Pillared-layer Metal-organic Framework Research Articles

Halogen-modified metal-organic frameworks for efficient separation of alkane from natural gas.

As a rich green energy source, natural gas is widely used in many fields such as the chemical industry, automobile energy, and daily life. However, it is very challenging to separate and recover C2H6 and C3H8 from natural gas. Metal-organic frameworks (MOFs) as an emerging type of multi-pore porous materials show huge potential in gas adsorption separation. Herein, we report pillar-layered MOFs, Ni (BDC)(DABCO)0.5 (DMOF-X), modified by halogen atoms (F, Cl, Br), and investigate their CH4/C2H6/C3H8 separation performance. The experimental results show that DMOF-Cl exhibited a extremely high adsorption capacity for C3H8 and C2H6. Under the conditions of 298 K and 100 kPa, the adsorption capacities for C3H8 and C2H6 on DMOF-Cl are as high as 6.23 and 4.94 mmol g-1, which are superior to the values for most of the porous materials that have been reported. In addition, DMOF-Cl also shows high C3H8/CH4 (5: 85, V/V) and C2H6/CH4 (10: 85, V/V) separation selectivities, with values of 130.9 and 12.5, respectively. Finally, DMOF-Cl also demonstrated great potential as an adsorbent for separating C3H8/C2H6/CH4.

Reduced thermal expansion by surface-mounted nanoparticles in a pillared-layered metal-organic framework

Control of thermal expansion (TE) is important to improve material longevity in applications with repeated temperature changes or fluctuations. The TE behavior of metal-organic frameworks (MOFs) is increasingly well understood, while the impact of surface-mounted nanoparticles (NPs) on the TE properties of MOFs remains unexplored despite large promises of NP@MOF composites in catalysis and adsorbate diffusion control. Here we study the influence of surface-mounted platinum nanoparticles on the TE properties of Pt@MOF (Pt@Zn2(DP-bdc)2dabco; DP-bdc2-=2,5-dipropoxy-1,4-benzenedicarboxylate, dabco=1,4-diazabicyclo[2.2.2]octane). We show that TE is largely retained at low platinum loadings, while high loading results in significantly reduced TE at higher temperatures compared to the pure MOF. These findings support the chemical intuition that surface-mounted particles restrict deformation of the MOF support and suggest that composite materials exhibit superior TE properties thereby excluding thermal stress as limiting factor for their potential application in temperature swing processes or catalysis.

Synthesis, structure, and lithium storage performance of non-conductive metal–organic frameworks for high-performance lithium-ion batteries

Some metal–organic frameworks (MOFs) cannot be used as electrode materials for lithium-ion batteries because of their inferior intrinsic electrocatalytic activity and poor conductivity. Herein, the application of two nickel (II) cluster-based pillar-layered MOFs, Ni-mba-Na ([Ni8(mba)6(Cl)2Na(OH−)3]n, H2mba is 2-mercaptobenzoic acid) and Ni-mba-K ([Ni8(mba)6(Cl)2K(OH−)3]n), as electrode materials are reported. They differ from conductive MOFs because they are insulators with small specific surface areas (<10 m2g−1) and H2mba is an inexpensive chemical raw material. The conductivities of Ni-mba-Na and Ni-mba-K at 30 ℃ are 4.002 × 10−10 and >10−11 S cm−1, respectively. They exhibit excellent lithium storage performance, stability, and high inherent density (1.835 and 1.838 g cm−3) and specific capacity (1091.6, and 905.6 mAh/g at the first cycle). Design recommendations for these MOFs are provided based on their structure and performance differences. This paper provides a novel application of non-conductive MOFs in the energy storage field and strategy for design of high-performance electrode materials for lithium-ion batteries.

Enhancing Ethane/Ethylene Separation Performance in Two Dynamic MOFs by Regulating Temperature-Controlled Structural Interpenetration.

