Zinc-based Metal-organic Framework Research Articles

Synthesis, Characterization, and Photoelectrochemical Catalytic Studies of a Water-Stable Zinc-Based Metal-Organic Framework.

Metal-organic frameworks (MOFs) are class of porous materials that can be assembled in a modular manner by using different metal ions and organic linkers. Owing to their tunable structural properties, these materials are found to be useful for gas storage and separation technologies, as well as for catalytic applications. A cost-effective zinc-based MOF ([Zn(bpcda)(bdc)]n ) is prepared by using N,N'-bis(pyridin-4-ylmethylene)cyclohexane-1,4-diamine [N,N'-bis(pyridin-4-ylmethylene)cyclohexane-1,4-diamine] and benzenedicarboxylic acid (bdc) linkers. This new material exhibits remarkable photoelectrochemical (PEC) catalytic activity in water splitting for the evolution of oxygen. Notably, this non-noble metal-based MOF, without requiring immobilization on other supports or containing metal particles, produced a highest photocurrent density of 31 μA cm-2 at 0.9 V, with appreciable stability and negligible photocorrosion. Advantageously for the oxygen evolution process, no external reagents or sacrificial agents are required in the aqueous electrolyte solution.

A boronate-decorated porous carbon material derived from a zinc-based metal–organic framework for enrichment of cis-diol-containing nucleosides

A new boronate-decorated carbon material derived from Zn-MOF was synthesized and used to selectively enrich cis-diol nucleosides.

A nanocomposite prepared from a zinc-based metal-organic framework and polyethersulfone as a novel coating for the headspace solid-phase microextraction of organophosphorous pesticides.

The authors describe a zinc-based metal-organic framework/polyethersulfone nanocomposite (TMU-4/PES) coating deposited on a stainless steel wire via a single-phase inversion method. The nanocomposite represents a novel fiber coating for headspace solid-phase microextraction of organophosphorous pesticides (OPPs) from environmental water and soil samples. The synergistic effects of the high surface area and unique porous structure of TMU-4 as well as the rich π electron stacking and mechanical attributes of the PES polymer result in a high affinity of the composite for OPPs. Following thermal desorption, the OPPS were quantified by gas chromatography with a nitrogen-phosphorus detector. The preparation of the coating is simple, and the coated fiber is highly stable and reusable in that it can be used in about 100 consecutive extractions/desorption cycles. A central composite design was used for assessing the effect of the experimental parameters on the extraction process. Under optimized conditions, the limits of detection are in the 5-8ng mL-1 range for the OPPs diazinon, fenitrothion, malathion and chlorpyrifos. The average repeatability and fiber-to-fiber reproducibility are 6.5% and 8.7%, respectively. The method was applied to the trace determination of OPPs in (spiked) water and soil samples where it gave good recovery (88-108%) and satisfactory reproducibility (5.9-10.1%). Graphical abstract A zinc-based metal-organic framework/polyethersulfone nanocomposite coating was prepared on a stainless steel wire via phase inversion. It was used as a novel fiber coating for headspace solid phase microextraction of organophosphorous pesticides from water and soil samples.

A new three-dimensional zinc-based metal-organic framework as a fluorescent sensor for detection of cadmium ion and nitrobenzene

In this study, a novel three-dimensional zinc-based metal-organic framework (Zn-MOF), i.e., {Zn2(L)2(DMF)2H2O}n (L = 2,5-bis(phenylamino)-1,4-benzenedicarboxylic acid) was designed and developed under solvothermal condition. As a proof-of-principle, a π-conjugated framework of carboxylate ligand capable of “bottom up” synthesis was integrated with metal ion to construct a novel MOF for sensing applications. As expected, the synthesized Zn-MOF exhibited fluorescence enhancement for cadmium ion (Cd2+) and sensing of nitrobenzene (NB) through fluorescence quenching. The detection limits were calculated to be 0.12 μM for Cd2+ and 1.19 μg mL−1 for NB based on signal-to-noise ratio of 3:1. Moreover, various techniques and density functional theory investigations verified that the possible sensing mechanisms for Cd2+ and NB included ion exchange and photoinduced electron transfer, respectively. Finally, their practical applications on real samples also demonstrated that the Zn-MOF-based sensor can be effectively utilized for detection and imaging of Cd2+ present in the real water samples and living cells. This study may inspire future research and design of target fluorescent MOFs with specific functions.

