Browsing by Author "Morris, Amanda"

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    Advancing computational materials design and model development using data-driven approaches
    Sose, Abhishek Tejrao (Virginia Tech, 2024-02-02)
    Molecular dynamics (MD) simulations find their applications in fundamental understanding of molecular level mechanisms of physical processes. This assists in tuning the key features affecting the development of the novel hybrid materials. A certain application demanding the need for a desired function can be cherished through the hybrids with a blend of new properties by a combination of pure materials. However, to run MD simulations, an accurate representation of the interatomic potentials i.e. force-fields (FF) models remain a crucial aspect. This thesis intricately explores the fusion of MD simulations, uncertainty quantification, and data-driven methodologies to accelerate the computational design of innovative materials and models across the following interconnected chapters. Beginning with the development of force fields for atomic-level systems and coarse-grained models for FCC metals, the study progresses into exploring the intricate interfacial interactions between 2D materials like graphene, MoS2, and water. Current state-of-the-art model development faces the challenge of high dimensional input parameters' model and unknown robustness of developed model. The utilization of advanced optimization techniques such as particle swarm optimization (PSO) integrated with MD enhances the accuracy and precision of FF models. Moreover, the bayesian uncertainty quantification (BUQ) assists FF model development researchers in estimating the robustness of the model. Furthermore, the complex structure and dynamics of water confined between and around sheets was unraveled using 3D Convolutional Neural Networks (3D-CNN). Specifically, through classification and regression models, water molecule ordering/disordering and atomic density profiles were accurately predicted, thereby elucidating nuanced interplays between sheet compositions and confined water molecules. To further the computational design of hybrid materials, this thesis delves into designing and investigating polymer composites with functionalized MOFs shedding light on crucial factors governing their compatibility and performance. Therefore, this report includes the study of structure and dynamics of functionalized MOF in the polymer matrix. Additionally, it investigates the biomedical potential of porous MOFs as drug delivery vehicles (DDVs). Often overlooked is the pivotal role of solvents (used in MOF synthesis or found in relevant body fluids) in the drug adsorption and release process. This report underscores the solvent's impact on drug adsorption within MOFs by comparing results in its presence and absence. Building on these findings, the study delves into the effects of MOF functionalization on tuning the drug adsorption and release process. It further explores how different physical and chemical properties influence drug adsorption within MOFs. Furthermore, the research explores the potential of functionalized MOFs for improved carbon capture, considering their application in energy-related contexts. By harnessing machine learning and deep learning, the thesis introduces innovative pathways for material property prediction and design, emphasizing the pivotal fusion of computational methodologies with data-driven approaches to advance molecular-level understanding and propel future material design endeavors.
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    Design and Fabrication of Polymer/Graphene Laminate Thin Films
    Croft, Zacary Lane (Virginia Tech, 2024-09-05)
    The development of graphene-based electronics may produce a new generation of electronic devices with enhanced performance over traditional materials. However, quality graphene electronics will require large-area, continuous graphene film produced by chemical vapor deposition (CVD), which is typically not stable when free-standing. Instead, CVD graphene may be coupled with polymer thin films to produce polymer/graphene laminates (PGLs), which show improved mechanical stability and good electrical conductivity over large areas. For example, single-layer graphene (SLG) has been coupled with polyetherimide (PEI) to produce thin film audio speakers with significantly enhanced energy efficiency compared to traditional speaker designs. However, the poor design and fabrication of PGLs may degrade the interfacial interactions of polymers with graphene and make the interface more susceptible to deformation. Interfacial weakening then limits their long-term reliability and performance in micro- and nano-electromechanical systems (MEMS/NEMS), in which materials are constantly subjected to dynamic loads. In this dissertation, we construct a framework for developing PGL thin films with controlled interfacial properties based on the rational design of polymer substrates and careful consideration of fabrication-induced defects. We evaluate this framework from several angles. First, the design of PEI/SLG film thickness is explored for controlling mechanical mixing and composite Young's modulus. Then, the role of thermal annealing during PEI/SLG fabrication is examined and its effect of mechanical mixing studied. Finally, we investigate mechanical fatigue in PEI/SLG thin films under dynamic loading with different pre-tensions. The design of mechanical properties in PGLs is crucial for ensuring long-term stability and operational performance. The Young's modulus is an important mechanical parameter governed by mechanical mixing in PGLs, and better mechanical mixing is facilitated by improved stress transfer efficiency at the polymer/graphene interface. Thus, the control of mechanical mixing through PGL design is an important research topic for developing PGL thin films with good mechanical performance. To this end, we evaluated the design of PEI/SLG thin films with precisely controlled thicknesses to afford control over mechanical mixing and the composite Young's modulus. PEI concentrations of 3–6 wt% were used to spin-coat PEI/SLG films at precisely controlled thicknesses of ~200–1000 nm, which enabled the design of PEI/SLG thin films based on thickness control. The design of PEI/SLG film thickness afforded control over the volume fraction of SLG, which is related to the composite Young's modulus of the films via the well-known mixing rule. To validate this approach, we measured the composite Young's modulus of PEI/SLG films and modelled the relationship between modulus and film thickness (i.e., volume fraction) using the mixing rule. However, we found that linear regression analysis yielded an unexpectedly high effective Young's modulus of 1.12 ± 0.05 TPa for SLG. Further investigation revealed the larger-than-expected value was due to the gradual deterioration of mechanical mixing between SLG and PEI at film thicknesses > 250 nm. Overall, our results demonstrate that the control of mechanical mixing in PGL thin films is achievable through the physical design of film thickness, which fits well within the proposed framework for PGL development. The fabrication of PGL materials is another important topic for controlling PGL properties. For example, the transfer process required for removing PGL thin films from a CVD substrate is known to introduce mechanical defects and electronic doping if improper processing conditions are used. However, little is known about the impact of thermal annealing on the properties of PGL materials. Normally, thermal annealing is thought to aid in the removal solvent and stress after polymer deposition on SLG, but we show that thermal annealing instead induces substantial structural damage and reduced film properties when poor conditions are used. Specifically, thermally annealing PEI/SLG in air past the Tg of PEI (~217 °C) caused widespread structural damage due to oxidation of the underlying Cu substrate. This conclusion was supported through an in-depth mechanistic investigation of annealing-induced deformation. First, changing the annealing atmosphere to high-purity nitrogen prevented widespread structural deformation from occurring during annealing, regardless of temperature. Second, the onset of film deformation during annealing in air was strongly associated with temperatures above the glass transition temperature of PEI. Finally, Arrhenius analysis yielded an activation energy of 159 kJ/mol for the deformation process, almost twice that associated with Cu oxidation and instead closer in scale