine oil systems, we demonstrated that the lubrication performance could be enhanced by formulating TiO2 nanoparticles modified by gallic acid esters, and polyether-based co(ter)polymers. Based on the tribochemical reaction mechanisms found in this study, we propose more designs of functionalized nanomaterials for advanced lubricant applications in future work.

archives@tulane.edu / Reactive Cavitation Erosion (RCE), a new materials processing technique for the production of functionalized nanomaterials in which acoustic cavitation erosion is performed in a reactive medium, is described herein. Background material on acoustic cavitation erosion in the form of a literature review is presented. The effects of fluid properties and ambient pressure on the bubble dynamics at the high acoustic pressures commensurate with RCE are studied. The solutions to the Rayleigh-Plesset equation (RPE) and Keller-Miksis equation (KME) are compared. It is shown that to a first approximation, the RPE and KME give similar results. Analyses of the RPE solutions for real-world fluids reveal that many fluids result in cavitation intensity comparable to or greater than that of water. The groundwork for future modelling of RCE was established through the development of the Hemispherical Pit Model (HPM). The HPM is based upon a simple geometrical model of the volume loss process and contains parameters that may be more directly related to material properties and experimental parameters. Formation of functionalized clinoatacamite nanoparticles is achieved through Reactive Cavitation Erosion of copper discs in a 1 M guanidine hydrochloride solution. From analyses, the mechanism for formation of the clinoatacamite proceeded from ablation of metallic copper from the disc surface followed by subsequent reactions in solution. / 1 / Jeremy William Wright

Nanostructured materials provide new and exciting approaches to the development of supercapacitor electrodes for high-performance electrochemical energy storage applications. One of the biggest challenges in materials science and engineering, however, is to prepare the nanomaterials with desirable characteristics and to engineer the structures in proper ways. This dissertation presents the successful preparation and application of very promising materials in the area of supercapacitor energy storage, including manganese dioxide and its composites, polyaniline and activated carbons. Attention has been paid to understanding their growth process and performance in supercapacitor devices. The morphological and electrochemical cycling effects, which contribute to the understanding of the energy storage mechanism of MnO2 based supercapacitors is thoroughly investigated. In addition, MnO2 based binary (MnO2-carbon nanocoils, MnO2-graphene) and ternary (MnO2-carbon nanotube-graphene) nanocomposites, as well as two novel electrodes (MnO2-carbon nanotube-textile and MnO2-carbon nanotube-sponge) have been studied as supercapacitor electrode materials, showing much improved electrochemical storage performance with good energy and power densities. Furthermore, a general chemical route was introduced to synthesize different conducting polymers and activated carbons by taking the MnO2 nanostructures as reactive templates. The electrochemical behaviors of the polyaniline and activated nanocarbon supercapacitors demonstrate the morphology-dependent enhancement of capacitance. Excellent energy and power densities were obtained from the template-derived polyaniline and activated carbon based supercapacitors, indicating the success of our proposed chemical route toward the preparation of high performance supercapacitor materials. The work discussed in this dissertation conclusively showed the significance of the preparation of desirable nanomaterials and the design of effective nanostructured electrodes for supercapacitor energy storage applications.

It is well established that cancer is one of the leading causes of death globally. Its complete eradication requires early detection and intensive drug treatment. In many cases it might also require surgery. Unfortunately, current medicine is still more focused on cancer treatment rather than elimination of its reason. The mechanism of tumor emergence and development is quite complicated, although, we are constantly advancing in this field. Nanomedicine is envisioned as the silver bullet against cancer. Thus, nanoscale systems with therapeutic and diagnostic modalities can simultaneously perform several functions: accurate detection of tumor site, precise targeting, and controlled drug release inside abnormal cells and tissues while being nontoxic to healthy ones. Moreover, surface modification of such nanoparticles allows them to be invisible to the immune system and have longer blood circulating time. The performed research in this dissertation is completely based on hybrid organicinorganic bridged silsesquioxane (also known as organosilica) nanomaterials, therefore comprising "soft" organic/bioorganic part which can imitate certain biorelevant structures and facilitates successful escape from the immune system for more efficient accumulation in cancer cells, while "hard" inorganic part serves as a rigid and stable basis for the creation of cargo nanocarriers and imaging agents. This dissertation discusses the 5 critical points of safe biodegradable nanoplatforms, delivery of large biomolecules, and cytotoxicity regarding the shape of nanoparticles. As a result novel fluorescent biodegradable oxamide-based organosilica nanoparticles were developed, light-triggered surface charge reversal for large biomolecule delivery was applied with hollow bridged silsesquioxane nanomaterials, and biocompatibility of periodic mesoporous organosilicas with different morphologies was studied. Furthermore, the current achievements and future perspectives of mesoporous silica organosilica, and silsesquioxane nanoparticles were considered in regards to their biomedical applications and summarized in two reviews.

