A contrivance for a dynamic porous framework: cooperative guest adsorption based on square grids connected by amide-amide hydrogen bonds

Flexible porous coordination polymers containing amide groups as a function origin have been synthesized and categorized as "Coordination Polymer with Amide Groups". Bispyridyl ligands with a spacer of amide group afford two-dimensional (2-D) motifs with a deformed square grid, resulting in three-dimensional (3-D) frameworks of [Co(NO(3))(2)(3-pna)(2)](n)(1), [Co(Br)(2)(3-pna)(2)](n)(2), and [[Co(NCS)(2)(4-peia)(2)].4Me(2)CO](n)(3 subset 4Me(2)CO) (3-pna = N-3-pyridylnicotinamide, 4-peia = N-(2-pyridin-4-yl-ethyl)-isonicotinamide), where the 2-D motifs are bound by complementary hydrogen bond between the amide groups. In the case of the 3 subset 4Me(2)CO, the amide groups form a contrivance for a dynamic porous framework because of their relevant position and orientation in the mutual nearest neighboring motifs. Consequently, 3 subset 4Me(2)CO shows amorphous (nonporous)-to-crystal (porous) structural rearrangement in the Me(2)CO adsorption and desorption process, where the framework of the 2-D motif is maintained. The adsorption isotherm has threshold pressure (P(th)), a sort of gate pressure. The heat of Me(2)CO adsorption (DeltaH(ad) = -25 kJ/mol) is obtained from the temperature dependence of threshold pressure (P(th)), which is close to acetone vaporization enthalpy (DeltaH(vap) = 30.99 kJ/mol).     

Controlled construction of metal-organic frameworks: hydrothermal synthesis, X-ray structure, and heterogeneous catalytic study

The role of pH in the formation of metal-organic frameworks (MOFs) has been studied for a series of magnesium-based carboxylate framework systems. Our investigations have revealed the formation of five different zero-dimensional (0D) to three-dimensional (3D) ordered frameworks from the same reaction mixture, merely by varying the pH of the medium. The compounds were synthesized by the hydrothermal method and characterized by single-crystal X-ray diffraction. Increase of the pH of the medium led to abstraction of the imine hydrogen from the ligand and a concomitant increase in the OH(-) ion concentration in the solution, facilitating the construction of higher dimensional framework compounds. A stepwise increase in pH resulted in a stepwise increase in the dimensionality of the network, ultimately leading to the formation of a 3D porous solid. A gas adsorption study of the 3D framework compound confirmed its microporosity with a BET surface area of approximately 450?m(2) g(-1). Notably, the 3D framework compound catalyzes aldol condensation reactions of various aromatic aldehydes with acetone under heterogeneous conditions.     

Synthesis and Characterization of Microporous Silica Prepared with Sodium Silicate and Organosilane Compounds

Microporous silica gels were prepared in the pH range of 3–4 using sodium silicate as a silica source. Surface polarity of these gels was modified by grafting hydrophobic groups into the silica gel matrix with the help of hydrophilic solvents (acetone, acetonitrile, ethanol and methanol) and alkoxysilane compounds containing nonhydrolyzable alkyl groups. The porous framework and hydrophobicity of the silica gels were evaluated using nitrogen adsorption/desorption and water adsorption measurement techniques. All the measured isotherms were found to be type I which is indicative of microporosity. The surface area and microporosity of these samples were estimated by analyzing the measured nitrogen adsorption/desorption data using BET, Langmuir and Dubinin-Radushkevich (D-R) adsorption isotherms. The micropore size distribution was determined from their nitrogen adsorption isotherms using the slit-pore model of the Horvath-Kawazoe equation. Silica gels with high surface area (over 500 m²/g) as well as high microporosity (over 0.2 cc/g) were obtained at gelation pH of 3.50 from the water-solvent system.     

