Ultrathin two-dimensional metal-organic framework nanosheets for efficient electrochemical CO2 reduction

Electrochemical CO2 reduction into CO or high-value products is regarded as a feasible pathway for energy conversion, which has attracted universal attention in...     

Rational design and crystal structure determination of a 3-D metal-organic jungle-gym-like open framework

A new three-dimensional (3-D) jungle-gym-like open metal-organic framework has been synthesized from a two-dimensional (2-D) layer compound using a heterogeneous pillar insertion reaction. Both the starting 2-D layer and the resulting 3-D open compounds have been characterized using X-ray crystallography.     

Investigating metal-organic framework as a new pseudo-capacitive material for supercapacitors

A new application of metal organic framework （MOF） as a pseudo-capacitive material for supercapacitors is investigated. To this end, a simple nickel-based MOF, formulated Ni3（btc）2.12H2O, is synthesized via a hydrothermal reaction. As an electro-active material, such nickel-based MOF exhibits superior pseudo- capacitive behavior in KOH aqueous electrolyte with a high specific capacitance of 726 F g-1. Also, it displays good electrochemical stability with 94.6% of the initial capacitance over consecutive 1000 cycles. In addition, a simple asymmetric supercapacitor with a high energy density of 16.5 Wh kg-1 is successfully built using the nickel-based MOF as positive electrode and commercial activated carbon as negative electrode in KOH electrolyte.     

A highly porous interpenetrated metal-organic framework from the use of a novel nanosized organic linker

The initial use of a novel elongated tricarboxylic acid H(3)hmpib in metal-organic framework (MOF) chemistry resulted in a [Zn(4)O(hmpib)(2)] MOF (UCY-1) with pyrite topology. The compound displays a remarkably high internal surface area despite its double-interpenetrated structure as well as high CO(2) uptake and selective adsorption for it over CH(4).     

Rational design of an AIE-active metal-organic framework for highly sensitive and portable sensing nitroaromatic explosives

Herein, we report a new metal-organic framework with an AIE ligand (H₄TCPP = 2,3,5,6-tetra-(4-carboxyphenyl)pyrazine) and Mg²⁺ ions, that is, [Mg₂(H₂O)₄TCPP]·DMF·5CH₃CN (Mg-TCPP, TCPP = tetra-(4-carboxyphenyl)pyrazine) for detection of nitroaromatic explosives. Due to the coordination effect and restricted intramolecular rotation, Mg-TCPP exhibits bright blue light. As a fluorescent sensor, Mg-TCPP exhibits high selectivity and sensitivity for sensing 2,4,6-trinitrophenol (TNP) by quenching behaviors with the Stern-Volmer quenching constant (K_SV) of 3.63×10⁵ L/mol and achieves the low limit of detection of 25.6 ppb, which is beyond most of the previously reported fluorescent materials. Notably, the portable Mg-TCPP films are prepared and it can be used for rapid and sensitive TNP detection in a variety of environments including organic solvent and aqueous solution. Moreover, TNP vapor can be detected within 3 min by naked eye and the film could be regenerated under simple solvent cleaning.     

A lanthanide-based metal-organic framework with a dynamic porous property

Hydrothermal reaction of La(NO(3))(3), NaHCO(3) and H(3)L (H(3)L = pyrazole-3,5-dicarboxylic acid) gives a 3D metal-organic framework with a dynamic porous property.     

Heterogeneity within order in crystals of a porous metal-organic framework

Generally, crystals of synthetic porous materials such as metal-organic frameworks (MOFs) are commonly made up from one kind of repeating pore structure which predominates the whole material. Surprisingly, little is known about how to introduce heterogeneously arranged pores within a crystal of homogeneous pores without losing the crystalline nature of the material. Here, we outline a strategy for producing crystals of MOF-5 in which a system of meso- and macropores either permeates the whole crystal to make sponge-like crystals or is entirely enclosed by a thick crystalline microporous MOF-5 sheath to make pomegranate-like crystals. These new forms of crystals represent a new class of materials in which micro-, meso-, and macroporosity are juxtaposed and are directly linked unique arrangements known to be useful in natural systems but heretofore unknown in synthetic crystals.     

