Zn Metal-organic Framework Research Articles

New topological Zn metal organic frameworks as multi-responsive fluorescent sensing materials for detecting Fe3+, Cr2O72−, CrO42− and tetracycline in aqueous system

Three new Zn metal organic frameworks (Zn-MOFs), {[Zn2(L)[H (1,4-bmib)]]·1.5(H2O)}n (1), {[Zn2(HL) (3,5-bip)2]·(H2O)}n (2), and {[Zn2(HL) (4,4′-bbibp)2]·4(H2O)}n (3), have been first synthesized based on a flexible H5L ligand with ether functional group (C–O–C) and successfully characterized (semi-flexible H5L ​= ​3,5-bis(3,5-dicarboxylphenoxy)benzoic acid, flexible 1,4-bmib ​= ​1,4-bis(2-methylimidazol-1-yl)butane, rigid 3,5-bip ​= ​3,5-bis(1-imidazolyl)pyridine, and rigid 4,4′-bbibp ​= ​4,4′-bis(benzoimidazo-1-ly)biphenyl). Zn-MOFs 1–3 are unique topological networks. As multi-responsive fluorescent sensing materials of 1 and 3, they show excellent response and sensitivity for Fe3+, CrO42− and Cr2O72−, and tetracycline (TC) in aqueous system. The quenching mechanism is also investigated in detail.

Synthesis, structural characterization, and carbon dioxide and hydrogen adsorption of a new three-dimensional metal organic framework Zn(BTC)4

A novel three-dimensional porous metal organic framework Zn(BTC)4 (BTC = benzene-1,3,5-tricarboxylic acid) is synthesized by the solvothermal method. This structure is characterized by single-crystal X-ray diffraction, scanning electron microscopy, and thermogravimetric analysis. This metal organic framework crystallizes in a monoclinic (P2(1)/n, V = 1795.7(2) Å3, Z = 4, Dc = 1.449 mg/cm3, α = 90.00°, β = 97.2200(10)°, γ = 90.00°, a = 9.5077(5) Å, b = 16.3950(16) Å, c = 11.6119(9) Å). The thermogravimetric analysis shows the material can be stabilized up to 350 °C, then the skeleton collapses between 350~510 °C. A luminescence test shows that the material gives out strong emission at 384 and 462 nm. The hydrogen storage capacity of this metal organic framework is 2.01 wt% at 77 K and a pressure of 10 bar. The carbon dioxide storage capacity of this metal organic framework is 4.17 mmol/g at 298 K and a pressure of 10 bar.

A nanostructure of reduced graphene oxide and NiO/ZnO hollow spheres toward attenuation of electromagnetic waves

A nanostructured composite composed of reduced graphene oxide (rGO) and NiO/ZnO hollow spheres was prepared via an in situ reaction involving pyrolysis and surface modification of a heterobimetallic Ni–Zn metal-organic framework with amine-functional group. The rGO sheet was successfully grafted on the surface of NiO/ZnO. The hybrid displayed excellent microwave absorbing performance in a polystyrene matrix. The optimal minimum reflection loss reached −42.5 dB at 13.2 GHz at a coating thickness of only 2.15 mm with a 4.5 GHz effective absorption frequency bandwidth, corresponding to a reflection loss of less than −10 dB (90% absorption). The grafting of rGO not only resulted in a hybrid composite with a larger contact area, but also benefited the synergistic effects with NiO/ZnO to endow the electromagnetic wave absorbing performance. Herein, the effective absorption capability of rGO@NiO/ZnO mainly contributed to the enrichment of interfacial polarization, dipole polarization, and dielectric loss followed by multiple reflection and scattering generated from heterogeneous components in the composite. This work is expected to provide a promising method for the development of high-performance microwave absorbers staring from rGO/heterobimetallic MOFs composites.

