Transition-Metal Porphyrin-Based MOFs In Situ-Derived Hybrid Catalysts for Electrocatalytic CO2 Reduction.

Excellent electrocatalytic CO2 reduction reaction activity has been demonstrated by transition metals and nitrogen-codoped carbon (M-N-C) catalysts, especially for transition-metal porphyrin (MTPP)-based catalysts. In this work, we propose to use one-step low-temperature pyrolysis of the isostructural MTPP-based metal-organic frameworks (MOFs) and electrochemical in situ reduction strategies to obtain a series of hybrid catalysts of Co nanoparticles (Co NPs) and MTPP, named Co NPs/MTPP (M = Fe, Co, and Ni). The in situ introduction of Co NPs can efficiently enhance the electrocatalytic ability of MTPP (M = Fe, Co, and Ni) to convert CO2 to CO, particularly for FeTPP. Co NPs/FeTPP endowed a high CO faradaic efficiency (FECOmax = 95.5%) in the H cell, and the FECO > 90.0% is in the broad potential range of -0.72 to -1.22 VRHE. In addition, the Co NPs/FeTPP achieved 145.4 mA cm-2 at a lower potential of -0.70 VRHE with an FECO of 94.7%, and the CO partial currents increased quickly to reach 202.2 mA cm-2 at -0.80 VRHE with an FECO of 91.6% in the flow cell. It is confirmed that Co NPs are necessary for hybrid catalysts to get superior electrocatalytic activity; Co NPs also can accelerate H2O dissociation and boost the proton supply capacity to hasten the proton-coupled electron-transfer process, effectively adjusting the adsorption strength of the reaction intermediates.

Nonenzymatic Electrochemical Sensing Platform Based on 2D Isomorphic Co/Ni-Metal-Organic Frameworks for Glucose Detection.

Two-dimensional metal-organic framework (MOF) crystalline materials possess promising potential in the electrochemical sensing process owing to their tunable structures, high specific surface area, and abundant metal active sites; however, developing MOF-based nonenzymatic glucose (Glu) sensors which combine electrochemical activity and environmental stability remains a challenge. Herein, utilizing the tripodic nitrogen-bridged 1,3,5-tris(1-imidazolyl) benzene (TIB) linker, Co2+ and Ni2+, two 2D isomorphic crystalline materials, including Co/Ni-MOF {[Co (TIB)]·2BF4} (CTGU-31) and {[Ni(TIB)]·2NO3} (CTGU-32), with a binodal (3, 6)-connected kgd topological net were firstly synthesized and fabricated with conducting acetylene black (AB). When modified on a glassy carbon electrode, the optimized AB/CTGU-32 (1:1) electrocatalyst demonstrated a higher sensitivity of 2.198 µA µM-1 cm-2, a wider linear range from 10 to 4000 µM, and a lower detection limit (LOD) value (0.09 µM, S/N = 3) compared to previously MOF-based Glu sensors. Moreover, AB/CTGU-32 (1:1) exhibited desirable stability for at least 2000 s during the electrochemical process. The work indicates that MOF-based electrocatalysts are a promising candidate for monitoring Glu and demonstrate their potential for preliminary screening for diabetes.

Ultrafast Response in Nonenzymatic Electrochemical Glucose Sensing with Ni(II)-MOFs by Dimensional Manipulation.

Metal-organic frameworks (MOFs) are emerging as promising candidates for electrochemical glucose sensing owing to their ordered channels, tunable chemistry, and atom-precision metal sites. Herein, the efficient nonenzymatic electrochemical glucose sensing is achieved by taking advantage of Ni(II)-based metal-organic frameworks (Ni(II)-MOFs) and acquiring the ever-reported fastest response time. Three Ni(II)-MOFs ({[Ni6L2(H2O)26]4H2O}n (CTGU-33), {Ni(bib)1/2(H2L)1/2(H2O)3}n (CTGU-34), {Ni(phen)(H2L)1/2(H2O)2}n (CTGU-35)) have been synthesized for the first time, which use benzene-1,2,3,4,5,6-hexacarboxylic acid (H6L) as an organic ligand and introduce 1,4-bis(1-imidazoly)benzene (bib) or 1,10-phenanthroline (phen) as spatially auxiliary ligands. Bib and phen convert the coordination mode of CTGU-33, affording structural dimensions from 2D of CTGU-33 to 3D of CTGU-34 or 1D of CTGU-35. By tuning the dimension of the skeleton, CTGU-34 with 3D interconnected channels exhibits an ultrafast response of less than 0.4 s, which is superior to the existing nonenzymatic electrochemical sensors. Additionally, a low detection limit of 0.12 µM (S/N = 3) and a high sensitivity of 1705 µA mM-1 cm-2 are simultaneously achieved. CTGU-34 further showcases desirable anti-interference and cycling stability, which demonstrates a promising application prospect in the real-time detection of glucose.