to that of glass transitions in amorphous polymers. A physical failure mechanism was proposed based on the in-plane shrinkage of PEI during the glass-to-rubber transition caused by the release of internal stress induced by spin-coating. In-plane contraction of PEI would then cause compression of SLG as internal stress was released, which we confirmed from a significant blue-shift in the 2D band of SLG by ~30 cm-1 after annealing both with and without visible deformation. Importantly, we demonstrate that common secondary processing steps, like thermal annealing, will have critical effects on film properties if conditions are not properly controlled. The mechanical fatigue and cycling stability of PGL thin films is another topic of interest for developing reliable PGLs with long operational lifetimes. Mechanical failure analysis might be used to evaluate failure mechanisms governing interfacial fatigue in PGL thin films. However, little work has been done understanding mechanical fatigue in PGLs. To this end, we explore the use of mechanical bulge testing for the evaluation of cycling fatigue in PGLs and construct a custom instrument, known as a bulge test apparatus (BTA), to perform fatigue measurements. In general, our BTA test platform provides a means of analyzing different fabrication/design conditions. To test its use, we prepared PEI/SLG thin films with different tensioning weights between 0 and 30 g. Then, the well-established methods for bulge testing were applied to the dynamic loading of PEI/SLG using the BTA. Specifically, the evolution of bulge-test-derived pre-stress in PEI/SLG was monitored as a function of cycle number and tensioning weight, which revealed large fluctuations in pre-stress with mechanical cycling up to ~200k cycles, which was unexpected for these films. To investigate the underlying mechanism, we further employed Raman spectroscopy, optical microscopy, and scanning electron microscopy (SEM) to determine the strain state of SLG before and after cycling and probe for structural changes. Raman measurements revealed that mechanical cycling induced a large redshift in the 2D and G peak positions of SLG by ~25.4 and ~10.1 cm-1, respectively, for 30 g-tensioned PEI/SLG, with similar shifts observed for 20 g-tensioned films. Optical and SEM images showed possible changes in the surface structure of SLG after cycling accompanying the shift in Raman characteristics. We discuss the possibility of interfacial failures involving in-plane slippage and out-of-plane buckling of SLG based on our results. If validated, the use of BTA may provide future insight regarding mechanical fatigue and failure at the PGL interface during dynamic loading. The practical relevance of methods for determining the influence of design and fabrication characteristics in PGLs will no doubt be invaluable for further development. Additional work in this area will be necessary to connect our analytical approach by BTA to underlying failure mechanisms in PGLs.
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    Design and synthesis of Ni-rich and low/no-Co layered oxide cathodes for Li-ion batteries
    Yang, Zhijie (Virginia Tech, 2023-02-23)
    Li-ion batteries (LIBs) have achieved remarkable success in electric vehicles (EVs), consumer electronics, grid energy storage, and other applications thanks to a wide range of electrode materials that meet the performance requirements of different application scenarios. Cathodes are an essential component of LIBs, which governs the performance of commercial LIBs. Layered transition metal oxide, i.e., LiNixCoyMn1-x-yO2 (NMC), is one family of cathodes that are widely applied in the prevailing commercial LIBs. With increasing demand for high energy density, the development of layered oxide cathodes is towards high Ni content because Ni redox couples majorly contribute to the battery capacity. Meanwhile, the battery community has been making tremendous efforts to eliminate Co in layered cathodes due to its high cost, high toxicity, and child labor issues during Co mining. However, these Ni-rich Co-free cathodes usually suffer from low electrochemical and structural stability. Several strategies are adopted to enhance the stability of Ni-rich Co-free cathodes, such as doping, coating, and synthesizing single crystal particles. However, the design principles and synthesis mechanisms of these approaches have not been fully understood. Herein, we design and synthesize stable Ni-rich and low/no-Co layered oxide cathodes by manipulating the chemical and structural properties of cathode particles. Our studies reveal the cathode formation mechanisms and shed light on the cathode design through complementary synchrotron microscopic and spectroscopic characterization methods. In Chapter 1, the motivation for LIB research is introduced from the perspective of its indispensable role in achieving carbon neutrality. We then comprehensively introduce the status of LIBs at present, including assessing their sustainability, worldwide supply chain and manufacturing, and cathode materials. Subsequently, we focus on the Co-free layered oxide cathodes and discuss their structure, limitations, and strategies to address the challenges. Finally, we discuss single crystal Ni-rich layered oxide cathodes and the challenges and strategies associated with their synthesis. In Chapter 2, we investigate the dopant redistribution, phase propagation, and local chemical changes of layered oxides at multiple length scales using a multielement-doped LiNi0.96Mg0.02Ti0.02O2 (Mg/Ti-LNO) as a model platform. We observed that dopants Mg and Ti diffuse from the surface to the bulk of cathode particles below 300 °C long before the formation of any layered phase, using a range of synchrotron spectroscopic and imaging diagnostic tools. After calcination, Ti is still enriched at the cathode particle surface, while Mg has a relatively uniform distribution throughout cathode particles. Our findings provide experimental guidance for manipulating the dopant distribution upon cathode synthesis. In Chapter 3, we synthesized Mn(OH)2-coated single crystal LiNiO2 (LNO) and used it as the platform to monitor the Mn redistribution and the structural and chemical evolution of the LNO cathode. We use in situ transmission X-ray microscopy (TXM) to track the Mn tomography inside the LNO particle and Ni oxidation state evolution at various temperatures below 700 °C. We further reveal chemical and structural changes induced by different extents of Mn diffusion at ensemble-averaged scale, which validates the results at the single particle scale. The ion diffusion behavior in the cathode is highly temperature dependent. Our study provides guidance for ion distribution manipulation during cathode modification. In Chapter 4, we successfully fabricated a surface passivation layer for NMC particles via a feasible quenching approach. A combination of bulk and surface structural characterization methods show the correlation of surface layer with bulk chemistry including valence state and charge distribution. Our design enables high interfacial stability and homogeneous charge distribution, impelling superior electrochemical performance of NMC cathode materials. This study provides insights into the cathode surface layer design for modifying other high-capacity cathodes in LIBs. In Chapter 5, we use statistical tools to identify the significance of multiple synthetic parameters in the molten salt synthesis of single crystal Ni-rich NMC cathodes. We also create a prediction model to forecast the performance of synthesized single crystal Ni-rich NMC cathodes from the input of synthetic parameters with relatively high prediction accuracy. Guided by the models, we synthesize single crystal LiNi0.9Co0.05Mn0.05O2 (SC-N90) with different particle sizes. We find large single crystals show worse capacity and cycle life than small single crystals especially at high current rates due to slower Li kinetics. However, large single crystal has higher thermal stability potentially because of smaller specific surface area. The findings of particle size effect on the performance provide insights into size engineering while developing next-generation single crystal Ni-rich NMC cathodes. The statistical and prediction models developed in this study can guide the molten salt synthesis of Ni rich cathodes and simplify the optimization process of synthetic parameters. Chapter 6 summarizes our efforts on the novel design and fundamental understanding of the state-of-the-art cathodes. We also provide our future perspectives for the development of LIBs.
