Synthesis of metal-organic frameworks: A mini review

Metal organic frameworks (MOFs) are porous crystalline materials of one-, two-, or three-dimensional networks constructed from metal ions/clusters and multidentate organic linkers via coordination bonding, which are emerging as an important group of materials for energy storage, CO₂ adsorption, alkane/alkene separation, and catalysis. To introduce newcomers in chemical engineering discipline to the rapidly expanding MOF research works, this review presents a brief introduction to the currently available MOFs synthesis methods. Starting from the conventional solvothermal/hydrothermal synthesis, microwave-assisted, sonochemical, electrochemical, mechanochemical, ionothermal, drygel conversion, and microfluidic synthesis methods will be presented. Examples will be limited to those representative MOF structures that can be synthesized using common organic ligands of 1,4-benzenedicarboxylic acid (and its functionalized forms) and 1,3,5-benzenetricarboxylic acid, in conjunction with metal nodes of Zn²⁺, Cu²⁺, Cr³⁺, Al³⁺, Fe³⁺ and Zr⁴⁺. Synthesis of widely-investigated zeolitic imidazolate framework (ZIF) structure, ZIF-8 is also included.     

金属有机骨架结构MIL-101的合成及其吸附脱硫的工艺研究

采用水热合成方法合成金属有机骨架化合物MIL-101,利用X射线粉末衍射(XRD),对其产品表征,并研究提高合成产率的影响因素;以MIL-101做为吸附剂,研究吸附脱除汽油模型油中噻吩的最佳工艺条件。实验结果表明,晶化时间提高到10h,pH值为1.5时,MIL-101的合成产率达到60%,产率比文献值提高10%;在空速150h-1,MIL-101质量为0.075g,噻吩质量分数为1×10-3时,噻吩在正辛烷中的穿透容量为0.69%,饱和吸附量为4.62%;MIL-101和4A分子筛分层装柱,并利用N2在100℃对床层进行活化处理,消除了溶解水对吸附脱硫过程的影响;以甲苯为脱附剂,在100℃,空速为100h-1对吸附剂进行再生处理,再生率为96.38%。     

Evaluation of the mercury ions adsorption capacity of copper-based metal-organic frameworks/poly (lactic acid) composites

ABSTRACT

The copper-based metal-organic frameworks (Cu-MOFs) was synthesized via the hydrothermal method and modified by 1,2-ethanedithiol. Then the Cu-MOFs/poly (lactic acid) (PLA) composites with various components were prepared by the melt blending extrusion and characterized. Their mercury ions (Hg²⁺) adsorption capacity was evaluated. Cu-MOFs could be dispersed well in PLA matrix. The glass transition temperature, crystalline temperature and melting temperature of the composites were increased as a result of the addition of Cu-MOFs. The thermal stability and crystallinity of the composites slightly improved. The Hg²⁺ adsorption efficiency of the composites enhanced with the increasing of Cu-MOFs content.     

Stabilization of immiscible polymer blends using structure directing metal organic frameworks (MOFs)

We have developed a novel approach for compatibilizing immiscible polymer blends using metal organic frameworks (MOFs). For the first time we demonstrated that the droplet diameter of the dispersed phase in a 1:1 immiscible polymer blend composed of 6FDA-DAM:DABA [copolymer of 4,4-hexafluoroisopropylidene diphthalic anhydride (6FDA), 2,4,6-trimethyl-1,3-phenylenediamine and 3,5-diaminobenzoic acid (DABA)], and polybenzimidazole (PBI), is dramatically reduced obtaining a uniform microstructure with the incorporation of as low as 5% (w/w) of the zeolitic imidazolate framework-8 (ZIF-8). This indicates a large improvement in the compatibility of the immiscible polymers with the inclusion of ZIF-8. As the ZIF-8 loading was further increased to 10% (w/w), the droplet diameter further decreased resulting in even higher compatibility. The compatibilizing effect can be attributed to a reduction in the interfacial energy of the immiscible polymers due to the interfacial localization of ZIF-8. This MOF based compatibilization of immiscible polymer blends can open up opportunities for the combination of different properties of polymers in membrane-based separations and in more applications.     