The separation of ethane from ethylene is an important but challenging process in the chemical industry because of their similar physicochemical properties. Generally, the adsorbents for C2H6/C2H4 separation require an appropriate and relatively small aperture. Herein, we report two dynamic pillar-layered metal-organic frameworks (MOFs) BUT-111 and BUT-112 with isomorphic frameworks but different degrees of interpenetration for efficient C2H4 purification. The dynamic behavior makes both the activated MOFs exhibit ultramicropores and reversed order adsorption behavior for C2H6 and C2H4, which could obtain highly purified C2H4 in one step from the C2H6/C2H4 mixture. BUT-111 and BUT-112 could work in a wide temperature range, and with the decrease in temperature, the C2H6/C2H4 selectivity would increase. Moreover, the degree of interpenetration could be well controlled by the synthetic temperature, and the increase in the interpenetration degree of BUT-112 enhanced the C2H4 purification effectively.

Pillar-Layered Metal-Organic Frameworks for Sensing Specific Amino Acid and Photocatalyzing Rhodamine B Degradation.

Metal-organic frameworks (MOFs) have presented potential for detection of specific species and catalytic application due to their diverse framework structures and functionalities. In this work, two novel pillar-layered MOFs [Cd6(DPA)2(NTB)4(H2O)4]n·n(DPA·5DMA·H2O) (1) and [Cu2(DPA)(OBA)2]n·n(2.5DMF·H2O) (2) [DPA = 2,5-di(pyridin-4-yl)aniline, H3NTB = 4,4',4''-nitrilotribenzoic acid, H2OBA = 4,4'-oxydibenzoic acid, DMA = N,N-dimethylacetamide, DMF = N,N-dimethylformamide] were successfully synthesized and structurally characterized. Both 1 and 2 have three-dimensional framework structures. The fluorescent property of 1 makes it possible for sensing specific amino acid such as L-glutamic acid (Glu) and L-aspartic acid (Asp). While MOF 2 was found to be suitable for photocatalytic degradation of Rhodamine B (RhB) in the presence of H2O2. The results imply that MOFs are versatile and metal centers are important in determining their properties.

Synergistic effect of metal node engineering and mixed-linker-architected on the energy storage activities of pillar-layered Cu2(L)2(DABCO) metal-organic frameworks

The most promising way to increase the properties of metal-organic frameworks (MOFs) to use in supercapacitor electrodes is rational design, and defects and high porosity are introduced via the use of bimetallic MOFs. In this work, we synthesized Cu-MOF and accommodated different ions in the structure to evaluate the effect of mixed metal and mixed linker in MOF structures. Pillar-layered metal-organic frameworks, M2(L)2(DABCO), M = Cu, Co, Ni, L = BDC (1,4-benzene dicarboxylic acid), NH2BDC (2-Aminoterephthalic acid), and DABCO = 1,4-diazabicyclo [2.2.2] octane, have been designed by accommodating ions and ligands in the structures and synthesizing in a facile manner. Various characteristic and electrochemical measurements were done to investigate our samples application's performance. According to the results, the best capacitance is for the mixed metal/ligand MOF, Cu–Co (NH2/50). Moreover, the asymmetric supercapacitor was set up using our MOF and activated carbon as the positive and negative electrodes, respectively. Our synthesized electrode performed maximum specific energy of 3.39 Wh/kg, maximum specific power of 750.0 W/kg, and capacity stabilization of 86% after 10000 cycles.

Facile synthesis of dptz-CuGeF6 at room temperature and its adsorption performance for separation of CO2, CH4 and N2

Efficient capture of CO2 from flue gas and removal of CO2 from biomethane by physical adsorption are in great need. Herein, we report the facile synthesis of a new pillared-layer metal-organic frameworks, dptz-CuGeF6 for CO2 separation from the flue gas or the biomethane. The resulting samples were characterized. Structurally, the dptz-CuGeF6 possess double-interpenetrated frameworks formed by two staggered, independent sql sheets, in which the cations Cu2+ are coordinated by four dptz ligands, making the dptz-CuGeF6 exhibit narrow and uniform ultra-micropores of 5.25 Å. Its CO2 capacity reached 2.17 mmol/g at 15 kPa and 3.23 mmol/g at 100 kPa separately, and its selectivity of CO2/CH4 (50:50) and CO2/N2 (15:85) reached as high as 80 and 175.5, respectively. The stability experiments demonstrated the intact structure of dptz-CuGeF6 was retained after exposure in moisture air (RH = 50% or RH = 80%) as well as in several polar solvents. Breakthrough experiments confirmed that CO2/CH4 or CO2/N2 binary mixture were efficiently separated. Molecule simulation revealed that both F···CCO2 and multiple C-H···OCO2 interactions in the pores of dptz-CuGeF6 played an important role in enhancing its selectivity of CO2 adsorption. The dptz-CuGeF6 would be promising for CO2 capture and separation from flue gas or biomethane.