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    Fundamental Investigations into the Metal-Organic Framework Redox-Hopping Charge Transport——Mechanisms and Improvement Strategies
    Yan, Minliang (Virginia Tech, 2024-10-16)
    Redox hopping is the dominant charge transport mechanism in many catalyst-modified metal-organic frameworks (MOFs). Previous studies have shown that ion diffusion is the rate-determining step of redox hopping, but the realization regarding to the fundamental mechanism of redox hopping in MOF is still infantile. In this dissertation, we will discuss the redox hopping process in MOFs from multiple perspectives, including how to use the Scholz model to analyze the coefficients in redox hopping, the influence of the type of carrier, the influence of electrolyte concentration, and the influence of temperature on redox hopping, so as to try to reveal the mechanism of the redox hopping process and make some constructive suggestions for the future design and application of MOF based on this topic.
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    Generation of Titanium Dioxide Parts using Cellulose Nanocrystal Aerogel Hard Templates
    Custer, Faulkner Paine (Virginia Tech, 2021-01-27)
    This project studies the generation of crystalline mesoporous structured titanium dioxide (TiO2) using cellulose nanocrystal (CNC) aerogel hard templates for photocatalytic and biomaterial applications. Suspensions of CNCs in water varying in solid loading from 20 mg/mL to 100 mg/mL were prepared and frozen at three different temperatures (-20 °C, -40 °C, or -80 °C) using four combinations of hollow cylindrical molds and mold plates with different thermal conductivities (stainless-steel or glass) placed on different heat conductive and insulative substrates (aluminum, polystyrene foam and cardboard). Frozen samples were then freeze dried to sublimate the ice and render a multiscale and mesoporous structure with a variety of microstructural features, including lamellar sheeting, flakes, ribbons, or striations. Ceramic green bodies are then produced by reacting Titanium isopropoxide with water through several different processes to generate amorphous TiO2 either in-situ in the CNC aerogel or as a suspension for infiltration under varying pressure. Green bodies are dried at room temperature, and the extent of ceramic coating of the template is visually determined using SEM imaging. Once dried, crystalline TiO2 are produced through a two-step heat treatment with a CNC burnout at 270 °C and crystallization and sintering at 500 °C, 600 °C, or 1000 °C. The final crystallinity and phase composition is examined using XRD, and the final porosity is determined using BET. Results have shown the ability to satisfactorily coat aerogels under 10 mm in one dimension with TiO2. These samples have been successfully heat-treated to produce both anatase and rutile phase TiO2 while maintaining the macrostructure of the CNC aerogel. Multiscale porosity has been achieved, and samples heat treated at 1000 °C have achieved structural integrity.
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    A Green Light at the Intersection of Metal-Organic Frameworks and Drug Delivery
    Cornell, Hannah D. (Virginia Tech, 2022-05-20)
    The development of controllable drug delivery systems is crucial for reducing toxicity and minimizing off-target drug effects for patients undergoing chemotherapy. Metal–organic frameworks (MOFs) are a class of hybrid materials that have become of interest in the field of drug delivery. MOFs are composed of metal nodes and organic bridging ligands. MOFs have a wide range of desirable properties including chemical stability, high porosity, and structural tunability which have positioned them as successful drug carriers. Through judicious choice of linker, stimuli-responsive MOFs can be synthesized to achieve precise control over cargo release. Previously, our lab developed a novel light-responsive drug delivery system using a framework known as UiO-AZB (UiO= University of Oslo, AZB=4,4ʹ-azobenzenedicarboxylic acid). This MOF contains a photoswitchable azobenzene linker. Upon irradiation with ultraviolet light, the compound undergoes a structural change known as photoisomerization, resulting in degradation of the MOF structure and simultaneous release of encapsulated cargo. To improve the clinical relevance of our framework, we focus on developing synthetic methods for production of visible light-responsive azobenzene photoswitches. A green light-responsive MOF (UiO-AZB-F) containing a 4,4ʹ-(diazene-1,2- diyl)bis(3,5-difluorobenzoic acid) linker was developed as a drug delivery system for the treatment of colorectal cancer. Our work also focuses on optimizing various aspects of MOF design to maximize and diversify cargo loading and precisely control cargo release rates. A combined computational and experimental investigation of drug adsorption process reveals that the presence of solvent can significantly impact the adsorption of drug molecules within MOF pores. To address these concerns, a variety of drug loading procedures were screened to determine conditions for maximizing the loading of diverse drug cargoes. Conditions for the loading of single agents as well as chemotherapy cocktails were explored to expand the application of our delivery platform to other cancer types including lung, pancreatic, bladder and cervical. To modulate the release of cargo, a series of MOFs containing precise ratios of green light-responsive linker were synthesized to create a platform for sustained release. Remarkably, several MOF derivatives showed enhancement in drug adsorption, highlighting the important role of host–guest interactions in nanocarrier development. Holistically, this work highlights the promise of stimuli-responsive MOFs as drug delivery platforms.
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    Intrinsic and Extrinsic Catalysis in Zirconium-based Metal-Organic Frameworks
    Gibbons, Bradley James (Virginia Tech, 2022-05-31)
    Metal-organic frameworks (MOFs) are a class of hybrid materials that offer a promising platform for a range of catalytic reactions. Due to their complex structure, MOFs offer unique opportunities to serve as novel catalysts, or as host to improve the properties of previously studied species. However, while other catalytic approaches have been studied for many decades, the recency of their discovery means that significant work is still needed to develop MOFs as a viable option for large scale application. Herein, we aimed to advance the field of MOFs as both novel catalysts, and as host platforms for other catalytic species. To this end, we studied synthetic pathways to produce favorable MOF properties such as higher porosity and active site concentration through introduction of defects and macromorphological control, as well as utilization of molecular catalysts imbedded in the MOF structure for multicomponent, light driven reactivity. Chapter 1 introduces the history MOFs and the pursuit of the stable structures commonly associated with MOF chemistry. The synthesis process for zirconium-based MOFs will be discussed, with specific attention given to the modulated synthesis process which can harnessed to change MOF properties and improve catalysis. Two specific reactions will be introduced which serve as a basis for study in this work. First, the hydrolysis of organophosphate nerve agents by MOFs acting as novel catalysts will be introduced. The mechanism of reaction, as well as previous work in this field will be discussed. Finally, water oxidation as part of artificial photosynthesis through incorporated molecular catalysts will be introduced. Chapter 2 presents a modulator screening study on a zirconium-based MOF, UiO-66. One of the most commonly studied MOFs, UiO-66 provides an excellent platform for synthetic modulation. Particle size and defect level were measured of 26 synthetic variations and synthetic conditions were found to isolate changes in defect level and particle size, which typically change coincident with each other. Hydrolysis of the organophosphate compound dimethyl 4-nitrophenylphosphate (DMNP) was used to study the impact of particle size and defect level on reactivity. The reaction was found to be surface limited, even at high levels of missing linker defects. In Chapter 3, the macromorphology of three zirconium-based MOFs were tuned through synthesis modification. MOF powders and xerogels were prepared and characterized to highlight the desirable properties obtained through the gelation process. The materials were compared in the hydrolysis of DMNP and significant enhancement was observed for UiO-66 and NU-1000 xerogels. This was largely attributed to the introduction of mesoporosity and nanocrystalline particle sizes, which significantly increase the number of reactive sites easily accessible for catalysis. In Chapter 4 the authors examine MOFs as a host for molecular catalysts for use in photoelectrochemical water oxidation. A ruthenium-based catalyst [Ru(tpy)(dcbpy)]2+ was incorporated into UiO-67 through a mixed linker synthesis and grown on a WO3 substrate (Ru-UiO-67/WO3). Previous work from our group demonstrated Ru-UiO-67 retained the catalytic activity as the molecular species, while improving the recyclability of the material. In this work, addition of WO3 as a light harvester allowed for the reaction to be driven at a photoelectrochemical underpotential, a first for MOF-based water oxidation. Finally, Chapter 5 offers a perspective of the field of MOF-based artificial photosynthesis. Particular attention is given to issues of diffusion, selectivity, stability, and moving towards integration of multiple components rather than the study of half-reactions.
