An immediate reduction in global CO2 emissions could be accomplished by replacing coal- or oil-based energy sources with purified natural gas. The most important process involved in natural gas purification is the separation of CO2 from CH4, where Pressure Swing Adsorption (PSA) technology on porous materials has emerged as a less energy demanding technology. Among porous materials which are used or could potentially be used in PSA, Metal Organic Frameworks (MOFs) have attracted particular interest owing to their record-breaking surface areas, high-porosity, and high tunability. However, the discovery of optimal MOFs for use in adsorption-based CO2 separation processes is remarkably challenging, as millions of MOFs can potentially be constructed from virtually limitless combinations of inorganic and organic secondary building units. To overcome this combinatorial problem, this thesis aims to (1) identify important design features of MOFs for CO2/CH4 separation through the investigation of currently existing MOFs as well as the high throughput computational screening of a large database of MOFs, and to (2) develop efficient computational tools for aiding the discovery of new MOF materials. To validate the computational methods and models used in this thesis, the first work of this thesis presents the computational modeling of CO2 adsorption on an experimental CuBDPMe MOF using grand canonical Monte Carlo simulations and density functional theory. The simulated CO2 adsorption isotherms are in good agreement with experiment, which confirms the accuracy of the models used in our simulations throughout this thesis. The second work of this thesis investigates the performance of an experimental MIL-47 MOF and its seven functionalized derivatives in the context of natural gas purification, and compares their performance with that of other well-known MOFs and commercially used adsorbents. The computational results show that introducing polar non-bulky functional groups on MIL-47 leads to an enhancement in its performance, and the comparison suggests that MIL-47-NO2 could be a possible candidate as a solid sorbent for natural gas purification. This study is followed by the compactional study of water effects on natural gas purification using MOFs, as traces of water is present in natural gas under pipeline specifications. From the study, it is found that water has a marginal effect on natural gas purification in hydrophobic MOFs under pipeline specifications. Following the aforementioned studies, a database of 324,500 hypothetical MOFs is screened for their performance in natural gas purification using the general protocol defined in this thesis. From the study, we identify 'hit' materials for targeted synthesis, and investigate the structure-property relationships with the intent of finding important MOF design features relevant to natural gas purification. We show that layered sheets consisting of poly-aromatic molecules separated by a perpendicular distance of roughly 7 Å are an important structural-chemical feature that leads to strong adsorption of CO2. Following the screening study, we develop efficient computational tools for the recognition of high-preforming MOFs for methane purification using Machine Learning techniques. A training set of 32,500 MOF structures was used to calibrate support vector machines (SVMs) classifiers that incorporate simple geometrical features including pore size, void fraction and surface area. The SVM machine learning classifiers can be used as a filtering tool when screening large databases. The SVM classifiers were tested on ~290,000 MOFs that were not part of the training set and could correctly identify up to 70% of high-performing MOFs while only flagging a fraction of the MOFs for more rigorous screening. As a complement to this study, we present ML classifier models for CO2/CH4 separation parameters that incorporate separately the Voronoi hologram and AP-RDF descriptors, and we compare their performance with the classifiers composed of simple geometrical descriptors. From the comparison, it is found that including AP-RDF and Voronoi hologram descriptors into the classifiers improves the performance of classifiers by 20% in capturing high-performing MOFs. Finally, from the screening data, we develop a novel chemiformatics tool, MOFFinder, for aiding in the discovery of new MOFs for CO2 scrubbing from natural gas. It has a user-friendly graphical interface to promote easy exploration of over 300,000 hypothetical MOFs. It enables synthetic chemists to find MOFs of interest by searching the database for Secondary Building Units (SBUs), geometric features, functional groups and adsorption properties. MOFFinder provides, for the first time the substructure/similarity query of porous materials for users and is publicly available on titan.chem.uottawa.ca/moffinger.

