Microporous MOF Research Articles

Remarkable C2H4 separation at ambient condition with a chemically sturdy porous MOF through pore confinement

An alternate to energy intensive cryogenic high-pressure distillation process for the separation of ethylene from its gas mixture with ethane is highly appealing. In this contribution, a highly chemically robust microporous MOF named 1 (stable in water, boiling water, and pH = 2–11) has been employed for preferential ethylene sorption with excellent selectivity. The simulation study disclosed the selective pore confinement of ethylene through non-covalent interactions with the amine and carboxylate sites of the framework backbone. Column breakthrough study unveiled 15.2 and 24.8 L kg−1 ethylene production per cycle at 298 K for the 50:50 and 90:10 (v/v) C2H4/C2H6 mixture which places this MOF as one of the best physisorbent material for ethylene separation. Industrial applicability is tested in a hydrous environment (displaying unaltered performance) as well as its regenerability under vacuum or mild heating for successive cyclic operations.

Metal-Organic Framework Supported Low-Nuclearity Cluster Catalysts for Highly Selective Carbon Dioxide Electroreduction to Ethanol.

It is still a great challenge to achieve high selectivity of ethanol in CO2 electroreduction reactions (CO2RR) because of the similar reduction potentials and lower energy barrier of possible other C2+ products. Here, we report a MOF-based supported low-nuclearity cluster catalysts (LNCCs), synthesized by electrochemical reduction of three-dimensional (3D) microporous Cu-based MOF, that achieves a single-product Faradaic efficiency (FE) of 82.5 % at -1.0 V (versus the reversible hydrogen electrode) corresponding to the effective current density is 8.66 mA cm-2. By investigating the relationship between the species of reduction products and the types of catalytic sites, it is confirmed that the multi-site synergism of Cu LNCCs can increase the C-C coupling effect, and thus achieve high FE of CO2-to-ethanol. In addition, density functional theory (DFT) calculation and operando attenuated total reflectance surface-enhanced infrared absorption spectroscopy further confirmed the reaction path and mechanism of CO2-to-EtOH.

Direct Ethylene Purification from a Four-Component Gas Mixture by a Microporous MOF with Aromatic Pore Surface and Carboxylates.

The single-step purification of ethylene (C2H4) from a mixture of carbon dioxide (CO2), acetylene (C2H2), ethylene (C2H4), and ethane (C2H6) was achieved through MOF Compound-1, where the aromatic pore surface and carboxylates selectively recognized C2H6 and CO2, respectively, resulting in a reversal of the adsorption orders for both gases (C2H6 > C2H4 and CO2 > C2H4). Breakthrough testing verified that the C2H4 purification ability could be enhanced 2.6 times after adding impure CO2. Grand Canonical Monte Carlo (GCMC) simulations demonstrate that there are interactions between CO2 and C2H6 molecules as well as between CO2 molecules themselves. These interactions contribute to the enhancement of the C2H4 purification ability upon the addition of CO2 and the increased adsorption of CO2.

Nonpolar microporous Metal-Organic framework decorated with multiple functional sites for efficient Ethane/Ethylene separation

Efficiently achieving one-step adsorption separation of ethylene (C2H4) from ethane (C2H6) is a highly sought-after yet challenging task in the petrochemical industry. This underscores the need for enhanced standards in designing functional groups to formulate physisorbent materials with exceptional C2H6 trapping capacity, high C2H6/C2H4 selectivity, and material stability. In this study, we introduced a novel C2H6-selective microporous MOF (Zn-IPA-F-dmtrz), characterized by a nonpolar pore surface decorated with distinct advantageous O/N/F binding sites, creating a specialized nano-trap for C2H6, thereby enabling high-purity C2H4 production from C2H6/C2H4 mixtures. The synthesized Zn-IPA-F-dmtrz exhibited a remarkable C2H6 capacity of 4.6 mmol/g, coupled with an excellent C2H6/C2H4 selectivity of 2.3 at 298 K and 1 bar, outperforming the performance of many top-ranking adsorbents reported in recent years. Molecular simulation further demonstrated multiple synergistic interactions between this framework and C2H6. Moreover, breakthrough experiments confirmed the good stability of Zn-IPA-F-dmtrz, indicating its effectiveness in separating C2H6/C2H4 mixtures even under high-humidity conditions. This work provides valuable insights into how purposeful functionalization of nonpolar pore surfaces contributes to the construction of MOF materials tailored for highly efficient C2H6/C2H4 separation applications.

