Immobilization of the Polar Group into an Ultramicroporous Metal-Organic Framework Enabling Benchmark Inverse Selective CO2/C2H2 Separation with Record C2H2 Production.

One-step harvest of high-purity light hydrocarbons without the desorption process represents an advanced and highly efficient strategy for the purification of target substances. The separation and purification of acetylene (C2H2) from carbon dioxide (CO2) by CO2-selective adsorbents are urgently demanded yet are very challenging owing to their similar physicochemical properties. Here, we employ the pore chemistry strategy to adjust the pore environment by immobilizing polar groups into an ultramicroporous metal-organic framework (MOF), achieving one-step manufacture of high-purity C2H2 from CO2/C2H2 mixtures. Embedding methyl groups into prototype stable MOF (Zn-ox-trz) not only changes the pore environment but also improves the discrimination of guest molecules. The methyl-functionalized Zn-ox-mtz thus exhibits the benchmark reverse CO2/C2H2 uptake ratio of 12.6 (123.32/9.79 cm3 cm-3) and an exceptionally high equimolar CO2/C2H2 selectivity of 1064.9 at ambient conditions. Molecular simulations reveal that the synergetic effect of pore confinement and surfaces decorated with methyl groups provides high recognition of CO2 molecules through multiple van der Waals interactions. The column breakthrough experiments suggest that Zn-ox-mtz dramatically achieved the one-step purification capacity of C2H2 from the CO2/C2H2 mixture with a record C2H2 productivity of 2091 mmol kg-1, surpassing all of the CO2-selective adsorbents reported so far. In addition, Zn-ox-mtz exhibits excellent chemical stability under different pH values of aqueous solutions (pH = 1-12). Moreover, the highly stable framework and excellent inverse selective CO2/C2H2 separation performance showcase its promising application as a C2H2 splitter for industrial manufacture. This work paves the way to developing reverse-selective adsorbents for the challenging gas separation process.

Hybrid MOF Template-Directed Construction of Hollow-Structured In2 O3 @ZrO2 Heterostructure for Enhancing Hydrogenation of CO2 to Methanol.

Direct hydrogenation of CO2  to methanol using green hydrogen has emerged as a promising method for carbon neutrality, but qualifying catalysts represent a grand challenge. In2 O3 /ZrO2  catalyst has been extensively applied in methanol synthesis due to its superior activity; however, the electronic effect by strong oxides-support interactions between In2 O3  and ZrO2  at the In2 O3 /ZrO2  interface is poorly understood. In this work, abundant In2 O3 /ZrO2  heterointerfaces are engineered in a hollow-structured In2 O3 @ZrO2  heterostructure through a facile pyrolysis of a hybrid metal-organic framework precursor MIL-68@UiO-66. Owing to well-defined In2 O3 /ZrO2  heterointerfaces, the resultant In2 O3 @ZrO2  exhibits superior activity and stability toward CO2  hydrogenation to methanol, which can afford a high methanol selectivity of 84.6% at a conversion of 10.4% at 290 °C, and 3.0 MPa with a methanol space-time yield of up to 0.29 gMeOH  gcat -1  h-1 . Extensive characterization demonstrates that there is a strong correlation between the strong electronic In2 O3 -ZrO2  interaction and catalytic selectivity. At In2 O3 /ZrO2  heterointerfaces, the electron tends to transfer from ZrO2  to In2 O3  surface, which facilitates H2  dissociation and the hydrogenation of formate (HCOO*) and methoxy (CH3 O*) species to methanol. This study provides an insight into the In2 O3 -based catalysts and offers appealing opportunities for developing heterostructured CO2  hydrogenation catalysts with excellent activity.

Tuning the Trade-Off between Ethane/Ethylene Selectivity and Adsorption Capacity within Isoreticular Microporous Metal-Organic Frameworks by Linker Fine-Fluorination.