In this thesis, we aim to investigate the thermoresponsive behaviour, especially negative thermal expansion (NTE), in metal dicarboxylate metal organic frameworks (MOFs) using X-ray diffraction techniques. Four materials with the UiO-66 topology [Zr6O4(OH)4(bdc)12], [Zr6O6(bdc)12], [Zr6O6(bpdc)12] and [Zr6O6(2,6-ndc)12] (bdc = 1,4-benzenedicarboxylate, bpdc = 4,4’-biphenyldicarboxylate and 2,6-ndc = 2,6-napthalenedicarboxylate) were investigated, all of which contain a zero-dimensional inorganic cluster. All four members show NTE behaviour over the observed temperature ranges as a result of the twisting motion of the carboxylate groups of the organic linkers. This twisting motion introduces a concerted rocking motion within the inorganic cluster which causes an apparent decrease in the size of the cluster and hence overall volume contraction. Alteration of the structure of the organic linker has an effect on the magnitude of the expansivity coefficient which is believed to be related to the existence of specific vibrational modes of that particular organic linker. Four members of the MIL-53 family [Al(OH)(bdc)], [AlF(bdc)], [Cr(OH)(bdc)] and [VO(bdc)] were studied. All four materials show elements of NTE behaviour related to a “wine rack” thermo-mechanical mechanism which is determined by the connectivity of the framework. The thermoresponsive behaviour in these materials is dominated by the changes in the plane of the pore opening. These changes result from a combination of three distinct types of motion of the bdc linker including the rotation of the bdc linker about the chain of the inorganic octahedra, the “knee cap” bending mode of the carboxylate groups about the O-O vector and possibly the transverse vibrations within the bdc linker. The latter motion was not evident in this work due to the limitations of the structure refinements. The former two motions appear to be correlated and depend on the rigidity of the metal-centred octahedra which is determined by the constituent metal cation and anion types. The rigidity of the octahedra is also found to play an important role in determining whether the material undergoes a “breathing” phase transition at low temperature. [Sc2(bdc)3] shows NTE behaviour over the observed temperature range which is partially driven by a “wine rack” thermo-mechanical mechanism, but with an opposite framework compression direction when compared to the MIL-53 types MOFs. This is due to the presence of an additional bdc connecting linker in the plane of the pore opening. This extra connection inverses the compression direction and also impedes the structural changes in the plane of the pore opening. The contraction of the chain of inorganic octahedra is the main contributor to the overall unit cell contraction and is caused by the twisting motion of the carboxylate groups of the bdc linker while the magnitude of this contraction is determined by the flexibility of the chain of inorganic octahedra.

A significant and ongoing challenge in materials chemistry and furthermore solid state chemistry is to design materials with the desired properties and characteristics. The field of Metal-Organic Frameworks (MOFs) offers several strategies to address this challenge and has proven fruitful at allowing some degree of control over the resultant materials synthesized. Several methodologies for synthesis of MOFs have been developed which rely on use of predetermined building blocks. The work presented herein is focused on the utilization of two of these design principles, namely the use of molecular building blocks (MBBs) and supermolecular building blocks (SBBs) to target MOF materials having desired connectivities (topologies). These design strategies also permit the introduction of specific chemical moieties, allowing for modification of the MOFs properties. This research is predominantly focused on two platforms (rht-MOFs and ftw-MOFs) which topologically speaking are edge transitive binodal nets; ftw being a (4,12)-connected net and rht being a (3,24)-connected net. These highly connected nets (at least one node having connectivity greater than eight) have been purposefully targeted to increase the predictability of structural outcome. A general trend in topology is that there is an inverse relationship between the connectivity of the node(s) and the number of topological outcomes. Therefore the key to this research (and to effective use of the SBB and MBB approaches) is identification of conditions which allow for reliable formation of the targeted MBBs and SBBs. In the case of the research presented herein: a 12-connected Group IV or Rare Earth based hexanuclear MBB and a 24-connected transition metal based SBB were successfully targeted and synthesized. These two synthetic platforms will be presented and used as examples of how these design methods have been (and can be further) utilized to modify existing materials or develop new materials for gas storage and separation applications for environmental and energy related applications including hydrogen, methane, carbon dioxide and hydrocarbon storage or separations.

京都大学 / 0048 / 新制・課程博士 / 博士(理学) / 甲第21589号 / 理博第4496号 / 新制||理||1645(附属図書館) / 京都大学大学院理学研究科化学専攻 / (主査)教授 北川 宏, 教授 竹腰 清乃理, 教授 吉村 一良 / 学位規則第4条第1項該当 / Doctor of Science / Kyoto University / DGAM

京都大学 / 0048 / 新制・課程博士 / 博士(理学) / 甲第22684号 / 理博第4625号 / 新制||理||1665(附属図書館) / 京都大学大学院理学研究科化学専攻 / (主査)教授 北川 宏, 教授 吉村 一良, 教授 有賀 哲也 / 学位規則第4条第1項該当 / Doctor of Science / Kyoto University / DGAM

