Adsorbed xenon propellant storage: are nanoporous materials worth the weight?
Nanoporous materials could be used to store xenon propellant onboard spacecraft.
36 MATERIALS SCIENCE↗
Engineering topics
Simon, Cory M.
Publications and source records attributed to Simon, Cory M..
Xenon Gas Separation and Storage using Metal-Organic Frameworks
The global demand for Xe, a noble gas with applications in electronics, lighting, and the medical industry, is expected to rise significantly over the coming decades. However, the low abundance of Xe in the earth’s atmosphere and the costly cryogenic distillation process that is used to obtain Xe commercially via air separation have limited the scale of applications of Xe. A physisorption-based separation using porous materials may be a viable and cost-effective alternative to cryogenic distillation. In particular, metal-organic frameworks (MOFs) have shown promise as highly Xe-selective, porous solids. In this review, we detail the recent advances of MOFs as adsorbents for noble gas adsorption/separation and the role of computer simulation in finding optimal materials for Xe adsorption.
MOFs, Xenon, Krypton↗
High-Throughput Computational Screening of Multivariate Metal–Organic Frameworks (MTV-MOFs) for CO 2 Capture
Multivariate metal–organic frameworks (MTV-MOFs) contain multiple linker types within a single structure. Arrangements of linkers containing different functional groups confer structural diversity and surface heterogeneity and result in a combinatorial explosion in the number of possible structures. Here, we carried out high-throughput computational screening of a large number of computer-generated MTV-MOFs to assess their CO 2 capture properties using grand canonical Monte Carlo simulations. The results demonstrate that functionalization enhances CO 2 capture performance of MTV-MOFs when compared to their parent (unfunctionalized) counterparts, and the pore size plays a dominant role in determining the CO 2 adsorption capabilities of MTV-MOFs irrespective of the combinations of the three functional groups (-F, -NH 2 , and -OCH 3 ) that we explored. We also found that the functionalization of parent MOFs with small pores led to larger enhancements in CO 2 uptake and CO 2 /N 2 selectivity than functionalization in larger-pore MOFs. Free energy contour maps are presented to visually compare the influence of linker functionalization between frameworks with large and small pores.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Materials Genome in Action: Identifying the Performance Limits of Physical Hydrogen Storage
Not Available
36 MATERIALS SCIENCE↗
Impact of the strength and spatial distribution of adsorption sites on methane deliverable capacity in nanoporous materials
The methane deliverable capacity of adsorbent materials is a critical performance metric that will determine the viability of using adsorbed natural gas (ANG) technology in vehicular applications. ARPA-E recently set a target deliverable capacity of 315 cc(STP)/cc that a viable adsorbent material should achieve to yield a driving range competitive with incumbent fuels. However, recent computational screening of hundreds of thousands of materials suggests that the target is unattainable. In this work, we aim to determine whether the observed limits in deliverable capacity (similar to 200 cc(STP)/cc) are fundamental limits arising from thermodynamic or material design constraints. Our efforts focus on simulating methane adsorption isotherms in a large number of systems, resulting in a broad exploration of different combinations of spatial distributions and energetics of adsorption sites. All systems were classified into five adsorption scenarios with varying degrees of realism in the manner that adsorption sites are created and endowed with energetics. The scenarios range from methane adsorption on discrete idealized lattice sites to adsorption in metal-organic frameworks with coordinatively unsaturated sites (CUS) provided by metalated catechol groups. Our findings strongly suggest that the ARPA-E target is unattainable, although not due to thermodynamic constraints but due to material design constraints. On the other hand, we also find that the currently observed deliverable capacity limits may be moderately surpassed. For instance, incorporation of CUS in IRMOF-10 is predicted to yield a 217 cc(STP)/cc deliverable capacity. The modified material has a similar to 0.85 void fraction and a heat of adsorption of similar to 15 kJ/mol. This suggests that similar, moderate improvements over existing materials could be achieved as long as CUS incorporation still maintains a relatively large void fraction. Nonetheless, we conclude that more significant improvements in deliverable capacity will require changes in the currently proposed operation conditions.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Adsorbate-induced lattice deformation in IRMOF-74 series
Here, IRMOF-74 analogues are among the most widely studied metal-organic frameworks (MOFs) for adsorption applications because of their one-dimensional channels and high metal density. Most studies involving the IRMOF-74 series assume that the crystal lattice is rigid. This assumption guides the interpretation of experimental data, as changes in the crystal symmetry have so far been ignored as a possibility in the literature. Here, we report a deformation pattern, induced by the adsorption of argon, for IRMOF-74-V. This work has two main implications. First, we use molecular simulations to demonstrate that the IRMOF-74 series undergoes a deformation that is similar to the mechanism behind breathing MOFs, but is unique because the deformation pattern extends beyond a single unit cell of the original structure. Second, we provide an alternative interpretation of experimental small-angle X-ray scattering profiles of these systems, which changes how we view the fundamentals of adsorption in this MOF series.
