Small molecule organic semiconductors such as phthalocyanines and their derivatives represent a very interesting alternative to inorganic semiconductor materials for the development of flexible electronic devices such as organic thin field effect transistors, organic Light Emitting Diodes and photo-voltaic cells. Phthalocyanine molecules can easily accommodate a variety of metal atoms as well in the central core of the molecule, resulting in wide range of magnetic properties. Exploration of optical properties of organic crystalline semiconductors thin films is challenging due to sub-micron grain sizes and the presence of numerous structural defects, disorder and grain boundaries. However, this can be overcome by fabricating macroscopically ordered semiconductor films by solution processing. Presence of fewer grain boundaries and defects while modifying the pi orbital overlap by controlling the molecular stacking by forming macroscopic long range ordered grains, was essential in understanding the delocalization and diffusion length and its role in magnetic exchange mechanisms in this system. The origins of magnetic exchange mechanism between delocalized ligand electrons and spins in organic semiconductors has been of key interest as it underlies many complex optical and transport properties and is investigated in this thesis. The interaction between magnetic ions in organic magnetic semiconductors is quite challenging to interpret due to competing exchange mechanisms present in crystalline thin films. Better understanding of these exchange mechanisms is essential for tuning of magnetic exchange interaction to suit the need of practical magnetic storage and spintronic devices. Optical techniques such as linear dichroism, magnetic circular dichroism and magneto-photoluminescence are used and provided key understanding about the relation between excitons, spin exchange mechanisms and collective magnetic behavior of delocalized electrons in organic semiconductors. An enhancement in the collective magnetization of the crystalline thin films with strong exchange coupling between the delocalized ligand electrons and d-electrons is observed. The electronic states responsible for magnetic exchange are identified utilizing magnetic field and temperature dependent studies. Furthermore, soluble organics allowed engineering of organic analogues to diluted magnetic semiconductors (DMS) by creation of metal/metal-free Pc alloys. Optical studies provided crucial information about delocalization and diffusion lengths in these systems allowing fine tuning of this delocalization length scale and metal-metal distance. The exploration of magnetic behavior in metal/metal-free Pc alloys opens an avenue for tuning magnetic properties through an exchange similar to Ruderman-Kittel-Kasuya Yosida (RKKY) type interaction in organic magnetic semiconductors.

The desire for pure diatomic hydrogen gas, H2(g), has been on the rise since the concept of the hydrogen economy system was proposed back in 1970. The production of hydrogen has been extensively examined over 40 + years as the need to replace current fuel sources, hydrocarbons, has become more prevalent. Currently there are only two practical and renewable production methods of hydrogen; landfill gas and power to gas. This study focuses on the later method; using various renewable energy sources, such as photovoltaics, to provide off-peak energy to perform water electrolysis. Efficient electrolysis takes place in electrochemical cells which maximize performance efficiency with the use of noble metal electrocatalyst. Optimizing these electrocatalyst to be less material dependent, highly durable, and more efficient will support the implementation of power to gas electrolysis into the energy infrastructure. The main focus of this study is to explore RuO2 nanorods as a possible electrocatalyst for Proton Exchange Membrane (PEM) water electrolysis. A PEM electrolyzer cell has been constructed and fitted with a RuO2 nanorod decorated, mixed metal oxide (MMO) ribbon mesh anode catalyst structure. The current density-voltage characteristics were measured for the RuO2 nanorod electrocatalyst while under water feed operation. The electrocatalytic behavior was compared to that of ribbon mesh anode catalyst structures not decorated with RuO2 nanorods; one coated with a Ir/Ta MMO catalyst, the other was stripped of the MMO coating resulting in a Ti ribbon mesh anode. The results of these experiments show increased activity with the RuO2 nanorod electrocatalyst corresponding to a decrease in electrochemical overpotential. Through the collection of experimental data from various electrolyzer cell configurations, these overpotenials were able to be identified, resulting in categorical attributions of the enhanced catalytic behavior examined.

