Luminescent nanoscale metal–organic frameworks for chemical sensing

Metal–organic frameworks(MOFs) are a fascinating class of crystalline materials constructed from selfassembly of metal cations/clusters and organic ligands. Both metal and organic components can be used to generate luminescence, and can further interact via antenna effect to increase the quantum yield,providing a versatile platform for chemical sensing based on luminescence emission. Moreover, MOFs can be miniaturized to nanometer scale to form nano-MOF(NMOF) materials, which exhibit many advantages over conventional bulk MOFs in terms of the facile tailorability of compositions, sizes and morphologies, the high dispersity in a wide variety of medium, and the intrinsic biocompatibility. This review will detail the development of NMOF materials as chemical sensors, including the synthetic methodologies for designing NMOF sensory materials, their luminescent properties and potential sensing applications.     

Advanced metal–organic frameworks for aqueous sodium-ion rechargeable batteries

Inexpensive and abundant sodium resources make energy storage systems using sodium chemistry promising replacements for typical lithium-ion rechargeable batteries(LIBs).Fortuitously,aqueous sodium-ion rechargeable batteries(ASIBs),which operate in aqueous electrolytes,are cheaper,safer,and more ionically conductive than batteries that operate in conventional organic electrolytes;furthermore,they are suitable for grid-scale energy storage applications.As electrode materials for storing Na~+ ions in ASIBs,a variety of multifunctional metal-organic frameworks(MOFs) have demonstrated great potential in terms of having porous 3 D crystal structures,compatibility with aqueous solutions,long cycle lives(≥1000 cycles),and ease of synthesis.The present review describes MOF-derived technologies for the successful application of MOFs to ASIBs and suggests future challenges in this area of research based on the current understanding.     

A two-dimensional microporous metal–organic framework for highly selective adsorption of carbon dioxide and acetylene

Solvothermal reaction of 3-aminoisonicotinic acid(Haina) and Cu(NO_3)_2·2.5H_2O gave a novel twodimensional(2D) microporous metal–organic framework, [Cu(aina)_2(DMF)]·DMF(1, DMF = N,N-dimethylformamide). Single-crystal X-ray crystallographic study of compound 1 revealed that Cu(II)ions are linked by ainaàligands forming square grid-like layers, which stack together via multiple hydrogen bonding interactions. The solvent-free framework of 1a displayed considerable porosity(void = 46.5%) with one-dimensional(1D) open channels(4.7 ? ? 4.8 ?) functionalized by amino groups.Gas sorption measurements of 1 revealed selective carbon dioxide(CO_2) and acetylene(C_2H_2) adsorption over methane(CH_4) and nitrogen(N_2) at ambient temperature.     

Phosphonate metal–organic frameworks used as dye removal materials from wastewaters

A very intense study class of complex porous materials, metal–organic frameworks (MOFs), composed of diverse central metallic ions attached to organic linkers, was used in this study as adsorbant materials from wastewaters. Phosphonate MOFs were prepared by the reaction of divalent inorganic salts (CoSO₄ · 7H₂O, NiSO₄ · 6H₂O, CuSO₄ · 5H₂O,) with vinyl phosphonic acid in hydrothermal conditions, obtaining cobalt, nickel, and copper vinylphosphonate (CoVP, NiVP, and CuVP). During synthesis the experimental conditions were varied in terms of time, temperature, and pH. The synthesized materials were characterized by Fourier transform infrared, thermogravimetric analysis, scanning electron microscopy, and X-ray crystallography. The efficiency of MOFs as adsorbents was investigated for diverse initial dye concentrations at different pH values and at three temperatures (25, 40, and 55°C). The synthesized materials presented good efficiency in the elimination of anionic as well as cationic type of dyes from aqueous solutions. The highest adsorption capacities were obtained working at optimum solution pH 4.2 for Acid Orange 7 and 10 for Basic Fuchsine, using 1 g/L of MOFs at room temperature (25°C). The adsorption capacities increase in the following order: CuVP < NiVP < CoVP.     

