Thesis advisor: Chia-Kuang (Frank) Tsung / The core-shell hybrid structure is the simplest motif of two-component systems which consists of an inner core coated by an outer shell. Core-shell composite materials are attractive for their biomedical, electronic and catalytic applications in which interface between core and shell is critical for various functionalities. However, it is still challenging to study the exact role that interface plays during the formation of the core-shell structures and in the properties of the resulted materials. By studying the formation mechanism of a well interface controlled one-to-one metal nanoparticle (NP)@zeolite imidazolate framework-8 (ZIF-8) core-shell material, we found that the dissociation of capping agents on the NP surface results in direct contact between NP and ZIF-8, which is essential for the formation of core-shell structure. And the amount of capping agents on the NP surface has a significant effect to the crystallinity and stability of ZIF-8 coating shell. Guided by our understanding to the interface, one-to-one NP@UiO-66 core-shell structure has also been achieved for the first time. We believe that our research will help the development of rational design and synthesis of core-shell structures, particularly in those requiring good interface controls. / Thesis (MS) — Boston College, 2017. / Submitted to: Boston College. Graduate School of Arts and Sciences. / Discipline: Chemistry.

This thesis explores the use of computational chemistry to aid in the design of metal-organic frameworks (MOFs) and other materials. A focus is placed on finding exceptional materials to be used for removing CO2 from fossil fuel burning power plants, with other avenues like vehicular methane storage and landfill gas separation being explored as well. These applications are under the umbrella of carbon capture and storage (CCS) which aims to reduce carbon emissions through selective sequestration. We utilize high-throughput screenings, as well as machine learning assisted discovery, to identify ideal candidate materials using a holistic approach instead of relying on conventional gas adsorption properties. The development of ideal materials for CCS requires all aspects of a material to be considered, which can be time-consuming. A large portion of this work has been with high-throughput, or machine learning assisted discovery of ideal candidates for CCS applications. The chapters of this thesis are connected by the goal of finding ideal materials for CCS. They are primarily arranged in increasing complexity of how this research can be done, from using high-throughput screenings with more simple metrics, up to multi-scale machine learning optimization of pressure swing adsorption systems. The work is not presented chronologically, but in a way to tell the best story. Work was done by first applying high-throughput computational screening on a set of experimentally realized MOFs for vehicular methane storage, post-combustion carbon capture, and landfill gas separation. Whenever possible, physically motivated figures of merits were used to give a better ranking and consideration of the materials. From this work, we were able to determine what the realistic limits might be for current MOFs. The work was continued by looking at carbon-based materials (primarily carbon nanoscrolls) for post-combustion carbon capture and vehicular methane storage. The carbon-based materials were found to outperform MOFs; however, further studies are needed to verify the results. Next, we looked at ways to improve the high-throughput screening methodology. One problem area was in the charge calculation, which could lead to unrealistic gas adsorption results. Using the split-charge equilibration method, we developed a robust way to calculate the partial atomic charges that were more accurate than its quick calculation counterparts. This led to gas adsorption properties which more closely mimicked the results determined from time-consuming quantum mechanically derived charges. Simplistic process optimization was then applied to nearly ~3500 experimental structures. To the best of our knowledge, this is the first time that any process optimization has been applied to more than 10s of materials for a study. The process optimization was done by evaluating the desorption at various pressures and choosing the value which gave the lowest energetic cost. It was found that a material synthesized by our collaborators, IISERP-MOF2, was the single best experimentally realized material for post-combustion carbon capture. What made this an interesting result is that by conventional metrics IISERP-MOF2 does not appear to be outstanding. Next, functionalized versions of MOFs were tested in a high-throughput manner, and some of those structures were found to outperform IISERP-MOF2. Although high-throughput computational screenings can be used to determine high-performance materials, it would be impossible to test all functionalized versions of some MOFs, let alone all MOFs. Functionalized MOFs are noteworthy because MOFs are highly tuneable through functionalization and can be made into ideal materials for a given application. We developed a genetic algorithm which, given a base structure and a target parameter, would be able to find the ideal functionalization to optimize the parameter while testing only a small fraction of all structures. In some cases, the CO2 adsorption was found to more than quadruple when functionalized. A better understanding of how materials perform in a PSA system was achieved by performing multi-scale optimizations. Experimentally realized MOFs were tested using atomistic simulations to derive gas adsorption properties. After passing through a few sensible filters, they were then screened using macro-scale pressure swing adsorption simulators, which model how gas separation may occur at a power plant. Using another genetic algorithm, the conditions that the pressure swing adsorption system runs at was optimized for over 200 materials. To the best of our knowledge, this is the highest amount of materials that have had been optimized for process conditions. IISERP-MOF2 was found to perform the best based on many relevant metrics, such as the energetic cost and how much CO2 was captured. It was also found that conventional metrics were unable to be used to predict a material’s pressure swing adsorption performance.