36 MATERIALS SCIENCE↗
Statistical mechanical model of gas adsorption in porous crystals with dynamic moieties
Some nanoporous, crystalline materials possess dynamic constituents, for example, rotatable moieties. These moieties can undergo a conformation change in response to the adsorption of guest molecules, which qualitatively impacts adsorption behavior. Here, we pose and solve a statistical mechanical model of gas adsorption in a porous crystal whose cages share a common ligand that can adopt two distinct rotational conformations. Guest molecules incentivize the ligands to adopt a different rotational configuration than maintained in the empty host. Our model captures inflections, steps, and hysteresis that can arise in the adsorption isotherm as a signature of the rotating ligands. The insights disclosed by our simple model contribute a more intimate understanding of the response and consequence of rotating ligands integrated into porous materials to harness them for gas storage and separations, chemical sensing, drug delivery, catalysis, and nanoscale devices. Particularly, our model reveals design strategies to exploit these moving constituents and engineer improved adsorbents with intrinsic thermal management for pressure-swing adsorption processes.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Effect of ring rotation upon gas adsorption in SIFSIX-3-M (M = Fe, Ni) pillared square grid networks
The study of the mobility/rotation of the organic linkers in porous metal-organic frameworks could provide a valuable information about the guest/framework interaction and the factors control the kinetics of adsorption. Here, we analyzed the dynamics of pyrazine ring rotation in a series of pillared square grid frameworks, namely SIFSIX-3-M (M = Fe, Ni). It was found that the rotation of pyrazine ring is influenced by the variation of metal cation, temperature and the guest molecule. The Fe-analogue, [Fe(pz)2(SiF6)2] (pz= Pyrazine), , showed no pronounced ring rotation and exhibited a high affinity toward Xe gas over Kr as exemplified by the sharp Xe uptake at low loading (~0.1 bar) and its high isosteric heat of adsorption (Qst~ 27.4 kJmol-1) compared to the current benchmark materials. The Ni analogue, on the contrary, showed a two-regime adsorption isotherm for Xe with a temperature-dependent inflection point. However, this behavior is not observed with the other gases such as CO2, N2, and Kr which showed one-step adsorption isotherms without any inflection. Using molecular models and simulations, we hypothesize that the inflection point is due to a disordered to ordered transition of the rotational configurations of the pz rings in SIFSIX-3-Ni. These results further support the impact of tuning the pore size and chemistry on the adsorption behavior of porous materials.
Elsaidi, Sameh K.↗
Noria: A Highly Xe‐Selective Nanoporous Organic Solid
Abstract Separation of xenon and krypton is of industrial and environmental concern; the existing technologies use cryogenic distillation. Thus, a cost‐effective, alternative technology for the separation of Xe and Kr and their capture from air is of significant importance. Herein, we report the selective Xe uptake in a crystalline porous organic oligomeric molecule, noria, and its structural analogue, PgC‐noria, under ambient conditions. The selectivity of noria towards Xe arises from its tailored pore size and small cavities, which allows a directed non‐bonding interaction of Xe atoms with a large number of carbon atoms of the noria molecular wheel in a confined space.
Patil, Rahul S.↗
Metal–organic framework with optimally selective xenon adsorption and separation
Nuclear energy is considered among the most viable alternatives to our current fossil fuel based energy economy.1 The mass-deployment of nuclear energy as an emissions-free source requires the reprocessing of used nuclear fuel to mitigate the waste.2 One of the major concerns with reprocessing used nuclear fuel is the release of volatile radionuclides such as Xe and Kr. The most mature process for removing these radionuclides is energy- and capital-intensive cryogenic distillation. Alternatively, porous materials such as metal-organic frameworks (MOFs) have demonstrated the ability to selectively adsorb Xe and Kr at ambient conditions.3-8 High-throughput computational screening of large databases of porous materials has identified a calcium-based nanoporous MOF, SBMOF-1, as the most selective for Xe over Kr.9,10 Here, we affirm this prediction and report that SBMOF-1 exhibits by far the highest Xe adsorption capacity and a remarkable Xe/Kr selectivity under relevant nuclear reprocessing conditions. The exceptional selectivity of SBMOF-1 is attributed to its pore size tailored to Xe and its dense wall of atoms that constructs a binding site with a high affinity for Xe, as evident by single crystal X-ray diffraction and molecular simulation.
11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