Robust Metal-organic Framework Research Articles

Bridging Atom Engineering for Low‐Temperature Oxygen Activation in a Robust Metal–Organic Framework

AbstractAchieving active site engineering at the atomic level poses a significant challenge in the design and optimization of catalysts for energy‐efficient catalytic processes, especially for a reaction with two reactants competitively absorbed on catalytic active sites. Herein, we show an example that tailoring the local environment of cobalt sites in a robust metal–organic framework through substituting the bridging atom from −Cl to −OH group leads to a highly active catalyst for oxygen activation in an oxidation reaction. Comprehensive characterizations reveal that this variation imparts drastic changes on the electronic structure of metal centers, the competitive reactant adsorption behavior, and the intermediate formation. As a result, exceptional low‐temperature CO oxidation performance was achieved with T25(Temperature for 25 % conversion)=35 °C and T100 (Temperature for 100 % conversion)=150 °C, which stands out from existing MOF‐based catalysts and even rivals many noble metal catalysts. This work provides a guidance for the rational design of catalysts for efficient oxygen activation for an oxidation reaction.

Bridging Atom Engineering for Low-Temperature Oxygen Activation in a Robust Metal-Organic Framework.

Achieving active site engineering at the atomic level poses a significant challenge in the design and optimization of catalysts for energy-efficient catalytic processes, especially for a reaction with two reactants competitively absorbed on catalytic active sites. Herein, we show an example that tailoring the local environment of cobalt sites in a robust metal-organic framework through substituting the bridging atom from -Cl to -OH group leads to a highly active catalyst for oxygen activation in an oxidation reaction. Comprehensive characterizations reveal that this variation imparts drastic changes on the electronic structure of metal centers, the competitive reactant adsorption behavior, and the intermediate formation. As a result, exceptional low-temperature CO oxidation performance was achieved with T25(Temperature for 25 % conversion)=35 °C and T100 (Temperature for 100 % conversion)=150 °C, which stands out from existing MOF-based catalysts and even rivals many noble metal catalysts. This work provides a guidance for the rational design of catalysts for efficient oxygen activation for an oxidation reaction.

A Robust Pyrazolate Metal-Organic Framework for Efficient Catalysis of Dehydrogenative C-O Cross Coupling Reaction.

Construction of robust heterogeneous catalysts with atomic precision is a long-sought pursuit in the catalysis field due to its fundamental significance in taming chemical transformations. Herein, we present the synthesis of a single-crystalline pyrazolate metal-organic framework (MOF) named PCN-300, bearing a lamellar structure with two distinct Cu centers and one-dimensional (1D) open channels when stacked. PCN-300 exhibits exceptional stability in aqueous solutions across a broad pH range from 1 to 14. In contrast, its monomeric counterpart assembled through hydrogen bonding displays limited stability, emphasizing the role of Cu-pyrazolate coordination bonds in framework robustness. Remarkably, the synergy of the 1D open channels, excellent stability, and the active Cu-porphyrin sites endows PCN-300 with outstanding catalytic activity in the cross dehydrogenative coupling reaction to form the C-O bond without the "compulsory" ortho-position directing groups (yields up to 96%), outperforming homogeneous Cu-porphyrin catalysts. Moreover, PCN-300 exhibits superior recyclability and compatibility with various phenol substrates. Control experiments reveal the synergy between the Cu-porphyrin center and framework in PCN-300 and computations unveil the free radical pathway of the reaction. This study highlights the power of robust pyrazolate MOFs in directly activating C-H bonds and catalyzing challenging chemical transformations in an environmentally friendly manner.

New Architecture Based on Metal-Organic Frameworks and Spin Crossover Complexes to Detect Volatile Organic Compounds.