The objective of this work was to develop a molecular simulation method with the capacity to represent the synthesis of metal-organic framework (MOF) structures to the extent of being able to accurately predict the MOF structures that form under specified reaction conditions. MOFs are a class of porous, crystalline solids composed of metal-ion vertices coordinated by organic linker molecules. MOFs are created in a self-assembly process in which the building blocks (reactants) retain their integrity. Under different experimental synthesis conditions, a particular combination of building blocks can react to form differing MOF structures. The structure of MOFs confers a large degree of tunability, allowing almost limitless potential for the materials to be designed with the capacity to fulfil the requirements of a specific application. Consequently, MOFs have shown promise for a variety of applications including gas storage, separation and catalysis. Thus, the ability to accurately predict the MOF formed by specifying reaction parameters such as temperature, pH and the concentrations of reactants has great potential because, upon identification of a promising hypothetical structure for a particular application, the synthesis conditions ascertained via the simulation method could be used as the basis for the determination of an experimental synthesis procedure. In addition, a simulation method with the capacity to predict MOF structures affords the opportunity to gain a fundamental understanding of the influence of the experimental synthesis conditions on the structures formed, so as to enable progress towards the rational design of MOFs. In this work, the experimental synthesis of MOFs via self-assembly is modelled using a kinetic Monte Carlo approach. Ideally, simulation of the self-assembly of the building blocks would be modelled atomistically with all atoms in the reactant and solvent molecules represented explicitly. However, due to the prohibitive computational requirements of such a simulation, in this work a “potential-of-mean-force” (PMF) approach was used to represent the solvent implicitly by encompassing the solvent-mediated behaviour in the interactions between building blocks, thereby reducing the computational cost. The PMF approach to the implicit representation of the solvent involved the utilisation of effective pairwise interactions between the constituents of the reactant species. Following extensive testing to ensure that the explicit-solvent behaviour of the reactants could be replicated using the PMF method, this approach allowed computationally efficient implicit-solvent simulations of the synthesis of MOF materials to be performed. Thorough assessment of a method developed to simulate the synthesis of MOFs required investigation of a system which, under different reaction conditions, forms differing structures. In this respect, the cobalt succinates represent an unparalleled test because under different reaction temperatures, reactant concentrations, pH and reaction time, seven different phases have been identified. Furthermore, the parameters within which the different phases form have been clearly delineated experimentally. The method developed has been employed, under the appropriate reaction conditions, to simulate the synthesis of two of the seven identified phases of the cobalt succinates. Whilst still subject to computational limitations, the MOF-synthesis simulation method yields structures characteristic of those expected experimentally under corresponding reaction conditions.

Porous metal-organic materials (MOMs) are assembled through coordination between two types of building units, metal or metal-containing nodes and organic linkers. Metal-organic frameworks (MOFs) have 3-D infinite structures and are especially known for high porosity and enormous surface area, leading to diverse applications such as selective gas separation, gas storage and catalysis. In contrast, metal-organic polygons/polyhedra (MOPs) as discrete molecular coordination assemblies are soluble in certain solvents, allowing us to study their solution-chemistry. In the first project, a microporous MOF with 1-dimensional (1D) bridging helical chain secondary building units (SBUs) shows facile transition from micro- to mesoporosity upon activation conditions. The quickly activated MOF shows permanent microporosity while the slow removal of coordinated aqua ligand results in formation of the mesopores in the microporous MOF. Second, a strategy to introduce not only the functional groups but also functionalized meso-cavities into microporous MOFs through metal-ligand-fragment coassembly has been studied. With this functionalization, the interior of the MOFs can be tuned by a wide range of functional groups on the ligand fragments, including polar and ionic ones. Depending on the functional groups on the ligand fragments, the introduced cavities can be extended to mesopores in a controllable manner. Third, a MOF constructed from dicopper paddlewheels and a predesigned ligand bearing carboxylate, pyridine, and amide groups enables selective adsorption of CO2 over CH4 and high H2 adsorption. The cooperative catalytic activity in a tandem one-pot deacetalization-Knoevenagel condensation was demonstrated. In the fourth and fifth section, an optically and thermally switchable azobenzene was introduced into a MOF and MOPs, respectively. The freshly synthesized MOF adsorbed a significant amount of CO2. Upon light irradiation, the adsorbed gas molecules were squeezed out of the MOF due to the change of conformation of the azobenzene groups inside the pores. The adsorbent returned to its original state when allowed to stay with gentle heating. In addition, solubility of srMOPs was optically controlled by trans-cis isomerization of the azobenzene moieties. Interestingly, guest molecules were trapped during cis to trans isomerization and released in the trans to cis conversion. This srMOP can be applied to uses requiring stimuli responsive capture and release of guest molecules, such as in controlled drug delivery systems. Finally, an organic linker with multiple conformations was used to synthesize both single and core-shell molecular squares, whose formations were controlled by reaction temperatures. Intriguingly the core-shell structure assembly was successfully employed as a template to prepare a heterobimetallic assembly, in which the metal substitution occurred exclusively in the core. This work might pave the way for the exploration of enzyme-mimicking molecular catalysts.

