Transmission electron microscopy (TEM) is a powerful tool for studying solidstate crystalline systems. With the advances in aberration correction, monochromation, and in situ capabilities, these microscopes are now more useful for addressing fundamental materials chemistry problems than ever before. This dissertation will illustrate the ways in which I have been using high-resolution imaging and in situ heating in the TEM during my Ph.D. research to investigate unique solid state chemistry questions. This dissertation will focus on four unique crystal systems: thermoelectric skutterudite crystals, vapor-liquid-solid (VLS) grown nanowires, and hafnium dioxide nanorods. Although these systems are very different from one another, high resolution and/or in situ heating in TEM is an integral part of each study. Through these techniques, we gain insight and knowledge of these systems that may have gone unknown through different analysis techniques. The experiments I will describe in some cases provide surprising and unexpected results that arise from the nanoscale nature of the materials and would be difficult to observe through bulk analytical methods. The work presented here helps to demonstrate the strength and versatility of TEM to address solid state chemistry questions.

ZnO nanowires are a promising material with great semiconductor properties. ZnO nanowires were prepared by carbothermal reduction and vapor-liquid-solid growth mechanism. Altering a variety of parameters ranging from mole to mole ratio of ZnO to C all the way to gas flow rate was examined. The nanowires were then characterized and their morphology examined under a SEM to observe what effect the parameter had on the morphology of the nanowires. From the experiments and the parameters tested it was observed that in order to produce the highest quality straight nanowires one should use a mole to mole ratio of ZnO to C graphite of 1 to 3. With a dwell temperature and time of 900 °C for 3 hours. A gold seed catalyst of 4nm and a gas flow rate of 50 to 100sccm of Ar provides the straightest nanowires. Understanding the effect of each parameter on the morphology of ZnO nanowires is vital for the current research. This will only lead to further the research and provide a better understanding of the growth mechanism of these wires and how the production of specific wires with certain morphologic features and characteristics can be achieved.

This work sought to enforce aromatic interactions between compatible π-molecular orbital systems with ionic bonding. In this case the interacting partners are oppositely charged discotic triangulene derivatives. The observed properties of the heterodimeric ion-pairs likely arise due to a hypothetical synergy between electrostatics and π-interactions. The work presented here describes investigation of putative covalency arising from this hypothetical synergy in the electrostatics driven π-stacking. In order to probe this, various hypotheses were made and experiments were designed to test their validity. The results from the experiments show existence of contact ion-pairs and complex solvent-separated discotic ions in solution. The formation of complex ion-pairs arise due to the fact that the electrostatic interaction that brings the discotic ions together is strong, but does not neutralize when the contact is made. So, the dipole created by the monopoles in a dimeric contact ion-pair can attract ions at both termini forming oligomers. This process apparently continues towards highly aggregated states and then to nanometric species and at some point the material precipitates. The propensity to aggregate and form complex-ions limited our approach to the measurement of the energetics of the ion-pairing for two reasons: (1) the observables had a complex dependence on temperature, solvent, concentration and ionic strength; and (2) the mass in solution was undergoing kinetic evolution towards solid states. The turbidimetric effects arising due to aggregate formation further complicated the extraction of weak interactions between the ions and hence effects determination of ion-pairing constants.

The focus of this dissertation is to utilize chemical functionalization as a probe to investigate the reactivity of N-doped multiwalled carbon nanotubes (N-MWCNTs). The surface of N-MWCNTs, being a set of potentially reactive graphene edges, provides a large number of reactive sites for chemical modification, so considerable changes in chemical and physical properties can be envisaged. We observed that both reduction (dissolving metal reduction/alkylation) and oxidation (H2SO4/HNO3 and H2SO4/KMnO4 mixtures) of N-MWCNTs lead to formation of interesting spiral channels and spiraled carbon nanoribbons. A variety of techniques, including TGA, SEM, TEM, XRD and surface area measurements were used to analyze these new textural changes. We have developed methods to demonstrate that specific chemistry has occurred on these new structures. To this end, we introduced metal-binding ligands that could be used as probes in imaging and spectroscopic techniques including TEM, STEM, EDX, and EELS. A proposal for the underlying structure of N-MWCNTs responsible for the formation of the new textures is presented. We have investigated the performance of our materials as potential negative electrodes for rechargeable lithium ion batteries.