Indiana University-Purdue University Indianapolis (IUPUI) / The expansion of the applications of direct band gap semiconductor nanocrystals (NCs) has been a result of the control colloidal synthetic methods offer on the optoelectronic properties. These properties are readily controlled by the surface chemistry and even a small change in the surface passivating ligand can show profound effects. Furthermore, the choice of surface passivating ligand also impacts the NC shape evolution, which in turn influence the surface area, quantum yield, and charge transport properties that are critical to optimize device fabrication. In this dissertation, the unique aspects of surface chemistry that control both NC shape evolution and optoelectronic properties are investigated. We began by investigating how surface chemistry controls the shape evolution of methyl ammonium lead bromide (CH3NH3PbBr3) perovskite NCs. In addition to the surface passivating ligand, the reaction temperature and solvent system were also examined. Through a series of control experiments, the critical parameter for the formation of quantum wires (QWs) was found to be the presence of a long chain acid, while the quantum platelets (QPLs) required a long chain amine and chlorinated solvent, and quantum cube (QC) formation was kinetically driven. The higher ordered stacking of the QPLs and bundling of the QWs was also found to be controlled by surface ligand chemistry. Next we further examined how surface chemistry impacts shape evolution, but in the system of metal chalcogenide NCs. We developed a versatile, low temperature, and gram scale synthesis of QWs, QPLs, and quantum rods (QRs) using both cadmium and zinc as metal precursors and sulfur and selenium as chalcogenide precursors. Through systematic investigation of both the surface chemistry and reaction progression, the growth and formation mechanism was also determined. The 1D QW growth required a long chain amine while the QPLs required the presence of both a long and short chain amine to drive 2D growth. Finally, the QRs would found to be a kinetically-controlled process. Ultrasmall semiconductor NCs are known to possess high surface to volume ratios and therefore even a minute change in surface chemistry will have a significant impact on the optoelectronic properties. Our investigation focused on (CdSe)34 NCs, and how exchanging native amine ligands with various chalcogenol based ligands influences these properties. These NCs lie in the strong confinement regime and therefore have a higher probability of undergoing exciton delocalization, resulting in red shifts of the first excitonic peak and reduction of the optical band gap. Additionally, we examined different characteristics of the ligand (level of conjugation, electron withdrawing or donating nature of para-substitution, binding mode and head group) to examine how these parameters impact exciton delocalization. We observed the highest shift in the optical band gap (of 650 meV) after exchanging the native amine ligands with pyrene dithiocarbamate. Through this investigation it was determined that ligand characteristics (specifically conjugation and binding mode) have significant influence in the proposed hole delocalization. Finally, we continued the investigation of how surface chemistry controls optoelectronic properties of ultrasmall NCs, but expand our work to those of methyl ammonium lead halide. We developed a low temperature and colloidal synthesis of white-light emitting NCs with a diameter of 1.5 nm. Through precise manipulation of the surface halide ions, it was possible to tailor the emission to match that of nearly pure white light.

The foundation for supramolecular chemistry is in nature; by studying these archetypes, chemists have devised methods of recreating these complex interactions in the laboratory. Of particular interest is the interplay between enzyme- more specifically, its active site- and the target substrate. Utilizing recent advancements in self-assembled monolayers, progress towards a more-accurate flavoenzyme model has been demonstrated.