The pore dimension and surface property directly dictate the transport of guests, endowing diverse gas selective adsorptions to porous materials. It is highly relevant to construct metal-organic frameworks (MOFs) with designable functional groups that can achieve feasible pore regulation to improve their separation performances. However, the role of functionalization in different positions or degrees within framework on the separation of light hydrocarbon has rarely been emphasized. In this context, four isoreticular MOFs (TKL-104-107) bearing dissimilar fluorination are rationally screened out and afforded intriguing differences in the adsorption behavior of C2 H6 and C2 H4 . Ortho-fluoridation of carboxyl allows TKL-105-107 to exhibit enhanced structural stabilities, impressive C2 H6 adsorption capacities (>125 cm3 g-1 ) and desirable inverse selectivities (C2 H6 over C2 H4 ). The more modified ortho-fluorine group and meta-fluorine group of carboxyl have improved the C2 H6 /C2 H4 selectivity and adsorption capacity, respectively, and the C2 H6 /C2 H4 separation potential can be well optimized via linker fine-fluorination. Meanwhile, dynamic breakthrough experiments proved that TKL-105-107 can be used as highly efficient C2 H6 -selective adsorbents for C2 H4 purification. This work highlights that the purposeful functionalization of pore surfaces facilitates the assembly of highly efficient MOF adsorbents for specific gas separation.

A pH-Stable TbIII-Based Metal-Organic Framework as a Turn-On and Blue-Shift Fluorescence Sensor toward Benzaldehyde and Salicylaldehyde in Aqueous Solution.

A new polydentate tetracarboxylic acid with a benzothiadiazole unit (4',4'''-(benzo[c][1,2,5]thiadiazole-4,7-diyl)bis([1,1'-biphenyl]-3,5-dicarboxylic acid), H4BTDBA) has been used to prepare a pH-stable three-dimensional TbIII-based metal-organic framework (MOF) with the formula {[(CH3)2NH2]0.7[Tb2(BTDBA)1.5(lac)0.7(H2O)2]·solvents}n (Hlac = lactic acid, JXUST-19). JXUST-19 exhibits a new (4,4,12)-connected topology based on tetranuclear [Tb4] clusters. JXUST-19 can remain stable when soaked in water for at least 1 week and in aqueous solutions with various pH values (2-12) for 24 h. Fluorescence study indicates JXUST-19 can be employed as a rare turn-on and blue-shift MOF sensor toward benzaldehyde (BZ) and salicylaldehyde (SA). To date, JXUST-19 represents the first TbIII-based turn-on MOF sensor toward salicylaldehyde in aqueous solution, and the fluorescence enhancement and naked-eye detection of BZ have been rarely reported. In addition, JXUST-19 based fluorescent test papers, light-emitting diode lamp beads, and portable composite films were developed to realize naked-eye detection of BZ and SA, which has great potential in practical applications.

Customizing Pore System in a Microporous Metal-Organic Framework for Efficient C2H2 Separation from CO2 and C2H4.

Selective-adsorption separation is an energy-efficient technology for the capture of acetylene (C2H2) from carbon dioxide (CO2) and ethylene (C2H4). However, it remains a critical challenge to effectively recognize C2H2 among CO2 and C2H4, owing to their analogous molecule sizes and physical properties. Herein, we report a new microporous metal-organic framework (NUM-14) possessing a carefully tailored pore system containing moderate pore size and nitro-functionalized channel surface for efficient separation of C2H2 from CO2 and C2H4. The activated NUM-14 (namely NUM-14a) exhibits sufficient pore space to acquire excellent C2H2 loading capacity (4.44 mmol g-1) under ambient conditions. In addition, it possesses dense nitro groups, acting as hydrogen bond acceptors, to selectively identify C2H2 molecules rather than CO2 and C2H4. The breakthrough experiments demonstrate the good actual separation ability of NUM-14a for C2H2/CO2 and C2H2/C2H4 mixtures. Furthermore, Grand Canonical Monte Carlo simulations indicate that the pore surface of the NUM-14a has a stronger affinity to preferentially bind C2H2 over CO2 and C2H4 via stronger C-H···O hydrogen bond interactions. This article provides some insights into customizing pore systems with desirable pore sizes and modifying groups in terms of MOF materials toward the capture of C2H2 from CO2 and C2H4 to promote the development of more MOF materials with excellent properties for gas adsorption and separation.

Incorporation of Active Metal Species in Crystalline Porous Materials for Highly Efficient Synergetic Catalysis.