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    Investigating Chemical and Structural Heterogeneities of High-Voltage Spinel Cathode Material for Li-ion Batteries
    Spence, Stephanie Leigh (Virginia Tech, 2023-03-20)
    Li-ion battery technologies have transformed the consumer electronics and electric vehicles landscape over the last few decades. Single-crystal cathode materials with controllable physical properties including size, morphology, and crystal facets can aid researchers in developing relationships between physical characteristics, chemical properties, and electrochemical performance. High-voltage LiNi0.5Mn1.5O4 (LNMO) materials are desirable as cathodes due to their low cost, low toxicity, and high capacity and energy density making them promising to meet increasing consumer demands for battery materials. However, transition metal dissolution, interfacial instability, and capacity fading plague these materials when paired with graphite, limiting their commercial capability. Furthermore, variation in Ni/Mn ordering can lead to complex multiphase co-existence and changes in Mn oxidation state and electrochemical performance. These properties can be adjusted during synthesis using a facile and tunable molten salt synthesis method. This dissertation focuses on the investigation of chemical and structural heterogeneities of LNMO prepared under different synthetic conditions at different length scales. In Chapter 2, the influences of molten salt synthesis parameters on LNMO particle size, morphology, bulk uniformity, and performance are evaluated revealing the difficulty of reproducible cathode synthesis. We utilize the X-ray nanodiffraction technique throughout this work, which provides high-resolution structural information. We develop a method to measure and relate lattice strain to phase distribution at the tens of nanometers scale. In Chapter 3, mapping lattice distortions of LNMO particles with varying global Mn oxidation states reveals inherent structural defects and distortion heterogeneities. In Chapter 4, we examine lattice distortion evolution upon chemical delithiation, Mn dissolution behaviors, and evaluate the chemical delithiation method as a means to replicate electrochemical cycling conditions. We further investigate lattice distortion spatially via in situ nanodiffraction during battery cycling in Chapter 5, illustrating the capabilities of the measurement to provide practical understanding of cathode transformations. From intra-particle to electrode materials level, heterogeneities that arise in cathode materials can dictate performance properties and degradation mechanisms and are necessary for researchers to understand for the improvement of Li-ion battery systems. The development of the nanodiffraction measurements aids in our understanding of inherent and dynamic materials chemical and structural heterogeneities.
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    Investigating the parameters of metal-organic framework crystal growth control for reverse osmosis membrane nanofillers and direct air capture of CO2
    Bonnett, Brittany Lauren (Virginia Tech, 2022-06-02)
    Inorganic nano- and micromaterials (NMMs) exhibit unique properties including high surface areas, tunable optical and electronic properties, low densities, thermal and chemical robustness, and catalytic capabilities, among others. One of the more novel subclasses of NMMs, metal-organic frameworks (MOFs), are crystalline porous coordination polymers consisting of metal nodes connected by organic linkers to form one-, two-, or three-dimensional frameworks. While the mechanism of MOF formation is complex, tuning the metal:ligand ratios, reaction temperature and vessel pressure, ligand concentration, modulator concentration, and H+ activity impacts particle size, morphology, dispersity, and isotropy of these materials. MOFs also exhibit post-synthetic modification capabilities, which, along with their tunable synthetic nature, make them promising candidates for composite materials such as functionalized nanofillers for reverse osmosis (RO) desalination. The work described herein investigates synthetic parameters of a zirconium-based porphyrinic MOF, PCN-222, to selectively control its crystal size, aspect ratio, and dispersity. Size-constrained PCN-222 was post-synthetically modified with fatty acids and zwitterions to be used as RO thin-film composite (TFC) membranes with improved membrane flux, salt rejection, and anti-fouling properties. The synthetic parameters of MOFs were also considered for the commercial scale-up of CO2 direct air capture (DAC) solid sorbents, including UiO-66, MIL-101-Cr, and Mg-MOF-74, to preserve CO2 uptake capacities between lab and industrial scales.