Thesis advisor: Jeffery A. Byers / Thesis advisor: Chia-Kuang (Frank) Tsung / Biological systems have evolved over time to favor structures beneficial for the efficient transformation of simple feedstocks to sophisticated products. In particular, enzymes have evolved such that cooperative and geometrically controlled interactions between active sites and substrates enhance catalytic activity and selectivity. Separation of these active sites from other incompatible catalytic components allows for chemical transformation in a stepwise fashion, circumventing the inherent limitations to performing reactions in a single step. This dissertation describes the use of porous crystalline materials called metal-organic frameworks (MOFs) as hosts to mimic the component separation and precise active site control observed in nature. The first phase of these efforts explores the use of dissociative “aperture-opening” linker exchange pathways in a MOF to encapsulate transition metal complexes for carbon dioxide hydrogenation to formate. This strategy is then used to separate two incompatible complexes and perform the cascade conversion of carbon dioxide to methanol, resulting in unique and previously unobserved network autocatalytic behavior. Finally, the modularity of the MOF host is leveraged to install beneficial functionality in close proximity to the encapsulated transition metal complex, leading to activity exceeding that of any reported homogeneous system for carbon dioxide reduction. The insights gained through these studies can inform the development of composites for other reactions, allowing for access to new and unique reaction manifolds. / Thesis (PhD) — Boston College, 2020. / Submitted to: Boston College. Graduate School of Arts and Sciences. / Discipline: Chemistry.

Thesis advisor: Chia-Kuang Tsung / Thesis advisor: Dunwei Wang / Metal-organic frameworks (MOFs), as a type of inorganic-organic hybrid porous materials, have attracted enormous research interests over the past two decades due to their extraordinary variability and richness of their chemistry and structures. The original design on MOFs is in pursuit of and high surface area, typically for gas storage. However, the properties in a simple MOF system could not meet the needs for a wide variety of advanced applications. Therefore, it is highly desirable to introduce multiplicities and impart functionalities into MOFs through materials design. In this regard, this dissertation focuses on engineering MOFs in two strategies, constructing heterostructures, fabricating thin films, and evaluating their impact on catalysis and energy conversions. The first chapter focuses on constructing a well-defined interface between materials with vast differences in structural dimensions. Another highlight of this study lies in developing characterization protocols to characterize interfacial structures. In the second part, a MOF-74 thin film with crack-free nature serves as a promising platform for the study of ion transport. The last part of this dissertation reports a new two-dimensional (2D) structure derived from UiO-66. The 2D structure was attained by limiting the coordination number and inducing anisotropic growth. The layered material could be further exfoliated and fabricated into thin films. This work presents strategies to impart functionality to MOFs with rational material design and elucidate their positive impacts on the performance of the whole system. / Thesis (PhD) — Boston College, 2021. / Submitted to: Boston College. Graduate School of Arts and Sciences. / Discipline: Chemistry.

Dans le domaine de la microélectronique, les préoccupations environnementales et sanitaires et l'évolution de la législation ont contraint l'industrie à limiter son utilisation du plomb. Les matériaux (à base d'étain, d'argent, de cuivre, de bismuth...) destinés au brasage de composants électroniques font l'objet de nombreux développements pour être conformes aux exigences réglementaires et techniques. Le potentiel des carboxylates de métaux en électronique a déjà été démontré dans le cadre du développement de procédés de décomposition métal-organique. La décomposition thermique sous atmosphère contrôlée de tels précurseurs mène à la création de nanoparticules métalliques avec une réactivité accrue par rapport à celle de particules de taille micronique. L'utilisation de nanomatériaux est une des voies explorées pour mettre au point des procédés d'assemblage à basse température pour l'électronique. Elle s'appuie sur le fait que les températures de fusion et de frittage de nanomatériaux diminuent avec la taille des particules. C'est dans ce contexte que s'inscrivent les travaux de cette thèse, qui présente l'étude de la décomposition contrôlée de précurseurs métal-organiques destinés à être intégrés à un procédé d'assemblage sans plomb à basse température. Le comportement en température de différents précurseurs métal-organiques d'étain et de bismuth et l'influence de l'atmosphère de décomposition ont été étudiés. La relation entre la taille des particules métalliques et leur point de fusion a été soulignée, ainsi que l'influence majeure de l'oxydation sur l'évolution de la taille des particules et leur capacité à former des assemblages. / Due to environmental and health concerns, new regulations led to a restriction in the use of lead in electronic equipment. Joining materials (based on tin, silver, copper, bismuth ...) for surface-mount technology are subject to many development work in order to comply with regulatory and technical requirements. The potential of metal carboxylates in electronics has already been demonstrated in the development of metal-organic decomposition processes. The thermal decomposition under controlled atmosphere of such precursors leads to the creation of metal nanoparticles with an increased reactivity compared to that of micron sized particles. The use of nanomaterials is a seriously considered way for developing low temperature joining processes for electronics. It is based on the well-known decrease of melting and sintering temperatures of nanomaterials with particle size. In this context, this work of thesis presents the study of the controlled decomposition of metal-organic precursors intended to be integrated into a low-temperature lead-free joining process. The thermal behavior of several metal-organic precursors of tin and bismuth, as well as the influence of the decomposition atmosphere, were studied. The relationship between the metal particles size and their melting point has been emphasized, as well as the major influence of oxidation on the evolution of particles size and their ability to make reliable joints.

