Isoreticular Contraction of Cage-like Metal-Organic Frameworks with Optimized Pore Space for Enhanced C2H2/CO2 and C2H2/C2H4 Separations.

The C2H2 separation from CO2 and C2H4 is of great importance yet highly challenging in the petrochemical industry, owing to their similar physical and chemical properties. Herein, the pore nanospace engineering of cage-like mixed-ligand MFOF-1 has been accomplished via contracting the size of the pyridine- and carboxylic acid-functionalized linkers and introducing a fluoride- and sulfate-bridging cobalt cluster, based on a reticular chemistry strategy. Compared with the prototypical MFOF-1, the constructed FJUT-1 with the same topology presents significantly improved C2H2 adsorption capacity, and selective C2H2 separation performance due to the reduced cage cavity size, functionalized pore surface, and appropriate pore volume. The introduction of fluoride- and sulfate-bridging cubane-type tetranuclear cobalt clusters bestows FJUT-1 with exceptional chemical stability under harsh conditions while providing multiple potential C2H2 binding sites, thus rendering the adequate ability for practical C2H2 separation application as confirmed by the dynamic breakthrough experiments under dry and humid conditions. Additionally, the distinct binding mechanism is suggested by theoretical calculations in which the multiple supramolecular interactions involving C-H···O, C-H···F, and other van der Waals forces play a critical role in the selective C2H2 separation.

Capture Fluorocarbon and Chlorofluorocarbon from Air Using DUT-67 for Safety and Semi-Quantitative Analysis.

Fluoro- and chlorofluorocabons (FC/CFCs) are important refrigerants, solvents, and fluoropolymers in industry while being toxic and carrying high global warming potential. Detection and reclamation of FC/CFCs based on adsorption technology with highly selective adsorbents is important to labor safety and environmental protection. Herein, the study reports an integrated method to combine capture, separation, enrichment, and analysis of representative FC/CFCs (chlorodifluoromethane(R22) and 1,1,1,2-tetrafluoroethane (R134a)) by using the highly stable and porous Zr-MOF, DUT-67. Gas adsorption and breakthrough experiments demonstrate that DUT-67 has high R22/R134a uptake (124/116 cm3 g-1) and excellent R22/R134a/CO2 separation performance (IAST selectivities of R22/CO2 and R134a/CO2 ranging from 51.4 to 33.3, and 31.1 to 25.8), even in rather low concentration and humid conditions. A semi-quantitative analysis protocol is set up to analyze the low concentrations of R22/R134a based on the high selective R22/R134a adsorption ability, fast adsorption kinetics, water-resistant utility, facile regeneration, and excellent recyclability of DUT-67. In situ single-crystal X-ray diffraction, theoretical calculations, and in situ diffuse reflectance infrared Fourier transform spectra have been employed to understand the adsorption mechanism. This work may provide a potential adsorbent for purge and trap technique under room temperature, thus promoting the application of MOFs for VOCs sampling and quantitative analysis.

Anionic Ni-Based Metal-Organic Framework with Li(I) Cations in the Pores for Efficient C2H2/CO2 Separation.

Acetylene (C2H2) is widely used as a raw material for producing various downstream commodities in the petrochemical and electronic industry. Therefore, the acquisition of high-purity C2H2 from a C2H2/CO2 mixture produced by partial methane combustion or thermal hydrocarbon cracking is of great significance yet highly challenging due to their similar physical and chemical properties. Herein, we report an anionic metal-organic framework (MOF) named LIFM-210, which has Li+ cations in the pores and shows a higher adsorption affinity for C2H2 than CO2. LIFM-210 is constructed by a unique tetranuclear Ni(II) cluster acting as a 10-connected node and an organic ligand acting as a 5-connected node. Single-component adsorption and transient breakthrough experiments demonstrate the good C2H2 selective separation performance of LIFM-210. Theoretical calculations revealed that Li+ ions strongly prefer C2H2 to CO2 and are primary adsorption sites, playing vital roles in the selective separation of C2H2/CO2.

A Robust Squarate-Cobalt Metal-Organic Framework for CO2/N2 Separation.