The application of Bimetallic metal–organic frameworks for antibiotics adsorption

Fe/Zr-base metal–organic frameworks(Fe/Zr-MOFs) were prepared using a solvothermal method from 1,3,5-phthalic acid (H₃BTC, 98 %) as the organic chain and ferrous heptahydrate (FeSO₄·7H₂O) and zirconium acetate Zr(CH₃COO)₄] as the metal ions. The resulting material was used to remove Doxycycline hydrochloride (DC). The experimental results showed that when the concentration of DC was 10 ppm and the mass of Zr/Fe-MOFs was 100 mg, the maximum removal rate after 5 h was 87.5 %. The results showed that the correlation coefficients (R²) of the pseudo-second-order kinetics model and Freundlich isotherm model of Zr/Fe-MOFs adsorption of DC were greater than 0.99, indicating good consistency. The results showed that the adsorption process of DC by Zr/Fe-MOFs was endothermic and spontaneous. Fe/Zr-MOFs had a high adsorption capacity for DC removal and good application prospects.     

Weak interactions in imidazole-containing zinc(II)-based metal–organic frameworks

The self-assembly of the two zinc(II) metal–organic frameworks, [Zn₂(L)(bdc)₂]·3MeOH·4H₂O}_n ( 1 , L = 2-(pyridin-4-yl)-3H-imidazo[4,5-c]pyridine, H₂bdc = 1,4-benzenedicarboxylic acid) and [Zn₂(L)(bdc)₂]·2DMF·H₂O}_n ( 2 ), was achieved under mild reaction conditions. Both compounds 1 and 2 were structurally characterized by single-crystal X-ray diffraction analysis. Interestingly, the coordination modes of the ligand L in two structures are entirely different. Compounds 1 and 2 were made up of paddle wheel-shaped {Zn₂(O₂C)₄} secondary building unit (SBU) clusters, which adopted three-dimensional structures with a pcu topology. Rich weak interactions were observed in the structures of both 1 and 2 . The uncoordinated imidazole and pyridine moieties exhibited electron donor–acceptor interactions, π–π stacking, hydrogen bonding, and CH–π interactions. These interactions also facilitated the abilities of the framework to adsorb CO₂ molecules. Gas adsorption studies revealed that compound 1 selectively adsorbed CO₂ (131.1 cm³/g) over N₂ (23.5 cm³/g) and H₂ (36.5 cm³/g) at a pressure of 1 atm.     

Cobalt imine–pyridine–carbonyl complex functionalized metal–organic frameworks as catalysts for alkene epoxidation

Aerobic epoxidation of alkene is a green and economical route to produce epoxides. For such reaction, transition metal complexes exhibit favorable catalytic activity. In this work, NH₂-MIL-101, a stable metal–organic framework (MOF) material with large surface area and high pore volume, was functionalized with pyridine-2,6-dicarbaldehyde and Co(NO₃)₂, to realize the immobilization of Co(II) via imine–pyridine–carbonyl (N,N,O) tridentate ligands bonding to MOF skeleton. The modified materials were applied as heterogeneous catalysts for the aerobic epoxidation of cyclohexene at ambient temperature, and multiple factors were studied to explore their influences on catalytic effects. Under the optimal reaction conditions, satisfactory substrate conversion and epoxide selectivity were reached. In addition, this catalytic system is suitable for a variety of alkene substrates. Furthermore, recycle experiments and infrared spectroscopy characterization illustrated that the coordination surroundings of Co are altering smoothly during the reaction process, thus having an impact on the performance of catalyst.