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    Light Harvesting and Energy Transfer in Metal-Organic Frameworks
    Shaikh, Shaunak Mehboob (Virginia Tech, 2021-06-24)
    A key component of natural photosynthesis are the antenna chromophores (chlorophylls and carotenoids) that capture solar energy and direct it towards the reaction centers of photosystems I and II. Highlighted by highly-ordered crystal structures and synthetic tunability via crystal engineering, metal–organic frameworks (MOFs) have the potential to mimic the natural photosynthetic systems in terms of the efficiency and directionality of energy transfer. Owing to their larger surface areas, MOFs have large absorption cross sections, which amplifies the rate of photon collection. Furthermore, MOFs can be constructed using analogues of chlorophyll and carotenoids that can participate in long-range energy transfer. Herein, we aimed to design photoactive MOFs that can execute one of the critical steps involved in photosynthesis - photon collection and subsequent energy transfer. The influence of spatial arrangement of chromophores on the efficiency and directionality of excitation energy transfer (EET) was investigated in a series of mixed-ligand pyrene- and porphyrin-based MOFs. Due to the significant overlap between the emission spectrum of 1,3,6,8-tetrakis(p-benzoic acid)pyrene (TBAPy) and the absorption spectrum of meso-tetrakis(4-carboxyphenyl)porphyrin (TCPP), the co-assembly of these two ligands in a MOF should enable facile energy transfer. Bearing this in mind, three TBAPy-based MOFs with markedly different network topologies (ROD-7, NU-901, and NU-1000) were chosen and a small number of TCPP units were incorporated in their backbone. To gain insight into the photophysical properties of mixed-ligand MOFs, we conducted time-resolved and steady-state fluorescence measurements on them. Stern-Volmer analysis was performed on the fluorescence lifetime data of mixed-ligand MOFs to determine the quenching constants. The quenching constant values for ROD-7, NU-901, NU-1000, and TBAPy solution were found to be 15.03 ± 0.82 M-1, 10.25 ± 0.99 M-1, 8.16 ± 0.41 M-1, and 3.35 ± 0.30 respectively. In addition, the ratio of the fluorescence intensities of TCPP and TBAPy was used to calculate the EET efficiencies in each of the three MOFs. EET efficiencies were in the following order: ROD-7 > NU-901 > NU-1000 > TBAPy-solution. Based on the trends observed for quenching constants and EET efficiencies, two conclusions were drawn: (1) the ligand-to-ligand energy transfer mechanism in MOFs outperforms the diffusion-controlled mechanism in solution phase, (2) energy transfer in MOFs is influenced by their structural parameters and spectral overlap integrals. The enhanced EET efficiency in ROD-7 is attributed to shorter interchromophoric distance, larger orientation factor, and larger spectral overlap integral. Directionality of energy transfer in these MOFs was assessed by calculating excitonic couplings between neighboring TBAPy linkers using the atomic transition charges approach. Rate constants of EET (kEET) along different directions were determined from the excitonic couplings. Based on the kEET values, ROD-7 is expected to demonstrate highly anisotropic EET along the stacking direction. In order to explore the mechanistic aspects of EET in porphyrin-based MOFs, we studied the energy transfer characteristics of PCN-223, a zirconium-based MOF containing TCPP ligands. After performing structural characterization, the photophysical properties of PCN-223 and free TCPP were investigated using steady state and time-resolved spectroscopy. pH-dependent fluorescence quenching experiments were performed on both the MOF and ligand. Stern-Volmer analysis of quenching data revealed that the quenching rate constants for PCN-223 and TCPP were 8.06 ± 1011 M-1s-1 and 2.71 ± 1010 M-1s-1 respectively. The quenching rate constant for PCN-223 is, therefore, an order of magnitude larger than that for TCPP. Additionally, PCN-223 demonstrated a substantially higher extent of quenching (q = 93%) as compared to free TCPP solution (q = 51%), at similar concentrations of quencher. The higher extent of quenching in MOF is attributed to energy transfer from neutral TCPP linkers to N-protonated TCPP linkers. Using the Förster energy transfer model, the rate constant of EET in PCN-223 was calculated. The magnitude of rate constant was in good agreement with the kEET values reported for other porphyrin-based MOFs. Nanosecond transient absorption measurements on PCN-223 revealed the presence of a long-lived triplet state (extending beyond 200 μs) that exhibits the characteristic features of a TCPP-based triplet state. The lifetime of MOF is shorter than that of free ligand, which may be attributed to triplet-triplet energy transfer in the MOF. Lastly, femtosecond transient absorption spectroscopy was employed to study the ultrafast photophysical processes taking place in TCPP and PCN-223. Kinetic analysis of the femtosecond transient absorption data of TCPP and PCN-223 showed the presence of three distinct time components that correspond to: (a) solvent-induced vibrational reorganization of excitation energy, (b) vibrational cooling, and (c) fluorescence. Materials that allow control over the directionality of energy transfer are highly desirable. Core-shell nanocomposites have recently emerged as promising candidates for achieving long-distance, directional energy transfer. For our project, we aim to employ UiO-67-on-PCN‐222 composites as model systems to explore the possibility of achieving directional energy transfer in MOF-based core-shell structures. The core–shell composites were synthesized by following a previously published procedure. Appropriate amounts of Ruthenium(II) tris(5,5′-dicarboxy-2,2′-bipyridine), RuDCBPY, were doped in the shell layer to produce a series of Ru-UiO-67-on-PCN‐222 composites with varying RuDCBPY loadings (CS-1, CS-2, and CS-3). The RuDCBPY-doped core–shell composites were characterized by powder X-ray diffraction (PXRD), scanning electron microscopy (SEM) imaging, Nitrogen adsorption-desorption isotherms, and diffuse reflectance spectroscopy. Efforts are currently underway to quantify RuDCBPY loadings in CS-1, CS-2, and CS-3. After completing structural characterization, the photophysical properties of CS-1, CS-2, and CS-3 will be investigated with the help of time-resolved and steady-state fluorescence spectroscopy.
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    Membrane Electrochemical Treatment of Landfill Leachate: Processes, Performance and Challenges
    Liu, Xingjian (Virginia Tech, 2020-04-13)
    Landfilling is the most common approach to dispose of municipal solid wastes but inevitably leads to leachate formation. Persistent UV quenching substances (UVQS) in landfill leachate can affect the effectiveness of UV disinfection in municipal wastewater treatment systems when leachate co-treatment is applied. Membrane electrochemical reactor (MER) treatment was investigated to reduce the UV quenching capability and simultaneously recover resources in the leachate as an effective onsite pre-treatment. Ion-selective membranes were used in this MER to create two different conditions: a low-pH anolyte for organic oxidation and a high-pH catholyte for ammonia recovery. The MER achieved significantly higher removals of both dissolved organic carbon and UV254nm absorbance than membrane-less electrochemical treatment. The MER was able to remove a large percentage of total nitrogen from the leachate while recovering about half of the influent ammonia in the catholyte with less specific energy consumption. The second study coupled MER with Fenton oxidation through providing synergistic benefits with the low solution pH, reduced organics, and ammonia removal. This two-stage coupled system reduced the more leachate COD than the standalone Fenton process treating raw leachate. Also, the usage of chemicals as Fenton reagents has been greatly reduced: FeSO4 and H2O2 by 39%, H2SO4 by 100%, and NaOH by 55%. Consequently, the sludge production was reduced by 51% in weight and 12% in volume. Despite electricity consumption by the MER, the coupled system cost $4.76 per m3 leachate less than the standalone Fenton treatment. More notably, direct Fenton oxidation removed only 21% of ammonia; in comparison, the MER-Fenton system removed ammonia by 98% with the possibility for recovery at a rate of 30.6 -55.2 kg N m-3 reactor d-1. Those results demonstrated that coupling MER with the Fenton process could mitigate some inherent drawbacks of Fenton oxidation such as ineffective ammonia removal, high acid and chemical reagents dose requirements, and a large amount of sludge generation. The third study investigated the formation of total halogenated organics (DBP) and the associated toxicity as the side effect of leachate treatment in the MER. Compared to the 4538±100 µg L-1 from the control membrane-less electrochemical oxidation reactor, the amount of DBP generated in the MER only accounted for 19.1±4.5 % after the same treatment period. The total toxicity value (26.6 ×10-3 ) was low for MER effluent, only 15.1% of that in the control group. Both high pH and high ammonia concentration introduced more DBP mass and toxicity production after MER treatment. DBP concentrations were shown to increase with applied current density and possible temperature raise. With 67.5% of DBP mass concentration and 74.4% of the additive toxicity removal, the granular activated carbon (GAC) electrode system was shown more effective than GAC adsorption alone in remediating DBP harmful effects. This dissertation introduced MER as a promising technology for the treatment of leachate through performance demonstration, process integration and by-product remediation.
