Gas Storage Applications Research Articles

Thermal Transport in Interpenetrated Metal–Organic Frameworks

In practice, the usefulness of metal–organic frameworks (MOFs) for many gas storage applications depends on their ability to rapidly dissipate the heat generated during the exothermic adsorption process. MOFs can be precisely designed to have a wide variety of architectures which can allow tuning their thermal conductivity. In this work, we use molecular dynamics simulations to investigate the effect of interpenetration on the thermal conductivity of MOFs. We find that the addition of a parallel thermal transport pathway yields a thermal conductivity nearly the sum of the two constituent frameworks. This relationship holds for a variety of interpenetrating MOFs with different atomic masses and a wide range of interframework interaction parameters. We show that both the strength and range of interactions between constituent frameworks play a significant role in framework mobility as well as framework coupling which can result in deviation from this relationship. We propose a simple model to predict thermal conductivity of the interpenetrated framework based on thermal conductivities of individual frameworks and an interframework interaction parameter which can account for this deviation.

Transient Mass and Thermal Transport during Methane Adsorption into the Metal-Organic Framework HKUST-1.

Methane adsorption into the metal-organic framework (MOF) HKUST-1 and the resulting heat generation and dissipation are investigated using molecular dynamics simulations. Transient simulations reveal that thermal transport in the MOF occurs two orders of magnitude faster than gas diffusion. A large thermal resistance at the MOF-gas interface (equivalent to 127 nm of bulk HKUST-1), however, prevents fast release of the generated heat. The mass transport resistance at the MOF-gas interface is equivalent to 1 nm of bulk HKUST-1 and does not present a bottleneck in the adsorption process. These results provide important insights into the application of MOFs for gas storage applications.

Heat of adsorption, adsorption stress, and optimal storage of methane in slit and cylindrical carbon pores predicted by classical density functional theory.

Temperature, pressure and pore-size dependences of the heat of adsorption, adsorption stress, and adsorption capacity of methane in simple models of slit and cylindrical carbon pores are studied using classical density functional theory (CDFT) and grand-canonical Monte-Carlo (MC) simulation. Studied properties depend nontrivially on the bulk pressure and the size of the pores. Heat of adsorption increases with loading, but only for sufficiently narrow pores. While the increase is advantageous for gas storage applications, it is less significant for cylindrical pores than for slits. Adsorption stress and the average adsorbed fluid density show oscillatory dependence on the pore size and increase with bulk pressure. Slit pores exhibit larger amplitude of oscillations of the normal adsorption stress with pore size increase than cylindrical pores. However, the increase of the magnitude of the adsorption stress with bulk pressure increase is more significant for cylindrical than for slit pores. Adsorption stress appears to be negative for a wide range of pore sizes and external conditions. The pore size dependence of the average delivered density of the gas is analyzed and the optimal pore sizes for storage applications are estimated. The optimal width of slit pore appears to be almost independent of storage pressure at room temperature and pressures above 10 bar. Similarly to the case of slit pores, the optimal radius of cylindrical pores does not exhibit much dependence on the storage pressure above 15 bar. Both optimal width and optimal radii of slit and cylindrical pores increase as the temperature decreases. A comparison of the results of CDFT theory and MC simulations reveals subtle but important differences in the underlying fluid models employed by the approaches. The differences in the high-pressure behaviour between the hard-sphere 2-Yukawa and Lennard-Jones models of methane, employed by the CDFT and MC approaches, respectively, result in an overestimation of the heat of adsorption by the CDFT theory at higher loadings. However, both adsorption stress and adsorption capacity appear to be much less sensitive to the differences between the models and demonstrate excellent agreement between the theory and the computer experiment.