We present here the encapsulation of a spin crossover complex C1 [FeII(L)] (L: 4-amino-, 2-(2-pyridinylmethylene)hydrazide) inside MOF-808(Zr), a chemically robust Metal-Organic Framework. The compound C1⊂MOF-808 retains its crystallinity as well as a partial porosity compared to pristine MOF and shows solvatochromism under Volatile Organic compounds (VOCs) sorption associated to a spin state change of the guest complex. More specifically, this compound shows an interesting reversible color change under formaldehyde and formic acid vapor sorption and can therefore be considered as a new kind of optical VOCs chemosensor, opening new doors for developing a broad range of VOCs optical sensors.

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.

A robust metal–organic framework for simultaneous C2H4/C3H6 capture and C2H2/CO2 separation

Simultaneously capturing and separating high-purity C2H4 and C3H6 from cracked gas mixtures presents a significant challenge. Herein, a robust metal–organic framework (Cu(BF4)2(4-DPDS)2) was designed featuring a gourd-shaped one-dimensional channel. Its specific alkenes match structure can only adsorb alkenes while completely excluding alkanes. With a remarkable adsorption selectivity of 76,203 for equimolar C2H4/C2H6 and high selectivity of 159 for equimolar C3H6/C3H8, Cu(BF4)2(4-DPDS)2 not only achieves >99 % purity separation of C2H4 and C3H6 from binary mixtures but also simultaneously captures and separates these compounds from seven-component cracking gases at ambient conditions. Its performance stability remains intact even under 75 % RH conditions, thanks to its robust framework. Based on the particular gourd-shaped channel, it can also achieve efficient C2H2/CO2 separation. Ab initio Molecular Dynamics simulations demonstrate the dynamic diffusion process of gas molecules in the structure, and in situ infrared analyses reveal the framework's rich C-H•••F and S•••π binding sites with C2H4 and C3H6. This material's robust structure, exceptional alkene sieving capabilities, and repeatable separation performance comprehensively showcase Cu(BF4)2(4-DPDS)2 as a unique metal–organic framework for simultaneous recognition and capture of C2H4 and C3H6.

Light-driven anisotropy of 2D metal-organic framework single crystal for repeatable optical modulation

Structural transformations of metal-organic frameworks (MOFs) go through a complex energy landscape with multiple intermediate states. Although the transformations allow controlling the functional properties of the MOFs, an imbalance between MOF flexibility and rigidity sets a fundamental barrier to achieving fast and multiple transformations. Here, we study the stimuli-responsive structural transformation in a 2D MOF assembled from paddle-wheel secondary building units joined by a semi-flexible organic ligand with 1,2,4-triazole and carboxylate groups with a rigid adamantane cage between them. The structure results in a distinctive combination of MOF flexibility and rigidity, thus, facilitating a continuous transformation driven by laser light. We reveal the laser-induced anisotropic thermal expansion nature of such transformation, initiating optical changes of the 2D MOF. The latter is utilized for fast and highly repeatable optical modulation of over 10,000 cycles. The endurance of such a 2D MOF-based optical modulator during 1 year of storage at ambient conditions paves the way to design tunable and robust MOFs for diverse applications.

Exploring the Role of Ligand Connectivity in MOFs Mechanical Stability: The Case of MIL-100(Cr).

The key parameters governing the mechanical stability of highly porous materials such as metal-organic frameworks (MOFs) are yet to be clearly understood. This study focuses on the role of the linker connectivity by investigating the mechanical stability of MIL-100(Cr), a mesoporous MOF with a hierarchical structure and a tritopic linker, and comparing it to MIL-101(Cr) having instead a ditopic linker. Using synchrotron X-ray diffraction and infrared spectroscopy, we investigate the high-pressure behavior of MIL-100(Cr) with both solid and fluid pressure transmitting media (PTM). In the case of a solid medium, MIL-100(Cr) undergoes amorphization at about 0.6 GPa, while silicone oil as a PTM delays amorphization until 12 GPa due to the fluid penetration into the pores. Both of these values are considerably higher than those of MIL-101(Cr). MIL-100(Cr) also exhibits a bulk modulus almost ten times larger than that of MIL-101(Cr). This set of results coherently proves the superior stability of MIL-100(Cr) under compression. We ascribe this to the higher connectivity of the organic linker in MIL-100(Cr), which enhances its interconnection between the metal nodes. These findings shed light on the importance of linker connectivity in the mechanical stability of MOFs, a relevant contribution to the quest for designing more robust MOFs.