The separation of CO2 from the industrial post-combustion flue gas is of great importance to reduce the increasingly serious greenhouse effect, yet highly challenging due to the extremely high stability, low cost, and high separation performance requirements for adsorbents under the practical operating conditions. Herein, we report a robust squarate-cobalt metal-organic framework (MOF), FJUT-3, featuring an ultra-small 1D square channel decorated with -OH groups, for CO2/N2 separation. Remarkably, FJUT-3 not only has excellent stability under harsh chemical conditions but also presents low-cost property for scale-up synthesis. Moreover, FJUT-3 shows excellent CO2 separation performance under various humid and temperature conditions confirmed by the transient breakthrough experiments, thus enabling FJUT-3 with adequate potentials for industrial CO2 capture and removal. The distinct CO2 adsorption mechanism is well elucidated by theoretical calculations, in which the hierarchical C···OCO2, C-O···CCO2, and O-H···OCO2 interactions play a vital synergistic role in the selective CO2 adsorption process.

Optimized Pore Nanospace through the Construction of a Cagelike Metal-Organic Framework for CO2/N2 Separation.

The development of metal-organic framework (MOF) adsorbents with a potential molecule sieving effect for CO2 capture and separation from flue gas is of critical importance for reducing the CO2 emissions to the atmosphere yet challenging. Herein, a cagelike MOF with a suitable cage window size falling between CO2 and N2 and the cavity has been constructed to evaluate its CO2/N2 separation performance. It is noteworthy that the introduction of coordinated dimethylamine (DMA) and N,N'-dimethylformamide (DMF) molecules not only significantly reduces the cage window size but also enhances the framework-CO2 interaction via C-H···O hydrogen bonds, as proven by molecular modeling, thus leading to an improved CO2 separation performance. Moreover, transient breakthrough experiments corroborate the efficient CO2/N2 separation, revealing that the introduction of DMA and DMF molecules plays a vital role in the separation of a CO2/N2 gas mixture.

High Water Adsorption MOFs with Optimized Pore-Nanospaces for Autonomous Indoor Humidity Control and Pollutants Removal.

The indoor air quality is of prime importance for human daily life and health, for which the adsorbents like zeolites and silica-gels are widely used for air dehumidification and harmful gases capture. Herein, we develop a pore-nanospace post-engineering strategy to optimize the hydrophilicity, water-uptake capacity and air-purifying ability of metal-organic frameworks (MOFs) with long-term stability, offering an ideal candidate with autonomous multi-functionality of moisture control and pollutants sequestration. Through variant tuning of organic-linkers carrying hydrophobic and hydrophilic groups in the pore-nanospaces of prototypical UiO-67, a moderately hydrophilic MOF (UiO-67-4Me-NH2 -38 %) with high thermal, hydrolytic and acid-base stability is screened out, featuring S-shaped water sorption isotherms exactly located in the recommended comfortable and healthy ranges of relative humidity for indoor ventilation (45 %-65 % RH) and adverse health effects minimization (40-60 % RH). Its exceptional attributes of water-uptake working capacity/efficiency, contaminants removal, recyclability and regeneration promise a great potential in confined indoor environment application.

Enhancing Photocatalytic Hydrogen Production via the Construction of Robust Multivariate Ti-MOF/COF Composites.

Titanium metal-organic frameworks (Ti-MOFs), as an appealing type of artificial photocatalyst, have shown great potential in the field of solar energy conversion due to their well-studied photoredox activity (similar to TiO2 ) and good optical responsiveness of linkers, which serve as the antenna to absorb visible-light. Although much effort has been dedicated to developing Ti-MOFs with high photocatalytic activity, their solar energy conversion performances are still poor. Herein, we have implemented a covalent-integration strategy to construct a series of multivariate Ti-MOF/COF hybrid materials PdTCPP⊂PCN-415(NH2 )/TpPa (composites 1, 2, and 3), featuring excellent visible-light utilization, a suitable band gap, and high surface area for photocatalytic H2 production. Notably, the resulting composites demonstrated remarkably enhanced visible-light-driven photocatalytic H2 evolution performance, especially for the composite 2 with a maximum H2 evolution rate of 13.98 mmol g-1 h-1 (turnover frequency (TOF)=227 h-1 ), which is much higher than that of PdTCPP⊂PCN-415(NH2 ) (0.21 mmol g-1 h-1 ) and TpPa (6.51 mmol g-1 h-1 ). Our work thereby suggests a new approach to highly efficient photocatalysts for H2 evolution and beyond.

Nanospace Engineering of Metal-Organic Frameworks through Dynamic Spacer Installation of Multifunctionalities for Efficient Separation of Ethane from Ethane/Ethylene Mixtures.

