Browsing by Author "Szulczewski, Greg"

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    The Effects of Functional Groups and Missing Linkers on the Adsorption Capacity of Aromatic Hydrocarbons in UiO-66 Thin Films
    (MDPI, 2020) Shankwitz, Jennifer; Speed, Daniel; Sinanan, Dillon; Szulczewski, Greg; University of Alabama Tuscaloosa
    The adsorption of benzene, toluene, ethylbenzene, and xylene isomers, also known as BTEX, from the gas phase into porous thin films of the metal-organic framework UiO-66-X, where X = H, NH2, and NO2, was measured to quantify adsorption capacity. The thin films were grown by a vapor-conversion method onto Au-coated quartz microbalance crystals. The MOF thin films were characterized by IR and Raman spectroscopy, X-ray diffraction, X-ray photoelectron spectroscopy and scanning electron microscopy. The thin films were activated by heating under high vacuum and exposed to each gas to calculate the Henry's constant. The results demonstrate that the functional groups in the organic linker and missing-linkers both play important roles in the adsorption capacity. Several trends can be observed in the data. First, all the compounds in the BTEX family have lower Henry's constants in the UiO-66-H films compared to the UiO-66-NH2 and UiO-66-NO2 films, which can largely be attributed to the absence of a functional group on the linker. Second, at 25 degrees C, the Henry's constants for all the BTEX compounds in UiO-66-NO2 films are larger than UiO-66-NH2 films. Third, the role of missing linkers is addressed by comparing the measured adsorption capacity to ideal pore filling. The results show that the UiO-66-H films are the most defect-free and the UiO-66-NO2 films have the most missing linker defects.
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    Study of thermoelectric generators and perovskite solar cells for renewable energy applications
    (University of Alabama Libraries, 2020) Ouyang, Zhongliang; Li, Dawen; University of Alabama Tuscaloosa
    This dissertation aims at explorations of two promising renewable energy devices: one is thermoelectric generators (TEGs) and the other is perovskite solar cells (PVSCs). The first half of this dissertation (Chapter 2 & 3) focuses on the simulation study of TEGs while the second half (Chapter 4 & 5) concentrates on the experimental study of PVSCs. Chapter 1 serves as an overall introduction of TEGs and PVSCs. Chapter 2 investigates simulation of segmented TEGs with various state-of-the-art thermoelectric (TE) materials between 300 K and 1000 K. The influence of thermal radiation, electrical and thermal contact effects have been studied. The results show that these effects, if well-regulated, do not prevent segmented TEGs from achieving high efficiency and output power density. In Chapter 3, segmented TEGs have been further modelled to find out the best cost-performance ratios. The results reveal that successful segmentation of TE materials can offer a cost-performance ratio of ~0.86 $ W-1, less than commercially desired cost-effectiveness of 1 $ W-1, while maintaining an efficiency of 17.8% and delivering a power density over 3 Watt cm-2. These results predict the commercial feasibility and competitiveness of segmented TEGs in the same dollar per watt metrics as other renewable energy devices. Chapter 4 presents a rapid layer-specific annealing on perovskite active layer enabled by ultraviolet (UV) light-emitting diode (LED) and efficiency close to 19% is achieved in a simple planar inverted structure. These results justify that if the UV dosage is well-managed, UV light is capable of annealing perovskite into high-quality film rather than simply damaging it. Moreover, the layer-specific photonic treatment allows accurately estimating the deposition energy required to form perovskite film at device quality level. Chapter 5 exhibits an effort towards scalable manufacturing of perovskite solar panels. Perovskite mini-modules have been demonstrated with blade-coating and rapid thermal processing (RTP) in ambient environment. Mini-modules with an active area over 2.7 cm2 exhibit a champion efficiency of 17.73%. These results pave the way for large-scale production of PVSCs through high-speed roll-to-roll printing. Chapter 6 summarizes the conclusions and proposes a possible future work.
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    Synthesis and Optical Studies of Organoboron Compounds
    (University of Alabama Libraries, 2024) Pennington, Michael Patrick; Rupar, Paul A.