Hydrogen adsorption in a highly stable porous rare-earth metal-organic framework: sorption properties and neutron diffraction studies

A highly stable porous lanthanide metal-organic framework, Y(BTC)(H2O).4.3H2O (BTC = 1,3,5-benzenetricarboxylate), with pore size of 5.8 A has been constructed and investigated for hydrogen storage. Gas sorption measurements show that this porous MOF exhibits highly selective sorption behaviors of hydrogen over nitrogen gas molecules and can take up hydrogen of about 2.1 wt % at 77 K and 10 bar. Difference Fourier analysis of neutron powder diffraction data revealed four distinct D2 sites that are progressively filled within the nanoporous framework. Interestingly, the strongest adsorption sites identified are associated with the aromatic organic linkers rather than the open metal sites, as occurred in previously reported MOFs. Our results provide for the first time direct structural evidence demonstrating that optimal pore size (around 6 A, twice the kinetic diameter of hydrogen) strengthens the interactions between H2 molecules and pore walls and increases the heat of adsorption, which thus allows for enhancing hydrogen adsorption from the interaction between hydrogen molecules with the pore walls rather than with the normally stronger adsorption sites (the open metal sites) within the framework. At high concentration H2 loadings (5.5 H2 molecules (3.7 wt %) per Y(BTC) formula), H2 molecules form highly symmetric novel nanoclusters with relatively short H2-H2 distances compared to solid H2. These observations are important and hold the key to optimizing this new class of rare metal-organic framework (RMOF) materials for practical hydrogen storage applications.     

Controlled Construction of Metal–Organic Frameworks: Hydrothermal Synthesis,X‐ray Structure,and Heterogeneous Catalytic Study

The role of pH in the formation of metal–organic frameworks (MOFs) has been studied for a series of magnesium‐based carboxylate framework systems. Our investigations have revealed the formation of five different zero‐dimensional (0D) to three‐dimensional (3D) ordered frameworks from the same reaction mixture, merely by varying the pH of the medium. The compounds were synthesized by the hydrothermal method and characterized by single‐crystal X‐ray diffraction. Increase of the pH of the medium led to abstraction of the imine hydrogen from the ligand and a concomitant increase in the OH^? ion concentration in the solution, facilitating the construction of higher dimensional framework compounds. A stepwise increase in pH resulted in a stepwise increase in the dimensionality of the network, ultimately leading to the formation of a 3D porous solid. A gas adsorption study of the 3D framework compound confirmed its microporosity with a BET surface area of approximately 450 m² g^?1. Notably, the 3D framework compound catalyzes aldol condensation reactions of various aromatic aldehydes with acetone under heterogeneous conditions.     

Polarized micropores in a novel 3D metal-organic framework for selective adsorption properties

A novel 3D porous metal-organic framework with 1D polarized channels was synthesized, and its adsorption properties for gas separation and chemical sensing were studied. The framework shows a preferential adsorption of CO(2) over N(2) with a selectivity of 22:1. It also exhibits a very good sensitivity to water with respect to most of the organic solvents in view of chemical sensing applications.     

Porous Organic Frameworks-derived Porous Carbons with Outstanding Gas Adsorption Performance

A series of porous carbon materials was synthesized via high temperature pyrolysis from well-defined and thermally stable precursors, namely porous organic frameworks(POFs), in inert atmosphere. The porous carbon materials showed enhanced gas adsorption capacities together with increased heat of adsorption and stronger affinity between the frameworks and the gases as compared to the precursor materials. To exemplify, sample C-POF-TBBP-1000 with a high BET surface area of 1290 m²/g can adsorb 2.8 mmol/g CH₄(273 K, 101.325 kPa), 5.4 mmol/g CO₂(273 K, 101.325 kPa) and 2.2% H₂(mass fraction, 77 K, 101.325 kPa), thereby surpassing most other porous adsorbent materials reported till date. The study highlights the potential of porous carbons derived from novel porous organic framework structures for gas adsorption applications.     