Efficient carbon dioxide capture from flue gas and natural gas by a robust metal–organic framework with record selectivity and excellent granulation performance

The design of porous materials for CO2 capture from flue gas and natural gas is highly demanded. However, it is challenging to target materials that combine high CO2 capacity and CO2 selectivity. In this work, we report a robust metal–organic framework (MOF) Zn-ox-mtz with one dimensional channels and narrow windows for excellent CO2 capture from CO2/N2 (simulated flue gas) and CO2/CH4 (simulated natural gas) with high selectivity. Zn-ox-mtz exhibits a high CO2 capacity (58.0 STP cm3 g−1 at 15 kPa), excellent CO2/N2 (15/85, S > 106) and CO2/CH4 (50/50, S > 105) selectivity and good chemical stability. In addition, the practical separation performance is demonstrated by breakthrough experiments under various process conditions. A efficient separation is achieved with the impressive CO2 capacity of 2.60 ± 0.12 mmol g−1 at 298 K. Importantly, the outstanding performance is sustained under high humidity. The molecular sieving mechanism investigated by theoretical calculations indicated that CO2 with small molecular size is tightly trapped by multiple C = O···H-C hydrogen bonding and O = C···O forces in the cavity while CH4 and N2 with larger molecular size display overlarge energy barrier to cross the contract pore windows. Moreover, the granulation of Zn-ox-mtz by hydroxypropyl cellulose is realized with high MOF loading (93.8 %) and the granulated Zn-ox-mtz beads retained the excellent CO2/N2 and CO2/CH4 separation performance.

Chiral Reticular Chemistry: A Tailored Approach Crafting Highly Porous and Hydrolytically Robust Metal-Organic Frameworks for Intelligent Humidity Control.

Control of humidity within confined spaces is critical for maintaining air quality and human well-being, with implications for environments ranging from international space stations and pharmacies to granaries and cultural relic preservation sites. However, existing techniques rely on energy-intensive electrically driven equipment or complex temperature and humidity control (THC) systems, resulting in imprecision and inconvenience. The development of innovative techniques and materials capable of simultaneously meeting the stringent requirements of practical applications holds the key to creating intelligent and energy-efficient humidity control devices. In this study, we introduce chiral reticular chemistry as a tailored synthetic approach, targeting a highly porous hea topological framework characterized by intrinsic interpenetrating pore architecture. This groundbreaking design successfully circumvents the traditional compromise between the pore volume and hydrolytic stability. Our metal-organic framework (MOF) exhibits an extraordinary working capacity, setting a new record at 1.35 g g-1 within the relative humidity (RH) range of 40-60%, without exhibiting hysteresis. Consequently, it emerges as a state-of-the-art candidate for intelligent humidity regulation within confined spaces. Utilizing single-crystal X-ray measurements and molecular simulations, we unequivocally elucidate the mechanism of water clustering and pore filling, underscoring the pivotal role of the linker functionality in governing the water seeding process. Our findings represent a significant advancement in the field, paving the way for the development of highly efficient humidity control technologies and offering promising solutions for diverse real-world scenarios.

Robust metal-organic framework catalysts for important reactions of industrial interest

Robust metal-organic framework catalysts for important reactions of industrial interest

Confinement of p‐Xylene in the Pores of a Bilanthanide Metal–Organic Framework for Highly Selective Recognition

AbstractThe rapid and accurate sensing of p‐xylene, an essential raw material with a multi‐billion‐dollar market, in xylene mixture is of great significance in industry; however, the highly similar molecular structures, energy levels, and spectral characteristics of xylene isomers make the selective recognition extremely challenging. Metal–organic frameworks (MOFs) exhibiting tailorable pores and potential binding sites provide prospects for xylene sensing but a comprehensive understanding of the pore effect is still elusive, primarily due to the intricacies involved in the sensing process. Herein, we reported a robust bilanthanide MOF NKU‐999‐EuTb with precisely engineered pores to accommodate p‐xylene, of which the binding sites were confirmed by single crystal X‐ray diffraction and dynamic magnetic susceptibilities. NKU‐999‐EuTb exhibits high‐performance in selective recognition for p‐xylene towards its isomers. Through a systematical study, it was revealed that absorbing p‐xylene into the pores governs the sensing performance. This work provides insights for developing advanced sensing materials for complex isomers.