At the intersection of materials chemistry and biology, biomaterials have been successfully employed in an array of medical applications. From diagnostic tools to targeted drug delivery, the modular physical and chemical properties of these materials provide numerous applications. For example, porous nanoparticles have been widely integrated as vehicles to carry chemotherapeutics to localized tumor sites. By encapsulating these cytotoxic compounds within a porous framework, the commonly associated adverse side effects of conventional chemotherapeutics, such as Doxorubicin, have been greatly reduced. One such material, mesoporous silica, has received widespread attention due to its excellent biocompatibility, high surface area to mass ratio, tunable pore diameters and volumes, and robust surface chemistry. However, recent studies have demonstrated that exposing silica nanoparticles, and other synthetic materials, to biological milieu envelops the particles in layers of proteins and biomolecules. The resulting protein coat, known as the "protein corona", has been shown to have profound effects on bioavailability, cellular targeting, and cytotoxicity. Thus, in order to develop safe and effective particle-based therapies, it is of utmost importance to establish a more thorough understanding of this process. To examine how changes in surface chemistry influence protein adsorption, monodisperse, spherical mesoporous silica nanoparticles, ca. 50 nm, were modified with a variety of surface functionalizations, -NH2, -COOH, and -PEG. Exposing these materials to biological fluid revealed drastically different protein fingerprints, suggesting a strong correlation between the surface chemistry and the identity and composition of the protein corona. Quantification of the protein corona, i.e. mg protein/mg particles, was then achieved by performing thermogravimetric analysis. These values, in concert with spectral counts obtained by shotgun proteomics, illustrates a method for quantifying individual proteins present in the corona. Spherical, silica particles of varying diameters, 70-900 nm, were then synthesized to investigate how particle diameter may affect the biomolecular identity of the protein corona. Applying the previously described methods, it was found that mesoporous particles exhibit a higher affinity for low-molecular weight proteins compared to dense silica particles of similar diameters. Finally, stochastic optical reconstruction microscopy (STORM) was used to map protein adsorption/diffusion throughout as-prepared (pore diameter ~ 30 Å) .and large pore (pore diameter > 60 Å) mesoporous silica particles. By collecting three-dimensional data on the protein-adsorbed materials, a sphere-fitting algorithm could be applied to determine the center and radius of the host particle. This calculation demonstrated that the depth by which specific proteins diffused into the porous framework was a function of both the protein's molecular weight as well as the pore diameter.

Tungsten oxide (WO3) is a semiconducting transition metal oxide with interesting electronic, structural, and chemical properties that have been exploited in applications including catalysis, gas sensing, electrochromic displays, and solar energy conversion. Nanocrystalline WO3 can absorb visible light to catalyze heterogeneous photooxidation reactions. Also, the acidity of the WO3 surface makes this oxide a good thermal catalyst in the dehydration of alcohols to various industrially relevant chemicals. This dissertation explores the photocatalytic and thermal catalytic reactivity of nanocrystalline porous WO3 microparticles. Furthermore, investigations into the changes in WO3 reactivity are carried out after modifying the porous WO3 particles with gold nanoparticles (Au NPs). On their own, Au NPs are an important class of materials that have had a large impact in many fields such as catalysis, biomedical imaging, and drug delivery. When combined with WO3, however, their influence as part of a composite Au/WO3 catalyst has not been widely studied. Porous WO3 microparticles were first prepared using mesoporous silica (SiO2) spheres as hard templates and the physical properties of these materials were fully characterized. A facile sonochemical method was used to deposit Au NPs on the WO3 surface. Using methylene blue (MB) as a photocatalytic probe, the reaction products and the catalytic activity of WO3 and Au/WO3 catalysts were compared. Composite Au/WO3 photocatalysts exhibited significantly greater rates of MB degradation compared to pure WO3. Interestingly, the observed mechanism of MB degradation was not vastly different between the two types of catalysts. The gas-phase photocatalytic oxidation of methanol (MeOH) was studied to further understand the role of WO3 and Au NPs in these photocatalysts. Porous WO3 showed greater photooxidation rates compared to bulk WO3 because of its increased active surface area. Pure WO3 and Au NPs on porous SiO2 (SiO2-Au) were both active MeOH photooxidation catalysts and were highly selective to formaldehyde (HCHO) and methyl formate (MF), respectively. Two different mechanisms, namely band gap excitation of WO3 and surface plasmon resonance (SPR) on Au NPs, were responsible for this result. Again, the Au/WO3 composite catalysts showed greater photocatalytic activity than WO3, which increased with Au loading. This high activity led to the complete photooxidation of MeOH to carbon dioxide (CO2) over Au/WO3 catalysts. Finally, the thermal catalytic transformation of MeOH under aerobic conditions was carried out to further characterize the acid and redox active sites of WO3 and Au/WO3 catalysts. Pure WO3 was highly selective for MeOH dehydration to dimethyl ether (DME), whereas Au/WO3 showed increased oxidation selectivity to products such as HCHO, FM, and COx. The Au NPs increased the reducibility of the WO3 species, which made surface oxygen atoms more labile and reactive towards MeOH. Also, the WO3 facilitated the formation of cationic Au (Au δ+) species. This combination of effects created through a strong Au/WO3 interaction increased the activity of WO3 species, but it decreased the activity of the Au NPs.