Dehydration‐Induced Cluster Consolidation in a Metal‐Organic Framework for Sieving Hexane Isomers

AbstractMetal‐organic frameworks (MOFs) that exhibit dynamic phase‐transition behavior under external stimuli could have great potential in adsorptive separations. Here we report on a zinc‐based microporous MOF (JNU‐80) and its reversible transformation between two crystalline phases: large pore (JNU‐80‐LP) and narrow pore (JNU‐80‐NP). Specifically, JNU‐80‐LP can undergo a dehydration‐induced cluster consolidation under heat treatment, resulting in JNU‐80‐NP with a reduced channel that allows exclusion of di‐branched hexane isomers while high adsorption of linear and mono‐branched hexane isomers. We further demonstrate the fabrication of MOF‐polymer composite (JNU‐80‐NP‐block) and its application in the purification of di‐branched isomers from liquid‐phase hexane mixtures (98 % di‐branched) at room temperature, affording the di‐branched hexane isomers with 99.5 % purity and close to 90 % recovery rate over ten cycles. This work illustrates an interesting dehydration‐induced cluster consolidation in MOF structure and the ensuing channel shrinkage for sieving di‐branched hexane isomers, which may have important implications for the development of MOFs with dynamic behavior and their potential applications in non‐thermal driven separation technologies.

A Highly Stable Microporous Calcium-Based MOF for C2H2/CO2 Separation with Low Regenerative Energy.

Most of the porous materials used for acetylene/carbon dioxide separation have the problems of poor stability and high energy requirements for regeneration, which significantly hinder their practical application in industries. Here, we report a novel calcium-based metal-organic framework (NKM-123) with excellent chemical stability against water, acids, and bases. Additionally, it has exceptional thermal stability, retaining its structural integrity at temperatures up to 300 °C. This material exhibits promising potential for separating C2H2 and CO2 gases. Furthermore, it demonstrates an adsorption heat of 29.3 kJ mol-1 for C2H2, which is lower than that observed in the majority of MOFs used for C2H2/CO2 separations. The preferential adsorption of C2H2 over that of CO2 is confirmed by dispersion-corrected density functional theory (DFT-D) calculations. In addition, the potential of industrial feasibility of NKM-123 for C2H2/CO2 separation is confirmed by transient breakthrough tests. The robust cycle performance and structural stability of NKM-123 during multiple breakthrough tests show great potential in the industrial separation of light hydrocarbons.

Improving Oxidative Catalytic Efficiency for Fuels Desulfurization Using Hybrid Materials Based in MOF‐808@SBA‐15

This work unveils a route for a new generation of heterogeneous polyoxometalate (POMs) based catalysts associated to the preparation of hybrid materials as a triad of POMs, mesoporous silica (SBA‐15) and microporous MOF structures (MOF‐808). The prepared catalyst, PMo12@MOF‐808@SBA‐15, with the main active center the phosphomolybdic acid (PMo12), was successfully applied for the desulfurization of a multicomponent fuel. Its oxidative catalytic performance showed to be considerable superior to the isolated POM@MOF and able to be recycled for more catalytic cycles without active loss. The higher catalytic performance seems to be directly related with the preparation of a more amorphous MOF structure within the channels of SBA‐15, in the presence of active POM guests.

Biogas upgrading using shaped MOF MIL-160(Al) by pressure swing adsorption process: Experimental and dynamic modelling assessment

Biogas has been introduced as a sustainable source of energy, which is considered as a promising alternative for conventional fossil fuels. Indeed, biogas requires to be upgraded from the impurities, specifically, carbon dioxide to be commercially utilized. In this study, the potential of shaped form MIL-160(Al) as a water stable Al dicarboxylate microporous MOF has been assessed concerning the biogas upgrading application. To this end, firstly, the dynamic fixed-bed adsorption of carbon dioxide and methane was investigated at 313 K and 4.0 bar. The measured breakthrough outcomes were simulated with a developed mathematical model, which the results confirmed an acceptable potential of model predictions. Afterwards, a pressure swing adsorption (PSA) process with 5-steps was designed relying on dynamic equilibrium results, and experimentally validated by a lab-scale PSA set-up for a 50:50 CO2/CH4 mixture. Finally, an industrial PSA process was designed to have a precise knowledge on the potential of MIL-160(Al) for biogas upgrading for large scale applications. The results demonstrated the purity and recovery of methane around 99 % and 63 %, respectively, which indicated the appealing capacity of this adsorbent for such a purpose.

A linker selective retention strategy to construct hierarchical porous metal-organic frameworks with high catalytic activity for oxidative desulfurization.