The design and development of efficient catalytic materials with synergistic catalytic sites always has long been known to be a thrilling and very dynamic research field. Crystalline porous materials (CPMs) mainly including metal-organic frameworks and zeolites with high scientific and industrial impact have recently been the subject of extensive research due to their essential role in modern chemical industrial processes. The rational incorporation of guest species in CPMs can synergize the respective strengths of these components and allow them to collaborate with each other for synergistic catalysis, leading to enhanced catalytic activity, selectivity, and stability in a broad range of catalytic processes. In this review, the recent advances in the development of CPMs-confined active metal species, including metal nanoparticles, metal/metal oxides heteroparticles, metal oxide, subnanometric metal clusters, and polyoxometalates, for heterogeneous catalysis, with a particular focus on synergistic effects between active components that result in an enhanced performance are highlighted. Insights into catalysts design strategies, host-guest interactions, and structure-property relationships have been illustrated in detail. Finally, the existing challenges and possible development directions in CPMs-based encapsulation-structured synergistic catalysts are discussed.

Pore-Space Partition through an Embedding Metal-Carboxylate Chain-Induced Topology Upgrade Strategy for the Separation of Acetylene/Ethylene.

Ethylene (C2H4) is one of the most significant substances in the petrochemical industry; however, the capture of acetylene (C2H2) in about 1% from C2H2/C2H4 mixtures is a difficult task because of the similarity of their physical properties. With the aggravation of the energy crisis, using metal-organic framework (MOF) materials to purify C2H4 through adsorptive separation is a promising way to save energy and reduce emission. Pore-space partition (PSP) with the aim of enhancing the density of the binding sites and the strength of the host-guest interactions is an effective means to promote a solution for the challenging gas separation problems. Herein, we report a new embedding metal-carboxylate chain-induced topology upgrade strategy within a MOF to realize PSP and separation of C2H2/C2H4 mixtures. As a proof of concept, we construct a microporous MOF (NUM-12) utilizing the in situ insertion of cobalt terephthalic chains into a pretargeted ant-type framework during synthesis. Because of the attainment of an elaborately tuned aperture size and a specific pore environment through this strategy, NUM-12a (activated NUM-12) not only has a remarkable gas sorption capacity and strong interactions for C2H2 but also possesses an excellent purification performance for C2H2/C2H4 mixtures. Both experiments and simulation calculations clearly reveal that NUM-12 is a promising candidate for the separation of C2H2/C2H4, proving the feasibility of this new strategy for developing newly fashioned MOFs with adjustable structure and performance.

Enhanced Gas Uptake in a Microporous Metal-Organic Framework via a Sorbate Induced-Fit Mechanism.

Physical adsorption of gas molecules in microporous materials is an exothermic process, with desorption entropy driving a decrease in uptake with temperature. Enhanced gas sorption with increasing temperature is rare in porous materials and is indicative of sorbate initiated structural change. Here, sorption of C2H6, C3H6, and C3H8 in a flexible microporous metal-organic framework (MOF) {Cu(FPBDC)]·DMF}n (NKU-FlexMOF-1) (H2FPBDC = 5-(5-fluoropyridin-3-yl)-1,3-benzenedicarboxylic acid) that increases with rising temperature over a practically useful temperature and pressure range is reported along with other small molecule and hydrocarbon sorption isotherms. Single X-ray diffraction studies, temperature-dependent gas sorption isotherms, in situ and variable temperature powder X-ray diffraction experiments, and electronic structure calculations were performed to characterize the conformation-dependent sorption behavior in NKU-FlexMOF-1. In total, the data supports that the atypical sorption behavior is a result of loading-dependent structural changes in the flexible framework of NKU-FlexMOF-1 induced by sorbate-specific guest-framework interactions. The sorbates cause subtle adaptations of the framework distinct to each sorbate providing an induced-fit separation mechanism to resolve chemically similar hydrocarbons through highly specific sorbate-sorbent interactions. The relevant intermolecular contacts are shown to be predominantly repulsion and dispersion interactions. NKU-FlexMOF-1 is also found to be stable in aqueous solutions including toleration of pH changes. These experiments demonstrate the potential of this flexible microporous MOF for cost and energy efficient industrial hydrocarbon separation and purification processes. The efficacy for the separation of C3H6/C3H8 mixtures is explicitly demonstrated using NKU-FlexMOF-1a (i.e., activated NKU-FlexMOF-1) for a particular useful temperature range.