A robust ethane-trapping metal-organic framework for efficient purification of ethylene

Owing to the similar physicochemical properties between ethane(C₂H₆)and ethylene(C₂H₄),obtaining polymerization-grade C₂H₄(≥99.95%pure)is still a tricky problem in the petrochemical industry.Here,we report a robust scandium-based metalorganic framework(Sc BPDC),which is connected by oxygen-rich phenyl ligand with exceptionally high thermal stability(up to873 K)and capacity of C₂H₆(4.94 mmol/g at 100 k Pa and 283 K),exhibiting superior separation performance of C₂H₆/C₂H₄ mixture(the IAST selectivity is up to 1.7 at 283 K).Importantly,Sc BPDC can produce 8.96 L/kg C₂H₄ with≥99.99%purity while the C₂H₄/C₂H₆(50:50,v/v)as the mixture injection and the low isosteric heat of Sc BPDC(16.4 k J/mol for C₂H₆)validates the facility of adsorbent regeneration.Furthermore,theoretical calculations demonstrate the C₂H₆ molecules are trapped in the nonpolar pore surface via C–H···πand C–H···O interactions between multiple hydrogen atoms of C₂H₆ and the host framework.     

Assembly of super-supertetrahedral metal-organic clusters into a hierarchical porous cubic framework

A porous framework comprising a super-supertetrahedral metal-organic cluster building block has been synthesized. Its cubic framework represents a multi-level hierarchical architecture and also possesses an interesting magnetic property.     

Ligand-elaboration as a strategy for engendering structural diversity in porous metal-organic framework compounds

A series of 4,4'-ethynylenedibenzoic acids were synthesized and used in the construction of Zn-based, mixed-ligand metal-organic frameworks; through variation of functionality in the 3- and 3'-positions of these linkers, a collection of MOFs with differing connectivities and varying levels of interpenetration was obtained.     

Guest-dependent high pressure phenomena in a nanoporous metal-organic framework material

The nanoporous metal-organic framework material Cu3(1,3,5-benzenetricarboxylate)2(H2O)3.{guest} exhibits anomalous compression under applied pressure that is associated with the hyper-filling of the pore network. This behavior involves a dramatic transition between a "hard" regime (bulk modulus, Khard approximately 118 GPa), where the pressure-transmitting fluid penetrates the framework cavities, and a "soft" regime (Ksoft approximately 30 GPa), where the guest-framework system compresses concertedly. Not only is the duality in compressibility triggered by the availability of potential guests but the size/penetrability of the guest molecules determines the pressure at which the hard-soft transition occurs. Specifically, the observed compression behavior depends on the size of the pressure-transmitting fluid molecules, the sample particle size (i.e., the extent of the pore network), and the rate at which the pressure is increased. The unprecedented pressure-induced phenomena documented here, illustrates the exotic high-pressure behaviors possible in this versatile class of advanced functional materials with broad implications for their structure-function relationships and accordingly their practical application.     

Highly efficient separation of a solid mixture of naphthalene and anthracene by a reusable porous metal-organic framework through a single-crystal-to-single-crystal transformation

The three-dimensional crystalline porous metal-organic framework [Ni(2)(μ(2)-OH(2))(1,3-BDC)(2)(tpcb)](n) (1) [1,3-H(2)BDC = 1,3-benzenedicarboxylic acid; tpcb = tetrakis(4-pyridyl)cyclobutane] was used to separate a solid mixture of naphthalene and anthracene at room temperature via selective adsorption of naphthalene. The process involved a single-crystal-to-single-crystal transformation. The guest naphthalene molecules could be exchanged with ethanol, and the host, 1, could be regenerated by removal of the guest ethanol molecules.     

On the mechanism of hydrogen storage in a metal-organic framework material

Monte Carlo simulations were performed modeling hydrogen sorption in a recently synthesized metal-organic framework material (MOF) that exhibits large molecular hydrogen uptake capacity. The MOF is remarkable because at 78 K and 1.0 atm it sorbs hydrogen at a density near that of liquid hydrogen (at 20 K and 1.0 atm) when considering H2 density in the pores. Unlike most other MOFs that have been investigated for hydrogen storage, it has a highly ionic framework and many relatively small channels. The simulations demonstrate that it is both of these physical characteristics that lead to relatively strong hydrogen interactions in the MOF and ultimately large hydrogen uptake. Microscopically, hydrogen interacts with the MOF via three principle attractive potential energy contributions: Van der Waals, charge-quadrupole, and induction. Previous simulations of hydrogen storage in MOFs and other materials have not focused on the role of polarization effects, but they are demonstrated here to be the dominant contribution to hydrogen physisorption. Indeed, polarization interactions in the MOF lead to two distinct populations of dipolar hydrogen that are identified from the simulations that should be experimentally discernible using, for example, Raman spectroscopy. Since polarization interactions are significantly enhanced by the presence of a charged framework with narrow pores, MOFs are excellent hydrogen storage candidates.     