In order to improve the oxidative desulfurization (ODS) performance of MOF materials, an effective way is to convert a microporous MOF into a hierarchical porous MOF (HP-MOF) by utilizing the linker selective retention strategy. Herein, UiO-66 with the introduction of an unstable linker ligand (dihydro-1,2,4,5-tetrazine-3,6-dicarboxylate, dhtz) can selectively remove dhtz ligands to form HP-MOF (HP-UiO-66-dhtz) through heat treatment at high temperature. While maintaining the original structure of UiO-66, HP-UiO-66-dhtz features mesopores and abundant Lewis acid sites, showing excellent ODS performance for diphenylthiophene (DBT).

In situ generated 2,5-pyrazinedicarboxylate and oxalate ligands leading to a Eu-MOF for selective capture of C2H2 from C2H2/CO2.

The separation of C2H2/CO2 mixtures is a very important but highly challenging task due to their comparable physical natures and relative sizes. Herein, we report a europium-based 3D microporous MOF with a 4-connected two-nodal net with {4·53·62}2{42·62·82} topology, {[Eu2(pzdc)(ox)2(H2O)4]·5H2O}n (1) (H2pzdc = 2,5-pyrazinedicarboxylic acid, H2ox = oxalic acid), prepared by a hydrothermal method involving in situ generation of 2,5-pyrazinedicarboxylate and oxalate ligands. Two different temperatures were utilized to create two porous materials (1a and 1b) with channels of 4.8 × 5.4 Å and 4.1 × 6.3 Å, and 4.8 × 5.4 and 4.6 × 8.7 Å2, respectively. 1b shows a superior ability to selectively capture C2H2 from C2H2/CO2 as compared with 1a. At 1 bar and 298 K, 1b takes up 4.10 mmol g-1 C2H2 and 1.84 mmol g-1 CO2, respectively. In addition, at 298 K and 1 bar, 1b has a high selectivity for C2H2 over CO2, with an IAST selectivity of 12.7 while the value for 1a is 3.2. The separation of C2H2/CO2 with 1b also exhibits good reusability.

Customized pore fluorination in a microporous metal-organic framework for efficient ethane/ethylene separation

High efficiency and energy-saving separation of C2H6/C2H4 mixtures to product high purity C2H4 is vital and very meaningful industrial task. However, it remains a formidable challenge to fabricate high-performance adsorbents with simultaneous high C2H6 uptake and moderate adsorption enthalpy. Here, we reported a microporous MOF (NKU-0821) with suitable aperture size and F atoms functional pore surface, which can capture efficiently C2H6 from C2H6/C2H4 mixture. Single-component adsorption experiments show that NKU-0821a (activated NKU-0821) exhibits preferred C2H6 uptake at the full-pressure region than C2H4. The corresponding C2H6 adsorption enthalpy of NKU-0821a is 27.3 kJ mol−1, which is lower than most famous C2H6-selective MOFs. The calculation of IAST selectivity and breakthrough experiments have shown NKU-0821a can effectively separate C2H6/C2H4 mixture under simulated industrial conditions. Moreover, GCMC simulations revealed the key role of fluorous surface.

A microporous dysprosium-based MOF for selective CO2 capture at ambient temperature

A new microporous dysprosium-based metal–organic framework, {[Dy(BTC)(H2O)](NMF)2(H2O)}n (Dy-MOF, H3BTC = 1,3,5-benzenetricarboxylic acid, NMF = N-methyl formamide), was solvothermal synthesized. Gas adsorption studies reveal the CO2 uptake of Dy-MOF reaches to 55.9 cm3 g–1 at 293 K and 1 atm, in contrast to lower than 13.6 cm3 g–1 for CH4, Ar, and N2. Meanwhile, the IAST selectivities (50:50, v/v) of CO2/CH4, CO2/Ar, and CO2/N2 for Dy-MOF are calculated to be 5.1, 26.7 and 24.3, respectively, showing its ability to be a potential candidate for selective CO2 capture at ambient temperature.