In this talk, I will discuss three problems related to the novel physics of two-dimensional quantum materials such as graphene, group-VI dichalcogenides family (TMDCs viz. MoS2 , WS2, MoSe2 , etc) and Silicene-Germanene class of materials. The first problem poses a simple question - how do the quantum excitations in a graphene membrane affect adsorption? Using the tools of diagrammatic perturbation theory, I will derive the scattering rates of a neutral atom on a graphene membrane. I will show how this seemingly naive model can serve as a non-relativistic condensed matter analogue of the infamous infrared problem in Quantum Electrodynamics. In the second problem, I will move from the framework of a single atom adsorption to a collective behavior of fluids near graphene and TMDC - interfaces. Following the seminal work of Dzyaloshinskii-Lifshitz-Pitaevskii on van der Waals interactions, I will develop a theory of liquid film growth on 2 dimensional surfaces. Additionally, I will report an exotic phenomenon of critical wetting instability which is a result of the dielectric engineering and discuss experimental and technological implications. Finally, the last problem will see the introduction of spin-orbit coupling effects in the 2D topological insulator family of Silicene-Germanene class of materials. I will present a unified theory for their in-plane magnetic field response leading to "anomalous", i.e electron interaction-dependent spin-flip transition moment. Can this correction to spin-flip transition moment be measured? I will propose magneto-optical experimental techniques that can probe the effects.

Numerous agents and mechanisms are known to affect the durability of a concrete structure during its service life. Examples include freezing and thawing, corrosion of reinforcing steel, alkali-aggregate reactions, sulfate attack, carbonation, and leaching by neutral or acidic ground waters. Among these, external sulfate attack was first identified in 1908, and led to the discovery of sulfate resistant Portland cement (SRPC). Besides SRPC, another way of coping with the problem of sulfate attack is the use of pozzolans either as an admixture to concrete or in the form of blended cements This study presents an investigation on the sulfate resistance of blended cements containing different amounts of natural pozzolan and/or low-lime fly ash compared to ordinary Portland cement and sulfate resistant Portland cement. Within the scope of this study, an ordinary Portland cement (OPC) and five different blended cements were produced with different proportions of clinker, natural pozzolan, low-lime fly ash and limestone. For comparison, a sulfate resistant Portland cement (SRPC) with a different clinker was also obtained. For each cement, two different mixtures with the water/cement (w/c) ratios of 0.485 and 0.560 were prepared in order to observe the effect of permeability controlled by water/cement ratio. The performance of cements was observed by exposing the prepared 25x25x285 mm prismatic mortar specimens to 5% Na2SO4 solution for 78 weeks and 50mm cubic specimens for 52 weeks. Relative deterioration of the specimens was determined by length, density and ultrasonic pulse velocity change, and strength examination at different ages. It was concluded that depending on the amount and effectiveness of the mineral additives, blended cements were considered to be effective for moderate or high sulfate environments. Moreover, the cement chemistry and w/c ratio of mortars were the two parameters affecting the performance of mortars against an attack. As a result of this experimental study it was found out that time to failure is decreasing with the increasing w/c ratio and the effect of w/c ratio was more important for low sulfate resistant cements with higher C3A amounts when compared to high sulfate resistant cements with lower C3A amounts.