A special zinc metal-organic frameworks-controlled composite nanosensor for highly sensitive and stable SERS detection

Using 5-mercapto-1-methyltetrazole as the bridge, a porous (~4 nm) Zn metal–organic frameworks coated cuprous oxide/silica core–shell nanostructure (Cu2O@SiO2@ZIF-8) was facilely fabricated. Subsequently, using it as a template, the precisely controlled growth of AgNPs with various sizes (2 nm~29 nm) was achieved. It was found that a strong interaction between AgNPs and ZIF-8 in the Cu2O@SiO2@ZIF-8 favored the AgNPs to be uniformly distributed in the Cu2O@SiO2@ZIF-8. When more AgNPs were obtained in the cavity of Cu2O@SiO2@ZIF-8 with large surface areas (~568.95 m2/g), higher SERS response towards phenol red was resulted in. Moreover, 4 nm AgNPs embedded Cu2O@SiO2@ZIF-8 substrate showed a lower limit of detection (5.76 × 10-12 mol·L-1) and limit of quantification (1.92 × 10-12 mol·L-1), and a higher enhancement factor of 1.7 × 107. Additionally, Raman activity of the Cu2O@SiO2@ZIF-8@Ag changed little within 35 days, and also the low concentration of phenol red in actual sample can be detected. Therefore, the Cu2O@SiO2@ZIF-8@Ag could be employed as highly sensitive and continuously stable 3D substrate for SERS detection of environmental contaminants.

Plasmon induced dual excited synergistic effect in Au/metal-organic frameworks composite for enhanced antibacterial therapy.

Efficient antibacterial therapy holds great promise for human health. However, it is often limited by the insufficient activity of antibacterial agents. Herein, we demonstrate that the localized surface plasmon resonance (LSPR) excitation of gold nanostars (AuNSs) can dramatically improve the antibacterial activity of a Zn-metal-organic frameworks (Zn-MOFs) nanosheet, which exhibits higher ability to generate reactive oxygen species (ROS) (∼2.5-fold) for bacterial inactivation under light irradiation. Mechanistic investigations demonstrate that the enhancement is closely related to a plasmon-induced "dual excited synergistic effect". On the one hand, the Zn-MOFs nanosheets as photosensitive agents can be excited to generate ROS with bacterial toxicity. More importantly, abundant plasmonic hot electrons are generated on the surface of AuNSs upon LSPR excitation, which are then transferred from AuNSs into the Zn-MOFs due to the energy matching. As a result, the Zn-MOFs nanosheet presents an electron-rich condition, which activates the adsorbed O2 molecule into a transition state followed by its decomposition into ROS for bacterial inactivation. This study highlights the superiority of LSPR excitation on improving the antibacterial activity of MOFs and provides a novel strategy for effective antibacterial therapy.

Cation exchange in a fluorescent zinc-based metal–organic framework for cadmium ion detection

A Zn metal–organic framework with a large aperture shows remarkable fluorescence characteristics for the detection of cadmium ions in aqueous solution and can adsorb CO2 and O2 selectively.

Lawsone derived Zn(ii) and Fe(iii) metal organic frameworks with pH dependent emission for controlled drug delivery

Fluorescent biocompatible porous carriers have been investigated as suitable probes for drug delivery and sensing applications owing to their intrinsic fluorescence and high surface area originating from their porous structure complemented with tunable pore size/surface properties.

P.187 Variability of schizophrenia-associated genetic variants across the populations

An anionic Zn(II) Metal-Organic Framework, [HDMA]2[Zn2(BDC)3(DMA)2].6DMF (HDMA+: dimethylamonnium, BDC2−: 1,4-benzenedicarboxilate, DMA: dimethylamine, DMF: N,N′-dimethylformamide), was served as a host for encapsulating I2. For comparison of the ad/desorption rates of iodide, the ion exchange process with organic cations have been done. Loading of the exchanged compounds were successfully done by suspending them in a solution of I2 in cyclohexane. Powder X-ray diffraction experiments and IR analysis showed that the exchanged crystalline lattices after adsorption and desorption of iodide remained the same. The delivery of I2 from the compounds performed in ethanol, were determined by UV/vis spectroscopy. Comparison of iodide adsorption and desorption rates in the exchanged compounds showed that presence of different organic cations have effective role in increasing iodine adsorption.

