Two-dimensional MOF Research Articles

Integration of ultrafine CuO nanoparticles with two-dimensional MOFs for enhanced electrochemical CO2 reduction to ethylene

To facilitate the electrochemical CO2 reduction (ECR) to fuels and valuable chemicals, the development of active, low cost, and selective catalysts is crucial. We report a novel ECR catalyst consisting of CuO nanoparticles with sizes ranging from 1.4 to 3.3 nm anchored on Cu metal-organic framework (Cu-MOF) nanosheets obtained through a one-step facile solvothermal method. The nanocomposites provide multiple sites for efficient ambient ECR, delivering an average C2H4 faradaic efficiency (FE) of ~50.0% at –1.1 V (referred to the reversible hydrogen electrode) in 0.1 mol/L aqueous KHCO3 using a two-compartment cell, in stark contrast to a C2H4 FE of 25.5% and 37.6% over individual CuO and Cu-MOF respectively, also surpassing most newly reported Cu-based materials under similar cathodic voltages. The C2H4 FE remains at over 45.0% even after 10.0 h of successive polarization. Also, a ~7.0 mA cm−2 C2H4 partial geometric current density and 27.7% half-cell C2H4 power conversion efficiency are achieved. The good electrocatalytic performance can be attributed to the interface between CuO and Cu-MOF, with accessible metallic moieties and the unique two-dimensional structure of the Cu-MOF enhancing the adsorption and activation of CO2 molecules. This finding offers a simple avenue to upgrading CO2 to value-added hydrocarbons by rational design of MOF-based composites.

Hierarchical Ni3S2@2D Co MOF nanosheets as efficient hetero-electrocatalyst for hydrogen evolution reaction in alkaline solution

Developing efficient and stable non-noble metal electrocatalysts for alkaline hydrogen evolution poses a challenge for current research. Herein, a novel hierarchical hetero-electrocatalyst of Ni3S2@2D Co MOF was synthesized with cobalt metal-organic frameworks (Co-MOFs) crystallization on carbon paper (CP) and in-situ electrodeposition of Ni3S2 nanosheets. The catalyst Ni3S2@2D Co-MOF/CP exhibited an excellent hydrogen evolution reaction (HER) activity with a low overpotential of 140 mV and a small Tafel slope of 90.3 mV dec−1 at a current density of -10 mA cm−2. This catalyst demonstrated a lower overpotential (395 mV) than commercial Pt/C catalyst at a high current density (>130 mA cm−2). The efficient and stable HER performance of Ni3S2@2D Co-MOF/CP was attributed to nickel sulfide honeycomb nanosheets grown on two-dimensional MOF frameworks, which were conducive to charge transfer and hydrogen evolution. The electron-rich nickel sulfide surface significantly diminished H* adsorption and reduced energy barrier of H2 generation to promote HER process. This work provides a new strategy for practical preparation of efficient and stable transition metal electrocatalysts.

All-fiber structure covered with two-dimensional conductive MOF materials to construct a comfortable, breathable and high-quality self-powered wearable sensor system

A comfortable, breathable, and high-quality self-powered wearable sensor system is fabricated using a two-dimensional conductive metal–organic skeleton.

π⋯π interaction directed 2D FeNi-LDH nanosheets from 2D Hofmann-MOFs for the oxygen evolution reaction

A two-dimensional (2D) MOFs transformation strategy was introduced to synthesize FeNi layered double hydroxides (FeNi LDHs) in NaBH4 solution, which show excellent OER catalytic activity in alkaline media.

Pillared Two-Dimensional Mof Constructed Via Bent Ditopic Carboxylate Linker, Synthesis and Structural Characterization

Pillared Two-Dimensional Mof Constructed Via Bent Ditopic Carboxylate Linker, Synthesis and Structural Characterization

A highly efficient Co-based catalyst fabricated by coordination-assisted impregnation strategy towards tandem catalytic functionalization of nitroarenes with various alcohols