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    Probing Morphology, Transport and Local Intermolecular Interactions in Polymeric Materials via NMR Diffusometry and Spectroscopy
    Korovich, Andrew George (Virginia Tech, 2022-04-11)
    Understanding transport of water molecules and salt ions from a molecular level up to macroscopic length scales is critical to the design of novel materials for many applications, including separations membranes for fuel cell and desalination applications, as well as rechargeable battery technology. This work aims to investigate and develop new models correlating the dynamics and structure of polymeric materials, to the transport of small molecules within them, using a variety of Nuclear Magnetic Resonance (NMR) techniques. We present three studies through which we utilize two chemically similar membranes: hydroxyethyl acrylate-co-ethyl acrylate (HEA-co-EA) and hydroxymethyl methacrylate-co-methyl methacrylate (HEMA-co-MMA), which greatly differ in glass transition temperature, in order to understand the fundamental relationships from polymer chain dynamics and small molecule diffusion. From observations of the micron scale diffusion of these materials we find that the more dynamic, rubbery HEA-co-EA exhibits lower water to salt selectivity than HEMA-co-MMA, and that this difference arises from nanoscale morphology of the materials. From this, we propose a new model for hydrophilic pathways inside polymeric materials consisting of nanometer scale interconnected pathways are interrupted by micron scale arrangements of so-called "dead ends". We also for the first time show the separation of material tortuosity into two regimes, ranging from the nanometer-bulk and micron-bulk length scales. We further separate the contributions of structure from chemical interactions in the chemically similar desalination materials by investigating the local activation energy of diffusion in both materials, as well as aqueous solutions of the hydrophilic monomers analogous to the internal membrane environment. We find that the effects of local geometric confinement are very similar between the two materials, however the intermolecular interactions between water and the hydrophilic monomers, with respect to water transport, are significantly different between the two hydrophilic species. Geometric confinement accounts for a 5 ± 1 kJ/mol increase in diffusive activation energy from solution to membrane for both chemistries, and a 4 ± 1 kJ/mol difference in activation energy is seen between the two chemistries in both solution and membrane form. We propose that the entropic contributions to transport, are strongly impacted by the rigid environment of the HEMA material, and is related to the increased water-salt selectivity, as well as the increasing selectivity with increased ionic size observed compared to the HEA system. Using Dynamic NMR spectroscopy, we further investigate the differences seen in water-monomer intermolecular proton exchange by NMR. We utilize an iterative least-squares solving method to fit our exchange lineshape to a model of an uncoupled, two-site exchange lineshape in order to obtain rate and equilibrium population data from -50 to 70 °C. We find that, similar to the diffusive activation energy, the HEA-water system shows reduced enthalpy and entropy of the transition state compared to HEMA-water, such that there is faster exchange between HEMA and water at all temperatures measured, in addition to more biased populations in the HEA-water system.
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    Studies on Corrosion, Fouling and Durability of Advanced Functional Nonwetting Surfaces
    Mousavi, Seyed Mohammad Ali (Virginia Tech, 2021-11-30)
    Superhydrophobic and lubricant-infused porous surfaces are two classes of non-wetting surfaces that are inspired by the adaptation of natural surfaces such as lotus leaves, pond skater legs, butterfly wings, and Nepenthes pitcher plant. This dissertation focuses on fabrication and in depth study of bioinspired functional metallic surfaces for applications such as power plant condensers and marine applications. Toward that, first, facile and scalable methods are developed for the fabrication of superhydrophobic surfaces (SHS) and lubricant-infused surfaces (LIS). Second, the corrosion inhibition mechanism of SHS was systematically studied and modeled via electrochemical methods to elucidate the role of superhydrophobicity and other parameters on corrosion inhibition. The anti-corrosion properties of SHS and LIS were systematically studied over a range of temperatures (23°C–90°C) to simulate an actual condenser environment. Moreover, the environment of application often involves using harsh cleaning chemicals. The fabricated non-wetting surfaces were examined over a wide range of acidity and basicity (pH=1 to pH=14). Third, the durability of SHS and LIS is systematically assessed using a set of testing protocols including water impingement tests, scratch wear tests, and accelerated chemical corrosion tests. Considering that industrial environments of application are often turbulent, in addition to static long term corrosion tests, long term dynamic durability was studied in a simulated turbulent condition. Fourth, the performance of the fabricated nonwetting surfaces was systematically studied against calcium sulfate scaling in turbulent conditions and different temperatures. An analytical relationship based on the Hill-Langmuir model is proposed for the prediction of fouling on nonwetting and conventional surfaces alike in dynamic conditions. Overall 1048 individual samples were studied via over 3000 measurements in this dissertation to establish a comprehensive fundamental knowledge base on fabrication and anti fouling characteristics of metallic nonwetting surfaces, which profoundly helps to design appropriate surfaces and fabrication methods based on the use environment.
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    Supramolecular Metal Halide Complexes for High-Temperature Non-linear Optical Switches
    Wang, Qian; Jin, Jianbo; Wang, Zhongxuan; Ren, Shenqiang; Ye, Qingyu; Dou, Yixuan; Liu, Sunhao; Morris, Amanda; Slebodnick, Carla; Quan, Lina (American Chemical Society, 2024-02-23)
    Nonlinear optical (NLO) switching materials, which exhibit reversible intensity modulation in response to thermal stimuli, have found extensive applications across diverse fields including sensing, photoelectronics, and photonic applications. While significant progress has been made in solid-state NLO switching materials, these materials typically showcase their highest NLO performance near room temperature. However, this performance drastically deteriorates upon heating, primarily due to the phase transition undergone by the materials from noncentrosymmetric to centrosymmetric phase. Here, we introduce a new class of NLO switching materials, solid-state supramolecular compounds 18-Crown-6 ether@Cu2Cl4·4H2O (1·4H2O), exhibiting reversible and stable NLO switching when subjected to near-infrared (NIR) photoexcitation and/or thermal stimuli. The reversible crystal structure in response to external stimuli is attributed to the presence of a weakly coordinated bridging water molecule facilitated by hydrogen bonding/chelation interactions between the metal halide and crown-ether supramolecules. We observed an exceptionally high second-harmonic generation (SHG) signal under continuous photoexcitation, even at temperatures exceeding 110 °C. In addition, the bridging water molecules within the complex can be released and recaptured in a fully reversible manner, all without requiring excessive energy input. This feature allows for precise control of SHG signal activation and deactivation through structural transformations, resulting in a high-contrast off/on ratio, reaching values in the million-fold range.