abstract: An urgent need for developing new chemical separations that address the capture of dilute impurities from fluid streams are needed. These separations include the capture of carbon dioxide from the atmosphere, impurities from drinking water, and toxins from blood streams. A challenge is presented when capturing these impurities because the energy cost for processing the bulk fluid stream to capture trace contaminants is too great using traditional thermal separations. The development of sorbents that may capture these contaminants passively has been emphasized in academic research for some time, producing many designer materials including metal-organic frameworks (MOFs) and polymeric resins. Scaffolds must be developed to effectively anchor these materials in a passing fluid stream. In this work, two design techniques are presented for anchoring these sorbents in electrospun fiber scaffolds. The first technique involves imbedding sorbent particles inside the fibers: forming particle-embedded fibers. It is demonstrated that particles will spontaneously coat themselves in the fibers at dilute loadings, but at higher loadings some get trapped on the fiber surface. A mathematical model is used to show that when these particles are embedded, the polymeric coating provided by the fibers may be designed to increase the kinetic selectivity and/or stability of the embedded sorbents. Two proof-of-concept studies are performed to validate this model including the increased selectivity of carbon dioxide over nitrogen when the MOF ZIF-8 is embedded in a poly(ethylene oxide) and Matrimid polymer blend; and that increased hydrothermal stability is realized when the water-sensitive MOF HKUST-1 is embedded in polystyrene fibers relative to pure HKUST-1 powder. The second technique involves the creation of a pore network throughout the fiber to increase accessibility of embedded sorbent particles. It is demonstrated that the removal of a blended highly soluble polymer additive from the spun particle-containing fibers leaves a pore network behind without removing the embedded sorbent. The increased accessibility of embedded sorbents is validated by embedding a known direct air capture sorbent in porous electrospun fibers, and demonstrating that they have the fastest kinetic uptake of any direct air capture sorbent reported in literature to date, along with over 90% sorbent accessibility. / Dissertation/Thesis / Doctoral Dissertation Chemical Engineering 2018

The present thesis mainly proposes to explore the potential of aza-macrocycles in metal-organic frameworks (MOFs) for applications related to unprecedented open macrocycle cavities. Strategies such as direct arylation of secondary amines as well as multidentate coordination were applied to constrain the intramolecular flexibility of as-obtained macrocyclic compounds. Several desired materials, i.e. MMCF-4, MMCF-5/MMCF-5t/MMCF-5t-aa, MMCF-5, HMMCF-1, were obtained. They are proved superior to traditional materials in the field of "turn-on" lanthanide luminescence, deep desulfurization of flue gas, recovery of Platinum-group metals, etc. Powder/single-crystal X-ray diffraction (PXRD/SCXRD), synchrotron-based X-ray and extended X-ray absorption fine structure (EXAFS), density functional theory (DFT) theoretical calculations, etc., were employed for deep-understanding the mechanisms. These studies shed light on the construction of hierarchically porous materials with two levels of porosity, i.e., one from the frameworks and the other one from the aza-macrocycles. Incorporation of aza-macrocycles into the MOF architectures not only leads to fundamental significance in bridging the chemistry of MOFs with supramolecular chemistry but also elicits unique properties from the hybrid materials obtained. As a paradigm for constructing frameworks with accessible macrocyclic cavities based on "constrained" aza-macrocycle ligands, this thesis paves the way for the further development of this framework family in the future.

No description available.