Metal-organic frameworks (MOFs) constructed from metal atoms connected by organic linkers have received extensive attention for greenhouse gas separation in the past decades. Moreover, their large surface area makes them a promising candidate as adsorbents for gas sorption. This project aims to develop MOFs via different synthesis instructions by utilizing  Mg-containing materials, including Commercial MgCO3  and Mesoporous Magnesium Carbonate (Upsalite) as a source of the metal part and four different organic linkers. Water, Ethanol, Methanol, and N, N-dimethylformamide were used as solvents. First, synthesis was performed at room temperature, followed by high temperature using an autoclave and reactor. Then, the successfully synthesized samples were characterized by different characterization methods. These characterization techniques included Powder X-ray Diffraction (PXRD), Scanning Electron Microscopy (SEM), and Infrared Spectroscopy (IR).  Porous properties of the MOFs were tested by gas adsorption techniques, including N2  and CO2 as adsorbate gases. As a result, it was found that synthesized MOFs have a high surface area and porosity to adsorb greenhouse gases and separate CO2 from N2. The highest surface area, N2, and CO2 adsorption amounts were 539 m²/g, 0.32 (mmol/g at 293K,1bar), and 3.31 (mmol/g  at 293K,1bar), respectively. CO2  adsorption is approximately ten times N2  adsorption in almost all MOF synthesized samples. To achieve the best result regarding the high amounts of surface area, N2, and CO2  sorption,  synthesis at room temperature using Commercial MgCO3, H2dhbq linker, and water solvent was the best approach.

Thesis advisor: Chia-Kuang Tsung / Heterogeneous catalysis is a critical field for chemical industry processes, energy applications, and transportation, to name a few. In all avenues, control over the activity and selectivity towards specific products are of extreme importance. Generally, two separate methods can be utilized for controlling the active surface areas; a below and above the surface approach. In this dissertation, both approaches will be addressed, first starting with controlling the active sites from a below approach and moving towards control through sieving and gating effects above the surface. For the first part half, the control of the product selectivity is controlled by finely tuning the atomic structures of nanoparticle catalysts, mainly Au-Pd, Pd-Ni-Pt, and Pd Ni3Pt octahedral and cubic nanoparticle catalysts. Through these shaped core-shell, occasionally referred to as core@shell, particles the shape is maintained in order to expose and study certain crystal facets in order to obtain a more open or closed series of active sites. With the core shell particles, the interior core particle (Au and Pd) is used for the overall shape but also to expansively/compressively strain the outer shell layer. By straining the surface, the surface electronic structure is altered, by raising or lowering the d-band structure, allowing for reactants to adsorb more or less strongly as well as adsorb on different surface sites. For the below the surface projects, the synthesized nanoparticle catalyst are used for electrochemical oxidation reactions, such as ethanol and methanol oxidation, in order to study the effect of the core and shell layers on initial activity, metal migration during cycling, as well as particle stability and activity using different crystal structures. In particular, the use of core shell, alloyed, and intermetallic (ordered alloys) particles are studied in more detail. In the second half of this dissertation, control of the selectivity will be explored from the top down approach; in particular the use of metal organic framework (MOF) will be utilized. MOF, with its inherent size selective properties due to caging effects from the chosen linkers and nodes, is used to coat the surface of catalysts for gas, liquid, and electrochemical catalysis. By using nanoparticle catalyst, the use of MOF, more explicitly the robust zirconium based UiO-66, as a crystalline capping agent is first explored. By incorporating both the nanoparticle and UiO-66 amino functionalized precursors in the synthesis, the nanoparticles are formed first and followed by coating in UiO-66-NH2, where the amino group acts as an anchor, completely coating the particles. The full coating is tested through size selective alkene hydrogenations with the NP surface further tested by liquid phase selective aldehyde hydrogenations; the UiO-66-NH2 pores help to guide the reactant molecule in a particular orientation for the carbonyl to interact rather than the unsaturated C=C bond. This approach is taken for more complex hybrid structures for electrochemical proton exchange membrane fuel cell (PEMFC) conditions. Through the gating effects, the UiO-66 blocks the Pt surface active sites from poisonous sulfonate groups off of the ionomer membrane while simultaneously preventing aggregation and leaching of Pt atoms during electrochemical working conditions. / Thesis (PhD) — Boston College, 2018. / Submitted to: Boston College. Graduate School of Arts and Sciences. / Discipline: Chemistry.