On the modulation/energy competing of Tb(III)/Eu(III) emission in microporous MOF host for peroxide recognition

Being an important chemical reagent having moderate oxidizability, peracitic acid (PAA) has been applied in modern industries and processing, as well as public safety. These versatile applications make PAA an important analyte to be precisely and sensitively detected. The present work chose the combination of rare-earth-based probe and a microporous host bio-MOF-1 ([Zn8(ad)4(BPDC)6O·2(Me2NH2)+]·G, ad = adenine, BPDC = 4,4′-biphenyl dicarboxylic acid, G = N,N-dimetylformamide and water). Two β-diketone ligands, 1,3-di(pyridin-3-yl)propane-1,3-dione (DPY) and 1,3-diphenylpropane-1,3-dione (DPP), were coordinated to Tb(III) and Eu(III) ions to form probe [RE(DPY/DPP)2]Cl which was loaded into bio-MOF-1 micropores with different loading contents via an ionic exchange operation. The resulting composite samples were fully characterized, including synthesis, morphology, composition, sensing performance and mechanism. The protonation/oxidization of DPY and DPP ligands adjusted their triplet energy level (T1) and consequently affected their energy transfer (ET) efficiency to RE ions, resulting in the variation of RE emission relative intensity. A new pathway for PAA optical sensing was thus proposed. Linear fitting equations were observed for DPY-based samples, showing fluorescence intensity ratio value of 8.80, response time of 9 s, and LOD of 8.08 μM within working region of 0–140 μM.

Efficient C2H2-selective separation in a microporous Zn(II)-based metal-organic framework via the dual-ligand strategy.

Implementing the dual-ligand strategy, a microporous Zn-based MOF 1 with nitro and amino groups was effectively produced. The activated interconnected pores of 1 exhibited high C2H2 uptake capacity and preferential adsorption behaviour for C2H2 over CO2, as identified by the experiments and simulations. This work provides a new approach for designing and synthesizing the MOFs with desired structures and properties by optimizing their pore environment via the dual-ligand strategy.

High‐Capacity Splitting of Mono‐ and Dibranched Hexane Isomers by a Robust Zinc‐Based Metal–Organic Framework

AbstractHigh‐efficiency separation of C6 alkanes, particularly the mono‐ and dibranched isomers by using porous solids, is of paramount significance in the petrochemical industry and, remains a daunting challenge. In this work, we report the complete separation of linear/monobranched hexanes from their dibranched isomers through selective size‐exclusion by a microporous MOF, Zn‐tcpt (H3tcpt=2,4,6‐tris(4‐carboxyphenoxy)‐1,3,5‐triazine), with a two‐fold interpenetrated structure of hms nets. Importantly, its adsorption capacity and selectivity are notably higher than those of the previously reported adsorbents that can split mono‐ and dibranched alkane isomers. Dynamic breakthrough measurements verify the excellent separation of C6 alkane isomers by Zn‐tcpt, and the size‐exclusion based separation mechanism has been confirmed by ab initio materials modeling. The high‐efficiency separation of alkane isomers by Zn‐tcpt can be attributed to its optimal pore dimensions as well as high porosity.

A microporous 2D cobalt-based MOF with pyridyl sites and open metal sites for selective adsorption of CO2

A new microporous 2D Co-based MOF, [Co3(C6H3NO2)2(cpna)2(DMA)2]n (1) (H2cpna = 6-(4-carboxylphenyl)nicotinic acid; DMA = N,N-dimethylacetamide), has been synthesized and structurally characterized. Complex 1 shows a 2D network with 1D channel of 6.4 × 9.3 Å2 along the a-axis. Activated 1 (1a) exhibits selective gas adsorption for CO2 as compared to other gas molecules (e.g. C2H2, CH4, CO, N2) from the experimental single-component gas-adsorption isotherm (at 273K and 298K), molecular simulation and breakthrough experiments (298K). And the adsorption selectivity (CO2/C2H2, CO2/CH4, CO2/CO, and CO2/N2) was calculated with the ideal adsorbed solution theory (IAST). Activated 1 shows 9.77 wt% (2.22 mmol/g) uptake of CO2 at 1 bar and 273 K. Furthermore, the activation of 1 exhibits high ideal selectivities in adsorption of CO2 over C2H2, CH4, CO, and N2 at 298 K (1 bar), which may be attributed to the pyridyl sites on the ligands and open metal sites on the nodes of the framework. Besides, 1a could adsorb more gas molecules due to thicker layer (10.97 Å) of 2D structure.