Carbon nano-onions (CNOs) discovered by Ugarte in 1992 are multi-layered fullerenes that are spherical analogs of multi-walled carbon nanotubes with diameters varying from 6 nm to 30 nm. Among the various methods of synthesis, CNOs prepared by graphitization of nanodiamonds (N-CNOs) and underwater electric arc of graphite rods (A-CNOs) are the subject of our research. N-CNOs are considered as more reactive than A-CNOs due to their smaller size, high curvature and surface defects. This dissertation focuses on structural analysis and surface functionalization of N- CNOs with diameters ranging from 6—10 nm. Synthetic approaches such as oleum- assisted oxidation, Freidel-Crafts acylation and Billups reductive alkylation were used to functionalize N-CNOs to improve their dispersion properties in aqueous and organic solvents. Functionalized N-CNOs were characterized using various techniques such as TGA, TG-MS, Raman spectroscopy and pH-titrimetry. We designed an experimental method to isolate polycyclic aromatic adsorbates formed on the surface of oleum oxidized N-CNOs (ON-CNOs) and characterized them. A-CNOs, on the other hand are bigger than N-CNOs with diameters ranging from 20—40 nm. In this dissertation, we discuss the preparation of graphene structures by unzipping of A-CNOs using KMnO4 as oxidizing agent. These graphene structures were characterized using powder X-ray diffraction, TGA, BET nitrogen adsorption/desorption studies and compressed powder conductivity. This dissertation also focuses on lithiation/delithiation studies of N-CNOs, A- CNOs and A-CNO-derived graphene structures to use them as negative electrode materials in lithium-ion batteries. The cycling performances of these materials at a charge/discharge rate of C/10 were discussed. The cycling performance of N-CNOs was tested at faster charge/discharge rate of C.

Acenes have been explored by a number of research groups in the field of organic electronics with a particular emphasis on transistor materials. This group has been actively studying acene‐based organic semiconductors for more than a decade using a crystal engineering approach and has developed acene derivatives for applications in field‐effect transistors, light‐emitting diodes, and photovoltaics. In addition to organic electronics, crystal engineering has important applications in a number of other fields, quite notably in the design of metal‐organic frameworks. Chapters 2 and 3 of this dissertation focus on applying crystal engineering to the synthesis of acene derivatives for use as solid‐state, long‐wavelength fluorescent organic dyes in the field of biomedical imaging. More specifically, this work studied the synthesis and properties of dioxolane‐functionalized pentacenes and hexacenes. One of these pentacene derivatives has already been demonstrated in biomedical imaging which may lead to improved treatment of tuberculosis. The dioxolane‐functionalized hexacene is still under evaluation for bioimaging applications. Chapters 4 and 5 focus on crystal engineering in relation to organic electronics. Chapter 4 deals with fine‐tuning of crystal packing and demonstrated that small differences in molecular structure can result in significant changes to the solid‐state structure which affects semiconductor properties. Finally, chapter 5 studies the use of singlet fission in photovoltaics and demonstrated that this process does occur in a solar cell incorporating a hexacene derivative. Pentadithiophenes were also synthesized for singlet fission photovoltaics, but they have yet to be studied further.

Carbon nano-onions (CNOs), concentrically multilayered fullerenes, are prepared by several different methods. We are studying the properties of two specific CNOs: A-CNOs and N-CNOs. A-CNOs are synthesized by underwater arc discharge, and N-CNOs are synthesized by high-temperature graphitization of commercial nanodiamond. In this study the synthesis of A-CNOs are optimized by designing an arc discharge aparatus to control the arc plasma. Moreover other synthesis parameters such as arc power, duty cycles, temperature, graphitic and metal impurities are controlled for optimum production of A-CNOs. Also, a very efficient purification method is developed to screen out A-CNOs from carboneseous and metal impurities. In general, A-CNOs are larger than N-CNOs (ca. 30 nm vs. 7 nm diameter). The high surface area, appropriate mesoporosity, high thermal stability and high electrical conductivity of CNOs make them a promising material for various applications. These hydrophobic materials are functionalized with organic groups on their outer layers to study their surface chemistry and to decorate with metal oxide nanoparticles. Both CNOs and CNO nanocomposites are investigated for application in electrochemical capacitors (ECs). The influences of pH, concentration and additives on the performance of the composites are studied. Electrochemical measurements demonstrate high specific capacitance and high cycling stability with high energy and power density of the composite materials in aqueous electrolyte.