A well-defined hexamethylenetetramine (abbreviated as HMTA) based two-dimensional (2D) MOFs metalloligand (termed Zn-HMTA), with free uncoordinated tertiary amine groups, has been synthesized via solution diffusion method for the first time. The crystal structure of 2D Zn-HMTA metalloligand was determined by the single crystal X-ray diffraction (SCXRD). The SCXRD and X-ray photoelectron spectroscopy (XPS) analyses have revealed that the 2D Zn-HMTA metalloligand is rich in- free tertiary amine groups, which are of strong coordination ability to transition metal ions (e.g. Ni2+, Co2+, Zn2+, Cu2+). As a result, a 2D bimetallic Co@Zn-HMTA MOFs was synthesized via coordination-assisted impregnation (CAI) strategy attributed to the unique feature of strong coordinated ability of free tertiary amine groups. Furthermore, a series of self-supported Co-ZnO-CN nanocatalysts were afforded upon the as-synthesized Co@Zn-HMTA MOFs served as a self-sacrificial template for pyrolysis at different temperatures. The optimized catalyst (termed as Co-ZnO@CN-CAI) demonstrated the excellent catalytic performance for hydrogenation-alkylation tandem reaction in comparison with the classic ZnO@CN composite (derived from Zn-HMTA MOFs) supported metallic Co catalyst (Co-ZnO@CN-IWI) prepared by incipient wetness impregnation method. Moreover, the kinetic study was also performed to confirm that the alkylation is the rate-determining step in the hydrogenation-alkylation tandem reaction. The origin of enhanced catalytic performance of Co-ZnO@CN-CAI and the role of Co@Zn-HMTA MOFs precursor have been explored by way of various characterizations, e.g. HADDF-STEM-EDS, SEM-EDS, 13C MAS NMR, XRD, Raman and XPS, etc. It is anticipated that the prepared low-cost and easily prepared 2D Zn-HMTA metalloligand will become a general template for synthesis of highly self-supported catalysts with coordination-assisted impregnation strategy (CAI) for various catalytic reactions.

Two-dimensional MOF Cu-BDC nanosheets/ILs@silica core-shell composites as mixed-mode stationary phase for high performance liquid chromatography

Here, silica microspheres were decorated with two-dimensional metal–organic frameworks (2D MOFs) nanosheets and ionic liquids, and evaluated as the mixed-mode stationary phase for chromatographic separation. The ionic liquids were used to assist the synthesis of 2D MOFs nanosheets, and also acted as adhesives among the nanosheets and silica. In contrast with the 2D MOFs-based column without ionic liquids and commercial columns, the prepared column exhibited enhanced chromatographic separation performance for partially hydrophilic compounds such as alkaloids, sulfonamides and antibiotics, etc. In addition to excellent chromatographic repeatability and stability, it has also been verified that the composites could be easily and repeatedly prepared. The relative standard deviation of the retention time of the same type of analyte between the three batches of materials was ranging from 0.21% to 1.7%. In short, these results indicated that the synthesized composites were promising separation material for liquid chromatography, which made it possible to broaden the application of 2D MOFs in the field of chromatography.

Ratiometric fluorescent sensor based on 2D MOF nanosheets modified by DNA for sensitive detection of Hg2+

Mercury is highly toxic and can accumulate throughout the food cycle, leading to water contamination and foodstuffs pollution. Therefore, increasing attention has been paid to explore effective detection of Hg2+. Here, we report a sensitive Hg2+ sensor based on single-stranded DNA (ssDNA) modified two-dimensional (2D) MOF nanosheets by a ratiometric fluorescent method. The chosen 2D MOF nanosheets possess intrinsic peroxidase-like catalytic ability, ssDNA adsorption and fluorescence quenching. We demonstrate that the adsorption of ssDNA can significantly improve the peroxidase mimetic activity of 2D MOF nanosheets, enhancing the fluorescence of substrate Amplex Red. Taking advantages of the favorable characteristics above, we fabricate an efficient Hg2+ sensor. In the presence of Hg2+, the ssDNA is released from 2D MOF nanosheets, which results in a decreasing of peroxidase mimetic activity of 2D MOF nanosheets and a fluorescence enhancement of attached fluorophore. A linear relationship between ratiometric fluorescence of substrate and fluorophore and Hg2+ concentrations is obtained. The detection limit is 5 nM, which is much lower than the maximal contamination level in drinking water (30 nM) by Word Health Organization. These findings show 2D MOF based ratiometric fluorescent sensor is a convenient and efficient strategy to detect Hg2+.

Two-dimensional MOFs: Design & Synthesis and Applications.

For the past few years, two-dimensional materials have attracted widespread attention owing to their special properties and potential applications. It is well-known that graphene, transition metal disulfide compounds (TMDC), carbon nitride, transition metal carbonitrides (Mxenes), silene and hexagonal boron nitride are typical two-dimensional materials. Compared with these traditional two-dimensional materials, two-dimensional MOF is favored by numerous researchers because of its unique structure. Based on the unique metal ion and organic ligand coordination of MOF and two-dimensional layered structure, the applications of two-dimensional MOF were getting serious, including catalysis, supercapacitor, gas adsorption/separation, sensors and so on. This review presents a relatively comprehensive summary of the design & synthesis and applications of two-dimensional MOF over the past few years. Furthermore, the opportunities and challenges have been discussed to supply a promising prospect to this field.