Roles of Sodium Dodecyl Sulfate on Tetrahydrofuran-Assisted Methane Hydrate Formation

Sodium dodecyl sulfate (SDS) markedly improved tetrahydrofuran (THF) - assisted methane hydrate formation. Firstly, methane hydrate formation with different THF amount, 1, 3, and 5.56 mol%, was studied. SDS with 1, 4, and 8 mM was then investigated for its roles on the methane hydrate formation with and without THF. The experiments were conducted in a quiescent condition in a fixed volume crystallizer at 8 MPa and 4°C. The results showed that almost all studied THF and SDS concentrations enhanced the methane hydrate formation kinetics and methane consumption compared to that without the promoters, except 1 mol% THF. Although, with 1 mol% THF, there were no hydrates formed for 48 hours, the addition of just 1 mM SDS surprisingly promoted the hydrate formation with a significant increased in the kinetics. This prompts the use of methane hydrate technology for natural gas storage application with minimal promoters.

Metal-Organic Framework-Derived Materials for Sodium Energy Storage.

Recently, sodium-ion batteries (SIBs) are extensively explored and are regarded as one of the most promising alternatives to lithium-ion batteries for electrochemical energy conversion and storage, owing to the abundant raw material resources, low cost, and similar electrochemical behavior of elemental sodium compared to lithium. Metal-organic frameworks (MOFs) have attracted enormous attention due to their high surface areas, tunable structures, and diverse applications in drug delivery, gas storage, and catalysis. Recently, there has been an escalating interest in exploiting MOF-derived materials as anodes for sodium energy storage due to their fast mass transport resulting from their highly porous structures and relatively simple preparation methods originating from in situ thermal treatment processes. In this Review, the recent progress of the sodium-ion storage performances of MOF-derived materials, including MOF-derived porous carbons, metal oxides, metal oxide/carbon nanocomposites, and other materials (e.g., metal phosphides, metal sulfides, and metal selenides), as SIB anodes is systematically and completely presented and discussed. Moreover, the current challenges and perspectives of MOF-derived materials in electrochemical energy storage are discussed.

Design of porous MOFs for gas storage applications

Design of porous MOFs for gas storage applications

Mechanical Properties in Metal-Organic Frameworks: Emerging Opportunities and Challenges for Device Functionality and Technological Applications.

Some of the most remarkable recent developments in metal-organic framework (MOF) performance properties can only be rationalized by the mechanical properties endowed by their hybrid inorganic-organic nanoporous structures. While these characteristics create intriguing application prospects, the same attributes also present challenges that will need to be overcome to enable the integration of MOFs with technologies where these promising traits can be exploited. In this review, emerging opportunities and challenges are identified for MOF-enabled device functionality and technological applications that arise from their fascinating mechanical properties. This is discussed not only in the context of their more well-studied gas storage and separation applications, but also for instances where MOFs serve as components of functional nanodevices. Recent advances in understanding MOF mechanical structure-property relationships due to attributes such as defects and interpenetration are highlighted, and open questions related to state-of-the-art computational approaches for quantifying their mechanical properties are critically discussed.

Controlled synthesis of conjugated polycarbazole polymers via structure tuning for gas storage and separation applications

A series of conjugated microporous polymers (CMPs) based on 1,3,6,8-tetrabromocarbazole (N4CMP-1–5) is synthesized via Suzuki cross-coupling or Sonogashira polycondensation. The porosity properties and surface area of these polymer networks can be finely tuned by using a linker with different geometries or strut length. These polymers show the Brunauer-Emmett-Tellerthe (BET) surface areas ranging from 592 to 1426 m2 g−1. The dominant pore sizes of the polymers on the basis of the different linker are located between 0.36 and 0.61 nm. Gas uptake increases with BET surface area and micropore volume, N4CMP-3 polymer can capture CO2 with a capacity of 3.62 mmol g−1 (1.05 bar and 273 K) among the obtained polymers. All of the polymers show high isosteric heats of CO2 adsorption (25.5–35.1 kJ mol−1), and from single component adsorption isotherms, IAST-derived ideal CO2/N2 (28.7–53.8), CO2/CH4 (4.6–5.2) and CH4/N2 (5.7–10.5) selectivity. Furthermore, N4CMPs exhibit the high CO2 adsorption capacity of 542–800 mg g−1 at 318 K and 50 bar pressure. These data indicate that these materials are a promising potential for clean energy application and environmental field.