Ionothermal synthesis of zeolites, metal-organic frameworks, and inorganic-organic hybrids

Ionothermal synthesis, the use of ionic liquids as both solvent and template (structure-directing agent), has been used to prepare zeolites and inorganic-organic hybrids such as metal-organic frameworks. The underlying properties of the ionothermal method are discussed, and it is compared with traditional hydrothermal preparative methods. The materials resulting from ionothermal synthesis are described, and any structural features that can be related to the ionic liquid used as the solvent are discussed. Future areas of potential interest are also considered.     

Metal and metal oxide nanoparticle synthesis from metal organic frameworks (MOFs): finding the border of metal and metal oxides

Herein, for the first time, we report a generalized strategy for the successful synthesis of highly crystalline metal and metal oxide nanoparticles embedded in a carbon matrix by the controlled thermolysis of metal organic frameworks (MOFs). The rationalized synthesis strategy of a broad range of metal and metal oxides nanoparticles, such as Cu/CuO, Co/Co(3)O(4), ZnO, Mn(2)O(3), MgO and CdS/CdO, by thermolysis of MOFs demonstrates for the first time that metal ions with a reduction potential of -0.27 volts or higher present in MOFs always form pure metal nanoparticles during thermolysis in N(2), whereas metal ions with a reduction potential lower than -0.27 volts form metal oxide nanoparticles during thermolysis in N(2). Another point of interest is the fact that we have found a unique relationship between the nanoparticle size and the distance between the secondary building units inside the MOF precursors. Interestingly, the crystallinity of the carbon matrix was also found to be greatly influenced by the environment (N(2) and air) during thermolysis. Moreover, these nanoparticles dispersed in a carbon matrix showed promising H(2) and CO(2) adsorption properties depending on the environment used for the thermolysis of MOFs.     

Bilayer and 3-D open framework: Pillared metal-organic frameworks based on zinc and cadmic (6,3)-layers

The (6,3)-layers of transition metals and 3,5-pyridinecarboxylate (3,5-PDC) containing terminal coordinated molecules offer a great potential for obtained porous frameworks via the “pillaring” approach. In this work, we have successfully obtained two porous frameworks based on the zinc and cadmic (6,3)-layers (compounds 1 and 2, respectively) pillared by 4,4′-pyridine (bipy). Interestingly, different metal centers of Zn(II) and Cd(II) in the (6,3)-layers lead to the pillared frameworks into bilayers with {6³}{6⁶} topology (compound 3) and 3-D open framework with {6³}{6⁹·8} hms topology (compound 4), respectively. It is believed that this work deserves further focus to enrich the design strategy of novel porous crystalline metal-organic frameworks (MOFs).     

Supramolecular control of reactivity in the solid state: from templates to ladderanes to metal-organic frameworks

We describe how reactivity can be controlled in the solid state using molecules and self-assembled metal-organic complexes as templates. Being able to control reactivity in the solid state bears relevance to synthetic chemistry and materials science. The former offers a promise to synthesize molecules that may be impossible to realize from the liquid phase while also taking advantage of the benefits of conducting highly stereocontrolled reactions in a solvent-free environment (i.e., green chemistry). The latter provides an opportunity to modify bulk physical properties of solids (e.g., optical properties) through changes to molecular structure that result from a solid-state reaction. Reactions in the solid state have been difficult to control owing to frustrating effects of molecular close packing. The high degree of order provided by the solid state also means that the templates can be developed to determine how principles of supramolecular chemistry can be generally employed to form covalent bonds. The paradigm of synthetic chemistry employed by Nature is based on integrating noncovalent and covalent bonds. The templates assemble olefins via either hydrogen bond or coordination-driven self-assembly for intermolecular [2 + 2] photodimerizations. The olefins are assembled within discrete, or finite, self-assembled complexes, which effectively decouples chemical reactivity from effects of crystal packing. The control of the solid-state assembly process affords the supramolecular construction of targets in the form of cyclophanes and ladderanes. The targets form stereospecifically, in quantitative yield, and in gram amounts. Both [3]- and [5]-ladderanes have been synthesized. The ladderanes are comparable to natural ladderane lipids, which are a new and exciting class of natural products recently discovered in anaerobic marine bacteria. The organic templates function as either hydrogen bond donors or hydrogen bond acceptors. The donors and acceptors generate cyclobutanes lined with pyridyl and carboxylic acid groups, respectively. The metal-organic templates are based on Zn(II) and Ag(I) ions. The reactivity involving Zn(II) ions is shown to affect optical properties in the form of solid-state fluorescence. The solids based on both the organic and metal-organic templates undergo rare single-crystal-to-single-crystal reactions. We also demonstrate how the cyclobutanes obtained from this method can be applied as novel polytopic ligands of metallosupramolecular assemblies (e.g., self-assembled capsules) and materials (e.g., metal-organic frameworks). Sonochemistry is also used to generate nanostructured single crystals of the multicomponent solids or cocrystals based on the organic templates. Collectively, our observations suggest that the organic solid state can be integrated into more mainstream settings of synthetic organic chemistry and be developed to construct functional crystalline solids.     