Synthese, structure of three Zn-MOFs and potential sensor material for tetracycline antibiotic in water: {[Zn(bdc)(4,4′-bidpe)]·H2O}n

Recently, enough attention has been paid to the pollution and damage of antibiotics in water. Zn-metal organic frameworks (Zn-MOFs), as a novel kind of sensing material, have been tentatively developed a highly effective candidate to detect antibiotics in water. A series of Zn-MOFs material named {[Zn (bdc)(4,4′-bidpe)]·H2O}n (1), {[Zn3 (bdc)2 (tib)2(HCOO)2]·4(H2O)·0.5(CH2Cl2)}n (2), [Zn (bdc)(bidpa)]n (3) were successfully constructed under the condition of solvothermal, using 4,4′-bis(imidazolyl)diphenyl ether (4,4′-bidpe), 1,3,5-tirs (1-imidazolyl)benzene (tib), 4,4′-bis(imidazolyl)diphenyl amino (4,4′-bidpa) and 1,4-benzenedicarboxylate (H2bdc). Three complexes were characterized by X-ray single-crystal diffraction, elemental analysis, IR spectra and thermogravimetric (TG) analysis. Complex 1 has a three-dimensional (3D) framework that crystallizes in the triclinic system, Pī space group. Complex 2 crystallizes in the monoclinic system, C2/c space group featuring a 3-nodal (3,3,4)-connected network with point symbol of 2{83}2{86}{8.102}. Complex 3 belongs to the tetragonal system, I41/acd space group with two-fold interpenetrating architecture. A linear pH sensing of complex 1 (I ​= ​1035.2 pH ​+ ​726.9) between the fluorescence intensity and pH values was achieved through the fluorescence quenching experiment in the acidic condition. The fluorescence quenching experimental results showed that complex 1 exhibits sensitive response to TC with detection limit of 3.72 ​× ​10−7 ​M based on its effective spectral overlap and adsorption preconcentration with tetracycline (TC).

Unpaired Electron-Induced Wide-Range Light Absorption within Zn (or Cu) MOFs Containing Electron-Withdrawing Ligands: A Theoretical and Experimental Study.

In photocatalysis, it is of general interest to understand and design wide-range light-absorbing inorganic/organic hybrid materials with an excellent photo-induced intramolecular charge-transfer (ICT) effect. To verify the role of unpaired electrons in enhancing ICT within electron-withdrawing ligand-based metal-organic frameworks (MOFs), the molecular structure, density of states (DOS), and electronic structure of strong electron-deficient pyridine-diketopyrrolopyrrole (P-DPP)-based Zn (or Cu) MOFs were calculated in Gaussian package to validate the unpaired electron ICT. The electron spin resonance technique has detected the unpaired electrons for the coordination systems containing Zn-O or Cu-O clusters and P-DPP ligand on photoexcitation. The estimated band gaps from the DOS calculation for P-DPP-Cu and P-DPP-Zn are 1.4 and 2.4 eV, respectively, showing a good agreement with the experimental UV-vis optical spectra. The partial DOS, dipole moment, and frontier orbital analysis prove that the ICT should happen from Zn-O or Cu-O clusters to P-DPP ligands. This research may contribute to a comprehensive understanding of electron-withdrawing ligand-induced ICT within MOFs and shed light on the design of light-absorbing MOFs with excellent ICT or conductivity.

Nanoporous Fluorinated Metal–Organic Framework-Based Membranes for CO2 Capture

The search for effective carbon-capture materials has permitted the disclosure and institution of nanoporous fluorinated metal–organic frameworks (MOFs) with a contracted pore system as benchmark CO2-selective adsorbents. Namely, the SIFSIX-3-M (M = Zn, Cu, and Ni) MOF adsorbents, encompassing a periodic arrangement of fluorine moieties in a confined one-dimensional channels, exhibit a remarkable CO2 adsorption-based selectivity over CH4 and H2 in various industrially related gas mixtures. Here, we report the successful transplantation/integration of this distinctive CO2 selectivity, distinguishing this class of nanoporous MOF adsorbents to pure MOF membranes for carbon capture. Markedly, the liquid-phase epitaxy (LPE) growth approach permitted, for the first time, the building of continuous, homogeneous, and defect-free MOF membranes based on the SIFSIX-3-M platform, MSiF6(Pyz)2 with M = Ni or Cu, on a porous alumina substrate. Single and mixed-gas permeation tests revealed that the resulting nanoporous MOF membrane is a CO2-selective membrane, exhibiting the foreseen favorable CO2-selectivity toward carbon dioxide over H2, and CH4, governed by the CO2-selective adsorption in the functional and contracted channels of the SIFSIX-3-M.

