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Covalent organic frameworks (COFs) have emerged as a versatile material platform for such applications as chemical separations, chemical reaction engineering, and energy storage. Their inherently low mechanical stability, however, frequently renders existing methods of pelletization ineffective, contributing to pore collapse, pore blockage, or insufficient densification of crystallites. Here, we present a process for the shaping and densifying of COFs into robust centimeter-scale porous monoliths without the need for templates, additives, or binders. This process minimizes mechanical damage from shear-induced plastic deformation and further provides a network of interparticle mesopores that we exploit in accessing analyte capacities above those achievable from the intrinsic COF structure. Using a lattice-gas model, we accurately capture the monolithic structure across the mesoporous range and tie pore architecture to performance in both gas-storage and -separation applications. Collectively, these results represent a substantial step in the practical applicability of COFs and other mechanically weak porous materials.

We are currently witnessing the dawn of hydrogen (H2) economy, where H2 will soon become a primary fuel for heating, transportation, and long-distance and long-term energy storage. Among diverse possibilities, H2 can be stored as a pressurized gas, a cryogenic liquid, or a solid fuel via adsorption onto porous materials. Metal–organic frameworks (MOFs) have emerged as adsorbent materials with the highest theoretical H2 storage densities on both a volumetric and gravimetric basis. However, a critical bottleneck for the use of H2 as a transportation fuel has been the lack of densification methods capable of shaping MOFs into practical formulations while maintaining their adsorptive performance. Here, we report a high-throughput screening and deep analysis of a database of MOFs to find optimal materials, followed by the synthesis, characterization, and performance evaluation of an optimal monolithic MOF (monoMOF) for H2 storage. After densification, this monoMOF stores 46 g L–1 H2 at 50 bar and 77 K and delivers 41 and 42 g L–1 H2 at operating pressures of 25 and 50 bar, respectively, when deployed in a combined temperature–pressure (25–50 bar/77 K → 5 bar/160 K) swing gas delivery system. This performance represents up to an 80% reduction in the operating pressure requirements for delivering H2 gas when compared with benchmark materials and an 83% reduction compared to compressed H2 gas. Our findings represent a substantial step forward in the application of high-density materials for volumetric H2 storage applications.

peer-reviewed, Crystal Engineering is the field of chemistry that studies the design, properties, and application of crystalline materials. An aspect of crystal engineering is the design of coordination networks using linker ligands that cross-link transition metal nodes. Coordination networks that can exhibit permanent porosity have attracted attention for their potential application in gas storage, separation, and catalysis. In the context of separations, 15% of global energy costs are associated with separation of chemical commodities. That some coordination networks are inherently modular through node/linker substitution enables crystal engineering studies that can provide insight into structure-function relationships. Square lattice (sql) coordination networks were perhaps the first class of coordination networks to undergo systematic study; thanks mainly to their propensity to form from many nodes and linkers. Further, some sql coordination networks can be pillared to afford primitive cubic (pcu) coordination networks, offering modularity that, in principle, has at least four variables: node, linker, pillar, interpenetration. A class of pillared sql coordination networks known as Hybrid Ultramicroporous Materials (HUMs) has recently set new benchmarks for several important gas separations thanks to their ultramicropores (≤0.7 nm) which are lined by inorganic pillars that can act as molecular traps for small gas molecules. For example, ethylene (C2H4) is the highest volume chemical feedstock and contains ca. 1% acetylene (C2H2) impurities that must be removed. The goal herein is to conduct crystal engineering studies of interpenetrated HUMs in the context of C2H2/C2H4 gas separations and hydrolytic stability. The insight found herein may afford better design principles for future porous coordination networks in terms of performance and stability. Chapter 1 introduces crystal engineering, coordination networks, and HUMs. Chapter 2 addresses the C2H2/C2H4 separation performance

peer-reviewed, Crystal Engineering is the field of chemistry that studies the design, properties, and application of crystalline materials. An aspect of crystal engineering is the design of coordination networks using linker ligands that cross-link transition metal nodes. Coordination networks that can exhibit permanent porosity have attracted attention for their potential application in gas storage, separation, and catalysis. In the context of separations, 15% of global energy costs are associated with separation of chemical commodities. That some coordination networks are inherently modular through node/linker substitution enables crystal engineering studies that can provide insight into structure-function relationships. Square lattice (sql) coordination networks were perhaps the first class of coordination networks to undergo systematic study; thanks mainly to their propensity to form from many nodes and linkers. Further, some sql coordination networks can be pillared to afford primitive cubic (pcu) coordination networks, offering modularity that, in principle, has at least four variables: node, linker, pillar, interpenetration. A class of pillared sql coordination networks known as Hybrid Ultramicroporous Materials (HUMs) has recently set new benchmarks for several important gas separations thanks to their ultramicropores (≤0.7 nm) which are lined by inorganic pillars that can act as molecular traps for small gas molecules. For example, ethylene (C2H4) is the highest volume chemical feedstock and contains ca. 1% acetylene (C2H2) impurities that must be removed. The goal herein is to conduct crystal engineering studies of interpenetrated HUMs in the context of C2H2/C2H4 gas separations and hydrolytic stability. The insight found herein may afford better design principles for future porous coordination networks in terms of performance and stability. Chapter 1 introduces crystal engineering, coordination networks, and HUMs. Chapter 2 addresses the C2H2/C2H4 separation performance