Industrial productions need the separation processes, but they are quite energyintensive, which occupy about half of the total energy consumption. Membranetechnology based on a non-thermal route is expected to reduce the associated energy duties by ~90%, but effective membrane materials capable of precisely isolating targeted species from complex mixtures are highly needed. Metal-organic frameworks (MOFs), possessing the tuneable pore size and geometry, are regarded as the promising platform for molecular separations and membrane design. This dissertation illustrates the rational design and the guided fabrication for various MOF membranes. Respectively, different gas separation applications were addressed by using these membranes, such as light hydrocarbon separations, carbon dioxide (CO2) captures and natural gas purifications. A versatile strategy for membrane fabrication is developed based on the electrochemical method. Following this, a family of face-centered cubic (fcu) MOF membranes were obtained, which possess different ligands and different clusters, namely rare-earth hexanuclear or zirconium hexanuclear clusters. Two MOF membranes based on fumarate (fum) linker, Zr-fum-fcu-MOF and Y-fum-fcu-MOF, showed efficient separation for the propylene/propane binary mixture, as well as the butane/isobutane equimolar mixtures, respectively. Further aperture editing applied to Zr-fum-fcu-MOF via mixed-linker approach permits the introduction of shape irregularity to the parent trefoil-shaped apertures, inducing an ideal shape-mismatch with tetrahedral CH4 molecules and blocking their transportation while affecting linear molecules slightly such as nitrogen (N2) and CO2. The resultant Zr-fum67-mesaconate (mes)33-MOF membranes exhibit great promise for natural gas purification, including efficient nitrogen rejection and simultaneous removal of CO2 and N2 from natural gas. In addition, a unique CO2-recognition membrane based on a fluorinated MOF (KAUST-7) is constructed for multipurpose CO2 capture, including CO2/H2, CO2/N2 and CO2/CH4 separation. The specific affinity to CO2 coupling with the molecular sieving capability of KAUST-7 enables the membrane to be nearly only permeable to CO2, excluding both smaller H2 molecule and larger N2 or CH4 molecules. Moreover, in order to be closer to the real applications, the defective Zr-fum-fcu- MOF nanoparticles based mixed-matrix membranes are constructed for natural gas purification under practical conditions

Biologics such as DNA and protein have immense biomedical applications, especially in diagnosis and therapy. However, many barriers hinder these applications, including biologics transport and liability in biological systems. Therefore, biocompatible and stable nanocarriers with high Biologics loading efficiency can provide a platform for advances in biologics applications. Metal-organic frameworks (MOFs) have gained significant interest within the biomedical field, mainly because of their building block versatility, porosity, stability, and chemical and biological functionality. Currently, increasing research is dedicated to improving MOFs biocompatibility, stability, and functionality for drug delivery. Using biomolecules as organic linkers could improve biocompatibility, physiological condition stability, and biological functionality. The main goal of this dissertation is to investigate the applicability of biomolecule-based Metal-organic frameworks (BioMOFs) as nanocarriers to achieve cellular delivery of active biologics. Herein, we analyzed adenine and saccharate metal−organic frameworks (BioMOF) in terms of biocompatibility, loading capability, protection, and cellular delivery of biologics. Our findings suggest that the usage of biomolecules as an organic linker generates BioMOFs with reduced cytotoxicity compared with the widely used MOFs such as Zinc Imidazole framework-8 (ZIF-8). In addition, the base-pairing functionality of coordinated adenine of KAUST-BioMOFs (KBMs) is preserved and can be used to load ssDNA. Both KAUST-BioMOFs (KBMs) and Zinc adenineated framework (ZAF) load, protect, and deliver functional ssDNA to cells. In addition, we showed the possibility of in situ encapsulation of active lysozyme in zinc saccharate (Zn-Sac) with modified synthesis procedures.

With the increasing demand for energy consumption and the limitations of traditional carbon-based energy sources, the importance of renewable energy generation is undeniable. Among the various methods for generating and storing energy, green hydrogen production through photocatalytic water splitting has gained significant interest. However, despite numerous studies dedicated to finding the perfect material, achieving large-scale industrial applications is still a distant goal. Metal-Organic Frameworks (MOFs) have emerged as a particularly intriguing option due to their exceptional tunability and versatility. Nevertheless, there remains a substantial gap in our understanding of their performance and fundamental aspects. In this study, we focus on Ti-based MOFs, which have shown great promise owing to the redox properties of titanium. We introduce a novel Ti-oxo chain pyrene MOF called ACM- 1, which exhibits remarkable activity in both the hydrogen evolution reaction (HER) and organic transformations. This outstanding performance can be attributed to the high mobility of photogenerated electrons and the strong localization of holes within the material. To further enhance the photocatalytic activity of ACM-1, we employ defect engineering techniques, specifically fluorination of the metal-oxo units. The introduction of fluorine effectively reduces the band gap of the material, leading to improved light absorption capabilities and a significant boost in photocatalytic performance. Additionally, we synthesize a new MOF named ICGM-1, which shares isochemical characteristics with the well-studied MIL-125-NH2. Despite the identical NH2-bdc linker, ICGM-1 differs in terms of its Ti-sbu composition, providing a unique opportunity to investigate the influence of node geometry on photocatalytic activity. Our study reveals that the rod-type geometry is unfavorable due to lower electron charge mobility, highlighting the importance of node architecture in designing efficient photocatalysts. Finally, we report the synthesis of two new Zr-based MOFs, ACM-10 and ACM-11, based on the redox-active TTFT linker. Through Ti grafting, we demonstrate the potential of ACM-10 for HER, further expanding the range of viable MOF photocatalysts.