Facile in Situ Transformation of NiOOH into MOF-74(Ni)/NiO OH Heterogeneous Composite for Enchancing Electrocatalytic Methanol Oxidation.

A new MOF-74(Ni)/NiOOH heterogeneous composite was synthesized via NiOOH microsphere precursor. The electrocatalytic methanol oxidation reactions' (MOR) performance was assessed. The as-prepared MOF-74(Ni)/NiOOH exhibited excellent activity with high peak current density (27.62 mA·cm-2) and high mass activity (243.8 mA·mg-1). The enhanced activity could be a result of the synergistic effect of the MOF-74(Ni)/NiOOH heterocomposite providing more exposed active sites, a beneficial diffusion path between the catalyst surface and electrolyte, and improved conductivity, favorable for improving MOR performance.

Synthesis of Semiconducting 2H-Phase WTe2 Nanosheets with Large Positive Magnetoresistance.

Tungsten ditelluride (WTe2) is provoking immense interest because of its unique electronic properties, but studies about its semiconducting hexagonal (2H) phase are quite rare. Herein, we report the synthesis of semiconducting 2H WTe2 nanosheets with large positive magnetoresistance, for the first time, by a simple lithium-intercalation-assisted exfoliation strategy. Systematic characterizations including high-resolution transmission electron microscopy, X-ray diffraction, and Raman and X-ray photoelectron spectroscopies provide clear evidence to distinguish the structure of 2H WTe2 nanosheets from the orthorhombic (Td) phase bulk counterpart. The corresponding electronic phase transition from metal to semiconductor is also confirmed by density of states calculation, optical absorption, and electrical transport property measurements. Besides, the 2H WTe2 nanosheets exhibit large positive magnetoresistance with values of up to 29.5% (10 K) and 16.2% (300 K) at 9 T. Overall, these findings open up a promising avenue into the exploration of WTe2-based materials in the semiconductor field.

Investigation on the Component Evolution of a Tetranuclear Nickel-Cluster-Based Metal-Organic Framework in an Electrochemical Oxidation Reaction.

Understanding the active species derived from metal-organic frameworks (MOFs) plays a vital role in the fabrication of highly efficient and stable oxygen evolution reaction (OER) electrocatalysts. Herein, a new alkaline-stable 3D nickel metal-organic framework (Ni-MOF), containing a 1D rod-packing chain structure fused with a tetranuclear nickel cluster [Ni4(µ3-OH)2], is used as a target material to explore its OER properties. The electrocatalytic activities of pure Ni-MOF and hybrid materials made from Ni-MOF with different acetylene black loaded electrodes, such as glassy carbon, fluorine-doped tin oxide, and nickel foam, have been evaluated. Further analysis unravels that the enhanced OER performance might be attributed to the synergistic interactions of two catalytic active species between in situ formed ß-Ni(OH)2 and a tetranuclear Ni4(µ3-OH)2 cluster in Ni-MOF. The findings will shed fresh light on the fabrication of MOF-derived catalysts for efficient electrochemical energy conversion.

Stable Bimetal-MOF Ultrathin Nanosheets for Pseudocapacitors with Enhanced Performance.

Exploring high-performance metal-organic frameworks (MOFs) for pseudocapacitors is quite meaningful for energy storage. Herein a bimetal NiCo-MOF with ultrathin thickness was prepared via a simple hydrothermal method, which shows excellent electrochemical performance with specific capacitances of 1945.83 and 1700.40 F/g at current densities of 0.5 and 1 A/g, respectively, while maintaining good stability. X-ray photoelectron spectroscopy and X-ray absorption near-edge spectroscopy spectra unravel that the strong coupling between Ni and Co species enhances the valence state of Ni2+ in the ultrathin nanosheets, which facilitates the charge transfer during the electrochemical reaction and results in greatly improved pseudocapacitive reactivity. This work provides guidance on the promising prospect of MOF materials for pseudocapacitor applications.

