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.     

金属有机框架MIL-100(Cr)和MIL-101(Cr)负载磷钨酸催化合成双酚F

采用两种具有相同拓扑结构而孔道不同的金属有机框架MIL-100(Cr)和MIL-101(Cr)负载磷钨酸(PTA),通过XRD、BET、FT-IR、TEM和ICP的对比测试分析,对它们负载磷钨酸前后及其不同负载量情况下的各种物化性质进行表征,并用于催化苯酚、甲醛合成双酚F。实验结果表明,在相同的W/Cr投料摩尔比下,MIL-100(Cr)的磷钨酸负载量大于MIL-101(Cr)的磷钨酸负载量;当MIL-100(Cr) 负载磷钨酸的W/Cr摩尔比为0.40时(磷钨酸负载量16.47%),其催化活性最好,双酚F收率和选择性分别达93.18%和96.11%,反应0.5 h双酚F 4,4'-位异构体比例高达74.24%,催化剂重复使用6次仍保持较高催化活性。     

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.     

Ionothermal synthesis,fluorescence, and DFT calculation of three lanthanide-based metal-organic frameworks

Three lanthanide-based metal-organic frameworks (MOFs), [Ln(SIP)(HSIP)][EMIm]₂, (Ln = La(1), Nd(2) Eu(3); H₂SIP = 5-sulfoisophthalic acid; EMImBr = 1-ethyl-3-methyl-imidazole bromine), were obtained under the ionic liquid medium. Crystal structure analysis reveals that there are two-dimensional metal-organic frameworks, which are built from the connection of {Ln_n} chains by SIP^3 − ligands. It is found that EMIm⁺ cations are filled in the void between 2D layers. Interestingly, the whole framework shows one new topology with the symbol of [3 · 4²]₂[3⁴ · 4⁶ · 5⁶ · 6⁸ · 7³ · 8]. Luminescence measurement exhibits that compound 3 has good emission property. Furthermore, DFT calculation results confirm that the emission mechanism can be attributed to the transition of f–f transition of Eu(III) ions, where SIP^3 − ligand acts as the role of electron carrier.     

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).     

金属有机骨架(MOFs)为壳的核壳结构材料研究进展

MOFs核壳结构材料是近十几年来化工材料领域的研究热点, 其中MOFs可作核, 亦可作壳。本文从不同的核出发综述了以MOFs为壳的核壳结构材料的合成方法, 如外延生长法、后合成修饰法等;概述了其展现出优于核层与壳层的特性(如选择性分离、催化性、磁性等)及以 MOFs为壳的核壳结构材料在气体吸附、催化剂、磁性分离等应用上的研究, 这给MOFs复合材料的产业化带来很大的潜力;而内核主要包括单质金属及非金属类内核、氧化物类内核、MOFs类内核;最后对MOFs为壳的核壳结构复合材料合成方法的改进和拓展、结构均一稳定、多功能化的发展作了展望。     

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.     

Various metal-organic frameworks from 1D, 2D to 3D with 1,6-bis(1,2,4-triazol-1-yl)hexane

Using Zn(II) or Cd(II) salts and the flexible ligand 1,6-bis(1,2,4-triazol-1-yl)hexane(L), a series of novel coordination polymers, {[Zn(L)Cl₂]}_n (1), [Cd(L)₂(SCN)₂]_n (2), {[M(L)₃](ClO₄)₂}_n (M = Zn, 3; Cd, 4), varying from one- to three-dimensionality, have been prepared and their crystal structures determined via X-ray single-crystal diffraction analysis. 1 and 2 are 1D zigzag chain and 2D (4,4) network, respectively. Isostructural compounds 3 and 4 are 3D threefold interpenetrating frameworks. This work suggests that metal/ligand ratio and anion play an important role in the self-assembly of 1D, 2D and 3D coordination polymers based on L.     

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.