Metal organic frameworks (MOFs) are a class of nanoporous materials composed through self-assembly of inorganic and organic structural building units (SBUs). MOFs show great promise for many applications due to their record-breaking internal surface areas and tunable pore chemistry. This thesis work focuses on gas separation applications of MOFs in the context of carbon capture and storage (CCS) technologies. CCS technologies are expected to play a key role in the mitigation of anthropogenic CO2 emissions in the near future. In the first part of the thesis, robust machine learning quantitative structure-property relationship (QSPR) models are developed to predict CO2 working capacity and CO2/H2 selectivity for pre-combustion carbon capture using the most topologically diverse database of hypothetical MOF structures constructed to date (358,400 MOFs, 1166 network topologies). The support vector regression (SVR) models are developed on a training set of 35,840 MOFs (10% of the database) and validated on the remaining 322,560 MOFs. The most accurate models for CO2 working capacities (R2 = 0.944) and CO2/H2 selectivities (R2 = 0.876) are built from a combination of six geometric descriptors and three novel y-range normalized atomic-property-weighted radial distribution function (AP-RDF) descriptors. 309 common MOFs are identified between the grand canonical Monte Carlo (GCMC) calculated and SVR-predicted top-1000 high-performing MOFs ranked according to a normalized adsorbent performance score. This work shows that SVR models can indeed account for the topological diversity exhibited by MOFs. In the second project of this thesis, computational simulations are performed on a MOF, CALF-20, to examine its chemical and physical properties which are linked to its exceptional water-resisting ability. We predict the atomic positions in the crystal structure of the bulk phase of CALF-20, for which only a powder X-ray diffraction pattern is available, from a single crystal X-ray diffraction pattern of a metastable phase of CALF-20. Using the predicted CALF-20 structure, we simulate adsorption isotherms of CO2 and N2 under dry and humid conditions which are in excellent agreement with experiment. Snapshots of the CALF-20 undergoing water sorption simulations reveal that water molecules in a given pore adsorb and desorb together due to hydrogen bonding. Binding sites and binding energies of CO2 and water in CALF-20 show that the preferential CO2 uptake at low relative humidities is driven by the stronger binding energy of CO2 in the MOF, and the sharp increase in water uptake at higher relative humidities is driven by the strong intermolecular interactions between water. In the third project of this thesis, we use computational simulations to investigate the effects of residual solvent on Ni-BPM’s CH4 and N2 adsorption properties. Single crystal X-ray diffraction data shows that there are two sets of positions (Set 1 and 2) that can be occupied by the 10 residual DMSO molecules in the Ni-BPM framework. GCMC simulations of CH4 and N2 uptake in Ni-BPM reveal that CH4 uptake is in closest agreement with experiment when the 10 DMSO’s are placed among the two sets of positions in equal ratio (Mixed Set). Severe under-prediction and over-prediction of CH4 uptake are observed when the DMSO’s are placed in Set1 and Set 2 positions, respectively. Through binding site analysis, the CH4 binding sites within the Ni-BPM framework are found to overlap with the Set 1 DMSO positions but not with the Set 2 DMSO positions which explains the deviations in CH4 uptake observed for these cases. Binding energy calculations reveal that CH4 molecules are most stabilized when the DMSO’s are in the Mixed Set of positions.

