Ultramicroporous Metal Organic Framework Research Articles

Mechanically robust MOF beads for efficient ethylene/ethane separation with fast adsorption kinetics

Shaping of metal-organic frameworks (MOFs) without obvious mass transfer resistance is crucial for scaled-up adsorption separation process. Herein, mechanically robust ultramicroporous MOF (ZU-901, also termed CPL-1-CH3) beads with hierarchical porosity were structured through the calcium alginate (CA) method, which preserved the adsorption separation performance and demonstrated fast gas diffusion rates. The highly crosslinked networks of CA contributed to the excellent mechanical properties of 95 % ZU-901@CA beads with Young’s modulus up to 1.81 MPa and a low abrasion rate of 0.32 %, superior to that of 95 % ZU-901@HPC extrudates (1.13 %). Compared with powder of ZU-901, the C2H4 capacity of ZU-901@CA beads showed only 3 % loss at 298 K. The C2H4 diffusion time constant of 95 % ZU-901@CA beads (7.06 × 10−3 s−1) was comparable to that of the powders (7.61 × 10−3 s−1) and higher than that of ZU-901@HPC extrudates (2.95 × 10−3 s−1). Breakthrough experiments confirmed that ZU-901@CA beads performed well in the dynamic separation of C2H4/C2H6 binary mixture, and could be easily regenerated at room temperature. In addition, after post modification on the exterior of ZU-901 beads, the water contact angle increased from 0° to 119°. Therefore, the mechanically robust ZU-901@CA beads showed great potential in energy-efficient C2H4/C2H6 separation.

Hydrogen Bonds Defined Pore Windows Enable Sieving Separation of Propylene from Propane in an Ultramicroporous Metal–Organic Framework

Hydrogen Bonds Defined Pore Windows Enable Sieving Separation of Propylene from Propane in an Ultramicroporous Metal–Organic Framework

Fabricating a Robust Ultramicroporous Metal-Organic Framework for Purifying Natural Gas and Coal Mine Methane.

Purifying methane (CH4) from natural gas and coal mine methane (CMM) is of great significance but challenging in the chemical industry. Herein, a robust ultramicroporous metal-organic framework (MOF) is reported, which can be synthesized on a gram scale by stirring under room temperature. Single-component adsorption isotherms of gases (CH4, ethane (C2H6), propane (C3H8), nitrogen (N2)) and breakthrough experiments indicate that the MOF can separate CH4 efficiently from CH4/C2H6/C3H8 ternary mixture, with super high purity-CH4 production of 154.7 cm3g-1. Additionally, the MOF shows higher CH4 capacity than N2, resulting in excellent separation performance for the CH4/N2 mixture. Notably, the binding sites of gases can be precisely determined by single-crystal X-ray data, further confirmed by molecular simulation. It is found that there are multiple hydrogen bonds and C─H···π interactions between the gases and the framework. This work offers an excellent candidate material for CH4 purification with both high capacity and separation efficiency.

Assembly of Solvent-Incorporated Rod Secondary Building Units to Ultramicroporous Metal–Organic Frameworks for Acetylene Purification

Assembly of Solvent-Incorporated Rod Secondary Building Units to Ultramicroporous Metal–Organic Frameworks for Acetylene Purification

A 1,3,5-triazine μ3-bridged neutral Cu(I) framework with enhanced stability and CO2 capture selectivity

Compounds with 1,3,5-triazine ring such as melamine derivatives, known for their low cost and high stability, offer potential for affordable, stable metal organic framework (MOF) synthesis. However, reported such frameworks are facing issues like low stability and reduced porosity. To overcome such problems, we explored organic ligands with protonated nitrogen atoms on the 1,3,5-triazine ring, facilitated by introducing hydroxyl groups on carbon atoms of the triazine ring to construct MOFs. By using 5-azacytosine, we have successfully synthesized SXU-121, a neutral ultramicroporous MOF with eta-topology and high density of open Cu(I) sites. SXU-121 features robust structural stability and significant CO2 adsorption capacity with high selectivity over N2 under ambient conditions. We believe SXU-121's development opens new avenues for creating a class of stable and low cost metal-triazine frameworks with potential diverse functionalities.