Structural lightweight aggregate concrete is an important and versatile material, which offers a range of technical, economic and environmental-enhancing and preserving advantages and is designed to become a dominant material in the new millennium. For structural application of lightweight concrete, the density is often more important than the strength. A decreased density for the same strength level reduces the self-weight, foundation size and construction costs. Structural lightweight aggregate concrete generally used to reduce dead weight of structure as well as to reduce the risk of earthquake damages to a structure because the earthquake forces that will influence the civil engineering structures are proportional to the mass of those structures. In this study, structural lightweight aggregate concrete was designed with the use of natural perlite aggregate that will provide an advantage of reducing dead weight of structure and to obtain a more economical structural lightweight concrete by the use of perlite powder as a replacement of the cement. Six mixes were produced with different cement content and with or without perlite powder. Six mixes divided into two groups according to their cement content. First group had a cement content of 300 kg/m3 and second group had cement content of 500 kg/m3 / also the water/cement ratios of groups were 0.49 and 0.35 respectively. Moreover, each group had three sub-mixes with 0%, 20% and 35% of perlite powder as cement replacement. According to results of experimental study, it was concluded that natural perlite aggregate can be used in the production of structural lightweight aggregate concrete. Based on the strength and density results of experimental work, it is possible to produce lightweight concrete with 20 MPa-40 MPa cylindrical compressive strength by using natural perlite aggregate. Also, the use of perlite powder, which will provide economy, can reduce dead weight further and increase performance.

In this study, relationships between aggregate shape parameters and compressive strength of concrete were investigated using digital image processing and analysis methods. The study was conducted based on three mix design parameters, gradation type, aggregate type and maximum aggregate size, at two levels. A total of 40 cubic concrete specimens were prepared at a constant water-cement ratio. After the compressive strength tests were performed, each specimen was cut into 4 equal pieces in order to obtain the digital images of cross sections using a digital flatbed scanner. A number of aggregate shape parameters were then determined from the digital image of the cross sections to investigate their relationships with the compressive strength. The results indicted that even though the aggregate type was found to give strong correlation with the compressive strength, weak correlations, however, exist between the compressive strength and the aggregate shape parameters. The study suggested that the analyses of relationships should be further investigated by including the effects of aggregate distribution within the specimen cross sections.

After the 1999 Kocaeli Earthquake, the use of chemically bonded post-installed anchors has seen a great growth for retrofits in Turkey. Currently, chemically bonded post-installed anchors are designed from related tables provided by adhesive manufacturers and a set of equations based on laboratory pullout tests on normal or high strength concretes. Unfortunately, concrete compressive strengths of existing buildings, which need retrofit for earthquake resistance, ranges within 5 to 16 MPa. The determination of tensile strength of chemically bonded anchors in low-strength concretes is an obvious prerequisite for the design and reliability of retrofit projects. Since chemically bonded anchors result in the failure of concrete, adhesive-concrete interface or anchored material, the ultimate resistance of anchor can be predicted through the sum of the contributions of concrete strength, properties of anchored material (which is steel for this work), and anchorage depth. In this work, all three factors and the predictions of current tables and equations related to anchorages are examined throughout site tests.

The extent of the benefits provided by use of SCMs in cementitious systems increases as their percentage amounts in total binder increases. However, the proportion of SCMs in cementitious systems is limited, especially for natural pozzolans, by some factors such as increase in water requirement and decrease in rate of strength development. Therefore investigations are needed to increase the amount of natural pozzolans in blended cements or in concrete as much as possible without decreasing their performance. This aim requires studies on cementitious systems with more reactive natural pozzolans than widely-used ones. The objective of the study was to investigate the pozzolanic activity of natural zeolites (clinoptilolite) from two localities in Turkey, and properties of cementitious systems containing low (15%), moderate (35%) and high (55%) amount of them. The study covers characterization of the natural zeolites used, evaluation of their pozzolanic activity in comparison with some popular mineral admixtures, and properties of pastes, mortars, and concrete mixtures containing low, moderate, and high amounts of natural zeolites. Reactivity of the natural zeolites with Ca(OH)2 was found to be higher than those of the fly ash and the non-zeolitic pozzolan, but lower than that of the silica fume. Natural zeolite blended cements were characterized with the following highlighted properties / faster setting than portland cement, low amounts of Ca(OH)2 and capillary pores larger than 50 nm in hardened pastes, relatively dense microstructure of hardened paste than portland cement, more compatibility with melamine-based superplasticizer than being with naphthalene-based one, and excellent compressive strength performance. Concrete mixtures containing natural zeolites as partial replacement for portland cement were characterized with the following properties / 7-day compressive strength of ~25 MPa and 28-day strength of 45-50 MPa with only 180 kg/m3 portland cement and 220 kg/m3 zeolite dosages (55% replacement), comparable modulus of elasticity with plain portland cement concrete, &ldquo / low&rdquo / and &ldquo / very low&rdquo / chloride-ion penetrability for low and large levels of replacement, respectively.