Two-dimensional MOF Research Articles

Colloidal crystal engineering with metal\u2013organic framework nanoparticles and DNA

Colloidal crystal engineering with nucleic acid-modified nanoparticles is a powerful way for preparing 3D superlattices, which may be useful in many areas, including catalysis, sensing, and photonics. To date, the building blocks studied have been primarily based upon metals, metal oxides, chalcogenide semiconductors, and proteins. Here, we show that metal–organic framework nanoparticles (MOF NPs) densely functionalized with oligonucleotides can be programmed to crystallize into a diverse set of superlattices with well-defined crystal symmetries and compositions. Electron microscopy and small-angle X-ray scattering characterization confirm the formation of single-component MOF superlattices, binary MOF–Au single crystals, and two-dimensional MOF nanorod assemblies. Importantly, DNA-modified porphyrinic MOF nanorods (PCN-222) were assembled into 2D superlattices and found to be catalytically active for the photooxidation of 2-chloroethyl ethyl sulfide (CEES, a chemical warfare simulant of mustard gas). Taken together, these new materials and methods provide access to colloidal crystals that incorporate particles with the well-established designer properties of MOFs and, therefore, increase the scope of possibilities for colloidal crystal engineering with DNA.

A thin and high loading two-dimensional MOF nanosheet based mixed-matrix membrane for high permeance nanofiltration

The performance of mixed matrix membranes (MMMs) is usually limited by thick separation layer, low filler loading, and boundary defect between polymer and filler. Herein, a new two-dimensional metal-organic framework (2D MOF), named BUT-203, is designed and synthesized. Remarkably, the micron-sized crystals of this MOF could be readily delaminated into nanosheets with thickness of ca. 3 nm and lateral size of hundreds of nanometers to several microns. This delaminated nanosheets with high dispersibility in ethanol have a good compatibility with the polycation polymer polyethyleneimine (PEI). Under the optimum condition, a thin (ca. 70 nm) and high filler loading (up to ca. 73%) MMM, named BUT-203/PEI-HPAN(73) can be fabricated on macroporous hydrolyzed polyacrylonitrile (HPAN) substrate by a simple blending-spin coating method. This membrane shows a high water permeance up to 870 L/(m2·h·MPa) and high rejections (over 97.9%) for anionic dye molecules. In addition, this membrane exhibits a long term running stability, high dye desalination ability, and excellent antifouling property. These results suggest the usefulness of the membrane in nanofiltration, and simultaneously this work demonstrates that rationally designed 2D MOFs have great potential as filler materials in fabricating MMMs for various applications.

Two-dimensional iron MOF nanosheet as a highly efficient nanozyme for glucose biosensing.

Two-dimensional (2D) nanomaterials are attractive in catalysis due to their rich accessible active sites. Iron-based metal organic frameworks (MOFs) are promising nanozymes because of their iron center and pore structure. However, it is challenging to obtain iron-based 2D MOF nanozymes due to the coordinated form of iron. Herein, we report a cation substitution strategy to transform an easily obtained Cu(HBTC)(H2O)3 (represented as Cu(HBTC)-1, the product of only two carboxylate groups in 1,3,5-benzenetricarboxylic acid (H3BTC) ligands linked by Cu ions) nanosheet into a 2D Fe-BTC nanosheet, which was characterized by SEM (scanning electron microscopy), AFM (atomic force microscopy), XPS (X-ray photoelectron spectroscopy), FT-IR (Fourier transform infrared spectroscopy), and XRD (X-ray diffraction). The 2D Fe-BTC nanosheet can catalyze TMB (3,3',5,5'-tetramethylbenzidine) oxidation by H2O2, showing its intrinsic peroxidase mimetic characteristic. The catalytic performance of 2D Fe-BTC was superior to those of its template Cu(HBTC)-1 nanosheet and 3D MIL-100(Fe). Their catalytic activities follow the order of 2D Fe-BTC > MIL-100(Fe) > 2D Cu(HBTC)-1. The peroxidase-like activity of 2D Fe-BTC is 77 times that of its template Cu(HBTC)-1, and 2.2 times that of MIL-100(Fe), a well known 3D crystalline form of iron trimesates. The Km values of 2D Fe-BTC for TMB and H2O2 were 0.2610 mM and 0.0334 mM, which were 1.6 and 1.9-fold lower than those of 3D MIL-100(Fe), respectively. The TMB oxidation rate and H2O2 reduction rate at unit mass concentration of the catalyst (Kw) for 2D Fe-BTC were 2.7-72.3 and 1.5-37.9 times those for the previously reported 3D MOF nanozymes, respectively. In terms of the excellent peroxidase mimetic characteristic of 2D Fe-BTC, a sensitive and selective colorimetric biosensing platform for hydrogen peroxide and glucose was developed. The linear ranges are 0.04-30 μM and 0.04-20 μM for H2O2 and glucose, with a low detection limit of 36 nM and 39 nM, respectively. The assay was satisfactorily applied to glucose determination in biological matrices.