A homochiral porous metal-organic framework for highly enantioselective heterogeneous asymmetric catalysis

A homochiral porous noninterpenetrating metal-organic framework (MOF), 1, was constructed by linking infinite 1D [Cd(mu-Cl)2]n zigzag chains with axially chiral bipyridine bridging ligands containing orthogonal secondary functional groups. The secondary chiral dihydroxy groups accessible via the large open channels in 1 were utilized to generate a heterogeneous asymmetric catalyst for the addition of diethyzinc to aromatic aldehydes to afford chiral secondary alcohols at up to 93% enantiomeric excess (ee). Control experiments with dendritic aromatic aldehydes of different sizes indicate that the heterogeneous asymmetric catalyst derived from 1 is both highly active and enantioselective as a result of the creation of readily accessible, uniform active catalyst sites inside the porous MOF.     

Rational design of porous titanophosphates

To rationally design new nanoporous materials based on titanophosphates, a small library of titanium phosphate crystalline nanoporous compounds has been build up and its compounds have been investigated by X-ray diffraction and by in- and ex-situ NMR. The main trends of the unusual titanium solution chemistry, of the prenucleation building units and of their assembling have been established. The classical trial and error strategy can therefore be replaced by a better control of the steps leading to the final targeted network.     

Microporous manganese formate: a simple metal-organic porous material with high framework stability and highly selective gas sorption properties

Novel microporous metal-organic framework material composed of Mn(II) and formate ions displays permanent porosity, high thermal stability, and size-selective gas sorption behavior. The framework is stable enough to maintain single crystallinity after the complete guest removal at 150 degrees C under a reduced pressure. Most importantly, it selectively adsorbs H2 and CO2 but not N2 and other gases with larger kinetic diameters, which appears to be due to the small aperture of the channels. Despite a moderate H2 storage capacity, which is however still higher than that of any zeolite, its H2 surface coverage is one of the highest among the known microporous materials. Thus this new zeolite-like material made of a simple organic building block may find useful applications in gas separation and sensor.     

A novel 3D porous metal-organic framework based on trinuclear cadmium clusters as a promising luminescent material exhibiting tunable emissions between UV and visible wavelengths

A novel 3D porous MOF built with trinuclear cadmium clusters exhibiting rhombohedral topology has been synthesized and characterized as a promising luminescent material that can give tunable emissions between UV and visible wavelengths by controlling the number of guest molecules.     

Conductive phthalocyanine-based metal-organic framework as a highly efficient electrocatalyst for carbon dioxide reduction reaction

Porous crystalline metal-organic frameworks(MOFs) are one class of promising electrode materials for CO_2 electroreduction reaction(CO_2 RR) by virtue of their large CO_2 adsorption capacities and abundant tunable active sites, but their insulating nature usually leads to low current density. Herein, a two-dimensional(2 D) Ni-phthalocyanine-based MOF(Ni Pc-Ni(NH)_4) constructed by 2,3,9,10,16,17,23,24-octaaminophthalocyaninato nickel(II)(Ni Pc-(NH_2)_8) and nickel(II) ions attained high electrical conductivity due to the high overlap of d-π conjugation orbitals between the nickel node and the Ni-phthalocyanine-substituted o-phenylenediamine. During CO_2 RR, the Ni Pc-Ni(NH)_4 nanosheets achieved a high CO Faradaic efficiency of 96.4% at -0.7 V and a large CO partial current density of 24.8 m A cm~(-2) at-1.1 V, which surpassed all the reported two-dimensional MOF electrocatalysts evaluated in an H-cell. The control experiments and density functional theory(DFT) calculations suggested that the Ni-N_4 units of the phthalocyanine ring are the catalytic active sites. This work provides a new route to the design of highly efficient porous framework materials for the enhanced electrocatalysis via improving electrical conductivity.     

One-pot synthesis of a novel chiral Zr-based metal-organic framework for capillary electrochromatographic enantioseparation

A novel chiral stationary phase (CSP) of Zr-based metal-organic framework, l -Cys-PCN-224, was prepared by one-pot method and applied for the enantioseparation by capillary electrochromatography. The CSP was characterized by X-ray diffraction, thermogravimetric analysis, X-ray photoelectron spectroscopy, Fourier-transform infrared spectra, nitrogen adsorption/desorption, circular dichroism spectrum, zeta-potential, and so on. The results revealed that the CSP had good crystallinity, high specific surface area (2580 m²/g), and good thermal stability. Meanwhile, the cross-section of l -Cys-PCN-224-bonded open-tubular (OT) column was observed by a scanning electron microscope, which proved the successful bonding of l -Cys-PCN-224 particles to the inner wall. Relative standard deviations of the column efficiencies were 3.87%–9.14%, and not obviously changed after 200 runs, which indicated that l -Cys-PCN-224-bonded OT column had the better stability and reproducibility. Excellent chiral separation performance was verified with nine kinds of natural amino acids including acidic, neutral, and basic as the analytes. All amino acids studied achieved good separation with the resolution of 1.38–13.9 and selector factor of 1.11–3.71. These results demonstrated that the CSP had an excellent potential in the chiral separation field.