Microporous Framework Research Articles

Post-Assembly Modification of Homochiral Titanium-Organic Cages for Recognition and Separation of Molecular Isomers.

A chiral metal-organic cage (MOC) was extended and fixed into a porous framework using a post-assembly modification strategy, which made it easier to study the host-guest chemistry of the solid-state MOC using a single-crystal diffraction technique. Anionic Ti4 L6 (L=embonate) cage can be used as a 4-connecting crystal engineering tecton, and its optical resolution was achieved, thus homochiral ΔΔΔΔ- and ΛΛΛΛ-[Ti4 L6 ] cages were obtained. Accordingly, a pair of homochiral cage-based microporous frameworks (PTC-236(Δ) and PTC-236(Λ)) were easily prepared by a post-assembly reaction. PTC-236 has rich recognition sites provided by the Ti4 L6 moieties, chiral channels and high framework stability, affording a single-crystal-to-single-crystal transformation for guest structure analyses. Thus it was successfully utilized for the recognition and separation of isomeric molecules. This study provides a new approach for the orderly combination of well-defined MOCs into functional porous frameworks.

Fabrication of 3D-interconnected microporous carbon decorated with microspheres for highly efficient hydrogen evolution reactions

Hydrogen generation via water electrolysis is of significant importance owing to its high efficiency, low cost, and sustainability. Herein, we propose a simple and low-cost technique for fabricating three-dimensional interconnected microporous carbon frameworks (MCFs) decorated with avalanches of microspheres for highly efficient hydrogen evolution reactions (HERs). The MCF electrode was fabricated via carbonization of a furan precursor, which was prepared by mixing a furan resin and table sugar. Although we aimed to develop a method for fabricating the MCF, we also discovered numerous accidental carbon microspheres on the sidewalls of the framework, which play a significant role in HER catalysis. We also confirmed the formation of microspheres at the interface between the furan resin and the sugar particles. The HER activity of the MCF electrode was evaluated in an alkaline solution and compared with that of commercially available nickel, nickel foam, and state-of-the-art Pt electrodes. The microporous carbon with a large pore size outperformed all electrodes except the Pt electrode, exhibiting a stable HER activity with an onset potential of 64 mV (vs. reversible hydrogen electrode (RHE)) and a current density of 10 mA/cm2 at −143 mV (vs. RHE). The HER performance of the large pore size carbon electrode was superior to that of other heteroatom-doped carbon electrocatalysts and is compatible with that of metallic electrocatalysts. The superior HER performance of the large pore size carbon electrode can be attributed to the unique microspheres, which provide an abundance of active sites for efficient water splitting.

Encapsulation of Redox p-Benzoquinone into Microporous Carbon Frameworks by a Diamine Covalent-Grafted Strategy for Aqueous Hybrid Supercapacitors

Aqueous hybrid supercapacitors (AHSs) with a wide operating voltage and intrinsic safety are emerging as promising energy storage devices, while their energy densities are still greatly restricted by carbon-based negative electrodes. Developing a high-performance redox system for carbon electrodes is one of the potential strategies to realize the practical utilization of AHSs. Herein, we present a covalent-grafted strategy to encapsulate redox p-benzoquinone (PBQ) into microporous carbon frameworks by using p-phenylenediamine (PPD) as a bridging agent. Both experimental and theoretical analysis reveal that the diamine groups from PPD play a vital role in chemically bonding PBQ with the microporous surfaces of carbon materials, which deliver a great deal of electronic delocalization throughout the redox-active sites and conductive carbon regions. As such, the obtained carbon electrodes grafted by the redox PBQ and PPD species facilitate charge transfer and consequently exhibit excellent charge storage performances. These are highlighted by an extremely high specific capacitance of 377 F g–1 at a current density of 0.5 A g–1 and 276 F g–1 at 100 A g–1 with a superior rate capability of 73%. Impressively, the assembled AHSs based on covalently grafted carbon electrodes (AC-PPD-PBQ) and NiCoAl-layered double hydroxides/carbon nanotubes (NiCoAl-LDH@CNT) demonstrate a maximum energy density of 70.9 W h kg–1 with a wide voltage window of 1.8 V and good cycling stability with 84.4% of initial capacitance after 5000 cycles. This work provides insights into the fabrication of high-performance carbon electrodes by encapsulating redox species into microporous frameworks.