Structural design, preparation and characterization of light, isotropic and robust statically determined organic frameworks as reusable adsorbents

Using (bi)adamantane “knots” and p-phenylene “rods” as building blocks, statically determined organic frameworks, viewed and termed as porous organic polymers (POP) were synthesized by Suzuki coupling polycondensation with high yields, 85–94%. The saturation of the polymer linking knot and rod groups was determined by FT-IR and 13C NMR spectroscopy. The POP material particles were light in weight (volumetric density of 0.1–0.24 g cm−3), porous (total pore volume of >0.35 cm3 g−1), and spherical in shape. The obtained POP materials were highly stable in its structural integrity, demonstrating both exceptional thermal stability upon heating at high temperatures and excellent chemical resistance to strong acid and base. In addition, X-ray scattering data indicated that the POP structures were amorphous in a long spacing distance (2–600 nm), being in an isotropic packing configuration with diffusive scattering contributed from all directions. The proof-to-concept of building POP structure on the molecular level in the form of multitopic knots and rods bridges paves the road for producing light, stable, and porous polymers structures with strong chemical bonds being effective in all directions. The CH4 and CO2 adsorption capacity of the obtained POPs at 273 K and 1 bar (1.4–2.3 wt% and 10.5–15.1 wt%, respectively) are comparable to many well-known porous polymer frameworks. Notably, the total uptake capability of aliphatic (n-hexane) and aromatic (benzene and toluene) organic vapors were maintained by a simple regeneration treatment, i.e., heating samples at 200 °C under vacuum. The adsorption results suggest their potential applications for gas storage and toxic organic vapor removal as reusable and thermochemically stable materials.

Thermodynamic Properties of Double Semiclathrate Hydrates Formed with Tetrabutylphosphonium Chloride + CH4

Phase equilibrium conditions for tetrabutylphosphonium chloride (TBPC) + CH4 double semiclathrate hydrates (SCHs) were determined to evaluate the stabilization effect of TBPC for potential applications of hydrate-based gas separation and storage. The equilibrium data revealed that TBPC strongly enhances the stability of CH4 hydrates by increasing the equilibrium temperature at a given pressure, and the system showed the strongest stabilization effect at a TBPC mass fraction of 0.30. The dissociation enthalpies of (TBPC + CH4) SCHs were calculated from the experimental data obtained in this work using the Clausius–Clapeyron equation and the Peng–Robinson equation of state. It was found that the mean dissociation enthalpies for (TBPC + CH4) SCHs with TBPC mass fractions of 0.05 to 0.50 were (135.49 to 158.32) kJ·(mol of CH4)−1, which were much higher than that of the pure CH4 hydrate. In addition, to identify the molecular behavior and hydrate structure, Raman spectroscopy measurements were conducted at 203...

Characterization Study of CO2, CH4, and CO2/CH4 Hydroquinone Clathrates Formed by Gas–Solid Reaction

Hydroquinone (HQ) is known to form organic clathrates with some gaseous species such as CO2 and CH4. This work presents spectroscopic data, surface and internal morphologies, gas storage capacities, guest release temperatures, and structural transition temperatures for HQ clathrates obtained from pure CO2, pure CH4, and an equimolar CO2/CH4 mixture. All analyses are performed on clathrates formed by direct gas–solid reaction after 1 month’s reaction at ambient temperature conditions and under a pressure of 3.0 MPa. A collection of spectroscopic data (Raman, FT-IR, and 13C NMR) is presented, and the results confirm total conversion of the native HQ (α-HQ) into HQ clathrates (β-HQ) at the end of the reaction. Optical microscopy and SEM analyses reveal morphology changes after the enclathration reaction, such as the presence of surface asperities. Gas porosimetry measurements show that HQ clathrates and native HQ are neither micro- nor mesoporous materials. However, as highlighted by TEM analyses and X-ray tomography, α- and β-HQ contain unsuspected macroscopic voids and channels, which create a macroporosity inside the crystals that decreases due to the enclathration reaction. TGA and in situ Raman spectroscopy give the guest release temperatures as well as the structural transition temperatures from β-HQ to α-HQ. The gas storage capacity of the clathrates is also quantified by means of different types of gravimetric analyses (mass balance and TGA). After having been formed under pressure, the characterized clathrates exhibit exceptional metastability: the gases remain in the clathrate structure at ambient conditions over time scales of more than 1 month. Consequently, HQ gas clathrates display very interesting properties for gas storage and sequestration applications.