Confinement of p-Xylene in the Pores of a Bilanthanide Metal-Organic Framework for Highly Selective Recognition.

The rapid and accurate sensing of p-xylene, an essential raw material with a multi-billion-dollar market, in xylene mixture is of great significance in industry; however, the highly similar molecular structures, energy levels, and spectral characteristics of xylene isomers make the selective recognition extremely challenging. Metal-organic frameworks (MOFs) exhibiting tailorable pores and potential binding sites provide prospects for xylene sensing but a comprehensive understanding of the pore effect is still elusive, primarily due to the intricacies involved in the sensing process. Herein, we reported a robust bilanthanide MOF NKU-999-EuTb with precisely engineered pores to accommodate p-xylene, of which the binding sites were confirmed by single crystal X-ray diffraction and dynamic magnetic susceptibilities. NKU-999-EuTb exhibits high-performance in selective recognition for p-xylene towards its isomers. Through a systematical study, it was revealed that absorbing p-xylene into the pores governs the sensing performance. This work provides insights for developing advanced sensing materials for complex isomers.

Photocatalytic Dehalogenative Deuteration of Halides over a Robust Metal–Organic Framework

AbstractDeuterium labelling of organic compounds is an important process in chemistry. We report the first example of photocatalytic dehalogenative deuteration of both arylhalides and alkylhalides (40 substrates) over a metal–organic framework, MFM‐300(Cr), using CD3CN as the deuterium source at room temperature. MFM‐300(Cr) catalyses high deuterium incorporation and shows excellent tolerance to various functional groups. Synchrotron X‐ray powder diffraction reveals the activation of halogenated substrates via confined binding within MFM‐300(Cr). In situ electron paramagnetic resonance spectroscopy confirms the formation of carbon‐based radicals as intermediates and reveals the reaction pathway. This protocol removes the use of precious‐metal catalysts from state‐of‐the‐art processes based upon direct hydrogen isotope exchange and shows high photocatalytic stability, thus enabling multiple catalytic cycles.

Photocatalytic Dehalogenative Deuteration of Halides over a Robust Metal-Organic Framework.

Deuterium labelling of organic compounds is an important process in chemistry. We report the first example of photocatalytic dehalogenative deuteration of both arylhalides and alkylhalides (40 substrates) over a metal-organic framework, MFM-300(Cr), using CD3 CN as the deuterium source at room temperature. MFM-300(Cr) catalyses high deuterium incorporation and shows excellent tolerance to various functional groups. Synchrotron X-ray powder diffraction reveals the activation of halogenated substrates via confined binding within MFM-300(Cr). In situ electron paramagnetic resonance spectroscopy confirms the formation of carbon-based radicals as intermediates and reveals the reaction pathway. This protocol removes the use of precious-metal catalysts from state-of-the-art processes based upon direct hydrogen isotope exchange and shows high photocatalytic stability, thus enabling multiple catalytic cycles.

A ROS reservoir based on a polyoxometalate and metal-organic framework hybrid for efficient bacteria eradication and wound healing