Some of the challenges faced when developing novel functional materials, cannot be resolved without the correct understanding of their structure‐property relationships. Metal‐organic frameworks (MOFs) constitute a representative example where in-depth structural knowledge can greatly help improve and optimise their application into industrially relevant settings. Fortunately, the inherent crystalline nature of MOFs allows for analysis using the wide range of crystallographic experimental techniques that are currently available. This work covers the study of the structural properties of a particular family of MOFs, which have shown significant potential as molecular sieves and for gas storage. Sc-based MOFs first attracted attention for their particularly robust and inert nature, bypassing some of the physical challenges many MOFs have when undergoing industrial implementation. After an initial review of the state of the art in the field of MOFs and the techniques utilised to analyse their properties, this work then focuses on the mechanical properties of a series of functionalised and unfunctionalised Sc‐dicarboxylate MOFs. Using nano‐indentation techniques and high‐pressure crystallography, the hardness and elasticity of these materials are correlated to their different structural features, confirming their relative robustness when compared to other MOFs in the literature. An interesting property of Sc2BDC3 is its selective uptake of CO2 over other fuel-related gases such as CH4 and CO. In this context, the in situ adsorption crystallographic analysis of Sc2BDC3 and its amino‐functionalised derivative Sc2(BDC‐NH2)3 (BDC‐NH2 = 1,4‐amino‐2‐benzenedicarboxylate) is described, as performed using the gas cell set up of beamline I19 at the Diamond Light Source synchrotron. This study is the first example of a mixed gas atmosphere experiment using single‐crystal diffraction, which in conjunction with in silico, adsorption and breakthrough experiments, provides direct insight into the interactions that drive the selective behaviour of both frameworks. Following this, the MOF Sc2BDC3 (BDC = 1,4‐benzenedicarboxylate), is selected as a case study for branched and unbranched alkane separation. Here, high‐pressure crystallography shows how these relatively oversized guest molecules, can be forced at thousands of atmospheres of pressure inside the narrow triangular channels (< 4 Å diameter) of the framework. It is also possible to resolve the structural changes the framework undergoes upon uptake of the different guests, as well as locate the adsorption sites of the hydrocarbons in the pores of Sc2BDC3, which can be then correlated to the gas adsorption behaviour of the different guests. To conclude, the high‐pressure inclusion study of both CO2 and CH4 inside Sc2BDC3 shows how combining cryoloading techniques and molecular crystallography for the first time, can provide improved models of the adsorbed gaseous guests inside Sc2BDC3. This example not only provides a novel alternative in which to study more easily the adsorption sites in MOFs via diffraction techniques, but also reveals some of the interesting structural behaviour MOFs can have in these extreme conditions.

>Magister Scientiae - MSc / Due to the rapid depletion of fossil fuel reserves and the production of environmentally harmful by-products such as carbon dioxide, there is an urgent need for alternate sustainable clean energy. One of the leading candidates in this endeavour is hydrogen, which can be used as an energy carrier since it has a high energy density, zero emissions and is produced from non-depletable resources such as water. The major challenge hindering a hydrogen economy is the lack of safe and effective storage technologies for mobile applications. A prospective solution to this problem lies in the use of porous powdered materials, which adsorb the hydrogen gas. However, the integration of these powdered materials into a storage tank system, results in the pipelines being contaminated during filling cycles. This necessitates the shaping of the porous powdered materials. Among the many shaping techniques available, the electrospinning technique has been proposed as a promising technology since it is a versatile process that is easily scaled-up making it attractive for the applications of the study. Furthermore, the electrospinning process enables the synthesis of nano-sized fibres with attractive hydrogen sorption characteristics. In this regard, the current study employs the electrospinning technique to synthesise electrospun composite fibres for mobile hydrogen storage applications. After electrospinning three polymers, polyacrylonitrile (PAN) was selected as the most suitable polymer because it yielded bead-free electrospun fibres. However, the diameter of the PAN fibres was large/thick which prompted further optimisation of the electrospinning parameters. The optimised electrospinning conditions that yield unbeaded fibres within the desired diameter range (of 300-500 nm) were a PAN concentration of 10 wt%, a flow rate of 0.4 mL/h, a distance of 10 cm between the needle tip and collector plate, and an applied voltage of 8 kV. The study then progressed to the synthesis and characterisation of the pristine porous powdered materials which adsorb hydrogen gas. The porous powdered materials investigated were commercial zeolite 13X, its synthesised templated carbon derivative (ZTC) and Zr (UiO-66) and Cr (MIL-101) based metal-organic frameworks (MOFs). ZTC was synthesised via liquid impregnation coupled with chemical vapour deposition (CVD), and the MOFs were synthesised by the modulated solvothermal method. Analysis of the ZTCs morphology and phase crystallinity show that the carbon templated process using zeolites was successful, however, ZTC was amorphous compared to crystalline zeolite template. The BET surface area was assessed with the aid of nitrogen sorption isotherms for both zeolite 13X and ZTC, and values of 730 and 2717 m²/g, respectively were obtained. The hydrogen adsorption capacity for zeolite 13X was 1.6 wt% and increased to 2.4 wt% in the ZTC material at 77 K and 1 bar. The successful synthesis of well defined, crystalline MOFs was evident from X-ray diffraction and morphological analysis. The BET surface area and hydrogen adsorption for Zr MOF were 1186 m²/g and 1.5 wt%, respectively at 77 K and 1 bar. Cr MOF had a BET surface area of 2618 m²/g and hydrogen adsorption capacity of 1.9 wt% at 77 K and 1 bar. The main focus of the study was to synthesise electrospun composite fibres that can adsorb hydrogen gas and thus provide significant insight in this field of research. As such it examined composite fibres that incorporates porous powdered materials such as zeolite 13X, ZTCs, UiO-66 (Zr) MOF and MIL-101 (Cr) MOF and investigated their ability to adsorb hydrogen gas, which have not been reported previously. The synthesis of composite fibres was achieved by incorporating the porous powdered materials into the PAN resulting in a polymeric blend that was then electrospun. Morphological analysis illustrated that the porous powdered materials were successfully supported by or incorporated within the PAN fibres, forming composite fibres. The BET surface area of the 40 wt% zeolite-PAN and 12.5 wt% ZTC-PAN composite fibres were 440 and 1787 m²/g respectively. Zr MOF and Cr MOF composite fibres had a BET surface area of 815 and 1134 m²/g, respectively. The BET surface area had reduced by 40, 34, 31 and 57% for zeolite 13X, ZTC, Zr MOF and Cr MOF, respectively after these porous powdered materials were incorporated into PAN. The hydrogen adoption capacity for 40 wt% zeolite-PAN, 12.5 wt% ZTC-PAN, 20 wt% Zr MOFPAN and 20 wt% Cr MOF-PAN composite fibres was 0.8, 1.8, 0.9 and 1.1 wt%, respectively. This decrease was attributed to the limited amount of porous powdered materials that could be incorporated into the fibres since only 40 wt% of zeolite 13X, 12.5 wt% of ZTC and 20 wt% of the MOFs were loaded into their respective composite fibres. This was due to the fact that incorporation of greater amounts of porous powdered materials resulted in a viscous polymeric blend that was unable to be electrospun. It is evident from the study that electrospinning is a versatile process that is able to produce composite fibres with promising properties that can potentially advance the research in this field thus providing a practical solution to the problem of integrating loose powdered materials into an on-board hydrogen storage system. / CSIR Young Researchers Establishment Fund (YREF)