基于溶剂原位傅克偶联反应合成杯芳烃有机多孔网络(CalixPOF)及其染料吸附特性

利用1,2-二氯乙烷(DCE)同时作为溶剂和偶联剂,通过溶剂原位傅克偶联反应合成杯芳烃有机多孔网络(CalixPOF)。采用红外光谱(FT-IR)和固体核磁碳谱(13 C-NMR)对CalixPOF的组成和分子结构进行了表征,验证了溶剂原位Friedel-Crafts偶联反应机理。采用氮气吸附、扫描电镜(SEM)、热重(TG)和紫外可见光谱(UV-vis)研究了CalixPOF的比表面积、微观结构、热稳定性和染料吸附效率等性能。结果表明:利用简单的溶剂原位傅克偶联反应可得到热稳定性良好、比表面积较大、可选择性吸附亚甲基蓝染料的CalixPOF,为自具主客体微腔的新型多孔聚合物网络的合成提供了新方法。     

新磷酸铝分子筛CFAP-2的合成与鉴定

新AlPO₄结晶分子筛相CFAP-2合成于TMEDA(N,N,N′,N′-四甲基乙基二胺)-P₂O₅-A1₂O₅-H₂O系统,反应物摩尔组成的范围是:TMEDA:P₂O₅:Al₂O₃:H₂O=(1-1.1):1:1:50,晶体形貌,X射线粉末衍射分析,热分析及红外光谱的研究表明:CFAP-2与A1PO₄-21的晶体结构不同,在350℃时,CFAP-2的原粉相转变为具有三维骨架孔结构的较稳定的结晶相。     

Porous magnesium carboxylate framework: synthesis, X-ray crystal structure, gas adsorption property and heterogeneous catalytic aldol condensation reaction

A new three-dimensional alkaline-earth metal-organic framework (MOF) compound, [Mg(Pdc)(H(2)O)](n) (1) (H(2)Pdc = pyridine-2,5-dicarboxylic acid), has been synthesized and structurally characterized by single crystal X-ray diffraction analysis. Compound 1 features a 3D porous framework afforded by the Mg(2)-diad centers through formation of interconnected chair like structural motifs. A nitrogen adsorption study confirms the microporosity of compound 1 with a BET surface area of 211 ± 12 m(2) g(-1). Upon dehydration, the BET surface area of 1 is enhanced to a value of 463 ± 36 m(2) g(-1) due to removal of coordinated water molecule. After rehydration, the compound reverts to its original form as evidenced by powder X-ray diffraction and IR spectroscopic analysis and N(2) sorption measurement. Compound 1 retains its pore structure with a variable BET surface area in several cycles of dehydration and rehydration processes indicating robustness of the framework in [Mg(Pdc)(H(2)O)](n) (1). Compound 1 catalyzes the aldol condensation reactions of various aromatic aldehydes with acetone and cyclohexanone in heterogeneous conditions. Notably, the catalytic activity of the compound is enhanced upon dehydration. The catalyst can be recycled and reused several times without significant loss of activity.     

Synthesis of porous ZnO nanospheres for gas sensor and photocatalysis

Monodispersed porous ZnO nanospheres with diameters about 400–600 nm were successfully fabricated by a facile and effective cationic surfactant assisted selective etching strategy. The as-synthesized ZnO materials were characterized by X-ray diffraction, scanning electron microscope, transmission electron microscope and N₂ adsorption–desorption. These samples were used as the gas sensor, showing the high, stable and fast response to acetone, revealing the potential application as gas sensor to detect acetone. In addition, the photocatalytic degradation property of the porous ZnO nanospheres for methyl orange (MO) under UV irradiation was investigated. The degradation efficiency of MO reaches 96 % of the porous ZnO samples after 50 min of UV-light irradiation.     