Efficient C3H6/C3H8 separation within a bifunctional ultramicroporous metal-organic framework with high purity and record packing density

Efficient C3H6/C3H8 separation within a bifunctional ultramicroporous metal-organic framework with high purity and record packing density

Ultramicroporous zinc-aminotriazole MOF with customized alkaline pore environments for highly efficient capture of CO2 from flue gas

CO2 capture from natural gas and N2-rich flue gas is essential for improving the utilization of natural resource gases reducing CO2 emission, thereby alleviating the greenhouse effect. However, achieving effective Adsorptive separation of CO2 from CH4, N2, and O2 based on molecular sieving is still challenging and rarely reported, but selectively capturing CO2 places high desires on maximizing separation efficiency. Here, we report a zinc-aminotriazole ultramicroporous metal–organic framework (ZnATZoxH2O), constructed from zinc carbonate, 3-amino-1,2,4-triazole (ATZ), and oxalic acid with water as the only solvent. ZnATZoxH2O features NH2-functionalized and pore channels around 3.6 Å, which preferentially adsorb CO2. This material exhibits high CO2 uptake of 61.9 cm3 g−1 at 298 K and 1 bar and significantly high IAST selectivity for CO2/N2 (>103) and CO2/CH4 (>105) and CO2/O2 (>104). Theoretical GCMC simulations reveal that negatively charged amino groups decorated on the pore channel surface and carboxylic acid in the pore environment enhance the binding affinity over CO2 through electrostatic interactions for preferential capture of CO2. Single-component adsorption experiments and dynamic breakthrough experiments mutually validated the superior separation performance of this material and dynamic column breakthrough tests to produce high dynamic CO2 separation productivity of 2.017 mmol g−1 and 3.4 mmol g−1 for CO2/N2 (15/85), CO2/CH4 (50/50), and 2.26mmol g−1 CO2/N2/O2 (15/80/5). Non-hazardous water as a synthetic solvent to assemble highly stable and efficient CO2-selective materials makes it promising for practical industrial applications.

Constructing local nanomolecular trap in a scalable, low-cost, and ultramicroporous metal–organic framework for efficient capture of greenhouse gases SF6 and CO2

The capture of sulfur hexafluoride (SF6) and carbon dioxide (CO2) is an important but challenging task for reducing greenhouse gas emission and thereby diminishing negative impacts of global climate change. Herein, we integrated local nanomolecular traps into an inexpensive cobalt-based metal–organic framework (MOF, namely GNU-3) with suitable pore sizes and functional pore surfaces for capturing greenhouse gases. Activated GNU-3a showed good adsorption and separation properties for SF6 and CO2. Especially for SF6, GNU-3a displayed the high SF6/N2 (10:90, v/v) selectivity of 317.6 and SF6 uptake capacity of 2.63mmol/g at 298 K and 1.0 bar. Grand canonical Monte Carlo simulations and first-principles dispersion-corrected density functional theory calculations identified that gas molecules were favorably trapped in polyaromatic ring functionalized channel centers and nanomolecular traps of pore walls by the strong hydrogen bond interactions. Excellent breakthrough results recommend practical separating properties of GNU-3a for binary SF6/N2 and CO2/N2 mixtures, and ternary SF6/CO2/N2 mixtures. Moreover, benefitting from superior features of cheap raw materials and large-scale synthesis, GNU-3 is expected to be applied to practical industrial scenarios. This work may provide insights into constructing prospectively industrial porous MOF adsorbents with optimal pore structures for greenhouse gas capture.

Highly efficient separation of CO2/N2 and CO2/CH4 via metal-ion regulation in ultra-microporous metal-organic frameworks

Efficient separation of CO2 from CH4 and N2 is crucial for industrial processes. This study presents a novel approach to enhance CO2/N2 and CO2/CH4 separation using metal-ion regulation in ultra-microporous metal–organic frameworks (MOFs). Specifically, we synthesized ZSTU-8-M (M=Cd, Zn) by coordinating norfloxacin ligands with different metal ions, achieving precise modulation of the pore structure. Ideal adsorption solution theory (IAST) calculations demonstrated that ZSTU-8-Cd exhibited superior selectivity for CO2/N2 (952) and CO2/CH4 (369) mixtures compared to ZSTU-8-Zn. Grand canonical Monte Carlo (GCMC) simulations and in situ single-crystal X-ray diffraction (SCXRD) confirmed the presence of specific CO2 binding sites within the pore channels. The CO2 molecule shows a unique strong adsorption mechanism of hydrogen bonding sites in this structure, and thus achieves high adsorption capacity at low pressure. Dynamic breakthrough experiments further validated the practical separation efficiency of ZSTU-8-Cd, with high retention times and saturated adsorption capacities for CO2. These findings highlight the ability of metal-ion modulation to achieve simultaneous improvement in adsorption capacity and selectivity, demonstrating the potential of MOFs for advanced gas separation applications.