Infections by bacteria always post significant challenges to global human health. Recent developed non-antibiotic treatment, such as using metal–organic frameworks (MOFs) to kill bacteria by generating reactive oxygen species (ROS) represents a promising strategy. However, drawbacks including low efficiencies of ROS generation and high concentrations of toxic metal ions released always exist. We have creatively designed a robust polyoxometalate (POM) and MOF hybrid (denoted as CuPOM-MOF@S) that functions as an efficient catalytic reservoir for cascaded generation of ROS (mainly ·OH) from H2O2 thus eradicating bacteria and enhancing wound healing at an administration dosage as low as 5 μg∙mL−1. The remarkable antibacterial capability surpasses those for most MOF-based materials reported thus far, which is mainly attributed to the reservation of massive catalytic copper ions, the synergistic effect regarding catalytic activity between MOFs and Keggin-type POMs as well as its bacteria-capturing ability by the coated surfactants. Its biological safety is investigated and confirmed by cell cytotoxicity and body weight assessment. This work presents a prospective strategy towards cascaded ROS generation by combining inorganic catalytic POMs with MOFs thus for multiple biomedical applications including treating bacterial infections and cancer as well as inducing biological signal responses.

Interpenetrated Robust Metal–Organic Framework with Urea-Functionality-Decked Pores for Selective and Ultrasensitive Detection of Antibiotics and Oxo-anions

Interpenetrated Robust Metal–Organic Framework with Urea-Functionality-Decked Pores for Selective and Ultrasensitive Detection of Antibiotics and Oxo-anions

Exquisitely Constructing a Robust MOF with Dual Pore Sizes for Efficient CO2 Capture.

Developing metal-organic framework (MOF) adsorbents with excellent performance and robust stability is of critical importance to reduce CO2 emissions yet challenging. Herein, a robust ultra-microporous MOF, Cu(bpfb)(bdc), with mixed ligands of N, N'-(1,4-phenylene)diisonicotinamide (bpfb), and 1,4-dicarboxybenzene (bdc) was delicately constructed. Structurally, this material possesses double-interpenetrated frameworks formed by two staggered, independent frameworks, resulting in two types of narrow ultra-micropores of 3.4 × 5.0 and 4.2 × 12.8 Å2, respectively. The above structural properties make its highly selective separation at 273~298 K with a CO2 capacity of 71.0~86.2 mg/g. Its adsorption heat over CO2 and IAST selectivity were calculated to be 27 kJ/mol and 52.2, respectively. Remarkably, cyclic breakthrough experiments corroborate its impressive performance in CO2/N2 separation in not only dry but also 75% RH humid conditions. Molecular simulation reveals that C-H···OCO2 in the pores plays a pivotal role in the high selectivity of CO2 adsorption. These results point out the huge potential application of this material for CO2/N2 separation.

Enhanced carbon capture with motif-rich amino acid loaded defective robust metal-organic frameworks

Enhanced carbon capture with motif-rich amino acid loaded defective robust metal-organic frameworks

Topological Design of Unprecedented Metal-Organic Frameworks Featuring Multiple Anion Functionalities and Hierarchical Porosity for Benchmark Acetylene Separation.

Separation of acetylene (C2 H2 ) from carbon dioxide (CO2 ) or ethylene (C2 H4 ) is industrially important but still challenging so far. Herein, we developed two novel robust metal organic frameworks AlFSIX-Cu-TPBDA (ZNU-8) with znv topology and SIFSIX-Cu-TPBDA (ZNU-9) with wly topology for efficient capture of C2 H2 from CO2 and C2 H4 . Both ZNU-8 and ZNU-9 feature multiple anion functionalities and hierarchical porosity. Notably, ZNU-9 with more anionic binding sites and three distinct cages displays both an extremely large C2 H2 capacity (7.94 mmol/g) and a high C2 H2 /CO2 (10.3) or C2 H2 /C2 H4 (11.6) selectivity. The calculated capacity of C2 H2 per anion (4.94 mol/mol at 1 bar) is the highest among all the anion pillared metal organic frameworks. Theoretical calculation indicated that the strong cooperative hydrogen bonds exist between acetylene and the pillared SiF6 2- anions in the confined cavity, which is further confirmed by in situ IR spectra. The practical separation performance was explicitly demonstrated by dynamic breakthrough experiments with equimolar C2 H2 /CO2 mixtures and 1/99 C2 H2 /C2 H4 mixtures under various conditions with excellent recyclability and benchmark productivity of pure C2 H2 (5.13 mmol/g) or C2 H4 (48.57 mmol/g).