PCN-250 under Pressure: Sequential Phase Transformation and the Implications for MOF Densification

Summary Metal-organic frameworks (MOFs) are an emerging class of porous materials with potential applications for gas storage and separation. With industrialization, MOFs inevitably encounter processing under mechanical pressure, whereas the behaviors of MOFs under such conditions are not commonly studied. Here, we chose PCN-250, a promising candidate for methane storage, to study the impact of uniaxial mechanical pressure on the MOFs' structures and properties as a model of an MOF extrusion process. A sequential phase transformation was observed and recorded by X-ray diffraction analysis, which involved N=N bond flipping and Fe‒O bond bending. Furthermore, the effects of pressure on the CH 4 adsorption capacity of PCN-250 were investigated by experiments and simulations. The PCN-250 pellet processed under optimized conditions shows an improved volumetric CH 4 uptake of 21% without obvious loss of gravimetric performance.

Three 3D metal coordination polymers based on triazol-functionalized rigid ligand: Synthesis, topological structure and properties

By using a triazol-functionalized tricarboxylate, three novel metal coordination polymers, namely, [Zn2L(OH)]·0.5H2O (1), [Co2L(OH)(H2O)]·5.5H2O (2), [Cu2(HL)] (3) L = ［5-(3-(4-carboxyphenyl)−5-methyl-4H-1,2,4-triazol-4-yl)isophthalate］ were synthesized under hydrothermal reactions. All the compounds were characterized by element analysis, IR spectroscopy, thermogravimetric analysis, power X-ray diffrcation and single-crystal X-ray diffrcation. Structural analysis reveals that compounds 1 and 2 have 3D networks with flu topologies where rigid trizaol-functionalized ligands as 4-connected nodes and Zn4(COO)6 or Co4(COO)6 clusters serves as 8-connected secondary building units. Compound 3 has 3D network with pcu topology where Cu4(COO)4 clusters serve as 6-connected secondary building units. Gas adsorption studies reveal that desolvated compoud 1 exhibits high H2 absorption capacity at 77K and highly selective separation abilities of CO2 and C3H8 over CH4 at room temperature. The results suggest that 1 has potential application in gas storage and separation. In addition, the magnetic properties of compound 2 were also investigated.

Angstrom-Resolved Metal-Organic Framework-Liquid Interfaces

Metal-organic frameworks (MOFs) are a class of crystalline materials with a variety of applications in gas storage, catalysis, drug delivery or light harvesting. The optimization of those applications requires the characterization of MOF structure in the relevant environment. Dynamic force microscopy has been applied to follow dynamic processes of metal-organic-framework material. We provide images with spatial and time resolutions, respectively, of angstrom and seconds that show that Ce-RPF-8 surfaces immersed in water and glycerol experience a surface reconstruction process that is characterized by the diffusion of the molecular species along the step edges of the open terraces. The rate of the surface reconstruction process depends on the liquid. In water it happens spontaneously while in glycerol is triggered by applying an external force.

Hydrothermal Synthesis, Crystal Structure, and Properties of 1D Zigzag Chain Zinc(II) Coordination Polymer Constructed from Nicotinic Acid and 1,4-Bis(imidazol-1-ylmethyl)benzene