Ultramicroporous metal-organic framework for efficient carbon dioxide capture from flue gas and natural gas

Carbon dioxide capture from flue gas (CO2/N2) and natural gas (CO2/CH4) is a challenging and cost-effective task. In this paper, ultramicroporous metal-organic frameworks (MOFs) (Co-norf and Ni-norf) are synthesized to realize the efficient separation of CO2/N2 and CO2/CH4 by metal ion regulation. The Ideal Adsorption Solution Theory (IAST) was calculated to evaluate the adsorption selectivity of activated Co-norf and Ni-norf for CO2/N2 (v/v = 15/85) mixtures and CO2/CH4 mixtures. The CO2/N2 selectivity of Co-norf and Ni-norf at 100 kPa was 734 and 96, respectively, which corresponds to an almost 7.6-fold increase by metal ion modulation. The specific binding sites of CO2 molecules within the pore channels were obtained by grand canonical Monte Carlo simulation (GCMC). Dynamic breakthrough experiments respond to the actual separation in systems simulating flue gas and natural gas, where the higher saturation adsorption and longer retention time proved that Co-norf is an ideal material for CO2 capture and separation. The present work provides a feasible approach for the application of MOF in gas separation.

Hemilabile Binding of Acetylene in an Amide-Rich Ultramicroporous MOF Enables Strong Acetylene Selectivity.

Thanks to a hemilabile amide-based binding site, a previously unreported amide-functionalized metal-organic framework (MOF) exhibits high acetylene affinity over ethylene, methane, and carbon dioxide, three-in-one.

Physicochemical Properties, Equilibrium Adsorption Performance, Manufacturability, and Stability of TIFSIX-3-Ni for Direct Air Capture of CO2.

The use of adsorbents for direct air capture (DAC) of CO2 is regarded as a promising and essential carbon dioxide removal technology to help meet the goals outlined by the 2015 Paris Agreement. A class of adsorbents that has gained significant attention for this application is ultramicroporous metal organic frameworks (MOFs). However, the necessary data needed to facilitate process scale evaluation of these materials is not currently available. Here, we investigate TIFSIX-3-Ni, a previously reported ultramicroporous MOF for DAC, and measure several physicochemical and equilibrium adsorption properties. We report its crystal structure, textural properties, thermal stability, specific heat capacity, CO2, N2, and H2O equilibrium adsorption isotherms at multiple temperatures, and Ar and O2 isotherms at a single temperature. For CO2, N2, and H2O, we also report isotherm model fitting parameters and calculate heats of adsorption. We assess the manufacturability and process stability of TIFSIX-3-Ni by investigating the impact of batch reproducibility, binderless pelletization, humidity, and adsorption-desorption cycling (50 cycles) on its crystal structure, textural properties, and CO2 adsorption. For pelletized TIFSIX-3-Ni, we also report its skeletal, pellet, and bed density, total pore volume, and pellet porosity. Overall, our data enable initial process modeling and optimization studies to evaluate TIFSIX-3-Ni for DAC at the process scale. They also highlight the possibility to pelletize TIFSIX-3-Ni and the limited stability of the MOF under humid and oxidative conditions as well as upon multiple adsorption-desorption cycles.

Spatially Confined π-Complexation within Pore-Space-Partitioned Metal-Organic Frameworks for Enhanced Light Hydrocarbon Separation and Purification.

Ultramicroporous metal-organic frameworks (MOFs) are demonstrated to be advantageous for the separation and purification of light hydrocarbons such as C2H2, C2H4, and CH4. The introduction of transition metal sites with strong π-complexation affinity into MOFs is more effective than other adsorption sites for the selective adsorption of π-electron-rich unsaturated hydrocarbon gases from their mixtures. However, lower coordination numbers make it challenging to produce robust MOFs directly utilizing metal ions with π-coordination activity, such as Cu+, Ag+, and Pd2+. Herein, a series of novel π-complexing MOFs (SNNU-33s) with a pore size of 4.6Å are precisely constructed by cleverly introducing symmetrically matched C3-type [Cu(pyz)3] (pyz = pyrazine) coordinated fragments into 1D hexagonal channels of MIL-88 prototype frameworks. Benifit from the spatial confinement combined with π-complex-active Cu+ of [Cu(pyz)3], pore-space-partitioned SNNU-33 MOFs all present excellent C2H2/CH4, C2H4/CH4, and CO2/CH4 separation ability. Notably, the optimized SNNU-33b adsorbent demonstrates top-level IAST selectivity values for C2H2/CH4 (597.4) and C2H4/CH4 (69.8), as well as excellent breakthrough performance. Theoretical calculations further reveal that such benchmark light hydrocarbon separation and purification ability is mainly ascribed to the extra-strong binding affinity between Cu+ and π-electron donor molecules via a spatially confined π-complexation process.