Integration of Semiconductor Oxide and a Microporous (3,10)-Connected Co6-Based Metal-Organic Framework for Enhanced Oxygen Evolution Reaction.

Developing high-efficiency and cost-effective electrocatalytic oxygen evolution reaction (OER) catalysts would determine the future distributions of energy conversion technologies. Metal-organic frameworks (MOFs), with unsaturated active metal sites, functionalized organic linkers, and large surface areas, are emerging heterogeneous electrocatalysts for the water oxidation process. Herein, we report an oxygen-evolving microporous (3,10)-connected Co6-based MOF (denoted as CTGU-14) for the electrocatalytic OER. Moreover, the integration of Co-MOF and SnO2, SnO2 (15%) & CTGU-14 composite attains remarkable electrochemical OER performance with a small Tafel slope of 68 mV·dec-1, a positive overpotential of 388 mV at 10 mA·cm-2, and overall durability in an alkali medium. The superior OER activities might be ascribed to more convenient electron transfer from the SnO2 additive to the electrode medium, effective surface area and unsaturated active cobalt centers, and more beneficial delivery for hydroxy radicals in the microporous Co-MOF skeleton in the process of the OER.

Bi-Microporous Metal-Organic Frameworks with Cubane [M4 (OH)4 ] (M=Ni, Co) Clusters and Pore-Space Partition for Electrocatalytic Methanol Oxidation Reaction.

Embedding cubane [M4 (OH)4 ] (M=Ni, Co) clusters within the matrix of metal-organic frameworks (MOFs) is a strategy to develop materials with unprecedented synergistic properties. Herein, a new material type based on the pore-space partition of the cubic primitive minimal-surface net (MOF-14-type) has been realized. CTGU-15 made from the [Ni4 (OH)4 ] cluster not only has very high BET surface area (3537 m2 g-1 ), but also exhibits bi-microporous features with well-defined micropores at 0.86 nm and 1.51 nm. Furthermore, CTGU-15 is stable even under high pH (0.1 m KOH), making it well suited for methanol oxidation in basic medium. The optimal hybrid catalyst KB&CTGU-15 (1:2) made from ketjen black (KB) and CTGU-15 exhibits an outstanding performance with a high mass specific peak current of 527 mA mg-1 and excellent peak current density (29.8 mA cm-2 ) at low potential (0.6 V). The isostructural cobalt structure (CTGU-16) has also been synthesized, further expanding the application potential of this material type.

Stable Hierarchical Bimetal-Organic Nanostructures as HighPerformance Electrocatalysts for the Oxygen Evolution Reaction.

The integration of heterometallic units and nanostructures into metal-organic frameworks (MOFs) used for the oxygen evolution reaction (OER) can enhance the electrocatalytic performance and help elucidate underlying mechanisms. We have synthesized a series of stable MOFs (CTGU-10a1-d1) based on trinuclear metal carboxylate clusters and a hexadentate carboxylate ligand with a (6,6)-connected nia net. We also present a strategy to synthesize hierarchical bimetallic MOF nanostructures (CTGU-10a2-d2). Among these, CTGU-10c2 is the best material for the OER, with an overpotential of 240 mV at a current density of 10 mA cm-2 and a Tafel slope of 58 mV dec-1 . This is superior to RuO2 and confirms CTGU-10c2 as one of the few known high-performing pure-phase MOF-OER electrocatalysts. Notably, bimetallic CTGU-10b2 and c2 show an improved OER activity over monometallic CTGU-10a2 and d2. Both DFT and experiments show that the remarkable OER performance of CTGU-10c2 is due to the presence of unsaturated metal sites, a hierarchical nanobelt architecture, and the Ni-Co coupling effect.

Ligand-Controlled Integration of Zn and Tb by Photoactive Terpyridyl-Functionalized Tricarboxylates as Highly Selective and Sensitive Sensors for Nitrofurans.

The integration of terpyridyl and tricarboxylate functionality in a novel ligand allows concerted 3:1 stoichiometric assembly of size-and charge-complementary Zn2+/Tb3+ ions into a water-stable 3D luminescent framework (CTGU-8) capable of highly selective, sensitive, and recyclable of nitrofurans.

A Multifunctional Tb-MOF for Highly Discriminative Sensing of Eu3+ /Dy3+ and as a Catalyst Support of Ag Nanoparticles.

