Fe(II)-based degradative solidification/stabilization (Fe(II)-DS/S) technology is the modification of conventional solidification/stabilization (S/S). Inorganic pollutants are immobilized by Fe(II)-DS/S while organic pollutants are destroyed. Experimental studies were conducted to identify the active agents for Tetrachloroethylene (PCE) degradation as well as the conditions that enhance the formation of the active agents in the Fe(II)-DS/S system. PCE was chosen as a model chlorinated aliphatic hydrocarbon in this study. First, the conditions that lead to maximizing production of the active agents were identified by measuring the ability of various chemical mixtures to degrade PCE. Results showed that Fe(II), Fe(III), Ca, and Cl were the the important elements that affect degradation activity. Elemental compositions of the mixtures and the conditions affecting solid formation might be the important factors in determining how active solids are formed. Second, instrumental analyses (XRD, SEM, SEM-EDS) were used to identify minerals in chemical mixtures that have high activities. Results indicate that active agents for PCE degradation in Portland cement slurries and in cement extracts might be one of several AFm phases. However, systems without cement did not form the same solids as those with cement or cement extract. Ferrous hydroxide was identified as a major solid phase formed in systems without cement. Finally, the effect of using different types of ordinary Portland cement (OPC) on PCE degradation rate during Fe(II)-DS/S was examined and the solids were examined by instrumental analyses (XRD, SEM, SEM-EDS). Four different OPC (Txi, Lehigh, Quikrete, and Capitol) showed different PCE degradation behaviors. Pseudo first-order kinetics was observed for Capitol and Txi OPC and second-order kinetics was observed for Quikrete. In the case of Lehigh cement, pseudo first-order kinetics was observed in cement slurry and second-order kinetics in cement extract. Calcium aluminum hydroxide hydrates dominated solids made with Txi, Quikrete, and Lehigh cements and Friedel’s salt was the major phase found in solids made with Capitol cements. Fe tended to be associated with hexagonal thin plate particles, which were supposed to be a LDH.

Thesis (M.S.)--University of North Texas, May, 2008. / Title from title page display. Includes bibliographical references.

Thesis (Ph. D.)--University of North Texas, Aug., 2009. / Title from title page display. Includes bibliographical references.

Thesis (PhD.(Chemical Engineering)--University of Pretoria, 2005. / Includes bibliographical references.

In this work, several materials possessing a layered structure were investigated using a technique of exfoliation in liquid phase to produce few- to mono-layers of the material. Materials exfoliated in such a way included graphite, boron nitride, molybdenum disulfide and tungsten disulfide. Subsequent transmission electron microscopy and accompanying electron diffraction patterns revealed that few and mono layer forms of these materials have been realized through this exfoliation method. Ultraviolet-visible spectroscopy confirmed the shifting of the band gaps in molybdenum and tungsten disulfides that is predicted in reducing the number of layers of these materials and was also used to confirm the band gap of the boron nitride. As a potential application, exfoliated molybdenum disulfide was used in the construction of electrodes for electrical charge storage in an electrochemical double layer capacitor, or supercapacitor, style device. Cyclic voltammetry, galvanostatic charge discharge, and electrochemical impedance spectroscopy measurements were performed using three different electrolytes, which showed good capacitive behavior for these devices. Using the data from electrochemical impedance spectroscopy, equivalent circuit models were generated to represent the systems in different electrolytes. From this, it was determined that the capacitive behavior of these systems was partially diffusion limited.

Layered mafic intrusions represent an important aspect of magmatism on earth and have occurred from Archean to present times. Literature on the geochemistry and petrology of these intrusions abounds but their physical properties, which could provide significant constraints on their formation, have seldom been investigated. Classic petrological methods such as whole-rock geochemistry, textural analysis and mineral chemistry have been applied to several intrusions of various ages. Most of these methods are relatively expensive or time intensive which limits high resolution studies. On the contrary, magnetic methods are typically inexpensive and fast and have been successfully applied to various occurrences of mafic rocks. In this study, several magnetic methods have been applied to a 600 m-long continuous borehole core drilled through one of the world's largest layered mafic intrusion, the Great Dyke of Zimbabwe. The main goal of this study is to constrain the magmatic history of the intrusion. More specifically, it is important to determine if the intrusion functioned as an open system, characterized by multiple magma pulses, or as a closed system, undergoing differentiation after a single magmatic pulse. The magnetic methods have also been validated by other independent approaches including image analysis, and electron microprobe. This study demonstrates that magnetic methods can be used to rapidly obtain critical information on the internal structure of this type of intrusion before applying more costly chemical analyses. The main scientific result of this study is to document the closed system nature of the Great Dyke of Zimbabwe, at least throughout the sequence investigated.