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

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.

Indiana University-Purdue University Indianapolis (IUPUI) / Extrusion-based 3D printing is one of the emerging additive manufacturing technologies used for printing a range of materials from metal to ceramics. In this process, the required material is extruded from the extruder in the form of a slurry. Zeolite and MOFs are mainly used for CO2 adsorption in the form of pellets and beads due to their good adsorptive property. Researchers are developing monoliths of Zeolite and MOFs and fabricate them using traditional extrusion and implement them in the gas adsorption applications as an option for beads and pellets by developing a monolithic structure. Previous research on Zeolite 13X and 5A have shown good structural and physical properties in monolith form. In this study, we developed slurry of two molecular sieve Zeolite 3A and 4A monoliths powders, mixing it with bentonite clay, methyl cellulose, and PVA as a binder. The slurry preparation was carried out at room temperature. Once the 3D printed samples are dried at room temperature, a sintering process was performed to increase mechanical strength. To be used in real-time applications, the 3D printed Zeolite sample need to have sufficient mechanical strength. The BET surface area test showed good results for Zeolite 13X compared to available literature. The surface area calculated for 3D printed Zeolite 13X was 767m2/g and available literature showed 498 m2/g for 3D printed Zeolite 13X. The microhardness values of 3D printed Zeolite samples were measured using a Vicker hardness tester. The hardness value of the 3D - printed Zeolite samples increased from 8.3 ± 2 to 12.5 ± 3 HV0.05 for Zeolite 13X, 3.3 ± 1 to 7.3 ± 1 HV0.05 for Zeolite 3A, 4.3 ± 2 to 7.5 ± 2 HV0.05 for Zeolite 4A, 7.4 ± 1 to 14.0 ± 0.5 HV0.05 for Zeolite 5A respectively. The SEM, EDS and XRD analysis was performed for 3D printed samples before and after sintering to evaluate their structural properties. The SEM analysis reveals that all 3D printed Zeolite samples retained their microstructure after slurry preparation and also after the sintering process. The porous nature of 3D printed Zeolite walls was retained after the sintering process. The EDS analysis showed that the composition of 3D printed Zeolite samples remained somewhat similar with minor variation for before and after sintering. The framework structure of Zeolite Type X for Zeolite 13X and Zeolite Type A for Zeolite 3A, 4A, 5A were in good shape after sintering as standard peak intensity points were retained. Zn-MOF74 was synthesized using solvothermal synthesis which is a well-established synthesis process used for the synthesis of MOFs. We also developed slurry for Zn-MOF-74 using bentonite clay and PVA as binders and printed small parts using hand printing.

京都大学 / 0048 / 新制・課程博士 / 博士(理学) / 甲第20603号 / 理博第4318号 / 新制||理||1620(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

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