Exploring novel multifunctional rare earth materials is very important because these materials have fundamental interests, such as new structural facts and connecting modes, as well as potential technological applications, including optics, magnetic properties, sorption, and catalytic behaviors. Especially, employing these nanomaterials for sensing or catalytic reactions is still very challenging. Herein, a new superstable, anionic terbium-metal-organic-framework, [H2 N(CH3 )2 ][Tb(cppa)2 (H2 O)2 ], (China Three Gorges University (CTGU-1), H2 cppa = 5-(4-carboxyphenyl)picolinic acid), is successfully prepared, which can be used as a turn-on, highly-sensitive fluorescent sensor to detect Eu3+ and Dy3+ , with a detection limitation of 5 × 10-8 and 1 × 10-4 m in dimethylformamide, respectively. This result represents the first example of lanthanide-metal-organic-frameworks (Ln-MOF) that can be employed as a discriminative fluorescent probe to recognize Eu3+ and Dy3+ . In addition, through ion exchanging at room temperature, Ag(I) can be readily reduced in situ and embedded in the anionic framework, which leads to the formation of nanometal-particle@Ln-MOF composite with uniform size and distribution. The as-prepared Ag@CTGU-1 shows remarkable catalytic performance to reduce 4-nitrophenol, with a reduction rate constant κ as large as 2.57 × 10-2 s-1 ; almost the highest value among all reported noble-metal-nanoparticle@MOF composites.

Anionic Lanthanide MOFs as a Platform for Iron-Selective Sensing, Systematic Color Tuning, and Efficient Nanoparticle Catalysis.

New porous anionic Ln-MOFs, namely, [Me2NH2][Ln(CPA)2(H2O)2] (Ln = Eu, Gd), have been prepared through the self-assembly of 5-(4-carboxy phenyl)picolinic acid (H2CPA) and lanthanide ions. They feature open anionic frameworks with 1-D hydrophilic channels and exchangeable dimethylamine ions. The Eu phase could detect Fe3+ ions with high selectivity and sensitivity in either aqueous solution or biological condition. The ratios of lanthanide ions on this structure platform could be rationally tuned to not only achieve dichromatic emission colors with linear correlation but also attain three primary colors (RGB) and even white light with favorable correlated color temperature. Furthermore, the Ag(I)-exchanged phases can be readily reduced to afford Ag nanoparticles. The as-prepared Ag@Ln-MOFs composite shows highly efficient catalytic performance for the reduction of 4-nitrophenol.

Efficient Gas-Sensing for Formaldehyde with 3D Hierarchical Co3O4 Derived from Co5-Based MOF Microcrystals.

Detecting formaldehyde at low operating temperature and maintaining long-term stability are of great significance. In this work, a hierarchical Co3O4 nanostructure has been fabricated by calcining Co5-based metal-organic framework (MOF) microcrystals. Co3O4-350 particles were used for efficient gas-sensing for the detecting of formaldehyde vapor at lower working temperature (170 °C), low detection limit of 10 ppm, and long-term stability (30 days), which not only is the optimal value among all reported pure Co3O4 sensing materials for the detection of formaldehyde but also is superior to that of majority of Co3O4-based composites. Such extraordinarily efficient properties might be resulted from hierarchically structures, larger surface area and unique pore structure. This strategy is further confirmed that MOFs, especially Co-clusters MOFs, could be used as precursor to synthesize 3D nanostructure metal oxide materials with high-performance, which possess high porosity and more active sites and shorter ionic diffusion lengths.

Surfactant-Assisted Phase-Selective Synthesis of New Cobalt MOFs and Their Efficient Electrocatalytic Hydrogen Evolution Reaction.

Reported herein are two new polymorphic Co-MOFs (CTGU-5 and -6) that can be selectively crystallized into the pure 2D or 3D net using an anionic or neutral surfactant, respectively. Each polymorph contains a H2 O molecule, but differs dramatically in its bonding to the framework, which in turn affects the crystal structure and electrocatalytic performance for hydrogen evolution reaction (HER). Both experimental and computational studies find that 2D CTGU-5 which has coordinates water and more open access to the cobalt site has higher electrocatalytic activity than CTGU-6 with the lattice water. The integration with co-catalysts, such as acetylene black (AB) leads to a composite material, AB&CTGU-5 (1:4) with very efficient HER catalytic properties among reported MOFs. It exhibits superior HER properties including a very positive onset potential of 18 mV, low Tafel slope of 45 mV dec-1 , higher exchange current density of 8.6×10-4  A cm-2 , and long-term stability.