A multifunctional zinc-based metal-organic framework for sensing and photocatalytic applications

A multi-functional metal-organic framework (MOF) with the formula [Zn2(L)(4,4′-bpy)(CH3OH)(H2O)2]·3.5H2O·CH3OH(MOF1) (H4L = 2,5-bis-(3,5-dicarboxyphenyl)thiopheneamide,4,4′-bpy = 4,4′-bipyridine) has been successfully synthesized under solvothermal condition and characterized by single crystal X-ray diffraction analysis, IR spectroscopy, thermogravimetric analyses (TGA) and powder X-ray diffraction spectra (PXRD). This material exhibits strong fluorescent emission in the solid state and ethanol suspension at room temperature. Therefore, it is chosen as fluorescence probe for sensing aromatic amines and metal ions. The results reveal that MOF1 has dual-functional sensing performance, which can sense anilines and Al3+ as well Fe3+ ions selectively and reversibly through fluorescence enhancement or quenching effect. In addition, the photocatalysis activities of MOF1 and Fe3+ doped composite material (named Fe3+@MOF1) for degradation of Rhodamine B (RhB) were also studied. The experiment results show that Fe3+@MOF1 has the improved photocatalytic activity than MOF1, suggesting that doping Fe3+ ions into the framework of MOFs would be an ideal option for enhancing their photocatalytic activities.

Facile preparation of nanocubes zinc-based metal-organic framework by an ultrasound-assisted synthesis method; precursor for the fabrication of zinc oxide octahedral nanostructures

Synthesis of metal-organic framework (MOF) materials via ultrasound (US) irradiation involves shorter reaction times and offers enhanced control of particle size and morphology compared to conventional electric (CE) heating. Nanocubes of an interpenetrated pillared-layer Zn(II) metal-organic framework, [Zn2(NH2-BDC)2(4-bpdh)]·3DMF (TMU-16-NH2) (NH2-BDC=amino-1,4-benzenedicarboxylate, 4-bpdh=2,5-bis(4-pyridyl)-3,4-diaza-2,4-hexadiene, DMF=N,N-dimethylformamide), have been synthesized by US process and characterized by Field Emission Scanning Electron Microscopy (FE-SEM), powder X-ray diffraction, thermogravimetric analysis (TGA), elemental analysis and FTIR spectroscopy. The role of initial reagent concentrations and power levels of US irradiation and also reaction time, on size and morphology of nanostructure TMU-16-NH2 have been studied. Moreover, ZnO octahedral nanoparticles were simply prepared through direct pyrolysis of the TMU-16-NH2 nanocubes asa precursor at 520°C without any surfactant or capping molecules.

Mesoporous ZnO microcube derived from a metal-organic framework as photocatalyst for the degradation of organic dyes

A cube-like porous ZnO architecture was synthesized by direct two-step thermolysis of a zinc-based metal-organic framework [(CH3)2NH2][Zn(HCOO)3]. The obtained ZnO microcube was characterized by powder X-ray diffraction, scanning electron microscopy, transmission electron microscopy and nitrogen adsorption and desorption isotherms. The mesoporous ZnO microcube was comprised by many nanoparticles, and inherited the cube shape from [(CH3)2NH2][Zn(HCOO)3] precursor. With large surface area and mesoporous structure, the ZnO microcube exhibits excellent photocatalytic activities against methyl orange (MO) and rhodamine B (RhB) under UV irradiation, and the degradation rates reached 99.7% and 98.1% within 120min, respectively.

Selective adsorption of Pb (II) over the zinc-based MOFs in aqueous solution-kinetics, isotherms, and the ion exchange mechanism.

Two series of metal-organic frameworks (MOFs) with similar formula units but different central metal ions (M) or organic linkers (L), M-BDC (BDC=terephthalate, M=Zn, Zr, Cr, or Fe), or Zn-L (L=imidazolate-2-methyl, BDC, BDC-NH2), were prepared and employed as the receptors for adsorption lead ions. It was found that the Zn-BDC exhibited a much higher adsorption capacity than the other M-BDC series with various metal ions which have very closely low capacities at same conditions. Furthermore, the Zn-L (L=imidazolate-2-methyl, BDC, BDC-NH2) still have highly efficient adsorption capacity of lead ions, although the adsorption capacity varies with different ligand, as well as the adsorption rate and the equilibrium pH of the solution. This significant high adsorption over Zn-L, different from other M-BDC series with various metal ions (Zr, Cr, or Fe), can be explained by ion exchange between the central metal ions of Zn-L and lead ion in solution. Based on the analysis of FT-IR, X-ray diffraction pattern, the nitrogen adsorption isotherms, the zeta potentials, and the results, a plausible adsorption mechanism is proposed. When equivalent Zn-L were added to equal volume of aqueous solution with different concentration of lead ion, the content of zinc ion in the solution increases with the increase of the initial concentration of lead ions. The new findings could provide a potential way to fabricate new metal organic frameworks with high and selective capacities of the heavy metal ions.