Construction of a photothermal hydrogel platform with two-dimensional PEG@zirconium-ferrocene MOF nanozymes for rapid tissue repair of bacteria-infected wounds

Because of increasing antibiotic resistance, careful construction of an efficient phototherm-nanozyme-hydrogel synergistic antibacterial platform is imperative for the treatment of bacteria-infected wounds. In this study, a carrageenan-based hydrogel embedded with polyethylene glycol dicarboxylic acid (COOH-PEG-COOH)-functionalized zirconium-ferrocene metal-organic frames nanosheets (PEG@Zr-Fc MOF hydrogel) was successfully constructed through COOH-PEG-COOH modification and physical assembly. The PEG@Zr-Fc MOF hydrogel could capture Gram-negative (Escherichia coli) and Gram-positive (Staphylococcus aureus) bacteria through reactive oxygen species (ROS) destruction and kill some bacteria by disintegration of H2O2 into toxic hydroxyl radicals (•OH). Significantly, by introducing the photothermal performance of the PEG@Zr-Fc MOF hydrogel, the catalytic activity of the target material could be improved to achieve a synergistic sterilization effect. The wound infection model experiment confirmed that the PEG@Zr-Fc MOF hydrogel had powerful bactericidal activity and could achieve a rapid tissue repair effect. More importantly, the PEG@Zr-Fc MOF hydrogel had negligible biological toxicity and reduced the risk of inflammation. This study reveals that phototherm-nanozyme-hydrogel synergy holds great potential for bacterial wound infection therapy. Additionally, this is the first study to use two-dimensional MOF nanozymes in combination with hydrogel for antimicrobial therapy. Statement of significanceBacteria-infected wound is one of the serious threats to public health, and this topic has attracted tremendous attention worldwide in recent decades. Although numerous traditional therapeutic strategies that depend on antibiotics have been developed and applied for treating bacteria-infected wound disease, the effect of wound treatment is becoming increasingly unsatisfactory due to bacterial resistance. The present study provides a feasible method to treat bacterial wound infection by constructing a carrageenan-based hydrogel embedded with polyethylene glycol dicarboxylic acid (COOH-PEG-COOH) functionalized zirconium-ferrocene metal organic frame nanosheets (PEG@Zr-Fc MOF hydrogel). The experiments with the wound infection model confirmed that the PEG@Zr-Fc MOF hydrogel had powerful bactericidal activity and could achieve a rapid tissue repair. This strategy provides a promising avenue to further accelerate the development of antibacterial therapy in biomedical fields.

Control of halogen interactions on morphology of metal-organic framework nanosheets

Two-dimensional (2D) MOFs nanosheets are prosperous regarding the novel peculiarity of nano-interface and broad development prospects, but the key to achieving the control and design of 2D nanomaterials’ morphology is still arduous. In this work, we prepared two complexes contained pyrazine ligand, namely Ni(pyz)2Cl2 and Ni(pyz)2Br2 (pyz = pyrazine), which derived from a synthesis of bridged pyrazine and nickel halogen nide. 2D nanomaterials of them were obtained by using the liquid phase exfoliation method to feature a series of structure and surface morphology. We investigated the difference in physical and chemical properties between 2D MOFs nanomaterials and bulk materials, and studied the influence of different halogen interactions on the morphology of nanomaterials. The results showed that the stacking force and electronic transition have made a significant influence on the 2D nanomaterials.

In situ growth of NiFe MOF/NF by controlling solvent mixtures as efficient electrocatalyst in oxygen evolution

Two-dimensional metal–organic frame (2D MOF) materials have attracted great attention due to the successful combination of the unique properties of MOF and chemical properties of 2D material. In this paper, NiFe MOF/NF with a two-dimensional layered vertical structure were prepared by bottom-up solvothermal method. We used different solvent mixtures (methanol/water, ethanol/water, acetone/water, N, N-dimethylformamide/water) to control the synthesis of MOF and found that the oligpolar solvent mixture of acetone and water was the best in controlling the formation of these two-dimensional MOFs. The obtained NiFe MOF/NF in acetone/water appeared the best performance as electrocatalyst for the oxygen evolution reaction, in which the NiFe MOF/NF delivered a current density of 50 mA·cm−2 at a low overpotential of 270 mV with a small Tafel slope of 55 mV·dec-1. In addition, NiFe MOF/NF has an excellent stability at a high current density of 100 mA·cm−2.