Herein, a dynamic spacer installation (DSI) strategy has been implemented to construct a series of multifunctional metal-organic frameworks (MOFs), LIFM-61/31/62/63, with optimized pore space and pore environment for ethane/ethylene separation. In this respect, a series of linear dicarboxylic acids were deliberately installed in the prototype MOF, LIFM-28, leading to a dramatically increased pore volume (from 0.41 to 0.82 cm3 g-1 ) and reduced pore size (from 11.1×11.1 Å2 to 5.6×5.6 Å2 ). The increased pore volume endows the multifunctional MOFs with much higher ethane adsorption capacity, especially for LIFM-63 (4.8 mmol g-1 ), representing nearly three times as much ethane as the prototypical counterpart (1.7 mmol g-1 ) at 273 K and 1 bar. Meanwhile, the reduced pore size imparts enhanced ethane/ethylene selectivity of the multifunctional MOFs. Theoretical calculations and dynamic breakthrough experiments confirm that the DSI is a promising approach for the rational design of multifunctional MOFs for this challenging task.

A Flexible-Robust Copper(II) Metal-Organic Framework Constructed from a Fluorinated Ligand for CO2/R22 Capture.

A flexible-robust copper(II) metal-organic framework, denoted as LIFM-100, has been successfully synthesized using a fluorinated linear dicarboxylate to link copper ions. LIFM-100 exhibits a breathing effect, which can transform reversibly between a large form (lp) and a narrow form (np) from single crystal to single crystal. In addition, LIFM-100 shows good thermal and chemical stability. By the introduction of trifluoromethyl functional groups and uncoordinated carboxyl acids, LIFM-100 features a good CO2/R22 adsorption/separation performance at 298 K, showing potential in natural gas purification and CO2/R22 capture.

Dynamic Coordination Chemistry of Fluorinated Zr-MOFs: Synthetic Control and Reassembly/Disassembly Beyond de Novo Synthesis to Tune the Structure and Property.

Known for excellent stability, porosity and functionality, the high-valent Zr4+ metal-organic frameworks (Zr-MOFs) still meets synthetic challenge in modulating the strength of Zr-Ocarboxylate linkage. Herein we explore the unusual coordination dynamics of fluorinated Zr-MOFs by designing two trifluoromethyl modified ligands with distinct geometry preference to form a family of thermodynamic and kinetic products. The low-connecting kinetic Zr-MOFs possess substitutable coordination sites to endow Zr6 -cluster with extra dynamic behaviors, thus opening a post-synthetic pathway to sequential reassembly/disassembly processes. Comprehensive factors, including ligand geometry, Zr6 -cluster connectivity, acid modulator and reaction temperature/concentration, have been studied for controllable syntheses. The stability, hydrophobicity and gas adsorption/separation properties of obtained Zr-MOFs are explored. This work sheds light on the understanding of the dynamic coordination chemistry of Zr-MOFs beyond strong Zr-O bond, which poses a versatile platform for modification and functionalization of Zr-MOFs.

Self-Generation of Surface Roughness by Low-Surface-Energy Alkyl Chains for Highly Stable Superhydrophobic/Superoleophilic MOFs with Multiple Functionalities.

We transformed the hydrophilic metal-organic framework (MOF) UiO-67 into hydrophobic UiO-67-Rs (R=alkyl) by introducing alkyl chains into organic linkers, which not only protected hydrophilic Zr6 O8 clusters to make the MOF interspace superoleophilic, but also led to a rough crystal surface beneficial for superhydrophobicity. The UiO-67-Rs displayed high acid, base, and water stability, and long alkyl chains offered better hydrophobicity. Good hydrophobicity/oleophilicity were also possible with mixed-ligand MOFs containing metal-binding ligands. Thus, a (super)hydrophobic MOF catalyst loaded with Pd centers efficiently catalyzed Sonogashira reactions in water at ambient temperature. Studies of the hydrophobic effects of the coordination interspace and the outer surface suggest a simple de novo strategy for the synthesis of superhydrophobic MOFs that combine surface roughness and low surface energy. Such MOFs have potential for environmentally friendly catalysis and water purification.

Pressure-Induced Multiphoton Excited Fluorochromic Metal-Organic Frameworks for Improving MPEF Properties.