A zinc–nicotinate complex, {[Zn(na) 2 ( µ- pbix)]∙H 2 O} n (1) , was obtained from the reaction of zinc(II) acetate with nicotinic acid (Hna) and 1,4-bis(imidazol-1-ylmethyl)benzene (pbix) in water at 120 °C under hydrothermal conditions and characterized by elemental analysis, IR spectroscopy, single crystal and powder X-ray diffraction. The thermal stability and luminescent property for 1 were also reported. The asymmetric unit of 1 consists of one zinc(II) center, one pbix ligand, two na anions and one non-coordinated water molecule, giving a formula of {[Zn(na) 2 ( µ- pbix)] ∙ H 2 O} n . The Zn(II) ion is coordinated by two nitrogen atoms from two different 1,4-bis(imidazol-1-ylmethyl)benzene ligands and two oxygen atoms from two different nicotinate (na) anions, thus showing a distorted tetrahedral geometry. The adjacent Zn(II) ions are linked into an infinite 1D zigzag chain by 1,4-bis(imidazol-1-ylmethyl)benzene ligands. Grand canonical Monte Carlo (GCMC) simulations were also performed to compute single-component H 2 adsorption isotherms at a pressure range of 0.01–100 bar and at 298 K and 77 K. The maximum H 2 uptake in 1 was found as 68 cm 3 / g STP at 100 bar and 77 K. This study will be useful to accelerate the hydrothermal synthesis of new coordination polymers for gas storage applications.

Investigation of zeolitic imidazolate frameworks using 13C and 15N solid-state NMR spectroscopy

Zeolitic imidazolate frameworks (ZIFs) are a subclass of metal-organic frameworks (MOFs) with extended three-dimensional networks of transition metal nodes (bridged by rigid imidazolate linkers), with potential applications in gas storage and separation, sensing and controlled delivery of drug molecules. Here, we investigate the use of 13C and 15N solid-state NMR spectroscopy to characterise the local structure and disorder in a variety of single- and dual-linker ZIFs. In most cases, a combination of a basic knowledge of chemical shifts typically observed in solution-state NMR spectroscopy and the use of dipolar dephasing NMR experiments to reveal information about quaternary carbon species are combined to enable spectral assignment. Accurate measurement of the anisotropic components of the chemical shift provided additional information to characterise the local environment and the possibility of trying to understand the relationships between NMR parameters and both local and long-range structure. First-principles calculations on some of the simpler, ordered ZIFs were possible, and provided support for the spectral assignments, while comparison of these model systems to more disordered ZIFs aided interpretation of the more complex spectra obtained. It is shown that 13C and 15N NMR are sufficiently sensitive to detect small changes in the local environment, e.g., functionalisation of the linker, crystallographic inequivalence and changes to the framework topology, while the relative proportion of each linker present can be obtained by comparing relative intensities of resonances corresponding to chemically-similar species in cross polarisation experiments with short contact times. Therefore, multinuclear NMR spectroscopy, and in particular the measurement of both isotropic and anisotropic parameters, offers a useful tool for the structural study of ordered and, in particular, disordered ZIFs.

Mesoporous carbon nanomaterials induced pulmonary surfactant inhibition, cytotoxicity, inflammation and lung fibrosis

Environmental exposure and health risk upon engineered nanomaterials are increasingly concerned. The family of mesoporous carbon nanomaterials (MCNs) is a rising star in nanotechnology for multidisciplinary research with versatile applications in electronics, energy and gas storage, and biomedicine. Meanwhile, there is mounting concern on their environmental health risks due to the growing production and usage of MCNs. The lung is the primary site for particle invasion under environmental exposure to nanomaterials. Here, we studied the comprehensive toxicological profile of MCNs in the lung under the scenario of moderate environmental exposure. It was found that at a low concentration of 10μg/mL MCNs induced biophysical inhibition of natural pulmonary surfactant. Moreover, MCNs at similar concentrations reduced viability of J774A.1 macrophages and lung epithelial A549 cells. Incubating with nature pulmonary surfactant effectively reduced the cytotoxicity of MCNs. Regarding the pro-inflammatory responses, MCNs activated macrophages in vitro, and stimulated lung inflammation in mice after inhalation exposure, associated with lung fibrosis. Moreover, we found that the size of MCNs played a significant role in regulating cytotoxicity and pro-inflammatory potential of this nanomaterial. In general, larger MCNs induced more pronounced cytotoxic and pro-inflammatory effects than their smaller counterparts. Our results provided valuable information on the toxicological profile and environmental health risks of MCNs, and suggested that fine-tuning the size of MCNs could be a practical precautionary design strategy to increase safety and biocompatibility of this nanomaterial.