Single-atom implanted two-dimensional MOFs as efficient electrocatalysts for the oxygen evolution reaction

A facile and controllable synthesis strategy for bimetallic electrocatalysts for the OER from a two-dimensional iron-based metal–organic framework precursor has been reported, in which the Fe/Ni type exhibits the best efficiency and conversion.

Facile preparation of well conductive 2D MOF for nonenzymatic detection of hydrogen peroxide: Relationship between electrocatalysis and metal center

Due to its nano-thickness, fast mass transfer and excellent electron transfer capability, two-dimensional (2D) MOF are an efficient strategy to develop good electrocatalytic materials. In this paper, 2D-MOF were synthesized by facile and cost-efficient methods. MOF can be fast prepared with nucleation and crystal growth in several minutes at room temperature, leading to very thin 2D Co-MOF. Herein, Co, Ni and NiCo-based 2D MOF as non-enzymatic H2O2 sensors at different oxidation potentials in KOH solution, the Co-MOF exhibited excellent H2O2 oxidation and detection performance including a wide linear range from 0.5 μM to 832.5 μM, low detection limit of 0.69 μM, and very fast sensing response in basic solution. By taking advantage of excellent conductivity, the Co-MOF showed the low oxidation potential for H2O2 and good detection performance at 0.25 V. It was comparable to most carbon materials and reported MOF materials for H2O2 detection. We insist that 2D MOF is effective for creating active catalysts. The 2D Co-MOF performed higher electrochemical sensitivity with high stability, conductivity, and selectivity. It indicates 2D MOF has potential employment in the fabrication of sensing devices.

Modifications of Metal and Ligand to Modulate the Oxygen Reduction Reaction Activity of Two-Dimensional MOF Catalysts

Metal–organic framework catalysts have attracted particular interest in recent years due to their good oxygen reduction reaction (ORR) activity in fuel cells. Herein, four Ni3(HITP)2 analogs (Co-TH...

Enhanced CO2/CH4 Separation Performances of Mixed Matrix Membranes Incorporated with Two-Dimensional Ni-Based MOF Nanosheets

Blending porous inorganic fillers into polymers to fabricate mixed matrix membranes (MMMs) is an efficient method to acquire good-quality membranes for CO2 separation and purification. The poor int...

Zero-Dimensional-g-CNQD-Coordinated Two-Dimensional Porphyrin MOF Hybrids for Boosting Photocatalytic CO2 Reduction.

It is urgent yet challenging to develop photocatalysts for visible-light-driven CO2 reduction with high efficiency and selectivity. Here, we report a novel hybrid catalyst by coordinating zero-dimensional (0D) carbon nitride quantum dots (g-CNQDs) with two-dimensional (2D) ultrathin porphyrin MOF (PMOF). Different from previously reported hybrid catalysts combined through physical or electrostatic interactions, in our prepared g-CNQDs/PMOF hybrids, g-CNQDs are coordinated with Co active sites in PMOF, which significantly shortens the migrating pathway of both photogenerated charge carriers and gaseous substrates from g-CNQDs to Co active centers. The resulting efficient electron-hole pair separation and long-lived trapped electrons at Co centers not only boost the photocatalytic CO2 reduction activity but also improve its selectivity for the eight-electron reduced product CH4. To our knowledge, this is the first example of a hybrid catalyst combined through coordination interaction. Remarkably, the prepared hybrid catalyst exhibits a 2.34-fold enhancement in the CO generation rate (16.10 μmol g-1 h-1) and a 6.02-fold enhancement in the CH4 evolution rate (6.86 μmol g-1 h-1) compared to the bare PMOF.