A COF-coated ordered porous framework as multifunctional polysulfide barrier towards high-performance lithium-sulfur batteries

The practical application of lithium-sulfur batteries (LSBs) is still hindered by the shuttle effect of lithium polysulfides (LiPS) and slow sulfur conversion kinetics. Herein, a LiPS inhibited covalent organic framework (COF)-coated conductive porous metal oxide design strategy is proposed towards the development of efficient and durable sulfur cathode in LSBs. This strategy is demonstrated by coating a TpPa-1 COF layer on cobalt-decorated titanium oxynirtide (TiOxNy) with a three-dimensional ordered microporous framework (3DOM) structure. In this strategy, the oxygen-deficient TiOxNy framework ensures a good conductivity and structural stability of the cathode during the charge/discharge process. The 3DOM macrospores provide a high capacity for sulfur accommodation and exposes active interfaces, whereas the coated TpPa-1 COF featured with ultrafine microspore offer an effective confinement of LiPS within the 3DOM framework, mitigating its shuttling effect. At the same time, the Co embedded in 3DOM TiOxNy servers as efficient catalyst promoting the sulfur electrochemical reaction. Attributed to these structural superiorities, the 3DOM TpPa-1@Co/TiOxNy/S cathode exhibits excellent performance even under high sulfur loading and low electrolyte condition. This work of using microporous COF coating with conductive macroporous metal oxides offers an effective alternative strategy for the design of practical sulfur battery.

Active Separation of Water Isotopologues by Local Molecular Motion in Microporous Framework Materials.

Around 10-15 % of the world's energy consumption is accounted for by the separation and purification of chemicals. Among them is the enrichment and separation of isotopologues which are an essential aspect of modern chemistry. In their recent work, Su et al. demonstrate the separation of water isotopologues by responsive dynamic pore windows in a microporous coordination polymer with unprecedented selectivity based on an elegant mechanism.

Active Separation of Water Isotopologues by Local Molecular Motion in Microporous Framework Materials

AbstractAround 10–15 % of the world's energy consumption is accounted for by the separation and purification of chemicals. Among them is the enrichment and separation of isotopologues which are an essential aspect of modern chemistry. In their recent work, Su et al. demonstrate the separation of water isotopologues by responsive dynamic pore windows in a microporous coordination polymer with unprecedented selectivity based on an elegant mechanism.

Ordered Macro-Microporous Single Crystals of Covalent Organic Frameworks with Efficient Sorption of Iodine.

Fashioning microporous covalent organic frameworks (COFs) into single crystals with ordered macropores allows for an effective reduction of the mass transfer resistance and the maximum preservation of their intrinsic properties but remains unexplored. Here, we report the first synthesis of three-dimensional (3D) ordered macroporous single crystals of the imine-linked 3D microporous COFs (COF-300 and COF-303) via a template-assisted modulated strategy. In this strategy, COFs crystallized within the sacrificial colloidal crystal template, assembled from monodisperse polystyrene microspheres, and underwent an aniline-modulated amorphous-to-crystalline transformation to form large single crystals with 3D interconnected macropores. The effects of the introduced macroporous structure on the sorption performances of COF-300 single crystals were further probed by iodine. Our results indicate that iodine adsorption occurred in micropores of COF-300 but not in the introduced macropores. Accordingly, the iodine adsorption capacity of COF single crystals was governed by their micropore accessibility. The relatively long diffusion path in the non-macroporous COF-300 single crystals resulted in a limited micropore accessibility (48.4%) and thus a low capacity in iodine adsorption (1.48 g·g-1). The introduction of 3D ordered macropores can greatly shorten the microporous diffusion path in COF-300 single crystals and thus render all their micropores fully accessible in iodine adsorption with a capacity (3.15 g·g-1) that coincides well with the theoretical one.