2D → 3D corrugated structure self‐assembled from 4,4′‐methylenebis(N‐(pyridin‐2‐ylmethylene)aniline and terephthalic acid: Crystal structure and selective anion separations via anion exchange

A new flexible cationic Zn(II)metal organic framework, {[Zn2(BDC)1.5(L)(DMF)]NO3·DMF·solvent}n, MOF 1, which is a corrugated two‐dimensional network, was synthesized by self‐assembly of Zn(NO3)2.6H2O with 4,4′‐methylenebis(N‐(pyridin‐2‐ylmethylene)aniline as a neutral ligand and terephthalic acid in dimethyl formamide (DMF) as solvent and characterized by X‐ray diffraction. Because of the presence of uncoordinated nitrate (NO3−) ions in the channels, the compound was employed for ion‐exchange applications. We report a detailed study of the host–guest interaction for a cationic metal–organic framework (MOF) that can reversibly capture nitrate. The recrystallization of the MOF was evaluated by monitoring the anion exchange dynamics using a combination of powder X‐ray diffraction and Fourier transform infrared spectra with various kinds of foreign anions. This MOF showed fast and highly efficient Cr2O72− and CrO42−, N3−, MnO4−, and SCN− exchange. The trapping capacities of Cr2O72−, CrO42−, N3−, MnO4−, and SCN− were 105,138, 44,104, and 25mg/g at 25°C after 3h, respectively, and there was good recyclability for capturing N3− and SCN−. {[Zn2(BDC)1.5(L)(DMF)]NO3}n exhibited anion exchange selectivity of SCN− in a solution containing a mixture of 0.025mmol N3−, SCN−, CrO4−2−, Cr2O72−, and MnO4− for 3h and exhibited anion exchange selectivity for SCN− and Cr2O72− in a solution containing a mixture of 0.001mmol N3−, SCN−, CrO42−, Cr2O72−, and MnO4−.

Environmentally benign benzyl alcohol oxidation and C-C coupling catalysed by amide functionalized 3D Co(II) and Zn(II) metal organic frameworks

The new 3D metal-organic frameworks (MOFs) [Co(1κN;2κOO′-μ-L)2]n.4n(DMF).1.5n(H2O) (1) and [Zn2(1κN;2κO-μ-L)2(κO4-μ4-BTC)]n.3n(DMF).2n(H2O) (2) [L = 4-(pyridin-4-ylcarbamoyl)benzoate; BTC = benzene-1,3,5-tricarboxylate] have been synthesized from the pyridyl amide functionalized benzoic acid (HL). They were characterized by elemental, FT-IR, powder X-ray and single crystal X-ray diffraction analyses. Topological analysis of 1 discloses a 2,3,7-connected trinodal net with a 4-connected uninodal net with 2-fold interpenetrating networks, whereas that of 2 shows a dia topology. The solid-state photoluminescent properties of HL and 2 were also investigated. The heterogeneous catalytic activity of 1 and 2, under eco-friendly conditions, was assessed in benzyl alcohol oxidation and C-C bond formation model reactions. 1 has good activity in the solvent-free microwave-assisted oxidation of benzyl alcohol to benzaldehyde using tert-butyl hydroperoxide (tBuOOH, TBHP) as oxidizing agent (yields up to 89%). Although with a lower activity, MOF 2 with a redox inactive Zn(II) site, also catalyses such alcohol oxidation, which is explained by DFT calculations according to a mechanism of a similar type to that followed by the peroxidative alkane oxidation. 2 is the most active one in the ambient temperature sonochemical Knoevenagel condensation of benzaldehyde and malononitrile (yields up to 94%) and in the ambient temperature Henry C-C coupling reaction of benzaldehyde with nitroethane in water (yields > 99%), showing appreciable diastereoselectivity towards the syn isomer. The recyclability of catalysts 1 and 2 was evaluated.