Efficient and selective capture of xenon over krypton by a window-cage metal–organic framework with parallel aromatic rings

Efficient capture and separation of xenon (Xe) and krypton (Kr) from nuclear fuel reprocessing plants is of great significance for the control of discharge of gaseous radioisotopes into the environment. However, due to the similar size and chemically inert spherical properties of Xe/Kr, the discovery of an adsorbent with both high adsorption capacity and high selectivity remains a challenge. Here, we report a microporous MOF (Ni-MOF, [Ni2IINiIII(μ3-OH)(bdc)3(tpt)]·guest) featuring two different cavities with an appropriate triangular hole window size. One is composed of parallel aromatic rings with spacings of approximately 4.3 Å comparable to the kinetic diameter of Xe (4.047 Å), affording excellent binding affinity for Xe while the larger one with narrow pore window provides sufficient space for gas adsorption. The Ni-MOF material exhibits an exceptionally high Xe uptake of 5.43 mmol/g and Xe/Kr selectivity of 7.66 at 298 K and 1 bar. The adsorption capacity is the highest among all MOFs without open-metal-sites. Furthermore, the sorption selectivity of Xe over Kr within Ni-MOF originates from a special sandwiched π-Xe-π interaction revealed by Van der Waals interaction calculations.

A microporous Tb-based MOF for multifunctional detection of the α-CHC, Cu2+ and Fe3+

Here, we successfully synthesized a Tb-MOF, [Tb4(TATB)2] (H3TATB ​= ​4,4′,4″-(1,3,5-triazine-2,4,6-triyl)tribenzoic acid) used 2-fluorobenzoic acid as the nuclear cluster direct agent by solvothermal conditions. As expected, the Tb-TATB produces the characteristic emission bands of Tb3+ ion and could be developed as a multifunctional sensor for the highly selective and sensitive detection of the α-CHC (α-cyano-4-hydroxycinnamic acid), Cu2+ and Fe3+. The detection limits (LOD) of the α-CHC interfering with tumor cell proliferation by inhibiting lactic acid oxidation to treat cancer is 1.96 ​μM. The LOD for Fe3+ and Cu2+ are 4.84 ​μM and 2.92 ​μM, respectively, which are comparable to that of some reported MOFs. Furthermore, the possible fluorescence quenching mechanisms in the detection process could be attributed to the competitive absorption of excitation energy and dynamic and static quenching.

Hierarchical graphite oxide decorated UiO-66 for ultrahigh adsorption of dye with synergistic effect of ultrasonication: Experimental and density functional theory study

Indiscriminate disposal of azodyes demands the development of potential strategies for water treatment. Composites with tuned structural and functional properties, synthesized by amalgamation of 2D carbon materials with MOFs, emerges as a new generation adsorbents.Accordingly, our study focused on the synthesis of graphite oxide decorated UiO-66 MOF and its performance evaluation in ultrasonication assisted adsorptive removal of toxic Congo red dye from aqueous solution. The incorporation of GO tunes the microporous MOF to a hierarchical mesoporous/microporous structure. Theoretical analysis using density functional theory (DFT) was performed to predict the adsorption behaviour.The key finding which makes our study outstanding is the ultrahigh adsorption capacity (Qm − 1250 mg/g) of the synthesized composite, which is much higher than pure UiO-66, GO, and other reported adsorbents. The synergistic effect of the increased mesopore volume and availability of functional groups upon GO incorporation in the MOF improves the adsorption capacity. Adsorption occurs due to long-range intermolecular covalent and noncovalent interactions. The superior dye removal efficiency of the synthesized adsorbent along with good regeneration characteristics makes it a promising material for contaminants removal from aqueous solutions.

Mixed-Ligand Strategy for the Creation of Hierarchical Porous ZIF-8 for Enhanced Adsorption of Copper Ions.

The adsorption of heavy metals using metal–organic framework-based adsorption technology has been pointed out as a promising technique for the removal of these toxic elements from water. However, their adsorption capacity needs to be enhanced. Thus, the current work reports the effect of using a mixed-ligand strategy on the MOF framework and its effect on the removal of copper ions from water by adding terephthalic acid (BDC) linker to the ZIF-8precursors (2-methylimidazole (mI) and Zn2+) under solvothermal synthesis, leading to the formation of a hierarchical microporous mesoporous MOF, named Zn-mI-BDC, which was characterized by SEM, EDX, XRD, TGA, BET, and FTIR. As a result, all of these techniques revealed that the addition of a controlled amount of BDC did not alter the crystallinity of ZIF-8, resulting in the creation of a pore size of 4.2 nm. The new hierarchical porous MOF was tested for the adsorption of copper and exhibited an enhanced adsorption capacity compared to pristine ZIF-8 and many other standard adsorbents. The adsorption isotherm matched well with the Langmuir isotherm model, suggesting that the adsorption process chemisorption had a dominant role in the adsorption of Cu2+ species. Therefore, the current work is considered as an important step toward the use of a mixed-ligand strategy in enhancing the adsorption capacity of heavy metals using MOF materials.