Maximizing Electrostatic Interaction in Ultramicroporous Metal-Organic Frameworks for the One-Step Purification of Acetylene from Ternary Mixture.

Developing efficient adsorbents for acetylene purification from multicomponent mixtures is of critical significance in the chemical industry, but the trade-off between regenerability and selectivity significantly restricts practical industrial applications. Here, we report ultramicroporous metal-organic frameworks with acetylene-affinity channels to enhance electrostatic interaction between C2H2 and frameworks for the efficient one-step purification of C2H2 from C2H2/CO2/C2H4 mixtures, in which the electrostatic interaction led to high regenerability. The obtained SNNU-277 exhibits significantly higher adsorption capacity for C2H2 than that for both C2H4 and CO2 at 298 K and 0.1 bar, while an ultrahigh selectivity of C2H2/C2H4 (100.6 at 298 K) and C2H2/CO2 (32.8 at 298 K) were achieved at 1 bar. Breakthrough experiments validated that SNNU-277 can efficiently separate C2H2 from C2H2/C2H4/CO2 mixtures. CO2 and C2H4 broke through the adsorption column at 4 and 14.8 min g-1, whereas C2H2 was detected until 177.6 min g-1 at 298 K. Theoretical calculations suggest that the framework is electrostatically compatible with C2H2 and electrostatically repels C2H4 and CO2 in the mixed components. This work highlights the importance of rational pore engineering for maximizing the electrostatic effect with the preferentially absorbed guest molecule for efficient multicomponent separation.

Increased CO2/N2 selectivity by stepwise fluorination in isoreticular ultramicroporous metal–organic frameworks

A series of isoreticular ultramicroporous fluorinated MOFs were synthesized. Both experimental and simulation studies showed that increasing the fluorine content leads to a marked increase in CO2/N2 selectivity owing to the CF⋯C(CO2) interactions.

Rapid synthesis of ultra-microporous metal-organic framework tubular Ni-LAP membranes for H2 separation by linker salt method

Recently, the development of pillar-layered metal-organic frameworks (MOFs) is receiving more and more attention because of their pore surface chemistry tunability and designability. In this work, we firstly synthesized various sizes of high-quality Ni-LAP [Ni2(L-asp)2(pz)] (L-asp = l-aspartic acid, pz = pyrazine) crystals key for secondary growth by manipulating the crystal thermal dynamics and kinetics of Ni-LAP synthesis solution simply through choosing the Ni(OAc)2 as metal source and pretreatment at 40 °C, followed by the fabrication of defect-free Ni-LAP membranes as a model in a short time of 4 h using the linker salt method. It is found the pretreatment of Ni(OAc)2 precursor solution at 40 °C with continuous stirring for 6 h can effectively promote deprotonation to form 250 nm crystals. The linker salt method enables a greener and more rapid synthesis of Ni-LAP membranes, with continuous and compact Ni-LAP membranes, where soluble metal precursors and organic linking salts provide the synthesis solution a higher degree of supersaturation, both of which play an important role in the rapid preparation of Ni-LAP membranes. The preparation parameters of the Ni-LAP membranes were investigated in detail, and the results from the Ni-LAP membrane gas separation performance showed that the preferential (111) orientation membrane (M9) exhibited the best H2/CO2 separation performance with separation factor of 23.8 and H2 permeance of 2.11 × 10−7 mol m−2 s−1 Pa−1 compared to the preferential (002) orientations (M3), which may attributed to the preferential (111) orientation being at an angle to the optimal a-axis aperture perpendicular to the support thereby reducing the mass transfer resistance. Furthermore, the generation of corrosive nitric acid during the preparation process can be greatly reduced and replaced by eco-friendly potassium nitrate. The superiority of the pore structure and the remarkable stability of these MOF membranes show the potential for H2 purification. Moreover, our preparation route demonstrates the universality of preparing other isomorphs, such as Ni-LAB and Co-LAP membranes.

Hydrogen Adsorption in Ultramicroporous Metal-Organic Frameworks Featuring Silent Open Metal Sites.