Achieving a stable COF with the combination of “flat” and “twist” large-size rigid synthons for selective gas adsorption and separation

A new type of covalent organic framework(COF) was achieved using combination of structrally rigid and conformationally othorganal building blocks. The N-2-aryl-substituted triazole derivative(NAT-CHO)was prepared with co-planar conformation among the three aromatic rings as the “flat” building block.The 4,4,4,4-(ethene-1,1,2,2-tetrayl)tetraaniline)(ETTA) was applied as the “twist” building block. A 2 D sheet of network was obtained through imine formation. The resulting NAT-COF gave excellent th...     

A sodalite-type porous metal-organic framework with polyoxometalate templates: adsorption and decomposition of dimethyl methylphosphonate

A sodalite-type porous metal-organic framework with polyoxometalate templates, H(3)[(Cu(4)Cl)(3)(BTC)(8)](2)[PW(12)O(40)]·(C(4)H(12)N)(6)·3H(2)O (NENU-11; BTC = 1,3,5-benzenetricarboxylate), was obtained by a hydrothermal reaction. As a reasonable candidate for eliminating nerve gas, NENU-11 displays good adsorption behavior for dimethyl methylphosphonate (15.5 molecules per formula unit). In virtue of the catalytic activity of polyoxometalate guests, this nerve gas mimic could be facilely decomposed by a hydrolysis reaction.     

Dynamic porous coordination polymer based on 2D stacked layers exhibiting high sorption selectivity for CO2

A new dynamic porous coordination polymer (PCP) [Ni(dcpy)(bipy)(0.5)(H(2)O)]·1.5H(2)O (1) was synthesized by assembly of 3-(2',5'-dicarboxylphenyl)pyridine (dcpy), 4,4'-bipyridine (bipy) and NiSO(4)via solvothermal, hydrothermal and microwave methods, displaying a wavelike 2D stacked layer framework. Gas adsorption studies for 1 shows a high selective adsorption of CO(2) over other gases (N(2), CH(4) and CO). The adsorption capacity for N(2) can be moderately altered by different activation temperatures demonstrating the framework flexibility of 1.     

Crystals as molecules: postsynthesis covalent functionalization of zeolitic imidazolate frameworks

A new crystalline zeolitic imidazolate framework, ZIF-90, was prepared from zinc(II) nitrate and imidazolate-2-carboxyaldehyde (ICA) and found to have the sodalite-type topology. Its 3D porous framework has an aperture of 3.5 A and a pore size of 11.2 A. The pores are decorated by the aldehyde functionality of ICA which has allowed its transformation to the alcohol functionality by reduction with NaBH4 and its conversion to imine functionality by reaction with ethanolamine to give ZIF-91 and ZIF-92, respectively. The N2 adsorption isotherm of ZIF-90 shows a highly porous material with calculated Langmuir and BET surface areas of 1320 and 1270 m2 g(-1). Both functionalized ZIFs retained high crystallinity and in addition ZIF-91 maintained permanent porosity (surface areas: 1070 and 1010 m2 g(-1)).     

Multifunctionality and crystal dynamics of a highly stable, porous metal-organic framework [Zn4O(NTB)2

A porous metal-organic framework [Zn(4)O(NTB)(2)].3DEF.EtOH (1), in which (3,6)-connected nets are doubly interpenetrated to generate curved three-dimensional channels, has been prepared. Framework 1 exhibits high permanent porosity (Langmuir surface area, 1121 m(2)/g; pore volume, 0.51 cm(3)/cm(3)), high thermal stability (up to 430 degrees C), high hydrogen adsorption capacity (1.9 wt % at 77 K and 1 atm), selective organic guest binding ability (K(f)()( )(): MeOH > pyridine > benzene > dodecane), and guest-dependent blue luminescence (lambda(max) depending on guest identity). Most interestingly, the framework sustains single crystallinity even at 400 degrees C and 10(-)(5) Torr, and the framework components undergo reversible dynamics, mainly rotational motion, in response to removal and rebinding of the guest molecules.     