In multiphoton excited fluorescence (MPEF), high-energy upconversion emission is obtained from low-energy excitation by absorbance of two or more photons simultaneously. In a pressure-induced fluorochromic process, the emission energy is switched by outer pressure stimuli. Now, five metal-organic frameworks containing the same ligand with simultaneous multiphoton absorption and pressure-induced fluorochromic attributes were studied. One-, two-, and three-photon excited fluorescence (1/2/3PEF) can be achieved in the frameworks, which exhibit pressure-induced blue-to-yellow fluorochromism. The performances are closely dependent with the topologies, flexibilities, and packing states of the frameworks and chromophores therein. The multiphoton upconversion performance can be intensified by pressure-related structural contraction. Over ten-fold increment in the 2PA active cross-section up to 2217 GM is achieved in pressed LIFM-114 compared with the 210 GM for pristine sample at 780 nm.

Catalysis through Dynamic Spacer Installation of Multivariate Functionalities in Metal-Organic Frameworks.

We demonstrate herein a facile strategy to engineer versatile catalytically active coordination interspace in the same primitive metal-organic framework (MOF) for variable heterogeneous catalysis. Different functional ligands can be reversibly inserted into and removed from proto-LIFM-28 individually or successively to bring in single or binary catalytic sites for specific reactions and switch the parent MOF to multipurpose catalysts. Alcohol-oxidation, Knoevenagel-condensation, click, acetal, and Baylis-Hillman reactions are achievable through simple exchange of a single catalytic spacer, while sequential or stepwise reactions are designable via selective combination of two catalytic spacers with different functionalities, thus making proto-LIFM-28 a multivariate MOF for multiuse and economic catalysis.

Unusual adsorption behaviours and responsive structural dynamics via selective gate effects of an hourglass porous metal-organic framework.

An hourglass porous metal-organic framework, LIFM-12, constructed on a T-shaped flexible ligand with Cu2+ paddle-wheel clusters, shows temperature and gas adsorption responsive structural dynamics upon reversible molecular guest binding. Temperature-dependent single crystal and powder X-ray diffraction experiments show that the open gate status of the framework with adaptive behaviours facilitates kinetic diffusion of gas molecules resulting in the sequential filling of pores of different sizes, thus creating a breathing behaviour reminiscent of the observation of several steps in adsorption isotherms. In addition, adsorption studies revealed that LIFM-12 performs exceptional adsorption selectivity of 10-25 for CO2 versus light gases N2, CH4, and CO and up to 200 for C3H6 versus CH4.

A Flexible Cu-MOF as Crystalline Sponge for Guests Determination.

A trifluoromethyl functionalized linker and Cu-O chain composed MOF, LIFM-100, was used as "crystalline sponge" to determine eight hardly crystallized liquids' configurations based on its flexibility conformation, suitable pore size, electron-rich channel environment, and low symmetric space group. The H bond interactions between host-guest and guest-guest were well analyzed.

Tunability of fluorescent metal-organic frameworks through dynamic spacer installation with multivariate fluorophores.

Through dynamic spacer installation, five fluorescent metal-organic frameworks (MOFs) have been constructed based on a proto-MOF LIFM-28 and multivariate ligands as fluorophores. The emissions are tunable via insertion of fluorescent ligands, demonstrating a versatile approach for luminescence tuning by virtue of dynamic spacer installation using swing-role MOFs.

Ru Nanoparticles-Loaded Covalent Organic Framework for Solvent-Free One-Pot Tandem Reactions in Air.

Condensation of benzene-1,3,5-tricarbohydrazide with benzene-1,4-dicarboxaldehyde generated a new covalent organic framework, COF-ASB (1), in which the organic units are held together via hydrazone linkage to form porous frameworks. COF-ASB (1) is highly crystalline and displays good chemical and thermal stability and is permanently porous. In addition, 1 can be an ideal support to load Ru nanoparticles (Ru NPs) to generate Ru@COF-ASB (2). The obtained composite material is able to highly promote one-pot tandem synthesis of imine products from benzyl alcohols and corresponding amines under solvent-free conditions in air.

Hydrophobic metallo-supramolecular Pd2L4 cages for zwitterionic guest encapsulation in organic solvents.

Hydrophilic zwitterionic guest encapsulation by metallo-supramolecular cages through synergetic coordination, H-bonding and hydrophobic interactions.

Stepwise engineering of pore environments and enhancement of CO2/R22 adsorption capacity through dynamic spacer installation and functionality modification.

Through stepwise post-synthetic spacer insertion and click reactions, six Zr-MOFs with different types and amounts of functional groups have been constructed based on proto-MOF PCN-700. Their gas adsorption capacities and selectivities have been greatly improved and finely tuned, demonstrating the combinatorial effect of pore surface modification and pore space partition.