A Water-Stable Luminescent ZnII Metal-Organic Framework as Chemosensor for High-Efficiency Detection of CrVI -Anions (Cr2 O72- and CrO42- ) in Aqueous Solution.

A new luminescent ZnII -MOF with 1D triangular channels along the b axis, namely NUM-5, has been successfully assembled and well characterized, which features good stability, especially in aqueous solution. Interestingly, this compound exhibits a fast, sensitive and selective luminescence quenching response towards CrVI (Cr2 O72- /CrO42- ) in aqueous solution. The detection limits towards Cr2 O72- and CrO42- ions are estimated to be 0.7 and 0.3 ppm, respectively, which are among the lowest detection limits reported for the MOF-based fluorescent probes that can simultaneously detect Cr2 O72- and CrO42- in aqueous environment. The possible detection mechanism has been discussed in detail. Moreover, it can be easily regenerated after detection experiments, indicative of excellent recyclability. All these results suggest NUM-5 to be a highly selective and recyclable luminescent sensing material for the quantitative detection of CrVI anions in aqueous solution.

Metal-Organic Framework Derived Core-Shell Co/Co3O4@N-C Nanocomposites as High Performance Anode Materials for Lithium Ion Batteries.

Metal-organic frameworks (MOFs) with diverse structures, adjustable pore sizes, and high surface areas have exhibited awesome potential in many fields. Here we report a simple carbonization strategy to obtain a series of core-shell structured Co/Co3O4 nanoparticles encapsulated into nitrogen-doped carbon shells from cobalt-based metal-organic framework precursors at different carbonization temperatures. When it is applied as an anodes for lithium ion batteries, the Co/Co3O4@N-C-700 electrode delivers a maximum initial discharge capacity of 1535 mAh g-1, the highest reversible capacity (903 mAh g-1 at a current density of 100 mA g-1 after 100 cycles), and the best rate performance (i.e., 774 mAh g-1 at a current density of 1.0 A g-1 after 100 cycles) in comparison with those of Co/Co3O4@N-C-600 and Co/Co3O4@N-C-800 electrodes. The excellent electrochemical performance could be mainly attributed to the unique core-shell structure, abundant graphited carbon, and the well-dispersed Co/Co3O4 nanoparticles which can promote the specific capacity through conversion reactions.

UTSA-74: A MOF-74 Isomer with Two Accessible Binding Sites per Metal Center for Highly Selective Gas Separation.

A new metal-organic framework Zn2(H2O)(dobdc)·0.5(H2O) (UTSA-74, H4dobdc = 2,5-dioxido-1,4-benzenedicarboxylic acid), Zn-MOF-74/CPO-27-Zn isomer, has been synthesized and structurally characterized. It has a novel four coordinated fgl topology with one-dimensional channels of about 8.0 Å. Unlike metal sites in the well-established MOF-74 with a rod-packing structure in which each of them is in a five coordinate square pyramidal coordination geometry, there are two different Zn(2+) sites within the binuclear secondary building units in UTSA-74 in which one of them (Zn1) is in a tetrahedral while another (Zn2) in an octahedral coordination geometry. After activation, the two axial water molecules on Zn2 sites can be removed, generating UTSA-74a with two accessible gas binding sites per Zn2 ion. Accordingly, UTSA-74a takes up a moderately high and comparable amount of acetylene (145 cm(3)/cm(3)) to Zn-MOF-74. Interestingly, the accessible Zn(2+) sites in UTSA-74a are bridged by carbon dioxide molecules instead of being terminally bound in Zn-MOF-74, so UTSA-74a adsorbs a much smaller amount of carbon dioxide (90 cm(3)/cm(3)) than Zn-MOF-74 (146 cm(3)/cm(3)) at room temperature and 1 bar, leading to a superior MOF material for highly selective C2H2/CO2 separation. X-ray crystal structures, gas sorption isotherms, molecular modeling, and simulated and experimental breakthroughs comprehensively support this result.

A Flexible Microporous Hydrogen-Bonded Organic Framework for Gas Sorption and Separation.