Rücktitelbild: Optimizing Acetylene Sorption through Induced‐fit Transformations in a Chemically Stable Microporous Framework (Angew. Chem. 7/2023)

Rücktitelbild: Optimizing Acetylene Sorption through Induced‐fit Transformations in a Chemically Stable Microporous Framework (Angew. Chem. 7/2023)

Back Cover: Optimizing Acetylene Sorption through Induced‐fit Transformations in a Chemically Stable Microporous Framework (Angew. Chem. Int. Ed. 7/2023)

Back Cover: Optimizing Acetylene Sorption through Induced‐fit Transformations in a Chemically Stable Microporous Framework (Angew. Chem. Int. Ed. 7/2023)

Optimizing Acetylene Sorption through Induced‐fit Transformations in a Chemically Stable Microporous Framework

AbstractDeveloping practical storage technologies for acetylene (C2H2) is important but challenging because C2H2 is useful but explosive. Here, a novel metal–organic framework (MOF) (FJI‐H36) with adaptive channels was prepared. It can effectively capture C2H2 (159.9 cm3 cm−3) at 1 atm and 298 K, possessing a record‐high storage density (561 g L−1) but a very low adsorption enthalpy (28 kJ mol−1) among all the reported MOFs. Structural analyses show that such excellent adsorption performance comes from the synergism of active sites, flexible framework, and matched pores; where the adsorbed‐C2H2 can drive FJI‐H36 to undergo induced‐fit transformations step by step, including deformation/reconstruction of channels, contraction of pores, and transformation of active sites, finally leading to dense packing of C2H2. Moreover, FJI‐H36 has excellent chemical stability and recyclability, and can be prepared on a large scale, enabling it as a practical adsorbent for C2H2. This will provide a useful strategy for developing practical and efficient adsorbents for C2H2 storage.

Optimizing Acetylene Sorption through Induced-fit Transformations in a Chemically Stable Microporous Framework.

Developing practical storage technologies for acetylene (C2 H2 ) is important but challenging because C2 H2 is useful but explosive. Here, a novel metal-organic framework (MOF) (FJI-H36) with adaptive channels was prepared. It can effectively capture C2 H2 (159.9 cm3 cm-3 ) at 1 atm and 298 K, possessing a record-high storage density (561 g L-1 ) but a very low adsorption enthalpy (28 kJ mol-1 ) among all the reported MOFs. Structural analyses show that such excellent adsorption performance comes from the synergism of active sites, flexible framework, and matched pores; where the adsorbed-C2 H2 can drive FJI-H36 to undergo induced-fit transformations step by step, including deformation/reconstruction of channels, contraction of pores, and transformation of active sites, finally leading to dense packing of C2 H2 . Moreover, FJI-H36 has excellent chemical stability and recyclability, and can be prepared on a large scale, enabling it as a practical adsorbent for C2 H2 . This will provide a useful strategy for developing practical and efficient adsorbents for C2 H2 storage.

Stable and microporous covalent organic frameworks via weak interactions for gas uptake

Here, we reported two stable and micro-porous covalent organic frameworks for gas uptake.

Photochemical and gas adsorption studies of Keggin polyoxometalate functionalized porous melamine terephthaldehyde material.

A compound containing a microporous melamine-terephthaldehyde framework is protonated by grinding with acetic acid, resulting in a mesoporous protonated melamine-terephthaldehyde network. The Keggin polyanion [PMo12O40]3- is then immobilized into this protonated melamine-terephthaldehyde network through a solid-state reaction. The polyanion interacts with the protonated microporous organic network through electrostatic interaction. Three different Keggin-melamine-terephthaldehyde materials were synthesized by varying the Keggin anion loading of 10 wt%, 15 wt% and 20 wt%. The Keggin-melamine-terephthaldehyde materials exhibit photochromism on irradiation with sunlight. The photochromism of the POM-organic hybrid material is due to reduction of the Keggin anion. The resulting blue reduced Keggin-melamine-terephthaldehyde materials are oxidized back by treatment with hydrogen peroxide. The N2, CO2 and H2 adsorption properties of all the synthesized materials, including protonated melamine-terephthaldehyde materials, were studied. The materials were characterized by IR, PXRD, DRS, TGA, EPR spectroscopy, and FESEM electron microscopy. The elemental composition was analysed with a CHN analyser and ICP-OES analysis.