A Comparative Study of Proton Conduction Between a 2D Zinc(II) MOF and Its Corresponding Organic Ligand

Until now, comparative studies on proton conductivity between organic ligands and related metal-organic frameworks (MOFs) have been very limited. Herein, a stable 2D Zn(II) MOF, [Zn(L)Cl]n (1), has been successfully synthesized by using a zwitterionic-type organic ligand, 2-(1-(carboxymethyl)-1H-benzo[d]imidazol-3-ium-3-yl)acetate (HL). It is found that there are a large amount of free carboxyl groups and hydrogen bonds in the solid-state structure of HL, and a large number of chlorine ions are aligned in the channels of 1, which is favorable to the efficient proton transfer. Correspondingly, the proton conductivity values of 1 and HL are almost of the same order of magnitude under the same conditions. Moreover, the optimal σ value of 1 (4.72 × 10-3 S/cm at 100 °C and 98% relative humidity) is almost four times higher than that (1.36 × 10-3 S/cm) of the HL ligand. On the basis of the crystal data, SEM images, and calculated Ea values, we discuss the differences on proton conductivities and conduction mechanisms of 1 and HL. This report provides an inspiration for the preparation of highly conductive materials with free carboxyl groups and chloride ions.

Thermodynamic Evidence of Structural Transformations in CO2-Loaded Metal-Organic Framework Zn(MeIm)2 from Heat Capacity Measurements.

Metal-organic frameworks are a class of porous compounds with potential applications in molecular sieving, gas sequestration, and catalysis. One family of MOFs, zeolitic imidizolate frameworks (ZIFs), is of particular interest for carbon dioxide sequestration. We have previously reported the heat capacity of the sodalite topology of the zinc 2-methylimidazolate framework (ZIF-8), and in this Article we present the first low-temperature heat capacity measurements of ZIF-8 with various amounts of sorbed CO2. Molar heat capacities from 1.8 to 300 K are presented for samples containing up to 0.99 mol of CO2 per mol of ZIF-8. Samples with at least 0.56 mol of CO2 per mol of ZIF-8 display a large, broad anomaly from 70 to 220 K with a shoulder on the low-temperature side, suggesting sorption-induced structural transitions. We attribute the broad anomaly partially to a gate-opening transition, with the remainder resulting from CO2 rearrangement and/or lattice expansion. The measurements also reveal a subtle anomaly from 0 to 70 K in all samples that does not exist in the sorbate-free material, which likely reflects new vibrational modes resulting from sorbate/ZIF-8 interactions. These results provide the first thermodynamic evidence of structural transitions induced by CO2 sorption in the ZIF-8 framework.

Chelated Zn–Metal–Organic Frameworks: Synthesis, Crystal Structure and Electrochemical Energy Storage

We have successfully synthesized the chelated Zn-EDTA metal–organic framework (Zn–MOF) by an eco-friendly hydrothermal route at 160 °C. The product obtained was confirmed by techniques such as ATRIR, SEM, SXRD, TGA, and BET. High stability, homogeneous topology, and significant surface area are the notable properties, which have been studied. The electrochemical redox behavior property of the as-prepared Zn–MOF electrode was investigated in 0.005 M K4Fe(CN)6 solution by Cyclic voltammetry. The CV nature obtained by the Zn–MOF electrode implies the typical battery act from the surface redox reaction. The chelated Zn–MOF electrode has been subjected to charge–discharge study to find out the specific capacity of the Zn–MOF electrode in KOH solution different temperatures and also in mixed electrolyte separately. Higher specific capacity of the Zn–MOF electrode about 243.2 mA hg−1 was found at room temperature in 0.1 M KOH at 1 Ag−1. Also, excellent capacity about 589.28 mA hg−1 was observed in mixed electrolytes. The Zn–MOF to be a promising candidate for energy (gas) storage application.

Highest and Fastest Removal Rate of PbII Ions through Rational Functionalized Decoration of a Metal-Organic Framework Cavity.

To overcome the challenge of developing a multipurpose adsorbent for effective removal of toxic and carcinogenic PbII ions from aqueous solutions, a made-for-purpose functional group (N1 ,N2 -di(pyridine-4-yl)oxalamide) was rationally designed and incorporated into the cavities of a Zn metal-organic framework (MOF), namely, TMU-56. Large enough pore size along with high densities of strong metal chelating sites lead not only to the highest uptake capacity for PbII ions, but also the fastest removal rate that has ever been reported for functionalized MOFs, occurring in just 20 s. Moreover, high concentrations of lead ions favor the ion exchange reaction, resulting in a high degree of metal exchange. In addition, TMU-56 can be a practical adsorbent because of its notable performance in the simultaneous removal of several toxic and carcinogenic heavy metals from wastewater, which has rare precedence.