New polyaniline(PAni)-polyelectrolyte (PDDMAC) composites: Synthesis and applications

Conducting and electroactive polymer blends of polyaniline (PAni) with polyelectrolyte, poly(diallydimethylammoniumchloride) (PDDMAC) have been synthesized by an in situ polymerization method and the resulting composites have been characterized by FT-IR, UV–Vis, XRD, AFM and electrochemical techniques. The blends are conducting and electroactive with even lower loadings of PAni and can be cast as films. The conductivity of the cast films containing 0.04–1.5 wt% PAni ranged from 4.5 × 10⁻⁶ to 42 × 10⁻⁶ S/cm. Some of the composites are tested for their corrosion inhibition property for pure iron in 1 M HCl solutions and were found to be active inhibitors.     

Graphite/Polyaniline (GP) composites: Synthesis and characterization

Ever since the discovery of inherently conducting polymers (ICPs), research dealing with the applications of these unique materials continues to grow. The use of ICPs, especially polyaniline (PANi) and polypyrrole (PPy), and carbon black (CB) as conductive additives in the thermoplastics industry have been limited due to undesirable properties of each at high temperatures. Carbon black-ICP composites, however, have shown improved properties at higher temperatures. The applications of these composites are still limited because the conductivities are below that of carbon black alone and about the same order of magnitude as PANi. Graphite/ICP composites have also been touted as possible electrode materials in rechargeable batteries and have numerous other applications. The exploration of graphite/PANi composites in our research lab has yielded conducting composites which exhibit conductivities greater than the graphite or PANi alone. In addition to higher conductivities, these graphite/PANi composites exhibit controllable conductivities as a function of pH.     

Synthesis,characterization, and glass fiber reinforced composites of poly(urethane-imide)s

Poly(urethane-imide)s (PUI)s were prepared by the intermolecular Diels-Alder (DA)reaction of 4-methyl-1,3-phenylene-bis(2-furanylmethylthioethylcarbamate) (MPFTC) with various bismaleimides. The DA reaction was carried out in 1,4-dioxane as a solvent as well as in bulk, followed by aromatization of tetrahydrophthalimide intermediates in the presence of acetic anhydride. All the polymers were characterized by elemental analysis, IR spectral studies and thermogravimetry. The PUIs exhibit moderate thermal stability. MPFTC and bismaleimides were polymerized (at 145 - 10°C) by an "in situ" DA intermolecular reaction into moderately thermally stable PUIs glass-fiber composite (i.e., laminates) and were characterized by their chemical resistance and mechanical properties.     

Acid-base properties and catalytic activity of metal-organic frameworks: A view from spectroscopic and semiempirical methods

This article summarizes several approaches for understanding the catalytic chemistry and “structure-surface acidity-reactivity” relationships in a multiplicity of catalytic applications of a continually increasing assemblage of metal-organic frameworks (MOFs) structures. The various spectroscopic techniques for acid-base characterization of MOFs are reviewed. The experimental requirements and the type and nature of probe molecules available are also discussed. Special emphasis is given to the revealing of the surface acid-base effect on the catalytic performance of MOFs.     