Submitted in fulfilment of the academic requirements for the Degree of Master's in Chemistry, Durban University of Technology, 2017. / Hydrotalcites (HT) and hydrotalcites-like (HTLc) compounds were synthesized by the co-precipitation method under low supersaturation. The synthesized binary Mg-Al hydrotalcites and ternary Cu/Mg-Al hydrotalcite-like compounds were characterized by various physico-chemical techniques such as inductively coupled plasma-optical emission spectroscopy (ICP-OES), powder X-ray diffraction (XRD), Fourier transform- infrared spectroscopy (FT-IR), ultraviolet-visible (UV-VIS) spectroscopy, thermogravimetric analysis (TGA), scanning electron microscopy (SEM) and BET surface area analysis. Elemental composition generated from ICP-OES data revealed a value of x in the region of 0.25 to 0.33 for all the compounds except for the MgAl-11 sample which revealed an x value of 0.5 while XRD patterns exhibited characteristic features indicative of an ordered layered material. FT-IR spectra confirmed the presence of characteristic functional groups and interlayer anions. Only Cu2+ which has a d9 configuration was accountable for the bands identified in UV-VIS spectra, whereas both Mg and Al with their d0 electron configurations showed no absorptive bands in the UV-VIS spectra. During thermal treatment by TGA, typical weight loss of Cu-Mg/Al HTLcs with temperature elevation was observed. The SEM images clearly demonstrated that all the Cu-Mg/Al HTLcs retained their characteristically layered structure morphologies. The BET surface area measurements showed no trend, however the surface area decreased with an increase in the copper concentration in some cases. For the heterogeneous hydroxylation of phenol using H2O2 as an oxidant, several reaction parameters such as solvent systems, catalyst amount, temperature, substrate/oxidant ratio, time and solvent volume were investigated. The product stream, monitored by gas chromatography showed that catechol (CAT) and hydroquinone (HQ) were the main products. Non-catalytic (blank) experiments were investigated to determine whether the reactants and the internal standard contributes to the conversion of phenol without the use of a catalyst. All blank reactions showed very low phenol conversions which were less than 1%, whereas the Mg/Al HTs showed low phenol conversions as well. All the Cu-Mg/Al catalysts showed measurable phenol conversion with Cu-Mg/Al-51a giving the highest conversion of 29.9% and a 56 and 44% selectivity towards CAT and HQ, respectively. The Cu-Mg/Al-15b catalyst, which had the lowest copper concentration, showed the lowest phenol conversion of 8.3% with a 55 % CAT selectivity and 45% HQ selectivity. In general, the phenol conversion increased with an increase in copper concentration. This reinforced the hypothesis that copper was the active centre in this reaction, since no measurable conversion was observed with Mg/Al HTs. / M

Abstract Layered composite materials consisting of thin orthotropic layers offer for a designer many possibilities to tailor the structure: the behaviour and properties of the structure can be influenced not only by varying the geometry and thicknesses of the structure but also by varying the lay-up of the laminate. As new orthotropic materials having high specific strength and stiffness are used in structures, the tailoring is essential to utilize all the benefits of these materials. In this thesis tailoring and optimization of thermomechanical properties of layered composite structures are considered. The tailoring problemis formulated and solved as a constrained nonlinear optimization problem. Different types of global thermomechanical properties, such as stiffnesses, coefficients of thermal expansion and natural frequencies and buckling loads of composite plates, as well as layer-wise properties, such as stresses and strains in a certain lamina, are considered. Also, coupled thermalstructural problems are studied. When lay-up parameters, i.e. number of layers, and their orientations and thicknesses, are employed as design variables, global as well as layer-wise properties of the laminate can be considered. As relations between thermomechanical properties and lay-up parameters are highly nonlinear, optimization may suffer from various local optima. However, in tailoring the global minima or maxima are not the points of interest but rather the points of design space, where appropriate values for considered properties are achieved. In the thesis optimization of global thermomechanical properties is presented also by applying so-called lamination parameters as design variables. The lamination parameters are defined as integrals of the functions, which consist of sines and cosines of the lay-up angles of different layers multiplied by the powers of the thickness co-ordinate z, through the thickness of the laminate. Thus, information of the lay-up of the laminate can be compressed into these parameters and only twelve lamination parameters are needed to describe the behaviour of a common laminate. The use of these parameters as design variables is advantageous, because the number of parameters needed is small and often formulating a convex optimization problem is possible. After finding optimal lamination parameters, a procedure is needed to generate a lay-up corresponding to these parameters. Explicit equations are derived for generating lay-ups having optimal bending lamination parameters. For creating a laminate having both optimal in-plane and bending lamination parameters, a new optimization problem searching laminates having lamination parameters as close as possible to the optimal ones is formulated. In that problem, also layer-wise properties and restrictions of manufacturing are taken into account. Agenetic algorithmsearch is employed for solving that later problem as the value of the objective function can be computed efficiently. Also, often the thicknesses and orientations of different layers can have only discrete values, which can be handled easily in the GA search, where all design variables are discrete in character.