Syntheses, structures and fluorescence properties of a Zn and a Cd(II) coordination polymer based on the mixed ligands

Two new compounds, [Zn(4-npa)(btmb)]n (1) and [Cd(4-npa)(btmb)0.5(H2O)2]n (2) (H24-npa = 4-nitrophthalic acid, btmb = 1,4-bis(1,2,4-triazol-1-ylmethyl)benzene) have been achieved under hydrothermal conditions and structurally characterized by elemental analysis, IR spectroscopy and single-crystal x-ray diffraction. The compound 1 crystallizes in monoclinic crystal system, space group P21/c and is characterized by a two-dimensional layer structure containing 1 D Zn-carboxylate chains. Wherein the central Zn(II) ion is coordinated by two carboxylate O atoms and two N atoms to give a distorted tetrahedral [ZnO2N2] geometry. In compound 2, The hexa-coordinated Cd(II) ion forms a slightly distorted octahedral [CdNO5] geometry. The two Cd(II) centers are bridged by pair 4-npa dianions adopting bidentate-bridging mode to form a dinuclear unit. The dinuclear units are linked together by 4-npa dianions to form a Cd-carboxylate layer, and further extend by btmb molecules to form a 3 D pillared-layer metal–organic framework. The thermogravimetric analyses and luminescent properties of two compounds are also investigated.

Tetragonal multilayered ZnO/CuO composites derived from Zn- and Cu-containing metal-organic framework: Effect of calcination temperature on physicochemical properties and photocatalytic activity

Tetragonal multilayered ZnO/CuO composites prepared by the annealing of a Zn- and Cu-containing pillar-layered metal-organic framework were characterized by using instrumental techniques and investigated as catalysts for the degradation of 4-nitrophenol (4-NP) under irradiation with UV–vis light. The as synthesized samples contained p-n junctions, amorphous-crystalline heterojunctions, which benefitted light absorption and charge separation. The calcination temperature significantly influenced both the physicochemical properties and photocatalytic activities of these composites. The sample obtained at 400 °C (TL-ZC-400) exhibited the best photocatalytic performance, achieving a 4-NP degradation efficiency of 93.93% after 40 min of illumination. The TL-ZC-400 still showed high photodegradation ability (97.2%) after four times recycling. Furthermore, the recombination of ZnO and CuO adjusted the band gap structure of TL-ZC-400. Radical trapping experiments showed that the degradation of 4-NP was mainly mediated by hydroxyl radicals and holes. A possible photocatalytic mechanism was also proposed in this study.

Constructing [Co6(μ3-OH)6]-based pillar-layered MOF with open metal sites via steric-hindrance effect on ligand for CO2 adsorption and fixation

With excellent structural tunability and well framework stability, pillar-layered metal-organic frameworks (PL-MOFs) are promising candidates as sorbents and catalysts. Yet, the open metal sites (OMSs) in PL-MOFs are usually fully occupied by the pillar ligands, mostly limiting their involvement in CO2 adsorption and fixation. Herein, in consideration of the 12-connected [Co6(μ3-OH)6]-based PL-MOFs (Co6-MOF-3), a strategy based on steric-hindrance effect on pillar linker is proposed to create OMSs on their metal cluster nodes. The 4,4′-(9,10-anthracenediyl)bis-Pyridine (ABPY) that possessed anthracene groups was selected as the pillar linker, and a new [Co6(μ3-OH)6]-based PL-MOF (DZU-6) with accessible open Co(ii) sites was successfully synthesized. Single crystal structure of DZU-6 analysis reveals that ABPY ligands which were firstly linked to the metal clusters prevented the other ABPY ligands from coordinating with the nodes due to the steric-hindrance effect on ligands, resulting that four sites on [Co6(μ3-OH)6] were occupied by the terminal solvent molecules. The coordinated solvent molecules in DZU-6 could be removed easily, meanwhile the porosity was preserved (BET surface 2566 m2 g−1). Importantly, CO2 adsorption and catalytic cycloaddition conversion of DZU-6 were performed that the CO2 uptake improved 40% and the catalytic conversion yield increased over 50% compared with isostructural Co6-MOF-3 without OMSs.