In this study, we utilized an ultramicroporous metal-organic framework (MOF) named [Ni3(pzdc)2(ade)2(H2O)4]·2.18H2O (where H3pzdc represents pyrazole-3,5-dicarboxylic acid and ade represents adenine) for hydrogen (H2) adsorption. Upon activation, [Ni3(pzdc)2(ade)2] was obtained, and in situ carbon monoxide loading by transmission infrared spectroscopy revealed the generation of open Ni(II) sites. The MOF displayed a Brunauer-Emmett-Teller (BET) surface area of 160 m2/g and a pore size of 0.67 nm. Hydrogen adsorption measurements conducted on this MOF at 77 K showed a steep increase in uptake (up to 1.93 mmol/g at 0.04 bar) at low pressure, reaching a H2 uptake saturation at 2.11 mmol/g at ∼0.15 bar. The affinity of this MOF for H2 was determined to be 9.7 ± 1.0 kJ/mol. In situ H2 loading experiments supported by molecular simulations confirmed that H2 does not bind to the open Ni(II) sites of [Ni3(pzdc)2(ade)2], and the high affinity of the MOF for H2 is attributed to the interplay of pore size, shape, and functionality.

A low cost and energy consumption Ultra-microporous CPM-20(Co) for CO2/N2 and CO2/CH4 separation

It is of vital importance to research carbon dioxide (CO2) removal from flue gas and natural gas. Metal-organic frameworks have been widely used in the adsorption field because of their high specific surface area, high porosity and special chemical properties. With the exception of separation performance, synthesis cost and energy consumption are also be considered in actual industry. Here, an ultra-microporous metal-organic framework CPM-20(Co) with mixed ligand was synthesized using cheap and convenient ligands (1,4-dicarboxybenzene and isonicotinic acid). The calculation shows the adsorption heat of CO2 was 20.16 kJ/mol resulting low regenerative energy. This material exhibits high selectivities of equimolar mixture CO2/N2 (350) and CO2/CH4 (45) at 298 K and 1 bar, which is better than other MOFs reported. Breakthrough experiments confirmed that CPM-20(Co) can separate CO2 from flue gas and natural gas under environmental conditions. It is speculated that the framework has suitable pore size and higher polarizability of CO2 are the key factor for CPM-20(Co) to achieve the adsorption separation of CO2/N2 and CO2/CH4. CPM-20(Co) has low regenerative energy and the material was easily obtained, which has a better application prospect in industry.

Simultaneous extraction of C3H8 and C2H6 from ternary C3H8/C2H6/CH4 mixtures in an ultra-microporous metal–organic framework

The efficient purification of methane from other light hydrocarbons is of prime importance in natural gas purification. However, the exploitation of stable adsorbents with both high selectivity and high adsorption capacity remains a challenge. Herein, an ultra-microporous Co-based metal–organic framework (Co-MOF) with abundant selective binding sites decorating the pore wall was applied for the highly efficient separation of ternary C3H8/C2H6/CH4 mixtures. The Co-MOF shows remarkable C3H8 and C2H6 adsorption capacities with uptakes of 59.4 cm3/g and 58.6 cm3/g, respectively, while only adsorbing a low amount of CH4 with an uptake of 16.6 cm3/g at 298 K and 100 kPa. The ideal adsorbed solution theory selectivities for C2H6/CH4 (v/v = 50/50) and C3H8/CH4 (v/v = 50/50) reach 26.0 and 290.0 at 298 K, respectively, surpassing most of the state-of-the-art MOF materials. The molecular simulation reveals that the excellent adsorption and separation performance of Co-MOF derives from its suitable pore size and functional pore surfaces. Furthermore, the breakthrough experiments reveal that the Co-MOF exhibits excellent separation performance of C3H8 and C2H6 from natural gas. Notably, the dynamic separation performance of Co-MOF can be well-maintained after five cycles, demonstrating its excellent cycling stability. The high stability and excellent separation performance make Co-MOF a promising adsorbent for natural gas purification.

(Invited) Metal Organic Frameworks for the Storage, Separation, and Purification of Gaseous Fuels

We have seen a surge of interest in metal organic frameworks (MOFs) over the past decades with more than 100,000 structures reported today. This interest is based on the modular building-block nature of their structure, which makes them tunable and widely applicable to many applications. Of particular interest is the storage, separation, and purification of gaseous fuels with MOFs as a much-needed alternative to the energy-intense processes currently in use. My talk will focus on results of a variety of MOFs that have been obtained by a close integration of synthesis, in situ vibrational spectroscopy, and ab initio materials modeling. In particular, we report on the development and characterization of four MOFs for the purpose of separating linear, mono, and dibranched alkane isomers through selective molecular sieving, which is of significant value in the petrochemical industry. The separation of such alkane isomers is a challenging and important industrial process for the production of premium gasoline, blending components with high research octane number. I will also show recent results that point towards non-standard kinetics in certain separation processes in MOFs as well as results for ultramicroporous MOFs that have the ability to effectively perform separations in the presence of water.