    Four-coordinate aryl borafluorenes with boron-oxygen and boron-nitrogen dative bondswere recently found to exhibit very large fluorescence Stokes shifts. The large Stokes shifts arehypothesized to arise from cleavage of the boron-donor dative bond in the excited state, via amechanism called bond-cleavage-induced intramolecular charge transfer (BICT). The primarygoal of this current investigation is to directly observe the BICT state by performing transientabsorption spectroscopy on four-coordinate borafluorenes which have improved optical stability.A family of four-coordinate borafluorenes was synthesized, each containing a dative B-O bondand two tert-butyl moieties on the aryl ring. Transient absorption spectroscopy (TAS) of the newborafluorenes showed existence of a single species in the excited state that is consistent with theBICT state. The TAS data is supported by fluorescence lifetime measurements and DFTcalculations.In 2016, Higuchi reported photochromic boronium-bipyridine complexes. It washypothesized that the photochromism arose from radical species that form via the photooxidationof iodide and other anions by the boronium cations. Although EPR data was provided to supportthis hypothesis, the EPR data was inconsistent with that expected for the proposed iodineradicals and boron center radicals. In the present work, boronium-bipyridine complexes withdifferent counter anions were synthesized to gain an understanding of how the anion affects thephotochromic properties of boronium-bipyridine complexes. EPR spectroscopy was employedto observe radicals generated on the complexes and further clarify the mechanism behind thephotochromic properties. The boronium-bipyridine complexes exhibited nearly identical radicalsignals to one another by EPR spectroscopy, however there was no evidence of radical formationon the anion, suggesting the reduction of the complex is occurring through a differentmechanism.The first polymer with pendant boronium-bipyridine complexes was designed andsynthesized to investigate the generation of photochromic polymer films. Electron paramagneticresonance experiments performed on the monomer complex suggested there is formation of aradical species in the solid-state following irradiation with UV light, coinciding withphotochromism. The resulting polymer lacked any photochromic characteristics, however thisallowed for better understanding of the photochromic mechanism of boronium-bipyridinecomplexes, paving a path forward to determine better designs to incorporate these complexesinto photochromic polymers.
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    Transition Metal Dichalcogenides for Use in Hydrogen Evolution Reaction, CO2 Reduction and Their Photoluminescence Spectroelectrochemistry
    (University of Alabama Libraries, 2021) Strange, Lyndi Elizabeth; Pan, Shanlin; University of Alabama Tuscaloosa
    Transition metal dichalcogenides (TMDs) are semiconductors of the form MX2, where M is a transition metal (Mo, W, etc.) and X is a chalcogen atom. They are structured in layers of M atoms sandwiched between two layers of X atoms. Two-dimensional TMDs (2D-TMDs) consist of a single layer of atoms that have the structure X-M-X and have electronic properties that differ from the bulk material. In the search for efficient and low-cost catalysts for renewable energy harvesting and conversion and storage, TMDs have emerged as promising catalysts for alternative energy such as photovoltaic water splitting anodes, hydrogen evolution reaction, CO2 reduction, photovoltaic absorber layers, and protective layers for photovoltaic devices. The structure of the TMDs can also be tuned at the monolayer level to increase catalytic activity by doping and introducing defects to enhance electrocatalytic hydrogen reduction. The highly tunable structure also leads to tunable optical properties that are useful in next-generation optoelectronics such as light-emitting diodes (LEDs), field-effect transistors (FETs), and ultra-sensitive molecular sensing due to their unique surface-sensitive optical properties. Learning how the structure affects the catalytic and optical properties serves as an important area of research to tune TMDs to produce more efficient catalysts and serve in various optical applications. This dissertation will focus on developing and understanding TMD catalysts for proton reduction, CO2 reduction, and also their spectroelectrochemical properties. Chapter 1 of this dissertation provides an overview of recent progress made in the field of TMDs and the goals of this doctoral research work. Chapter 2 summarizes the operation principles of the critical instrumental and experimental methods of this research work. Chapter 3 describes proton reduction characteristics of electrodeposited TMD thin-film electrodes and structural confirmation with advanced characterization techniques such as XPS depth profiling to understand the synthesized structure. Chapter 4 is devoted to the investigation of the photophysical properties and spectroelectrochemistry performance of 2D TMDs using SECM, SECCM, and spectroelectrochemical techniques. Chapter 5 describes the electrocatalytic CO2 reduction characterization of liquid exfoliated MoS2 film and an extensive literature overview of the field of photocatalytic CO2 reduction with TMD heterostructures. Finally, Chapter 6 summarizes the entire research work and challenges and proposed plans to address these challenges.