Two-dimensional MOF and COF nanosheets for next-generation optoelectronic applications

The development of optoelectronics technology greatly contributes to our daily life and industrial evolution. In particular, two-dimensional (2D) materials with ultrathin structure have received worldwide research interests in the field of optoelectronics mainly owing to the intrinsic electronic and optical attributes. The on-going researches indicate that electrically conducting MOF and COF demonstrate distinctive properties and promising surface functionality, while their inherent band structure and electronic features can be rationally controlled by structural modification. With rapid development of 2D materials-based optoelectronic devices, the utilization of 2D polymer MOF and COF semiconductors has become a new tendency to meet the scope of adaptive, low-cost, and flexible device fabrication. In this review, the recent research activities on 2D MOF and COF materials are provided. The fabrication and semiconducting properties of 2D MOF and COF materials have been explained. Apart from that, both advantages and limitations of the newly developed 2D MOF and COF materials regarding their potential in optoelectronic devices have been discussed. Additionally, different types of 2D MOF and COF materials and performance adjusting strategies have been systematically summarized. Furthermore, the remaining challenges and current prospects of applying 2D MOF and COF into optical-to-electrical and electrical-to-optical conversion devices have been introduced.

Two host-guest 2D MOFs based on hexyl viologen cations: Photochromism

Two host-guest two-dimensional (2D) MOFs based on N,N′-bis(n-hexyl)-4,4′-bipyridinium dibromide (HVBr2) were prepared {(HV)0.5(C2H8N)[Zn3O(m-BDC)3(H2O)2]·DMF}n (1), {(HV)[Cd3(m-BDC)4(H2O)2]·DMF·4H2O}n (2) (m-H2BDC = 1,3-benzenedicarboxylic acid), which were investigated on the basis of crystal structures, chromic properties, and molecular orbitals. Each metal ion connects m-BDC2− ligands to form a 2D anionic framework, which is constructed in a grid-like square cavities with the intersections of HV2+ cations to achieve charge balance. MOFs 1 and 2 each exhibit photochromic properties. The B3LYP/6–311 (d,p) method of density functional theory (DFT) was applied to explore electronic structures and matching rules between donors and receptors. The results indicate that the balance between electron transfer and photochromic properties is achieved by the regulation of receptors and donors.

Rational construction of dual cobalt active species encapsulated by ultrathin carbon matrix from MOF for boosting photocatalytic H2 generation

Dual cocatalyst which integrates the merits of metal and metal oxide has been endowed with competitive advantages over noble metals for achieving efficient H2 evolution. In this case, developing spatially separated dual cocatalyst in carbon substrate with more efficient charge extraction and separation would be beneficial for further enhancing the photocatalytic activity. Herein, we utilized ultrathin two-dimensional (2D) Co-based MOF (Co-MOF) nanosheets as specific precursors for preparing carbon matrix encapsulated dual cobalt active species (Co and CoOx) on the surface of CdS for high-efficient photocatalytic H2 evolution under visible-light irradiation. The fundamental roles of 2D-MOF derived carbon matrix towards rational construction of dual cobalt active species have been visualized by combining a series of in-situ and ex-situ temperature-dependent analytic strategies. The carbon matrix as well as co-existed dual cobalt active species bring great improvement on charge carrier transportation and photogenerated electron-hole separation for enhanced photocatalytic activities, and an approximate 12.5-fold enhancement of H2 generation performance from 0.161 mmol h−1 of CdS to 1.997 mmol h−1 of the newly formed CdS-Co-CoOx@C with the apparent quantum efficiency of 43.7 % at 420 nm has been achieved. This work might provide the basic understanding and new opportunities in manipulating MOF structure through pyrolysis to fabricate high efficient cocatalysts for versatile photocatalytic reactions.

Introducing two-dimensional metal-organic frameworks with axial coordination anion into Pebax for CO2/CH4 separation

Two-dimensional (2D) MOF named Cu(BPY)2(OTF)2 (OTF = trifluoromethanesulfonic acid anion (CF3SO3−), BPY = 4,4-bipyridine) possessing axial coordination anion was prepared, and then combined into Pebax® MH 1657 (Pebax) polymer to fabricate mixed matrix membranes (MMMs) for the separation of CO2/CH4 gas mixtures. The inherent microporous structure and interlayer nanochannel that constructed by axial coordination anion CF3SO3− of Cu(BPY)2(OTF)2 nanosheets provide selective transfer channels for CO2. In addition, the group that has an affinity for CO2, such as pyridine group and CF3SO3− anion, locating in the surface and the interlayer of Cu(BPY)2(OTF)2 nanosheets, present better binding affinity and molecule selectivity for CO2. Owing to the synergistic effect between structure and functional groups of Cu(BPY)2(OTF)2 nanosheets, the optimized CO2 separation performance (permeability and selectivity) of the MMMs compared with that of pure Pebax were increased by 86.65% and 47.59%, respectively, under the conditions of pure gas, 0.1 MPa and 25 °C. The open narrow nanochannels and axial coordination anion in Cu(BPY)2(OTF)2 nanosheet, making Cu(BPY)2(OTF)2 a promising material to prepare efficient mixed matrix membrane.