Single Crystal to Single Crystal (SC‐to‐SC) Transformation from a Nonporous to Porous Metal–Organic Framework and Its Application Potential in Gas Adsorption and Suzuki Coupling Reaction through Postmodification

A new amino‐functionalized strontium–carboxylate‐based metal–organic framework (MOF) has been synthesized that undergoes single crystal to single crystal (SC‐to‐SC) transformation upon desolvation. Both structures have been characterized by single‐crystal X‐ray analysis. The desolvated structure shows an interesting 3D porous structure with pendent ?NH₂ groups inside the pore wall, whereas the solvated compound possesses a nonporous structure with DMF molecules on the metal centers. The amino group was postmodified through Schiff base condensation by pyridine‐2‐carboxaldehyde and palladium was anchored on that site. The modified framework has been utilized for the Suzuki cross‐coupling reaction. The compound shows high activity towards the C?C cross‐coupling reaction with good yields and turnover frequencies. Gas adsorption studies showed that the desolvated compound had permanent porosity and was microporous in nature with a BET surface area of 2052 m² g^?1. The material also possesses good CO₂ (8 wt %) and H₂ (1.87 wt %) adsorption capabilities.     

Dual‐template crown ether‐functionalized hierarchical porous silica: Preparation and application for adsorption of energy metal lithium

Lithium is the lightest energy metal element on earth and it has applications in lithium batteries and nuclear fusion. With the development of high‐tech and widespread applications of lithium, the demand for lithium continues to increase. In this work, a hierarchical porous lithium adsorbent (2M12C4‐HPS) was synthesized from a precursor of hierarchical porous silica (HPS), the HPS being obtained via a dual‐template technique. The microstructure and morphology of 2M12C4‐HPS were characterized using scanning electron microscopy, transmission electron microscopy, X‐ray diffraction and nitrogen adsorption–desorption measurements. The obtained hierarchical porous 2M12C4‐HPS containing two kinds of pores with different sizes (peaking at about 2.01 and 7.82 nm) has a high specific surface area (1143.56 m² g^?1). Fourier transform infrared spectroscopy and thermogravimetric analysis were used to confirm the surface organic functional groups of 2M12C4‐HPS, indicating that the functional group 2‐methylol‐12‐crown‐4 (2M12C4) was grafted on HPS successfully. The lithium adsorption properties, kinetics and isotherms of 2M12C4‐HPS were investigated. The adsorption kinetics can be described by the pseudo‐second‐order kinetic model and the adsorption isotherms well fit the Langmuir isotherm equation. In addition, 2M12C4‐HPS exhibited excellent specificity towards Li⁺. And the maximum adsorption rate of 2M12C4‐HPS is up to about 94.34%. The obtained results indicate that 2M12C4‐HPS has a broad commercial application prospect for adsorption of lithium.     

Highly CO2-selective organic molecular cages: what determines the CO2 selectivity

A series of novel organic cage compounds 1-4 were successfully synthesized from readily available starting materials in one-pot in decent to excellent yields (46-90%) through a dynamic covalent chemistry approach (imine condensation reaction). Covalently cross-linked cage framework 14 was obtained through the cage-to-framework strategy via the Sonogashira coupling of cage 4 with the 1,4-diethynylbenzene linker molecule. Cage compounds 1-4 and framework 14 exhibited exceptional high ideal selectivity (36/1-138/1) in adsorption of CO(2) over N(2) under the standard temperature and pressure (STP, 20 °C, 1 bar). Gas adsorption studies indicate that the high selectivity is provided not only by the amino group density (mol/g), but also by the intrinsic pore size of the cage structure (distance between the top and bottom panels), which can be tuned by judiciously choosing building blocks of different size. The systematic studies on the structure-property relationship of this novel class of organic cages are reported herein for the first time; they provide critical knowledge on the rational design principle of these cage-based porous materials that have shown great potential in gas separation and carbon capture applications.