Modulating Carbon Dioxide Storage by Facile Synthesis of Nanoporous Pillared-Layered Metal-Organic Framework with Different Synthetic Routes.

A Zn(II)-based paddle wheel pillared-layered metal-organic framework, [Zn2 (DBrTPA)2(DABCO)].(DMF)2 (MUT-4), containing 1,4-diazabicyclo[2.2.2]octane (DABCO) and 2,5-dibromoterephthalic acid (DBrTPA) has been successfully synthesized with different synthetic methods, including solvothermal, sonochemical, and their mixing methods, some of which are energy-efficient, rapid, and room-temperature synthetic procedures. Structural characterization of MUT-4 with single-crystal X-ray crystallography showed that it crystallizes in the tetragonal I41/acd space group. MUT-4 has shown higher performance than known MOFs in the CO2 adsorption such as UiO-66, UiO-66-NH2, UiO-66-NO2, PCN-66, ZIF-68, UiO-67, bio-MOF-11, MIL-101, MOF-177, ZIF-8, and ZIF-82. It has shown even better CO2 adsorption performance in comparison to the previously reported DMOFs such as DMOF-1 and other DMOF analogues such as NO2-DMOF-1, NH2-DMOF-1, Br-DMOF-1, and Azo-DMOF-1. Furthermore, it has performed even better than modified known MOFs. Also, the carbon dioxide storage capacity of MUT-4 obtained using several different synthetic routes shows a significant difference. Thus, this study exhibited that CO2 gas adsorption of MUT-4 could be modulated by optimizing its synthetic methods.

Structure modulation, selective dye adsorption and catalytic CO2 transformation of four pillared-layer metal-organic frameworks

In this paper, a series of metal-organic frameworks (MOFs), namely, [Co(pip)(4,4′-bpy)]n (1), [Co2(pip)2(bibp)]n (2), [Mn(pip)bidmp]n (3) and [Ni(pip)(bibp)(H2O)]n (4) (bpy ​= ​4,4′-bipyridine, bibp ​= ​4,4-bis(imidazolyl)biphenyl, bidmb ​= ​1,4-bis(1-imidazoly)-2,5-dimethylbenzene), have been solvothermally synthesized based on the main ligand 6-(3-pyridyl)isophthalic acid (H2pip) and structurally characterized by various methods. These MOFs all present three dimensional (3D) pillared-layer frameworks, and through systematic modulation of auxiliary ligands and metal ions, their structures can be well regulated from nonporous to porous. Considering their excellent thermal and water stability, the dye removal properties from water solutions of these MOFs were further studied, and notably, 2 which has the largest porosity of the four MOFs, exhibits very fast selective adsorption of methyl orange over Rhodamine B (MO/RhB) with a total MO uptake amount of 83.4 ​mg ​g−1. Moreover, the catalytic CO2 transformation properties of these MOFs were also carried out under mild conditions, of which 2 exhibited the highest catalytic activity with 69.57% yield for propylene carbonate and 50.55% for butylene carbonate, respectively.

A pillared-layer metal–organic framework for efficient separation of C3H8/C2H6/CH4 in natural gas

Metal-organic frameworks (MOFs) have great potentials as adsorbents for natural gas purification. However, the trade-off between selectivity and adsorption capacity remains a challenge. Herein, we report a pillared-layer metal-organic framework Ni(HBTC)(bipy) for efficiently separating the C 3 H 8 /C 2 H 6 /CH 4 mixture. The experimental results show that the adsorption capacity of C 3 H 8 and C 2 H 6 on Ni(HBTC)(bipy) are as high as 6.18 and 5.85 mmol·g −1 , while only 0.93 mmol·g −1 for CH 4 at 298 K and 100 kPa. Especially, the adsorption capacity of C 3 H 8 at 5 kPa can reach an unprecedented 4.52 mmol·g −1 and for C 2 H 6 it is 1.48 mmol·g −1 at 10 kPa. The ideal adsorbed solution theory predicted C 3 H 8 /CH 4 selectivity is as high as 1857.0, superior to most of the reported materials. Breakthrough experiment results indicated that material could completely separate the C 3 H 8 /C 2 H 6 /CH 4 mixture. Therefore, Ni(HBTC)(bipy) is a promising material for separation of natural gas.