The Expanding Energy Prospects of Metal Organic Frameworks

Metal-organic frameworks (MOFs) and their composites and derivatives, with high porosity and tailorable chemical components, have recently aroused tremendous research interest in renewable energy and environmental science. In this inaugural issue of Joule , Lou and coworkers 1 summarize the latest progresses in the fabrication strategies of MOF-based materials and their applications in gas adsorption, energy conversion, and storage, while Dincâ and colleagues 2 demonstrate the promising application of MOFs in thermoelectrics.

Chemically Activated Covalent Triazine Frameworks with Enhanced Textural Properties for High Capacity Gas Storage.

Chemical activation of porous/nonporous materials to achieve high surface area sorbents with enhanced textural properties is a very promising strategy. The chemical activation using KOH, however, could lead to broad distribution of pores originating from the simultaneous pore deepening and widening pathways. Accordingly, establishing correlation between the chemical/textural properties of starting porous/nonporous materials and various pore formation mechanisms is quite critical to realize superior porosity and gas uptake properties. Here, we show that the chemical and textural properties of starting porous organic polymers, that is, covalent triazine frameworks (CTF), have profound effect on the resulting porosity of the frameworks. The chemical activation of microporous CTF-1 using KOH at 700 °C enabled the preparation of chemically activated CTF-1, caCTF-1-700, which predominantly showed pore deepening, leading to an increased surface area of 2367 m2 g-1 and significantly enhanced gas adsorption properties with CO2 uptake capacities up to 6.0 mmol g-1 at 1 bar and 1.45 mmol g-1 at 0.15 bar and 273 K along with a isosteric heats of adsorption (Qst) of 30.6 kJ mol-1. In addition, a remarkable H2 uptake capacity of 2.46 and 1.66 wt % at 77 and 87 K, 1 bar along with the Qst value of 10.95 kJ mol-1 at zero coverage was also observed for the caCTF-1-700. Notably, the activation of mesoporous CTF-2 under the same conditions was accompanied by a decrease in its surface area and also in the conversion of mesopores into the micropores, thus leading to a pore deepening/narrowing rather than widening. We attributed this result to the presence of reactive weak spots, triazine moieties, for the chemical activation reaction within the CTF backbone. These results collectively suggest the critical role of chemical and pore characteristics of porous organic polymers in chemical activation to realize solid-sorbents for high capacity gas storage applications.

NLDFT Pore Size Distribution in Amorphous Microporous Materials.

The pore size distribution (PSD) is one of the most important properties when characterizing and designing materials for gas storage and separation applications. Experimentally, one of the current standards for determining microscopic PSD is using indirect molecular adsorption methods such as nonlocal density functional theory (NLDFT) and N2 isotherms at 77 K. Because determining the PSD from NLDFT is an indirect method, the validation can be a nontrivial task for amorphous microporous materials. This is especially crucial since this method is known to produce artifacts. In this work, the accuracy of NLDFT PSD was compared against the exact geometric PSD for 11 different simulated amorphous microporous materials. The geometric surface area and micropore volumes of these materials were between 5 and 1698 m2/g and 0.039 and 0.55 cm3/g, respectively. N2 isotherms at 77 K were constructed using Gibbs ensemble Monte Carlo (GEMC) simulations. Our results show that the discrepancies between NLDFT and geometric PSD are significant. NLDFT PSD produced several artificial gaps and peaks that were further confirmed by the coordinates of inserted particles of a specific size. We found that dominant peaks from NLDFT typically reported in the literature do not necessarily represent the truly dominant pore size within the system. The confirmation provides concrete evidence for artifacts that arise from the NLDFT method. Furthermore, a sensitivity analysis was performed to show the high dependency of PSD as a function of the regularization parameter, λ. A higher value of λ produced a broader and smoother PSD that closely resembles geometric PSD. As an alternative, a new criterion for choosing λ, called here the smooth-shift method (SSNLDFT), is proposed that tuned the NLDFT PSD to better match the true geometric PSD. Using the geometric pore size distribution as our reference, the smooth-shift method reduced the root-mean-square deviation by ∼70% when the geometric surface area of the material is greater than 100 m2/g.