     

N-doped graphitic carbon encapsulating cobalt nanoparticles derived from novel metal–organic frameworks for electrocatalytic oxygen evolution reaction

Nitrogen-doped carbon catalysts with hierarchical porous structure are promising oxygen evolution reaction (OER) catalysts due to the faster mass transfer and better charge carrying ability. Herein, an exquisite high nitrogen-containing ligand was designed and readily synthesized from the low-cost biomolecule adenine. Accordingly, three new MOFs (TJU-103, TJU-104 and TJU-105) were prepared using the Co(II) or Mn(II) ions as metal nodes. Through rationally controlling pyrolysis condition, in virtue of the high nitrogen content in well-defined periodic structure of the pristine MOFs, TJU-104–900 among the derived MOFs with hierarchical porous structure, i.e., N-doped graphitic carbon encapsulating homogeneously distributed cobalt nanoparticles, could be conveniently obtained. Thanks to the synergistic effect of the hierarchical structure and well dispersed active components (i.e., C=O, Co‒N_x, graphitic C and N, pyridinic N), it could exhibit an overpotential of 280 mV@10 mA/cm² on carbon cloth for OER activity. This work provides the inspiration for fabrication of nitrogen-doped carbon/metal electrocatalysts from cost-effective and abundant biomolecules, which is promising for practical OER application.     

Quasi-solid electrolyte membranes with percolated metal–organic frameworks for practical lithium-metal batteries

High-energy Li-metal batteries (LMBs) suffer from short cycle life and safety issues due to severe parasitic reactions and dendrite growth of Li metal anode (LMA) in liquid electrolytes [1–3].It is generally believed that replacing liquid electrolytes with solidstate electrolytes (SSEs) would be a feasible approach for practical LMBs [4,5]. Conventional SSEs including ceramic and polymer electrolytes have been studied for decades.     

Chemical chaperone delivered nanoscale metal–organic frameworks as inhibitor of endoplasmic reticulum for enhanced sensitization of thermo-chemo therapy

Thermotherapy and chemotherapy have received extensive attention to tumor treatment. However, thermal tolerance and drug resistance severely limit clinical effect of tumor therapy owing to endoplasmic reticulum(ER) stress. Reducing thermal tolerance and drug resistance of tumors is an urgent challenge to be solved. In this work, we design a nanoplatform of PBA-Dtxl@MIL-101 as an ER inhibitor. Amino functionalized Fe-metal organic framework(MIL-101) nanoparticles are synthesized as p H and microw...     

Structural diversity of metal–organic frameworks via employment of azamacrocycles as a building block

Research on incorporating macrocycles into metal–organic frameworks (MOFs) has been performed intensively due to the opportunities afforded by merging a merit of macrocycles with MOF chemistry, which lead to novel hybrid materials for potential application. Among the numerous kinds of macrocycles, azamacrocycles are used as traditional and popular chelating agents in supramolecular coordination chemistry, because they are very easily functionalized by joining pendant arms and possess a strong propensity to complex metal cations, accounting for the amine functionalities. With this as background, many types of azamacrocyclic MOFs have been synthesized, granting compositionally and topologically new MOFs. The macrocyclic rings can serve as additional adsorption sites or catalytic sites, and the pendant arms on the macrocycles can also play versatile roles such as structure-directing agents, pore-decorating moieties, or rotatable molecular gates for opening/closing pores. In this review, we comprehensively discuss the syntheses, structures, and features of azamacrocyclic MOFs reported to date. Based on representative studies, advantages of these compounds are described, such as how the azamacrocycles increase the structural diversity and complexity of the MOFs and induce novel structural properties within the architectures.     

Worm-like mesoporous carbon synthesized from metal–organic coordination polymers for supercapacitors

A green and efficient route has been employed to synthesize a worm-like mesoporous carbon with high specific surface area (2587 m² g^?1) and large pore volume (3.14 cm³ g^?1). Three electrochemical methods have been used to measure its electrochemical performance. Worm-like mesoporous carbon performs the high specific capacitance (344 F g^?1) at constant-current densities of 50 mA g^?1.     

A novel method for predicting decomposition onset temperature of high-energy metal–organic frameworks

Journal of Thermal Analysis and Calorimetry - The decomposition onset temperature, Tdecom, is an important parameter for investigating the thermal stability of chemicals. A novel method is...     