Efficient adsorption removal of NO2 by covalent triazine frameworks with fine-tuned binding sites

One promising method for mitigating low-temperature and low-concentration NO 2 pollution is selective adsorption using porous solid materials. However, the corrosive nature of NO 2 renders the development of an adsorbent with high and cyclable NO 2 uptake a formidable challenge. Herein, we attempted to address this challenge by developing a microporous covalent triazine framework (CTF) as effective adsorbents for NO 2 capture, achieving unprecedented high cyclable capacity enabled by simultaneous high adsorbent stability and moderate adsorption affinity via tuning specific binding sites. Using dynamic column breakthrough experiments, we demonstrated that the pristine CTF exhibited a high NO 2 adsorption capacity (dry: 3.83 mmol/g; wet: 5.26 mmol/g) overtaking most reported solid adsorbents, thanks to abundant active sites (e.g., nitrogen/carbon/triazine rings). Post-synthesis converted the surface nitrogen to protonated nitrogen site and further to transition metal site affording more effective binding sites that allows for moderately strong adsorption, resulting in elevated NO 2 adsorption capacity (dry: 6.11 mmol/g; wet: 8.97 mmol/g) and a highest reversible NO 2 adsorption (retaining 91% and 64% at dry and wet conditions after five cycles, respectively), as illustrated by our mechanistic study using in-situ DRIFTS and DFT calculations. This work affords not only promising adsorbents for real-world applications in mitigating NO 2 pollution, but also a strategy of developing robust adsorbents with desired affinity generally applicable to adsorptive capture of corrosive and toxic gases. • Covalent triazine frameworks (CTFs) were firstly demonstrated as effective NO 2 adsorbents with highly reversible capacity. • Various active bindings sites were rationally introduced to CTFs via postsynthesis. • The functionalized CTFs exhibited the highest cyclable NO 2 capacity (5.74 mmol/g after 5 th cycle) to date. • Combined in situ DRIFTS and DFT calculations revealed the NO 2 adsorption mechanism.

Construction of microporous covalent organic frameworks for high gas uptake capacities

Covalent organic frameworks (COFs) show excellent stability, high porosity, and a designable skeleton, making them an ideal platform for gas capture.

Molecular dissolution behaviors on porous membrane surface using hierarchical metal–organic framework lamellar membrane

AbstractLamellar membranes, especially assembled by microporous framework nanosheets, have excited interest for fast molecular permeation. However, the underlying molecular dissolution behaviors on membrane surface, especially at pore entrances, remain unclear. Here, hierarchical metal–organic framework (MOF) lamellar membranes with 7 nm‐thick surface layer and 553 nm‐thick support layer are prepared. Hydrophilic (–NH2) or hydrophobic (–CH3) groups are decorated at pore entrances on surface layer to manipulate wettability, while –CH3 groups on support layer provide comparable, low‐resistance paths. We demonstrate that molecular dissolution behaviors are determined by molecule–molecule and molecule–pore interactions, derived from intrinsic parameters of molecule and membrane. Importantly, two dissolution model equations are established: for hydrophobic membrane surface, dissolution activation energy (ES) obeys ES = Kmln[(γL‐γC)μd2], while turns to ES=Kaln[(γL‐γC)δeμd2] for hydrophilic one. Particularly, hydrophilic pore entrances exert strong interaction with polar molecules, thus compensating the energy consumed by molecule rearrangement, giving fast permeation (>270 L m−2 h−1 bar−1).

Atomic Mechanisms of Cation Adsorption/Exchange in Octahedral Molecular Sieves.

Octahedral molecular sieves (OMSs) based on MnO2 have been widely studied in the fields of deionization, geochemistry, and energy storage due to their microporous tunnel framework capable of adsorbing and exchanging various ions, particularly cations. The understanding of cation adsorption/exchange within OMS tunnels demands atomic-scale exploration, which has been scarcely reported. Here, we disclose how various cations (K+/Ag+/Na+) interplay within the OMS tunnel space on an atomic scale. Not only are the lattice sites for each adsorbed cation species pinpointed but the scenario of dual-cation adsorption within single tunnels is also demonstrated, together with the discovery of characteristic concentration-dependent cation ordering. Moreover, compared with the theoretical parent tunnel phase, the heterogeneous tunnels, though sparsely distributed, exhibit a distinct yet orderly cationic accommodation, highlighting the non-negligible role of tunnel heterogeneity in regulating OMS physiochemistry. Our findings clarify the long-existing ambiguities in nano- and atomic-scale science of the ion adsorption process in OMS materials and are expected to inspire their structural/compositional engineering toward functionality enhancement in various fields.