A sensing platform for hypoxanthine detection based on amino-functionalized metal organic framework nanosheet with peroxidase mimic and fluorescence properties

The amino-functionalized metal organic framework (NH2-Cu-MOF) was fabricated via bottom-up synthesis strategy. Detailed characterization using electron microscopy, X-ray photoelectron spectroscopy and atomic force microscopy demonstrated that the as-synthesized NH2-Cu-MOF was two-dimensional nanosheet (a thin thickness ∼4.2 nm). Results showed that the as-synthesized NH2-Cu-MOF nanosheet possessed fluorescence property (λem = 425 nm) as well as peroxidase mimic activity. On the basis of these two properties, we proposed a biosensor for hypoxanthine detection. The fluorescence intensity had a linear relationship with the hypoxanthine concentration in the range of 10–2000 μM. The limit of detection was 3.93 μM (S/N = 3). This work contributes to the synthesis of a new two-dimensional MOF nanosheet and extends the application of two-dimensional MOF nanosheet on biological luminescent sensors.

DOPO-Modified Two-Dimensional Co-Based Metal-Organic Framework: Preparation and Application for Enhancing Fire Safety of Poly(lactic acid).

Co-based metal-organic framework (Co-MOF) nanosheets were successfully synthesized by the organic ligands with Schiff base structure. The laminated structure gives Co-MOF nanosheets a great advantage in the application in the flame retardant field. Meanwhile, -C═N- from Schiff base potentially provides active sites for further modification. In this work, 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) was used to modify Co-MOF (DOPO@Co-MOF) to further enhance its flame retardant efficiency. It is attractive that DOPO has a synergistic effect with Co-MOF on improving fire safety of poly(lactic acid) (PLA). The obvious decrease in the values of peak heat release (27%), peak smoke production (56%), and total CO yield (20%) confirmed the enhanced fire safety of PLA composites. The possible flame retardant mechanism was proposed based on characterization results. Moreover, the addition of DOPO@Co-MOF had a positive influence on the mechanical performance, including tensile properties and impact resistance. This work designed and synthesized two-dimensional MOFs with active groups. As-prepared Co-MOF with expected structure shows a novel direction of preparing MOFs for flame retardant application.

SC–SC transformation of two-dimensional MOFs to three dimensions by [2+2] photodimerization

SC–SC transformation of two-dimensional MOFs to three dimensions by [2+2] photodimerization

Small gas molecules access into void space of H-bonded 3D network consist of 2D cadmium(II) layer

Hydrothermal reaction of Cd(NO3)2·4H2O with 3,3′-azodibenzoic acid (H2abb) in water at 140°C afforded 2D cadmium(II) coordination polymer [Cd(abb)H2O]n(1). The compound has been characterized spectroscopic and single-crystal X-ray diffraction analysis. In the crystal structure, cadmium ions are sitting along crystallographic c axis while the ligands are bridged through b axis to form a 2D layer structure in ac plane. The hepta-coordinated cadmium ion is surrounded by six oxygen atoms from carboxylic acid group and one water molecule. Each 2D layer interacts by hydrogen bonding to form a 3D supramolecular structure. Notably, compound 1 exhibits unprecedented high uptake of hydrogen amongst the two-dimensional MOFs. Besides, photoluminescence property of [Cd(abb)H2O]n(1) also has been investigated.

Hydrogen storage in a layered flexible [Ni2(btc)(en)2]n coordination polymer

[Ni2(btc)(en)2]n coordination polymer exhibits a layered two-dimensional structure with weak interaction between the layers. Correlation of experimental measurements, DFT calculations and molecular simulations demonstrated that its structural features, primarily the inherent flexibility of the layered polymeric structure, lead to improved hydrogen storage performance at room temperature, due to significant enhancement in isosteric heats of hydrogen adsorption. Volumetric measurements of hydrogen adsorption at room temperature show up to 0.3 wt.% hydrogen absorbed at 303 K and 2.63 bar of hydrogen pressure, with isosteric heats of adsorption of about 12.5 kJ mol−1. Predicted performance at room temperature is 1.8 wt.% at 48 bar and 3.5 wt.% at 100 bar, better than both MOF-5 and NU-100, with calculated values of isosteric heats for adsorption of hydrogen in 8–13 kJ mol−1 range at both 77 K and 303 K. Grand canonical Monte Carlo calculations show that this material, at 77 K, exhibits gravimetric hydrogen densities of more than 10 wt.% (up to 8.3 wt.% excess) with the corresponding volumetric density of at least 66 gL−1, which is comparable to MOF-5, but achieved with considerably smaller surface area of about 2500 m2 g−1. This study shows that layered two-dimensional MOFs could be a step towards MOF systems with significantly higher isosteric heats of adsorption, which could provide better room temperature hydrogen storage capabilities.