Room temperature synthesis of pillared-layer metal-organic frameworks (MOFs).

A pillared-layer MOF, {[Cu2(Fu)2(BPY)]·H2O} n , was synthesized at room temperature employing a mixture of water and methanol as the reaction solvent. By using the sodium salts of fumarate, instead of the native acids, the target MOF could be readily prepared in aqueous media. The PXRD of this MOF was found to be in good agreement with the simulated diffractogram from single crystal data of related MOF made at a higher temperature using DMF as the solvent. In addition to characterization by PXRD, TGA, and ESEM, N2-sorption measurements revealed the formation of mesopores in the MOF's structure under study. The electronic band gap and magnetic properties of this pillared-layer MOF were also studied.

A robust metal-organic framework with guest molecules induced splint-like pore confinement to construct propane-trap for propylene purification

A propane-trapping pillar-layered metal–organic framework with splint-like pore confinement for propylene purification exhibits excellent separation performances of C 3 H 8 /C 3 H 6 mixture. • C 3 H 8 /C 3 H 6 -induced splint-like pore confinement can be constructed in a robust MOF. • It shows excellent separation performance of C 3 H 8 /C 3 H 6 with the record selectivity. • Breakthrough experiments indicate the complete separation of C 3 H 8 /C 3 H 6 mixture. • C 3 H 6 productivity is the highest with good regenerability in dynamic separation. • Theoretical calculations and control experiments confirm the separation mechanism. It is an extremely challenging task to capture C 3 H 8 from the C 3 H 8 /C 3 H 6 mixture, which requires an adsorbent with a specific pore structure. Herein, an ultramicroporous pillared metal–organic framework Ni(ADC)(TED) 0.5 is reported for efficient C 3 H 8 /C 3 H 6 separation. Theoretical calculations revealed that the ADC ligand may form a splint-like pore confinement structure induced by the introduction of guest molecules to construct a propane-trap in the framework. As a result, excellent separation performance for C 3 H 8 /C 3 H 6 is obtained. A record-high IAST-predicted selectivity (6.4), C 3 H 8 /C 3 H 6 uptake ratio (111.0%), C 3 H 8 Henry constant (2159.2 mmol g −1 bar −1 ), and separation potential (1943.0 mmol L -1 ) exceed those in porous adsorbents reported so far. Breakthrough experiments indicate that Ni(ADC)(TED) 0.5 can completely separate C 3 H 8 /C 3 H 6 mixture with the highest C 3 H 6 productivity (0.085 mmol g −1 ) and good regenerability. These results show that this material has great potential application in C 3 H 8 /C 3 H 6 separation.

Molecular Dynamics Simulations of the Breathing Phase Transition of MOF Nanocrystallites II: Explicitly Modeling the Pressure Medium.

One of the most investigated properties of porous crystalline metal-organic frameworks (MOFs) is their potential flexibility to undergo large changes in unit cell size upon guest adsorption or other stimuli, referred to as “breathing”. Computationally, such phase transitions are usually investigated using periodic boundary conditions, where the system’s volume can be controlled directly. However, we have recently shown that important aspects like the formation of a moving interface between the open and the closed pore form or the free energy barrier of the first-order phase transition and its size effects can best be investigated using non-periodic nanocrystallite (NC) models [Keupp et al. (Adv. Theory Simul., 2019, 2, 1900117)]. In this case, the application of pressure is not straightforward, and a distance constraint was used to mimic a mechanical strain enforcing the reaction coordinate. In contrast to this prior work, a mediating particle bath is used here to exert an isotropic hydrostatic pressure on the MOF nanocrystallites. The approach is inspired by the mercury nanoporosimetry used to compress flexible MOF powders. For such a mediating medium, parameters are presented that require a reasonable additional numerical effort and avoid unwanted diffusion of bath particles into the MOF pores. As a proof-of-concept, NCs of pillared-layer MOFs with different linkers and sizes are studied concerning their response to external pressure exerted by the bath. By this approach, an isotropic pressure on the NC can be applied in analogy to corresponding periodic simulations, without any bias for a specific mechanism. This allows a more realistic investigation of the breathing phase transformation of a MOF NC and further bridges the gap between experiment and simulation.