MOF/COF heterostructure hybrid composite-based molecularly imprinted photoelectrochemical sensing platform for determination of dibutyl phthalate: A further expansion for MOF/COF application

A novel metal-organic framework (MOF)/covalent-organic framework (COF) heterostructure hybrid composite (NH2-UiO-66/TpPa-1-COF) with excellent photoactivity was developed, which further acted as the photoelectrochemical sensitized layer of a molecularly imprinted photoelectrochemical (MIP-PEC) sensor for extremely sensitive and selective determination of dibutyl phthalate (DBP). The NH2-UiO-66/TpPa-1-COF was synthesized using a simple one-step solvothermal method, which showed improved photocurrent response owing to heterojunction formation, favorable energy-band configuration and strong light absorption capacity. To improve the sensing performance, molecularly imprinted polymer (MIP) was developed by sol-gel polymerization method as the recognition component of PEC sensor. The specific binding of imprinting sites towards DBP could block the electron transfer, causing decreased photocurrent response of the MIP-PEC sensor. The MIP-PEC sensor showed a wide detection range from 0.1 nmol L−1 to 100 μmol L−1 with a limit of detection of 3.0 × 10−11 mol L−1 under optimal conditions. Meanwhile, the proposed MIP-PEC sensor showed good stability, selectivity, reproducibility, and applicability in real samples. This is the first attempt to apply MOF/COF heterostructure hybrid composite for MIP-PEC sensor construction, providing new insight into the potential applications of microporous crystalline framework heterostructure hybrid composite in the sensing field.

Two Cu(II) microporous frameworks based on a bifunctional linker and selective gas adsorption properties for CO2

Two microporous metal-organic frameworks assembled of Cu(II) ions and bifunctional imidazoly/carboxylate containing organic compound (4-(1H-imidazole-4-yl) benzoate), namely [Cu2(L)4]·DMA·3H2O (1) and [Cu(L)2]·2H2O (2), are structurally characterized. Compound 1 shows 3-fold interpenetrating binodal 4-connected CdSO4 microporous architecture with Point (Schläfli) symbol of (65·8), while complex 2 is a supramolecular framework by stacking in an ···AAA··· configuration from two-dimensional 44 layers with one-dimensional open channels with 11.99 ​× ​11.99 ​Å2. MOF 1 shows selective adsorption capacity for CO2 (32.24 ​cm3/g) over N2 and CH4, while 2 has the uptake of 45.67 ​cm3/g for CO2 and 23.81 ​cm3/g for CH4. The corresponding the heat of adsorption calculated by Clausius–Clapeyron equation are 28.5 and 32.3 ​kJ ​mol−1. The adsorption capacity of CO2 is comparative higher than CH4 and N2, ascribing to the electrostatic interactions between CO2 and narrow pores decorated with uncoordinated imidazoly-N atoms.

A crystalline and stable microporous framework based on the dative B←N bonds

<h2>Summary</h2> The concept of making use of dative boron–nitrogen (B←N) bonds for the construction of microporous crystalline organic framework (BNF) materials has been proposed but not fulfilled, and they have not been fully explored for their diverse functions because of the difficulty to stabilize their pore structures under thermal/vacuum activation. In this study, we report the first such stable crystalline framework in which the single-crystal X-ray structures of the as-synthesized BNF-1, activated BNF-1a, and C₂H₂-loaded BNF-1a have been clearly characterized. Here, the 2D framework sheets of BNF-1 were interlocked with one another, generating the stable and crystalline framework with a Brunauer-Emmett-Teller (BET) surface area of 255 m²/g. Also, the material takes up more C₂H₂ than CO₂ molecules, and breakthrough experiments demonstrate its separation performance for C₂H₂/CO₂ mixtures. The molecular recognition mechanism of this BNF-1 for the preferential binding of C₂H₂ molecules over CO₂ has been comprehensively studied by both single-crystal X-ray diffraction and molecular modeling.