peer-reviewed, Separation of the C8 aromatic isomers, p-xylene (PX), m-xylene (MX), o-xylene (OX) and ethylbenzene (EB), is relevant thanks to their widespread application as chemical feedstocks but challenging because of their similar boiling points and close molecular dimensions. Physisorptive separation could offer an energy-efficient solution to this challenge but sorbents which exhibit strong selectivity for one of the isomers remain a largely unmet challenge despite recent reports of OX or PX selective sorbents with high uptake capacity. For example, the square lattice, sql, topology coordination network [Co(bipy)2(NCS)2]n (sql-1-Co-NCS) exhibits the rare combination of high OX selectivity and high uptake capacity. Herein we report that a crystal engineering approach enabled isolation of the mixed-linker sql coordination network [Co(bipy)(bptz) (NCS)2]n (sql-1,3-Co-NCS, bipy = 4,4′-bipyridine, bptz = 4,4′-bis(4-pyridyl)tetrazine) and study of its C8 vapour and liquid sorption properties. sql-1,3-Co-NCS was found to exhibit high adsorption capacity from liquid xylenes (∼37 wt%) and is to our knowledge the first sorbent to exhibit high selectivity for each of xylene isomer over EB (SOX/EB, SMX/EB, SPX/EB > 5). Insights into the performance of sql-1,3-Co-NCS are gained from structural studies which reveal stacking interactions between electron-deficient bptz linkers and the respective xylenes. sql-1,3-Co-NCS is the first N-donor mixed-linker sql coordination network studied for its gas/vapour sorption properties and represents a large and diverse class of understudied coordination networks.

peer-reviewed, Physisorbent metal–organic materials (MOMs) have shown benchmark performance for highly selective CO2 capture from bulk and trace gas mixtures. However, gas stream moisture can be detrimental to both adsorbent performance and hydrolytic stability. One of the most effective methods to solve this issue is to transform the adsorbent surface from hydrophilic to hydrophobic. Herein, we present a facile approach for coating MOMs with organic polymers to afford improved hydrophobicity and hydrolytic stability under humid conditions. The impact of gas stream moisture on CO2 capture for the composite materials was found to be negligible under both bulk and trace CO2 capture conditions with significant improvements in regeneration times and energy requirements.

peer-reviewed, CO2 accumulation in confined spaces represents an increasing environmental and health problem. Trace CO2 capture remains an unmet challenge because human health risks can occur at 1000 parts per million (ppm), a level that challenges current generations of chemisorbents (high energy footprint and slow kinetics) and physisorbents (poor selectivity for CO2, especially versus water vapor, and/or poor hydrolytic stability). Here, dynamic breakthrough gas experiments conducted upon the ultramicroporous material SIFSIX-18-Ni- reveal trace (1000 to 10,000 ppm) CO2 removal from humid air. We attribute the performance of SIFSIX-18-Ni- to two factors that are usually mutually exclusive: a new type of strong CO2 binding site and hydrophobicity similar to ZIF-8. SIFSIX-18-Ni- also offers fast sorption kinetics to enable selective capture of CO2 over both N2 (SCN) and H2O (SCW), making it prototypal for a previously unknown class of physisorbents that exhibit effective trace CO2 capture under both dry and humid conditions.

peer-reviewed, Representative compounds from three classes of microporous solids, namely metal-organic frameworks (MOFs), hybrid ultramicroporous materials (HUMs) and porous-organic polymers (POPs), were investigated for their nitric oxide gas uptake and release behavior. Low pressure sorption studies indicated strong chemisorption of NO on the free amine groups decorating the MOF UiO-66-NH2 when compared to its non-amine functionalized parent. The HUMs demonstrated reversible physisorption within the low pressure regime but interestingly in one case there was evidence for chemisorption following pressurization with NO at 10 bar. Significant release of chemisorbed NO from the UiO-66-NH2 and one of the HUMs was triggered by addition of acid to the medium, a pH change from 7.4 to 5.4 being sufficient to trigger NO release. An imidazole-based POP exhibited chemisorption of NO at high pressure wherein the ring basicity facilitated both NO uptake and spontaneous release upon contact with the aqueous release medium.

peer-reviewed, Fine-tuning of hybrid ultramicroporous materials (HUMs) can significantly impact their gas sorption performance. This study reveals that offset interpenetration can be antagonistic with respect to C2H2 separation from C2H2/C2H4 gas mixtures.