Metal–organic framework nanosheets for fast-response and highly sensitive luminescent sensing of Fe3+

The first luminescent two-dimensional MOF nanosheets NTU-9-NS Ti2(HDOBDC)2(H2DOBDC) (H2DOBDC = 2,5-dihydroxyterephthalic acid) fabricated via top-down delamination have been realized for the highly sensitive sensing of Fe3+ with a fast response.

Zinc-seamed pyrogallol[4]arene dimers as structural components in a two-dimensional MOF

Computational methods were used as a proof of principle in the synthesis of a two-dimensional coordination polymer constructed from zinc-seamed pyrogallol[4]arene dimeric nanocapsules and 4,4′-bipyridine.

Synthesis, structure and dielectric properties of a novel Gd coordination polymer based on 2-(pyridin-4-yl)-1H-imidazole-4,5-dicarboxylate

Abstract A new Gd coordination polymer based on 2-(pyridin-4-yl)-1H-imidazole-4,5-dicarboxylate (H3PIDC) has been synthesized under hydrothermal conditions, formulated as {[Gd3(HPIDC)3(PIDC)(H2O)4]·3H2O}n (1). The compound crystallizes in the monoclinic system, space group C2/c with a = 20.951(7), b = 9.515(3), c = 27.483(10) A, β = 106.176(6)°, Z = 4, V = 5262(3) A3, C40H45Gd3N12O30, Dc = 2.071 g/cm3, Mr = 1645.63, λ (MoKa) = 0.71073 A, μ = 3.846 mm−1, F(000) = 3204, the final R = 0.0390 and wR = 0.1332. Complex 1 is a two-dimensional MOF built up from T-shaped 3-connected HPIDC2−, PIDC3− and 4-connected metal nodes. Dielectric constant of complex 1 was measured at different frequencies with temperature variation.

Design and synthesis of two-dimensional pillared MOF layers by connecting infinite one-dimensional chains via 4,4′-bipyridine

Two novel metal-organic frameworks, [Cd(Bna)(DMF)2(H2O)2]n · nDMF (I) (Bna = 2,2′-dihydroxy-l,l′-dinaphthyl-3,3′-dicarboxylate) and [Cd(Bna)(Bipy)(DMF)2]n (II) (Bipy = 4,4′-bipyridine) have been synthesized under mild conditions and structurally characterized. Crystal structural analyses reveal that complex I adots a 1D spiral structure with DMF guest molecules in the spiral by hydrogen bondings. Complex II is constructed by -Cd-Bna-Cd- zigzag chains, which are further connected by Bipy into a 2D sheet. X-ray powder diffraction and thermogravimetric analyses for I and II show that they are highly themally stable in the solid state.

CO2 selective dynamic two-dimensional ZnII coordination polymer

A CO2 selective dynamic two-dimensional (2D) MOF system, [Zn(glu)(μ-bpe)]·2H2O (·2H2O) (glu = glutarate, bpe = 1,2-bis(4-pyridyl)ethylene), is prepared. Based on variable temperature PXRD patterns, I·2H2O exhibits a structural transformation of the framework upon desolvation. Various gas sorption analyses at low temperatures reveal that solvent-free I selectively adsorbs CO2 over N2, H2, and CH4. Stepped CO2 isotherms for solvent-free I with a large hysteresis between adsorption and desorption branches at 196 K indicate that I is a dynamic framework. Moreover, I·2H2O shows efficient heterogeneous catalytic reactivity for transesterification of various esters. The catalyst can be recycled multiple times without losing its original activity.

Design and Synthesis of Two-dimensional Pillared MOF Layers by Connecting Infinite One-Dimensional Chainsvia4,4'-Bipyridine

Design and Synthesis of Two-dimensional Pillared MOF Layers by Connecting Infinite One-Dimensional Chains<i>via</i>4,4'-Bipyridine

Self-assembly of highly crystalline two-dimensional MOF sheets on liquid surfaces

The formation process of the highly crystalline MOF nanosheet, NAFS-1 at the liquid surface was studied by UV-visible spectroscopy and synchrotron grazing incidence X-ray diffraction – self-assembly of the molecular building metalloporphyrin units and the metal ion joints occurs through a coordination reaction at the air/liquid interface without the necessity of pressing the surface.