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    Surface Interactions of Diborane
    Jones, Nathan B. (Virginia Tech, 2022-08-22)
    Diborane (B2H6) is a hydride gas often employed in high-purity industrial surface processes such as chemical vapor deposition or epitaxial layer growth. The use of diborane at industrial scales is complicated by the formation of higher-order borane contaminants in pure diborane gas via a complex series of gas-phase reactions. An advanced, rationally designed sorbent could stabilize diborane through interfacial interactions, dramatically reducing the decomposition rate without permanently trapping the molecule. However, the design of such a sorbent would require a nuanced understanding of diborane's fundamental surface chemistry, about which little is known. In the work presented in this thesis, a novel ultra-high vacuum (UHV) system was designed and employed to characterize the fundamental interactions of diborane with a variety of surfaces. In situ Fourier-transform infrared (FTIR) spectroscopy and temperature-programmed desorption (TPD) experiments were used in conjunction with density-functional theory (DFT) calculations to elucidate binding geometries and interaction mechanisms. On non-functionalized model surfaces such as CaF2 or amorphous carbon, diborane adsorbed only at cryogenic temperatures. Hydroxylated surfaces such as amorphous silica (SiO2) adsorbed significantly more diborane, which remained at slightly higher temperatures. FTIR spectra indicated the presence of hydrogen bonding between diborane and surface hydroxyl groups. DFT calculations revealed that the interaction takes the form of a novel bifurcated dihydrogen bond. In contrast with previous reports, diborane exhibited only weak interactions with the surface hydroxyl groups of silica. DFT calculations further elucidated that the irreversible reaction of diborane with surface hydroxyls is only possible in the presence of a second nucleophile (such as adventitious water). On the metal-organic framework (MOF) UiO-66 NH2, unique chemistry was observed in which diborane reacted with the –NH2 groups of the MOF linkers, yielding stable surface-bound products. DFT calculations determined the reaction mechanism to be dissociative adsorption of diborane, resulting in two amine-bound –BH3 moieties. Importantly, it was found that these fragments persisted at room temperature and could only leave the surface via the reverse reaction. The discovery that diborane can be stored as separate fragments that re-combine to yield the parent molecule has important implications for the development of new diborane sorbents. We hypothesize that surfaces designed with fixed, precisely spaced nucleophiles could enable the reversible storage of diborane.
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    Understanding How Tape Casting Titanium Diboride Shifts its Processing-Microstructure-Properties Paradigm Toward New Applications
    Shirey, Kaitlyn Ann (Virginia Tech, 2023-09-07)
    The manufacturing of UHTC materials has significantly advanced over recent years, allowing for the development of new microstructures, architectures, shapes, and geometries to explore new properties and applications for these materials beyond aerospace. One of the UHTCs, titanium diboride (TiB2) exhibits high electrical and thermal conductivity that could satisfy the needs of functional ceramic component applications, like battery cathodes, by tailoring its microstructure and architecture. This thesis represents one of the first detailed studies to understand how the processing-microstructure-properties relationship of TiB2 can be shifted to explore new applications. In order to do that, TiB2 has been manufactured with a processing technique never used before, with significant porosity, exploration of which has been very limited for this material. Additionally, this thesis also explores the synthesis and utilization of novel anisotropic particles to further explore this material relationship. In this work, aqueous tape casting of TiB2 has been investigated. Zeta potential measurements and suspension rheology were used to understand the role of dispersant, binder and plasticizer in the suspension and their interaction with the surface chemistry of the TiB2 particles to develop a stable, homogenous suspension, with minimum additive amounts (0-2 wt%). Homogeneous, flexible and strong TiB2 tapes were prepared using suspensions with 30 vol% solids and characterized to compare different compositions, mixing methods, and thicknesses. The characterization shows the tailoring of the properties as a function of the controlled suspension formulation with minimum amount of additives. Green tapes with 2 wt% dispersant, 1 wt% binder, and 2 wt% plasticizer had similar microstructure to those with half the plasticizer but quintuple the Young's modulus (1.96 GPa). The effect on other relevant properties is also discussed. Tape casting aligns anisotropic particles along the direction of casting, which can be taken advantage of for increasing fracture toughness directionally or producing aligned pore networks using sacrificial fillers. The relationship between alignment, porosity, and the mechanical properties of titanium diboride has not been studied. In this work, we characterize the porous sintered bodies produced through aqueous tape casting of non-spherical TiB2 particles of aspect ratio close to 1, as well as composites with an added high aspect ratio particle (2 wt% PCN-222). Synthesis of uniform, spherical ZrC is difficult and generally not cost-effective, as is the case for most ultra-high temperature ceramics. High aspect ratio particles for reinforcement of ceramic composites are even more difficult to synthesize. Metal organic frameworks (MOF) are crystalline coordination polymers composed of multidentate organic linkers bridging metal nodes to form porous structures. Thermal decomposition of MOFs presents a new and cost-effective route to synthesis of ZrC. In this study, heat treatment at 2000°C of MOF PCN-222 produces zirconium carbide (ZrC) within a highly anisotropic particle. The resulting rod-shaped, glass-like carbon matrix embedded with ZrC crystals is described. These rods have potential as reinforcements for iii high temperature applications and as a synthetic route for ultra-high temperature ceramics with unique morphologies. It is the first time that this type of transformation from a MOF into a UHTC has been reported. We have determined through analysis of SEM images that regardless of tape casting speed, about 57% of the TiB2 particles are aligned with the tape casting direction. The mechanical properties are dominated by the effects of the porosity (38%), but the alignment exhibited here could be further exploited for anisotropic behavior across the sintered tapes. Composites cast with high aspect ratio particles exhibited strong alignment in the casting direction. Further work is required to understand the interplay between alignment and porosity and their effects on material properties.