MOF-derived multifractal porous carbon with ultrahigh lithium-ion storage performance

Porous carbon is one of the most promising alternatives to traditional graphite materials in lithium-ion batteries. This is not only attributed to its advantages of good safety, stability and electrical conductivity, which are held by all the carbon-based electrodes, but also especially ascribed to its relatively high capacity and excellent cycle stability. Here we report the design and synthesis of a highly porous pure carbon material with multifractal structures. This material is prepared by the vacuum carbonization of a zinc-based metal-organic framework, which demonstrates an ultrahigh lithium storage capacity of 2458 mAh g−1 and a favorable high-rate performance. The associations between the structural features and the lithium storage mechanism are also revealed by small-angle X-ray scattering (SAXS), especially the closed pore effects on lithium-ion storage.

Enhancement of photocatalytic performance in two zinc-based metal–organic frameworks by solvent assisted linker exchange

Solvent-assisted linker exchange (SALE) was performed on two pillared metal–organic frameworks (MOFs), [Zn2(oba)2(4-bpdb)]n·(DMF)2 (TMU-4) and [Zn(oba)(4-bpmb)0.5]n·(DMF)1.5 (TMU-6), to tune their photocatalytic properties.

Fluorescence Zn-based metal–organic frameworks for the detection of hydrogen sulfide in natural gas

Fluorescent zinc-based metal–organic frameworks (Zn-MOFs) were synthesized via the solvothermal method.

Flexibility in metal–organic frameworks derived from positional and electronic effects of functional groups

The position of functional groups and the subsequent e-density of the benzene rings in a bi-/tri-functionalized zinc-based metal–organic framework (MOF) have been controlled to reveal structural differences.

Synthesis of the homochiral metal–organic framework DUT-129 based on a chiral dicarboxylate linker with 6 stereocenters

A dicarboxylate linker with an exceptionally high density of stereogenic centers for the development of new chiral metal–organic frameworks (MOFs) was synthesized. A bicyclic functionality forms the backbone of the linker, creating a linear structural analogue of terephthalic acid. The linker includes two side chains bearing secondary amine functionalities, which could induce catalytic activity of the resulting MOF structures for nucleophilic organocatalysis. The new chiral linker was used to synthesize a zinc-based MOF structure, named DUT-129. Single crystal X-ray analysis identified the porous framework with a sodalite (sod) topology. The bulky side groups of the chiral linker limit the pore accessibility of DUT-129, which was proven by liquid phase adsorption experiments. The calculated pore limiting diameter of 5.2 A indicates pore accessibility exclusive for small molecules, such as linear and branched alkanes. Therefore, the new MOF DUT-129 is expected to show high size selectivity in adsorption and separation applications in combination with high enantiomeric discrimination.

Beyond pristine MOFs: carbon dioxide capture by metal–organic frameworks (MOFs)-derived porous carbon materials

Porous carbon materials were synthesized by pyrolysis of zinc-based MOFs. These materials exhibited superior CO2 capacities and better CO2 separation ability under humid conditions compared to those of the pristine MOFs.

Redox-active organic molecules functionalized nitrogen-doped porous carbon derived from metal-organic framework as electrode materials for supercapacitor

Metal-organic frameworks (MOFs) have been turned out to be an excellently self-sacrificing template for preparing porous carbon. Herein, we synthesized a nitrogen-doped porous carbon materials (NPCs) by direct thermolysis of zinc-based MOFs (ZIF-8). Fortunately, the NPCs with high specific surface area and abundant pore structure was suitable for using as conductive substrate to anchor organic molecules. Anthraquinone (AQ), 1, 4-naphthoquinone (NQ) and tetrachlorobenzoquinone (TCBQ) were selected to functionalize NPCs via noncovalent interactions, respectively. As a consequence, the multielectron redox centers possessed by AQ, NQ and TCBQ were implanted in the NPCs. More interestingly, the electrochemical rate-determining step for the functionalized NPCs was surface process rather than diffusion, which is similar to capacitive behavior of the electrical double layer. The functionalized NPCs revealed an enhanced overall capacitance (about 1.4 times higher than NPCs) because the electrochemical capacitance was superposed on the electrical double layer capacitance. Furthermore, the as-assembled asymmetrical supercapacitor (ASC) exhibited excellent energy storage performance. The topological structure of MOFs skeleton and the potential self-matching behavior between the positive and negative electrodes were responsible for high energy density (23.5Whkg−1 at 0.7kWkg−1, which is 1.54 times higher than that of NPCs symmetrical supercapacitor) of the device.

Nanoscale zinc-based metal-organic framework with high capacity for lithium-ion batteries

Layered zinc-based metal-organic framework ([Zn(4,4′-bpy)(tfbdc)(H2O)2], Zn-LMOF) nanosheets were synthesized by a facile hydrothermal method (4,4′-bpy = 4,4′-bipyridine, H2tfbdc = tetrafluoroterephthalic acid). The materials were characterized by IR spectrum, elemental analysis, thermogravimetric analysis, powder X-ray diffraction, transmission electron microscope (TEM), scanning electron microscope (SEM), and the Brunauer–Emmett–Teller (BET) surface. When the Zn-LMOF nanosheets with the thickness of about 24 ± 8 nm were used as an anode material of lithium-ion batteries, not only the Zn-LMOF electrode shows a high reversible capacity, retaining 623 mAh g−1 after 100 cycles at a current density of 50 mA g−1 but also exhibits an excellent cyclic stability and a higher rate performance.