A 2D-layered Cd(II) MOF as an efficient heterogeneous catalyst for the Knoevenagel reaction

A Cd(II) coordination polymer based on a polytopic compartmental ligand was synthesized, and used as an efficient heterogeneous catalyst for the Knoevenagel reaction between benzaldehyde and malononitrile under mild reaction conditions. The solid catalyst was characterized using single crystal XRD, X-ray powder diffraction, SEM, TGA, UV diffuse reflectance, infrared spectroscopy and elemental analysis. The compound is a two-dimensional (2D) MOF with a grid structure. Topological analysis of the framework revealed that it is a 2,4-connected binodal net. The catalytic activity was tested between various benzaldehydes containing different substituents with malononitrile. The effect of reaction parameters such as solvent, time, reactant ratio and catalyst amount was investigated. Furthermore, the catalyst stability was examined through reusability experiments and it is observed that the catalyst can be recycled at least five times without significant drop in its activity.

Theoretical study on the two-dimensional bis(iminothiolato)rhodium as oxygen reduction reaction catalyst

ABSTRACT Metal–organic porous materials provide a feasible strategy for designing electrocatalysts due to high surface area and well-defined porous structures. Herein, the catalytic activity and reaction mechanism for oxygen reduction reaction (ORR) on bis(iminothiolato)rhodium (RhIT) monolayer have been investigated by means of density functional theory. Our results indicate that *OOH hydrogenation to form *OH + *OH pathway is the kinetically most favourable pathway. The formation of two *OH intermediates is the rate-determining step with an energy barrier of 0.89 eV, close to 0.80 eV for pure Pt catalyst. The calculated working potential is 0.79 V, which is also close to 0.78 V for pure Pt. Thus, RhIT could be a potential ORR catalyst. We expect that the results of this work can offer fundamental insights for the design of highly efficient ORR catalysts by two-dimensional MOFs materials.

Efficient multifunctional electrocatalyst based on 2D semiconductive bimetallic metal-organic framework toward non-Pt methanol oxidation and overall water splitting

As the efficient approaches for obtaining clean H2 energy, methanol oxidation (MOR) and water over slitting reactions have been increasingly essential. A series of novel semiconductive CoNi bimetal–organic framework (CoxNi3-x(HAB)2 MOF) have been prepared using hexaaminobenzene (HAB) as an organic linker. The obtained series of CoxNi3-x(HAB)2 MOFs were then explored as efficient multifunctional electrocatalysts for the non-Pt MOR and overall water splitting in alkaline medium. The basic characterizations of CoxNi3-x(HAB)2 MOFs revealed that they comprised multiple metal valence states (Co0/Co2+/Co3+ and Ni2+/Ni3+) and graphene-like nanostructures embedded with abundant CoNi alloy nanoparticles. Compared with the sole-metal MOFs (Co3(HAB)2 MOF and Ni3(HAB)2 MOF), the CoxNi3-x(HAB)2 MOF with a mass ratio of Co:Ni = 1:3 (CoxNi3-x(HAB)2 MOF-2) exhibited superior electrocatalytic performance for MOR. It gave a high current density of 92.8 mA cm−2 at 1.6 V vs. reversible hydrogen electrode (RHE) for MOR, along with the low overpotentials at the current density of 10 mV cm−2 (η10) and Tafel slopes toward hydrogen evolution reaction (η10 = 119 mV, Tafel slope = 46 mV dec-1) and oxygen evolution reaction (η10 = 1.35 V, Tafel slope = 26 mV dec−1). The analysis on the catalysis mechanism of MOR and water splitting in alkaline medium was also proposed. The voltages applied to the three- and two-electrode systems based on the bifunctional CoxNi3-x(HAB)2 MOF-2 catalyst for overall water splitting are 1.52 V vs. RHE and 1.45 V vs. silver/silver chloride (Ag/AgCl), respectively. This work provides a novel strategy for investigating the applications of promising two-dimensional semiconductive MOF as multifunctional electrocatalysts with boosted electrocatalytic activities in energy fields.

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.