A microporous three-dimensional hydrogen-bonded organic framework (HOF-5) has been constructed from a new organic linker 4,4',4″,4‴-tetra(2,4-diamino-1,3,5-triazin-6-yl)tetraphenylethene. Activated HOF-5a exhibits a stepwise N2 adsorption isotherm at 77 K, suggesting framework flexibility. The structure of activated HOF-5a has been established by powder X-ray diffraction studies, indicating a significant framework contraction from as-synthesized HOF-5 to activated HOF-5a of ∼21% by volume. HOF-5a shows moderately high porosity with a Brunauer-Emmett-Teller (BET) surface area of 1101 m(2)/g, and takes up a large amount of acetylene and carbon dioxide under ambient conditions. Powder neutron diffraction studies and theoretical calculations reveal that suitable pore sizes, curvatures, and functional sites collectively enable HOF-5a to encapsulate a high density of carbon dioxide molecules packed in a pseudo-one-dimensional array along the pore channel.

Targeted structure modulation of "pillar-layered" metal-organic frameworks for CO2 capture.

Two new zinc MOFs with similar "pillar-layered" framework structures based on 1,1'-biphenyl-2,2',6,6'-tetracarboxylic acid (H4bpta) and two different bipyridine pillar ligands, namely {[Zn4(bpta)2(4-pna)2(H2O)2]·4DMF·3H2O}n (1) and {[Zn2(bpta)(bpy-ea)(H2O)]·2DMF·H2O}n (2) (4-pna = N-(4-pyridyl)isonicotinamide and bpy-ea = 1,2-bis(4-pyridyl)ethane), have been synthesized and investigated with their CO2 adsorption properties. By analysis of the structure properties and the CO2 adsorption performances of these two MOFs, it was found that the introduction of polar acylamide groups via 4-pna resulted in 1 with enhanced CO2 capacity and CO2/CH4 selectivity at low pressure. In contrast, the framework of 2 shows flexible properties originating from the flexibility of the ethanediylidene group in the bpy-ea ligand, which benefits the sieve effect of pores to give higher CO2/CH4 selectivity at a relatively high pressure range.

Zn(II)-benzotriazolate clusters based amide functionalized porous coordination polymers with high CO2 adsorption selectivity.

Two new porous coordination polymers (PCPs) based on different nanosized C3 symmetry ligands and Zn(II)-benzotriazolate clusters have been synthesized solvothermally. Both of the desolvated complexes show selective uptake of CO2 over CH4 and N2 at ambient temperature.

2-Methylimidazole-modulated 2D Cu metal-organic framework for 5-hydroxymethylfurfural hydrodeoxygenation.

Preparation of the high value-added chemical 2,5-dimethylfuran (2,5-DMF) from the biomass-derived platform molecule 5-hydroxymethylfurfural (HMF) is of great significance in the preparation of biofuels. Here, a bottom-up strategy was used to prepare a metal-organic framework (MOF) material with a two-dimensional nanosheet morphology, named CPM, in which an additive 2-methylimidazole was introduced into the hydrothermal process of Cu2+ ions and terephthalic acid. Subsequently, CPM-700 prepared by heat treatment under an inert atmosphere showed excellent catalytic performance in the reaction of HMF hydrodeoxygenation to 2,5-DMF. The materials before and after pyrogenation were characterized by PXRD, XPS, TEM, N2 adsorption and desorption and so on. It was confirmed that compared with the catalyst derived from the cubic MOF material self-assembled by Cu2+ and terephthalic acid, the morphology of 2D nanosheets was beneficial for the reaction of HMF to 2,5-DMF. Combined with the experimental data, the possible reaction path of 2,5-DMF preparation from HMF is that 2,5-dihydroxymethylfuran was formed by hydrogenation of the aldehyde group on the furan ring, and then 2,5-DMF was obtained by hydrogenolysis. This paper provides an effective route for 2D MOF-derived catalytic materials in the selective hydrogenation of HMF.

A microporous bismuth-based MOF for efficient separation of acetylene from carbon dioxide.