A new pillared-layer metal-organic framework for gas adsorption and Fe3+ ion detection

Herein, based on single organic ligand as bridging linker and metal trimer as structural nodes, one new pillared-layer metal–organic framework (MOF), Zn3(TDC)4·2DMA (TDC = 2,5-Thiophenedicarboxylic acid, DMA = dimethylamine), has been synthesized and structurally characterized. The pillared-layer architecture is formed by Zn3(TDC)2 layer and pillared TDC ligand where TDC ligand acts as a bifunctional linker. Porous structure of MOF was investigated with potential applications in gas molecule adsorption and metal ion fluorescence sensor.

Investigation of CO2 Orientational Dynamics through Simulated NMR Line Shapes*.

The dynamics of carbon dioxide in third generation (i. e., flexible) Metal‐Organic Frameworks (MOFs) can be experimentally observed by 13C NMR spectroscopy. The obtained line shapes directly correlate with the motion of the adsorbed CO2, which in turn are readily available from classical molecular dynamics (MD) simulations. In this article, we present our publicly available implementation of an algorithm to calculate NMR line shapes from MD trajectories in a matter of minutes on any current personal computer. We apply the methodology to study an effect observed experimentally when adsorbing CO2 in different samples of the pillared layer MOF Ni2(ndc)2(dabco) (ndc=2,6‐naphthalene‐dicarboxylate, dabco=1,4‐diazabicyclo‐[2.2.2]‐octane), also known as DUT‐8(Ni). In 13C NMR experiments of adsorbed CO2 in this MOF, small (rigid) crystals result in narrower NMR line shapes than larger (flexible) crystals. The reasons for the higher mobility of CO2 inside the smaller crystals is unknown. Our ligand field molecular mechanics simulations provide atomistic insight into the effects visible in NMR experiments with limited computational effort.

Mechanochemical synthesis of three-component metal-organic frameworks for large scale production

Two pillared-layer metal-organic frameworks with pcu network were synthesized by the mechanochemical reaction of three components (ZnO, 3-amino-1,2,4-triazole (Hatz) or 3,5-diamino-1,2,4-triazole (Hdatz), and isophthalic acid (H2ipa) at room temperature with space-time yield up to 4800 ​kgm−3 day−1. The mechanochemically-synthesized [Zn2(atz)2(ipa)] (Zn-atz-ipa) and [Zn2(datz)2(ipa)] (Zn-datz-ipa) exhibit the high purity and porosity with BET surface areas of 655 and 572 m2g-1 respectively, which are comparable with those synthesized by the traditional solvothermal method. In C2H4/C2H6 (v/v ​= ​1/1) breakthrough experiment, Zn-datz-ipa can preferentially adsorb C2H6 over C2H4, showing a great potential for one-step purification of C2H4. In addition, this mechanochemical method can be scaled up to 100 ​mmol magnitude with single-pass production up to 20.0 ​g.

The Effect of Amine-Functional Group on Heavy Metal Ion Detection of a Cu-Based Metal-Organic Framework

Owing to their enriched host-guest chemistry and high porosity, metal-organic frameworks ‎‎(MOFs) applied extensively in the detection of a large variety of hazardous chemicals, ‎especially metal ions, using different instrumental methods, such as photoluminescence. In this ‎study, two pillar-layered MOFs, [Cu2(BDC)2(DABCO)] and its amine-functionalized ‎isostructure, [Cu2(NH2-BDC)2(DABCO)], were successfully prepared to highlight the amino ‎group role in the metal ions sensing via exploiting photoluminescence-based method. These ‎materials could recognize copper(II) cations efficiently by changing the luminescent response ‎in less than 20 minutes. With increasing the concentration of Cu(II) solution, first, the ‎luminescent response changes occurred intensely, then equilibrium was reached and no more ‎changes were observed. In the presence of other metal cations, the sensors almost recognized ‎the analyte selectively. At the end of the experimental tests, the reasonable mechanism of ‎sensing was proposed using FTIR spectroscopy and PXRD patterns. They confirmed that the ‎introduction of analyte does not collapse the structure, so just the chemical interaction between ‎the walls of pores and Cu(II) ions are responsible for the purposed application.‎