Mechanical properties of concrete are most commonly determined using destructive tests including: compression, flexure, and fracture notch specimen tests. However, nondestructive tests exist for evaluating the properties of concrete such as ultrasonic pulse velocity and impact echo tests. One of major issues with concrete (which has cement as its prime ingredient) is that unlike steel it is quasi-brittle material. It tends to want to crack when tensile stresses develop. Fibres have been added to concrete for many years to reduce the amount of and size of cracks cause by temperature changes or shrinkage. In more recent years, significant research has been carried out into the effect of the addition of basalt fibres to cement has on its mechanical strength. As well, developing concrete that is more durable, flexible, stronger, and less permeable than traditional concrete has been explored. It has become important to test and verify improvements that are made to the cement by basalt fibres as well as testing the general strength of concrete to stand up to constant pressure at varied strengths.

When attempting to study the learning process of undergraduate chemistry student, the classroom and any interaction that take place within it constitute the social context of interest. By studying how different approaches can foster different classroom environments, it is possible to approach course design from an informed and scientifically sound perspective. Thus, it becomes necessary to identify and quantify the factors that have a positive or negative effect on the classroom environment. Social comparison concerns, comfort levels and self-efficacy have been shown to be social factors that affect each other as well as the learning process and have therefore been deemed suitable for use in this study. POGIL, a pedagogic approach to teaching chemistry based on small-group work and active learning, has been shown to lead to positive academic outcomes and is currently employed by several faculties at Virginia Commonwealth University. This study seeks to investigate differences in the learning environment observed in lecture and POGIL based chemistry courses, by adapting Micari’s survey for measuring social comparison, comfort levels and self-efficacy in small-group science learning. Reliance on the combustion of fossil-fuels, such as coal, oil and natural gas, as sources of energy has, since the industrial revolution, caused atmospheric CO2 to increase to the current level of 400ppm by volume; an increase of 25% from the 1960s when monitoring started. Climatologists predict that an increase to 450 ppm would have irreversible effects on the Earth’s environment and recommend that, in order to preserve the conditions in which civilization developed, levels be reduced to below 350 ppm. The use of porous organic polymers for capture and separation of CO2 from industrial sources has been at the forefront of research attempting to curb CO2 emission into the atmosphere. Benzimidazole based polymers have shown a high selectivity for CO2.7 To attempt to improve on the capture abilities of these polymers, we sought to synthesize sulfur containing analogs presenting thiazole moieties. Two such polymers were synthesized using a pyrene-based linker. Furthermore, the pyrene-derived fluorescence of these polymers enabled their use as chemosensors targeting nitroaromatic compounds and mercury

Research on metal nanoparticles (MNPs) synthesis and their applications for optoelectronic devices has been a recent interest in the fields of nanoscience and nanotechnology Photovoltaics are one of such systems in which MNPs have shown to be quite useful, due to unique physical, optical, magnetic, and electronic properties, including the metal nanoparticles synthesized in this research. Owing to the challenges with the most common physical and chemical methods of preparing MNPs, including the use of high temperatures, toxic reducing agents, and environmentally hazardous organic solvents, there is a critical need for a benign synthesis procedure for MNPs. In this work, a simple, versatile, and environmentally and economically responsible synthesis method for making iron, nickel, zinc, and bimetallic alloy nanoparticles (ANPs) has been developed and functionalization with organic capping agents were performed to form metal-organic hybrid nanocomposites with tunable properties. The size, shape, elemental composition, photophysical properties, and crystallinity of particles and their hybrids have been evaluated. Monometallic nanostructures of iron, nickel, and zinc oxide were synthesized via aqueous-phase reduction of metal(II) chloride salts with sodium borohydride. Upon optimization of the standard method described here, reaction parameters like reaction time, reagent molar ratios, and capping-agent molar ratio were evaluated. Characterization techniques such as transmission electron microscopy (TEM), scanning electron microscopy (SEM), energy-dispersive x-ray (EDS), IR, and UV-visible spectroscopies, selected area electron diffraction (SAED), and power x-ray diffraction (XRD) were performed as necessary. Well-defined, reproducible nickel and iron nanoparticles were produced with average diameters of 26±4 nm and 50±26 nm, respectively, arranged into chain-like structures. Much smaller (6-9 nm) zinc oxide particles that self-assembled into single-particle thick, hexagonal hierarchical microstructures were formed from a modified standard method. Similarly, iron-nickel ANPs with the average size of 20.9±3.3 nm were also synthesized and successful grafting with the polymer capping agent, polyvinylpyrrolidone was confirmed. Because of size, ordered self-assembly, and benign synthesis procedure, the nanoparticles described here are ideal candidates for photovoltaic and thermoelectric device applications. Moreover, these particles have shown to disperse well in various organic and inorganic media, and therefore have wide versatility in thin-film deposition methods.