The separation of acetylene from carbon dioxide is challenging due to their almost identical molecular sizes and volatilities. Metal-organic frameworks (MOFs) in general are strong candidates for the separation of gas mixtures owing to the presence of functional pore surfaces that can selectively capture specific target molecules. Herein, we report a stable and easily synthesized bismuth-based MOF, Bi-BTC, which can achieve the separation of acetylene and carbon dioxide. We performed a detailed analysis of the sorption properties of the Bi-MOF. Bi-BTC shows good adsorption capacities for C2H2 with a capacity of 53.8 cm3 g-1 at 298 K and 1.0 bar, and C2H2/CO2 selectivity of 5.14/7.69 at 298 K and 1.0/0.1 bar. IAST selectivity calculations indicate that Bi-BTC possesses good separation capacity, and dynamic breakthrough experiments were performed to prove the separation of C2H2 and CO2. Bi-MOFs as a group of relatively less studied types of MOFs have interesting adsorption characteristics, and this study on Bi-based MOF will enrich three-dimensional Bi-MOF adsorbents for gas adsorption and separation applications.

A new ditopic ratiometric receptor for detecting zinc and fluoride ions in living cells.

The synthesis, characterization and ion binding properties of a new ditopic ratiometric receptor (1), based on 2-(4,5-dihydro-1H-imidazol-2-yl)phenol and crown ether moieties, have been described. The ditopic ratiometric receptor has been studied in sensing both F(-) and Zn(2+) ions, exhibiting different fluorescent colour changes from cyan green to blue/black observable by the naked eye under UV-light. The addition of Zn(2+) to the solution of 1 induced the formation of a 2 : 2 ligand-metal complex 1-Zn(2+), which displays a remarkable blue shift of the emission maxima of 1 from 455 nm to 400 nm due to the inhibition of excited-state intramolecular proton transfer (ESIPT) mechanism. The sensing processes were monitored by fluorescence/absorption titrations, and further confirmed by Job's plot and (1)H NMR titrations. The crystal structure of 1-Zn(2+) reveals that 1 binds Zn(2+) in four-coordinated modes. Furthermore, 1 is cell permeable and may be applied to detect trace Zn(2+) and F(-) during the development of a living organism.

A controllable gate effect in cobalt(II) organic frameworks by reversible structure transformations.

With H2 O or NH3 stimuli, the blue cobalt-based metal-organic framework (MOF) BP can reversibly transform to red RP. The removal/recovery of terephthalate ligands accompanied by the transformation leads to a gate effect, which allows the encapsulation and release of small solvent molecules under certain conditions. This is the first example of topology transformation from a self-penetrating to interpenetrating net in 3D MOFs.

Confining Co-Based Nanocatalysts by Ultrathin Nanotubes for Efficient Transfer Hydrogenation of Biomass Derivatives.

Catalytic transfer hydrogenation (CTH) based on non-noble-metal catalysts has emerged as an environmentally friendly way for the utilization of biomass resources. However, the development of efficient and stable non-noble-metal catalysts is crucially challenging due to their inherent inactivity. Herein, a metal-organic framework (MOF)-transformed CoAl nanotube catalyst (CoAl NT160-H) with unique confinement effect was developed via a "MOF transformation and reduction" strategy, which exhibited excellent catalytic activity for the CTH reaction of levulinic acid (LA) to γ-valerolactone (GVL) with isopropanol (2-PrOH) as the H donor. Comprehensive characterizations and experimental investigations uncovered that the confined effect of the ultrathin amorphous Al2O3 nanotubes could modulate the electronic structure and enhance the Lewis acidity of Co nanoparticles (NPs), thus contributing to the adsorption and activation of LA and 2-PrOH. The synergy between the electropositive Co NPs and Lewis acid-base sites of the CoAl NT160-H catalyst facilitated the transfer of α-H in 2-PrOH to the C atom of carbonyl in LA during the CTH process via a Meerwein-Ponndorf-Verley mechanism. Moreover, the confined Co NPs embedded on am-Al2O3 nanotubes endowed the CoAl NT160-H catalyst with superior stability and the catalytic activity was nearly unchanged for at least ten cycles, far surpassing that of the Co/am-Al2O3 catalyst prepared by the traditional impregnation method.

Fe20 cluster units based coordination polymer from in situ ligand conversion and trapping of an intermediate.

A coordination polymer based on an unprecedented Fe(20) core has been constructed by in situ ligand conversion, including trapping of an intermediate.