Novel HBD-Containing Zn (dobdc) (datz) as efficiently heterogeneous catalyst for CO2 chemical conversion under mild conditions

A novel Zn-based metal–organic framework Zn (dobdc) (datz) [Zn2(H2dobdc) (datz)2·1.5DMF] with plentiful hydrogen bond donors (HBD) groups was facilely synthesized from mixed ligands. The dual activation of metal Zn sites and HBD groups for epoxides by forming Zn–O adduct and hydrogen bonds facilitated the ring-opening of epoxide substrate, which is critical for the subsequent CO2 fixation. Also, the existence of micropores and N-rich units in Zn (dobdc) (datz) afforded affinity towards CO2, which is beneficial to further improvement on catalytic CO2 conversion performance. Satisfactorily, Zn (dobdc) (datz)/Bu4NBr system was proved efficient heterogeneous catalyst for the CO2 cycloaddition with epoxides, and 98% propylene carbonate yield was obtained under mild conditions (80 °C, 1.5 MPa and solvent-free). In addition, Zn (dobdc) (datz)/Bu4NBr exhibited remarkable versatility to different epoxides and could be completely recycled over six runs with high catalytic activity. The highly stable, easily recycle and solvent-free Zn-based MOF reported here displays eco-friendly and efficient performance to CO2 conversion.

Core-shell Zn/Co MOFs derived Co3O4/CNTs as an efficient magnetic heterogeneous catalyst for persulfate activation and oxytetracycline degradation

Herein, we report a facile and straight strategy to synthesize a highly efficient and recyclable heterogeneous catalyst through a pyrolysis–oxidation of core–shell Zn/Co metal organic frameworks (MOFs). The selected Zn MOF crystals was used as a single precursor to form a nanostructured hollow framework through the evaporation of Zn at high pyrolysis temperature. Meanwhile, the numerous carbon nanotubes (CNTs) was formed on the surface of a hollow nanostructured framework under the catalytic effect of the Co nanoparticles. After subsequent acid etching to remove some large Co particles on its surface, and convert the Co/CNTs to Co3O4/CNTs after low temperature oxidation in air. The structure and surface elements distribution of as-synthesized Co3O4/CNTs catalyst were characterized using XRD, SEM, XPS, VSM and N2 adsorption-desorption experiment. Besides, the resultant nanostructured catalyst Co3O4/CNTs had a high degradation rate of 93.6% for oxytetracycline (OTC) within 80 min and a rapid catalytic degradation rate of 0.034 min−1 in a wide range of pH from 3.0 to 9.0. The degradation mechanism and pathway, and the effects of various parameters on degradation experiments were also studied. The material exhibited superior activity after continuously repeated use five times, and can be collected conveniently through a magnet within 2 min.

Utilization of counter anions for charge transportation in the electrical device fabrication of Zn(II) metal-organic frameworks.

The present work reports the fabrication of anion-induced electrical devices with Zn(ii) metal-organic frameworks. The essence of our electronic device fabrication is to utilize the anionic species entrapped inside of the three-dimensional network of the MOFs for charge transportation. The idea is to generate MOFs as a host-guest system with encapsulated anions or anion-solvent clusters as guests and a cationic yet insulating three-dimensional framework as the host. Accordingly, we have synthesized two Zn(ii) MOFs using a neutral bispyrazole-based ligand, which results in a cationic chassis with substantial void space and porous channels inside the network. For both MOFs, the porous channels are occupied by infinitely hydrogen bonded networks of anions and anion-solvent clusters. This provides an excellent platform for anionic species-induced charge transportation and improved electrical conductivity. Indeed, the impedance spectroscopy data and current density-voltage (J-V) characteristics of the fabricated electrical devices further vindicate our idea. The current-voltage measurements clearly indicate the usefulness of modified host-guest-type MOFs for electronic device fabrication with corroborating conductivity values of 8.71 × 10-5 S m-1 and 5.79 × 10-4 S m-1 for compound 1 and compound 2, respectively.