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    Understanding the Chemistry and Mechanical Properties of Metal-Organic Framework-Polymer Composites
    Yang, Xiaozhou (Virginia Tech, 2023-07-27)
    Metal-organic frameworks (MOFs) are an emerging class of materials exhibiting desirable properties and functionalities for a variety of applications, including catalysis, molecular separation, gas storage, and mechanical reinforcement. However, the majority of MOFs exist as particulate powders, limiting their transportability and applicability in practical fields. Polymers, on the other hand, are one of the most widely used materials in the world owing to their facile processability and low production cost. Combining MOFs and polymers to form MOF-polymer composites can potentially maintain the merits of both materials while overcoming drawbacks of each individual component. Specifically, MOFs are promising candidates as mechanical reinforcers for polymers because of their low density, high specific modulus, and controllable dimensions. Herein, we aim to provide a comprehensive investigation into the chemistry and mechanical properties of MOF-polymer composites. Various governing parameters, including particle aspect ratio (AR), MOF-particle interface, and intrinsic mechanical properties of MOFs, were thoroughly studied to construct an optimal pathway for fabricating mechanically reinforced MOF-polymer composites. Chapter 1 presents an introduction to MOFs, polymer composites, and mechanical properties and characterizations of polymeric materials. It serves as a foundation of this dissertation and outlines essential concepts for the scientific background. The primary factors that impact the mechanical properties of polymer composite are highlighted, leading to the following three research chapters. Comprehensive background on various characterization techniques that aim at mechanical properties is covered in detail. Chapter 2 focuses on the role of MOF AR on the mechanical properties of MOF-polymer composites. PCN-222, a Zr-MOF with porphyrin linkers, was synthesized with AR ranging from 3.4 to 54. The crystallinity and chemical structure of the MOFs remained consistent for different ARs, ensuring that the AR was the only variable in determining the mechanical reinforcement. Fabricated through the doctor-blade technique, the MOF-PMMA composite films showed homogeneous MOF distribution and alignment. Tensile tests revealed that Young's modulus of the composites increased with MOF AR, exhibiting a good agreement with a modified Halpin-Tsai model. Both storage and loss moduli were also enhanced following increased MOF AR. In addition, the thermal stability was also improved with the addition of MOF particles. In Chapter 3, the authors extend the understanding of mechanical properties of MOF-polymer composites to the interfacial properties between the two materials. Pristine MOFs often lack strong interactions with a polymer matrix due to the difference in chemical/physical properties. The authors developed a three-step synthetic route to grow PMMA on the surface of PCN-222. Owing to an efficient surface-initiated polymerization technique, the PMMA was successfully grafted with high molecular weight and grafting density. The molecular weight of PMMA could be controlled by simply varying polymerization time. The PMMA-grafted PCN-222 was manufactured along with PMMA matrix to form composite films. Mechanical analysis proved that the mechanical reinforcement was improved with increasing grafted molecular weight. Chapter 4 presents an experimental approach to unveil the structure-mechanical property of MOF single crystals, which provides insights on designing MOFs with desired mechanical strength. Zeolitic imidazolate frameworks (ZIFs), a subdivision of MOFs, were chosen as the template owing to their facile synthesis, structural diversity, and high crystallinity. Two types of micron-sized ZIFs, ZIF-8 with Zn2+ node and ZIF-67 with Co2+ node, were synthesized to compare the effect of metal-linker bond. Moreover, the linker composition was varied to examine the difference in crystal structure and defect level. The mechanical properties of these ZIF samples were revealed by nanoindentation on single particles. Overall, the stronger metal-linker bond and high crystallinity were able to yield the highest elastic modulus and hardness. Finally, Chapter 5 offers a comprehensive review on polymer-grafted MOF particles regarding the synthesis and applications associated with surface-anchored polymers. Various polymerization techniques were summarized, and their adjustment and limitations with respect to MOFs were highlighted. The novel and unique applications arisen from polymer-grafted MOFs and Mixed Matrix Membranes were thoroughly discussed.
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    Zirconium-Based Metal-Organic Frameworks for Artificial Electrochemical Photosynthesis
    Thomas, Benjamin David (Virginia Tech, 2025-02-21)
    The utilization of porous materials for electrocatalytic applications has been of high interest due to their high surface area and increase in electrode-electrolyte interface. Metal-organic frameworks (MOFs) are an emerging class of 3-D porous materials consisting of inorganic nodes bound by multidentate organic linkers. MOFs have permanently large surface area, high stability, and the tunability of the structure. The metal source or the organic linker can be swapped to create a material with desirable features. MOFs have been explored for applications in electrocatalysis, conductivity and energy storage. The fundamental charge transfer methods of MOF thin films is discussed and the utilization of these conductive materials for the key reactions in artificial photosynthesis is explored to highlight methods to improve the efficiency of these materials for electrocatalysis. The Morris group has previously shown that charge transfer in MOFs can occur through a redox hopping mechanism in which the charge hops from redox center to redox center through space followed by the movement of a charge balancing ions. In Chapter 2, the charge transfer mechanism within the MOF is further investigated by utilization of spectroelectrochemistry. The incorporation of a redox center, Ru(bpy)2(dcbpy), "RuBPY" where bpy = 2,2′-bipyridine; bpy-(COOH)2 = 5,5′-dicarboxylic acid-2,2′-bipyridine into the UiO-67 framework creates a conductive MOF that is also electrochromic. RuBPY is a deep orange color in the standard RuII state and upon oxidation to RuIII it is pale green. The change in absorption profile of the redox center allows for the rate of oxidation to be determined through absorbance measurements. The material showed minimal change in absorbance upon applying an oxidative potential. The incorporation of a sulfonate group into the backbone of the RuBPY-UiO-67-SO3H MOF allowed for a much higher change in absorbance converting the entire MOF into the oxidized state. The change in level of absorbance indicates that the sulfonate groups improve the conductivity within the pores of the MOF allowing for oxidation of previously electrochemically inaccessible redox centers. The sulfonate groups are thought to break ion pairs of the electrolyte and increase effective electrolyte concentration within the pores. The sulfonate groups' ability to improve the conductivity within the MOF can be further investigated to improve charge transfer through porous materials. The sulfonate groups were again incorporated into the UiO-67 MOF framework for use in electrocatalytic applications by also incorporating the known water oxidation catalyst, RuTPY, Ru(tpy)(dcbpy)H2O. A RuTPY-UiO-67 film had previously shown reactivity as a water oxidation catalyst with improved activity over a monolayer of RuTPY on fluorine-doped tin oxide, FTO. The sulfonate groups were added to create a proton transfer chain that shuttled the generated protons away from the catalytic site to improve reactivity. The incorporation of sulfonate groups again showed improved charge transfer from the MOF materials with the RuTPY-UiO-67-SO3H being 100% electrochemically accessible. The water oxidation capabilities improved giving the material increased oxygen generation upon oxidation of water. The improvement of catalytic activity of RuTPY-UiO-67-SO3H was beyond the increased electrochemical accessibility means the proximal sulfonate groups were aiding in catalysis in some manor. This work highlights the use of multivariate approaches to MOFs to improved efficiency in various applications. The fourth chapter discusses the other half of artificial photosynthesis, CO2 reduction. The known CO2 reduction catalyst, Ni(cyclam), is incorporated into a zirconium-based MOF, VPI-100. The VPI-100 powder was electrochemically deposited onto a glassy carbon electrode and the film was used for electrochemical CO2 reduction into carbon dioxide. The film successfully generated CO as a major product with a faradaic efficiency of 56%. The film was stable under electroreduction conditions and was able to be recycled for continuous production of CO. The final chapter is a review that discusses the utilization of MOFs as photocatalysts for CO2 conversion using only abundant earth metals. While most CO2 catalysts are expensive noble metals, the development of cheap abundant catalytic materials is extremely relevant to a clean energy future.