A new rigid ligand anthraquinone-1,4,5,8-tetracarboxylic acid (H4AQTC) and its two new porous metal-organic frameworks: Syntheses, structures and properties

A new rigid multicarboxylates anthraquinone-1,4,5,8-tetracarboxylic acid (H₄AQTC) was synthesized based on a modified synthetic procedure from 2,5-dimethylfuran and maleic anhydride. This rigid ligand can be widely utilized to construct rigid porous MOFs which may be candidates of porous materials. Two new rigid porous MOFs {[Cd(AQTC)_0.5(H₂O)₃]·H₂O}_n (1) and {[Ni(AQTC)_0.5(BPY)_0.5(H₂O)₃]·2H₂O}_n (2) based on this rigid ligand are reported (BPY = 4,4'-bpy). The adsorption properties of complexes 1 and 2 are investigated, and the Langmuir surface areas are measured to be 43.25 m²/g and 389.14 m²/g.     

Molecularly imprinted polymer based on metal-organic frameworks: synthesis and application on determination of dibutyl phthalate

ABSTRACT

The molecular surface imprinted graft copolymer of metal-organic framework MOF-5 with methacrylic acid were prepared by free radical polymerization with dibutyl phthalate as the template molecule using initiator of azobisisobutyronitrile as adsorption system. The prepared MIPs@MOF-5 were characterized by fourier transform infrared spectroscopy, scanning electron microscopy, Brunner?Emmet?Teller measurements, adsorption isotherms, kinetics and selectivity experiments, which showed higher specificity, sensitivity, stability, and better adsorption performance. The results suggested that MIPs@MOF-5 had two sites of adsorption behavior and can recognize sensitively and selectively the template molecules. Moreover, the MIPs@MOF-5 was successfully applied to the analysis of tap water sample.     

A novel condensation-addition-type phenolic resin (MPN): Synthesis, characterization and evaluation as matrix of composites

This paper reports a novel methylol and propargyl-containing dual-cure-mechanism novolac-based phenolic resin (MPN). MPN resins with varying contents of reactive groups were synthesized by a two-step one-pot method facilly and characterized by Flourier transfer infrared spectra (FT-IR), hydrogen magnetic resonance spectra (¹H NMR), gel permeation chromatography (GPC), dynamic scanning calorimetry (DSC) and dynamic mechanical analysis (DMA) techniques. The resins could be thermally cured by two gradual but fused stages: Condensation of methylol groups and addition polymerization of propargyl groups. This novel resin has advantages over conventional condensation-cure and addition-cure phenolic resins in processing capability. The results of DMA and thermogravimetry analysis (TGA) showed the cured resins possessed high thermal properties. Evaluation of MPN as matrices for advanced composites indicated the enhanced crosslink network derived from dense reactive groups in one single molecule was beneficial to the admirable thermal stability, but was detrimental to the mechanical properties of the resultant composites. MPN resin was amongst ideal candidates for matrices of high temperature materials.     

A Life-Cycle Assessment (LCA) study on the various recycle routes of pet bottles

A life-cycle assessment (LCA) study on various recycle routes of plastic materials has been conducted using the case of polyethylene terephthalate (PET) bottles as an example. The energy consumed and the emissions released during the entire life-cycle of the plastic material were accounted for using the energy and material balances on each stage of the life-cycle. A mathematical model including a simple nonlinear relation for the collection process of the bottles was derived for the system which encompasses all possible recycle alternatives. This model contains several adjustable parameters representing each alternative step of the recycle routes. Then through parameter sensitivity analysis and optimization analysis we could both identify environmentally favorable recycle routes and determine the optimal conditions for the best one. The methodology of this study can be easily applied to the comparison of the general waste management alternatives determining their relative advantages and disadvantages viewed from the associated environmental burdens. Those results will be reported elsewhere.