Since the discovery of graphene, a new era of physics called "Two Dimensional (2D)Materials" has emerged. Group IV and Group III Selenides such as SnSe and InSe arepromising members of the 2D family. Structure of Group IV selenides is unique and highlysensitive to pressure and temperature. To further tweaking their properties by structuralchanges, thorough understanding of how the structure relates to the electronic bands is veryimportant. Based on the results from DFT calculations, I carefully analyzed electronic bandstructures of layered SnSe with various interlayer stacking. The first part of this dissertationdiscussed the possible stacking-dependent indirect-direct transition of bilayer SnSe.By further analysis, these results reveal that the directionality of interlayer interactionsdetermine the critical features of their electronic band structures. Further, it demonstratedthat such changes can be achieved by substitutional chemical doping. Using a multi-scalemodeling approach by combining the result of DFT and Boltzmann Transport Theory, Idiscussed the electron transport properties of co-doped SnSe, a class of thermodynamicallyand dynamically stable structures. The second part discussed on charge transfer across InSe/Gas interface, which showsbi-polar transport properties. This finding is in a good agreement with the recent experimentalobservations. Fundamental understanding of charge transfer in few-layer InSe /gasinterfaces at the atomic level is expected to pave the path for designing gas sensing devices.

The generation of electron-hole pairs in materials has great importance. In direct bandgap semiconductor materials, the mechanism of radiative recombination of electron-hole pairs leads to the emission of photons, which is the basis of Light Emitting Diodes (LEDs). The excitation of electron-hole pairs by absorption of photons is the active process in photodiodes, solar cells, and other semiconductor photodetector devices. In optoelectronic devices such as optical switches which are based on transmission and reflection of the photons, electron-hole pairs excitation is a key for the device performance. Diodes and transistors are also great discoveries in electronics which rely on the generation and recombination of electron-hole pairs at p-n junctions. In three-dimensional topological insulators (3D TIs) materials nanostructures excitation of electron-hole pairs can be utilized for the quantum memory, quantum information and quantum teleportation. In two-dimensional (2D) layered materials like graphene, MoS2, MoSe2, WS2 and WSe2 generation and recombination of electron hole pairs is main process at p-n junctions, infrared detectors and sensors. This PhD thesis is concerned with the physics of different types of electron-hole pairs in various materials, such as wide-bandgap semiconductors, 3D topological insulators, and plasmonic excitations in metallic nanostructures. The materials of interest are wide bandgap semiconductors such as TiO2 , 3D TIs such as Pb1-xSnxTe and the 2D layered materials such as MoS2 and MoO3. We study the electronic and optical properties in bulk and nanostructures and find applications in the area of semiclassical and quantum information processing. One of the interesting applications we focus in this thesis is shift in surface plasmon resonance due to reduction in index of refraction of surrounding dielectric environment which in turns shifts the wavelength of surface plasmon resonance up to 125 nm for carrier density of 10^22/cm^3. Employing this effect, we present a model of a light controlled plasmon switching using a hybrid metal-dielectric heterostructures. In 3D TIs nanostructures, the time reversible spin partners in the valence and conduction band can be coupled by a left and a right handed circular polarization of the light. Such coupling of light with electron-hole pair polarization provides an unique opportunity to utilize 3D TIs in quantum information processing and spintronics devices. We present a model of a 3D TI quantum dot made of spherical core-bulk heterostructure. When a 3D TI QD is embedded inside a cavity, the single-photon Faraday rotation provides the possibility to implement optically mediated quantum teleportation and quantum information processing with 3D TI QDs, where the qubit is defined by either an electron-hole pair, a single electron spin, or a single hole spin in a 3D TI QD. Due to excellent transport properties in single and multiple layers of 2D layered materials, several efforts have demonstrated the possibility to engineer electronic and optoelectronic devices based on MoS2. In this thesis, we focus on theoretical and experimental study of electrical property and photoluminescence tuning, both in a single-layer of MoS2.We present theoretical analysis of experimental results from the point of view of stability of MoO3 defects in MoS2 single layer and bandstructures calculation. In experiment, the electrical property of a single layer of MoS2 can be tuned from semiconducting to insulating regime via controlled exposure to oxygen plasma. The quenching of photoluminescence of a single sheet of MoS2 has also been observed upon exposure to oxygen plasmas. We calculate the direct to indirect band gap transitions by going from MoS2 single sheet to MoO3 single sheet during the plasma exposure, which is due to the formation of MoO3 rich defect domains inside a MoS2 sheet.