Metal‐Organic Frameworks as curing accelerators for benzoxazines

AbstractBenzoxazine resins, although exhibiting attractive properties; particularly high thermal stability and near zero‐ shrinkage, suffer from a major drawback associated with its high curing temperature. In view of the Lewis acidity associated with the Zn4O nodes in a zinc based metal organic framework [Zn4O(BDC)3, MOF5], we considered it of interest to explore its potential as a curing accelerator for a representative biobased benzoxazine resin. MOF 5 was solvothermally synthesized and characterized using different techniques including powder X‐ray diffraction (PXRD), Scanning Electron Microscopy (SEM), Thermogravimetric Analysis (TGA), Fourier transform infrared spectroscopy (FT‐IR) and Nitrogen physisorption measurements. Bio‐based benzoxazine resin was synthesized by mannich type condensation of cardanol and aniline with formaldehyde under solventless conditions, the structure of which was confirmed using FT‐IR and 1H‐NMR. The curing behavior of the synthesized resin was systematically investigated using non‐isothermal Differential Scanning Calorimetry (DSC). Introduction of MOF 5 led to a shift in the curing profile to lower temperature, the extent of which was proportional to the amount of MOF 5 in the formulation. DSC studies were performed at different heating rates to establish the kinetic parameters associated with the curing of the resin. Activation energy, as calculated using Kissinger Akahira Sunose method, was found to concomitantly decrease from 98 kJ/mol to 58 kJ/mol upon addition of MOF 5 (5 % w/w).

Aromatic Substituent Effects on the Flexibility of Metal-Organic Frameworks.

The flexibility (or breathing behavior) of zinc-based metal-organic frameworks (MOFs) has been manipulated by regioisomeric and positional control of organic functionalities. Ten new regioisomeric BDC (ortho- or para-disubstituted benzene-1,4-dicarboxylic acid) ligands have been synthesized and applied to a DMOF (dabco MOF) system, which has a zinc(II) paddle-wheel SBU (secondary building unit). Among the new regioisomeric MOFs, the NH2-OMe combination showed significant flexibility (breathing behavior) changes by simply altering the functional group positions (from 2,3 to 2,5). The electronic density of the benzene ring was considered to be a major factor in the flexibility changes in the regioisomeric MOF system.

Exploring a thiol-functionalized MOF for elimination of lead and cadmium from aqueous solution

A thiol-functionalized metal organic framework material (called HS-mSi@MOF-5) was successfully prepared by the thiol modification which taking the silica gel layer as a medium, on the basis of zinc based metal organic framework (MOF-5) synthesized by hydro-thermal method. The novel material was characterized by Fourier transfer infrared spectroscopy, scanning electron microscopy and X-ray powder diffraction. It was also investigated to remove lead and cadmium ions from aqueous solution. In view of adsorption capacity and adsorption rate, HS-mSi@MOF-5 was shown to be a more convenient and effective adsorbent (312.5mg/g; 65.2g/mg·min0.5) than unmodified MOF-5 (211mg/g; 4.2g/mg·min0.5). Besides, in the hydrostability test, unmodified MOF-5 would leak its own component when present in acid solution, whereas the thiol-functionalized material was stable owing to its synthesis process taking the silica gel layer as a medium. At last, electrostatic attraction and the thiol coordination interaction with potentially toxic metals played vital roles in the adsorption of lead and cadmium ions on HS-mSi@MOF-5.

Comparison of MOF-5- and Cr-MOF-derived carbons for hydrogen storage application

Nanoporous carbons which possess high surface areas and narrow pore size distributions have become one of the most important classes of porous materials with potential to be utilized for hydrogen storage. In recent times, several metal–organic frameworks (MOFs) have been shown to be promising precursors for creating nanoporous carbons due to their high surface areas and tunable pore sizes. The pore structure and surface area of the resultant carbon materials can be tuned simply by changing the calcination temperature. In this work, a zinc-based MOF (MOF-5) and a chromium-based MOF (Cr-MOF) were both used as precursors for syntheses of nanoporous carbons by the direct carbonization technique at different temperatures. The resultant carbon nanostructure from MOF-5 possessed higher surface area, higher pore volume and enhanced hydrogen storage capacity as compared to pristine MOF. Meanwhile, the derived carbons from Cr-MOF displayed lower surface areas, pore volumes and hydrogen uptake than the parent MOF due to the formation of chromium oxide and carbide species in the pores of the Cr-MOF-derived carbons.