A low-temperature synthesis-induced defect formation strategy for stable hierarchical porous metal–organic frameworks

A stable hierarchical porous metal–organic framework PCN-56 with abundant Lewis acid sites (denoted as Defective-PCN-56) was synthesized by the low-temperature synthesis-induced defect formation method. The existence of mesopore in structure was confirmed by N₂ sorption isotherm and the successful encapsulation of large dye molecules. The Defective-PCN-56 has higher loading capacity toward anti-cancer drug Doxo compared with that of “nearly ideal-crystal” (denoted as Ideal-PCN-56) synthesized at high temperature, showing potential application as drug carrier. The low-temperature synthesis-induced defect formation strategy presented here provides a new and facile way to synthesize stable MOFs with the combination of intrinsic micropore and additional mesopore as well as abundant Lewis acid sites.     

Conversion of carbon dioxide to propionaldehyde over cobalt and rhodium nanoparticles supported on MIL-53 (Al) metal–organic framework

The two-step conversion of carbon dioxide to propionic acid and propionaldehyde has been studied in the presence of novel catalysts, cobalt and rhodium nanoparticles supported on MIL-53(Al) microporous metal–organic framework. The first step is hydrogenation of carbon dioxide with formation of synthesis gas over cobalt-containing catalyst Co/MIL-53(Al) (500°C, 1 atm), and the second step is continuous (without separation) Rh/MIL-53 (Al)-catalyzed hydroformylation of ethylene with the synthesis gas formed in the first step.     

Zn(II) and Cd(II) metal–organic frameworks (MOFs) constructed from a symmetric triangular semirigid multicarboxylate ligand: Synthesis,structures and luminescent properties

Three transition metal coordination polymers [Zn₂(H₂L)(2,2′-bpy)₂(H₂O)]_n∙2nH₂O (1), [Zn₂(H₂L)(2,2′-bpy)₂]_n (2), and [Cd₂(H₂L)(2,2′- bpy)₂(H₂O)₂]_n∙2nH₂O (3), have been assembled from a semirigid triangular multicarboxylate ligand 3,3′,3″-(1,3,5-phenylenetri(oxy))triphthalic acid (H₆L) with the help of 2,2′-bipyridine (2,2′-bpy) ligand. X-ray single crystal diffraction analysis reveals that complex 1 crystallizes in the space group of Pī and displays a one-dimensional (1D) ladder chain structure constructed from 2,2′-bpy ligand and H₂L ligand, which stacks together in an -ABCABC- motif, featuring a mutually embedded chained structure. In complex 2, the H₂L ligands bridge the adjacent Zn(II) atoms into a complicated ribbon chain along the b axis. There is π–π stacking interaction between the chains, which results in the formation of a 2D supramolecular structure. Complex 3 also exhibits a 1D ladder-like chain. The different molecular structures for complexes 1 and 2 formed from the same H₆L and Zn(NO₃)₂∙6H₂O in different metal-to-ligand ratios in the presence of NaOH, reveals the influence of metal–ligand ratio on the structure of the coordination polymer. In contrast, a series of same reaction using Cd(NO₃)₂∙4H₂O as a starting material instead of Zn(NO₃)₂∙6H₂O only led to the formation of 3, illustrating the fact organic ligands display different coordination preferences at different metal ions. In addition, the thermal and luminescent properties of complexes 1–3 were also investigated.     

Identifying promising metal–organic frameworks for heterogeneous catalysis via high-throughput periodic density functional theory

Metal–organic frameworks (MOFs) are a class of nanoporous materials with highly tunable structures in terms of both chemical composition and topology. Due to their tunable nature, high-throughput computational screening is a particularly appealing method to reduce the time-to-discovery of MOFs with desirable physical and chemical properties. In this work, a fully automated, high-throughput periodic density functional theory (DFT) workflow for screening promising MOF candidates was developed and benchmarked, with a specific focus on applications in catalysis. As a proof-of-concept, we use the high-throughput workflow to screen MOFs containing open metal sites (OMSs) from the Computation-Ready, Experimental MOF database for the oxidative C—H bond activation of methane. The results from the screening process suggest that, despite the strong C—H bond strength of methane, the main challenge from a screening standpoint is the identification of MOFs with OMSs that can be readily oxidized at moderate reaction conditions. © 2019 Wiley Periodicals, Inc.