A Robust Luminescent Tb(III)-MOF with Lewis Basic Pyridyl Sites for the Highly Sensitive Detection of Metal Ions and Small Molecules.

A new luminescent terbium-metal-organic framework [Tb3(L)2(HCOO)(H2O)5]·DMF·4H2O (1) (H4L = 4,4'-(pyridine-3,5-diyl)diisophthalic acid) has been successfully assembled by Tb(3+) ions and an undeveloped pyridyl-tetracarboxylate. Compound 1 exhibits a 3D porous (3,8)-connected (4.5(2))2(4(2).5(12).6(6).7(5).8(3)) topological framework with fascinating 1D open hydrophilic channels decorated by uncoordinated Lewis basic pyridyl nitrogen atoms. In particular, the Tb-MOF (1) can detect Cu(2+) ions with high selectivity and sensitivity, and its luminescence is nearly entirely quenched in N,N-dimethylformamide (DMF) solution and biological system. In addition, 1 still has high detection for the trace content of nitromethane with 70 ppm, which suggests that 1 is a promising example of dual functional materials with sensing copper ions and nitromethane.

An Ultrastable Europium(III)-Organic Framework with the Capacity of Discriminating Fe2+/Fe3+ Ions in Various Solutions.

An ultrastable luminescent europium-organic framework, {[Eu(L)(H2O)2]·NMP·H2O}n (CTGU-2; NMP = N-methyl-2-pyrrolidone), can first detect Fe2+/Fe3+ cations in different medium systems with high selectivity and sensitivity, and it also exhibits high sensitivity for Cr2O72- anion and acetone with a wide linear range and a low detection limit.

Three novel lanthanide metal-organic frameworks (Ln-MOFs) constructed by unsymmetrical aromatic dicarboxylatic tectonics: synthesis, crystal structures and luminescent properties.

Three novel Ln(III)-based coordination polymers, {[Ln2 (2,4-bpda)3 (H2O)x]·yH2O}n (Ln = La (III) (1), x = 2, y = 0, Ce (III) (2), Pr (III) (3), x = 4, y = 1) (2,4-H2bpda = benzophenone-2,4-dicarboxylic acid) have been prepared via a solvothermal method and characterized by elemental analysis, IR, and single-crystal X-ray diffraction techniques. Complex 1 exhibits a 3D complicated framework with a new 2-nodal (3,7)-connected (42·5) (44·51·66·8) topology. Complexes 2 and 3 are isomorphous, and feature a 3D 4-connected (65·8)-CdSO4 network. Moreover, solid-state properties such as thermal stabilities and luminescent properties of 1 and 2 were also investigated. Complex 1 crystallized in a monoclinic space group P21/c with a = 14.800 (3), b = 14.500 (3), c = 18.800 (4) Å, ß = 91.00 (3), V = 4033.9 (14) Å3 and Z = 4. Complex 2 crystallized in a monoclinic space group Cc with a = 13.5432 (4), b = 12.9981 (4), c = 25.7567 (11) Å, ß = 104.028 (4), V = 1374.16 (7) Å3 and Z = 4.

Hierarchical chiral MOFs with the induced chirality of AIE ligands exhibiting non-reciprocal CPL.

Two pairs of chiral MOFs with hierarchical chiral structures were constructed through assembly of achiral AIE-type multidentate linkers and chiral camphoric acid. Non-reciprocal circularly polarized luminescence (CPL) can be observed on the macroscopic due to the coexistence of optical anisotropic and chiroptical nature. This study provides a new perspective to recognize and construct chiral crystalline materials.

Co5/Co8-cluster-based coordination polymers showing high-connected self-penetrating networks: syntheses, crystal structures, and magnetic properties.

Two novel Co(II)-cluster-based coordination polymers--namely, [Co5(µ3-OH)2(1,4-ndc)4(bix)2]n (1) and {[Co8(µ3-OH)4(1,4-ndc)6(btp)(H2O)6]·H2O}n (2)--were prepared by hydrothermal reactions of Co(II) perchlorate with 1,4-naphthalenedicarboxylic acid (1,4-H2ndc) and different N-donor coligands (bix = 1,4-bis(imidazol-1-ylmethyl)benzene and btp = 4,4'-bis(triazol-1-ylmethyl)biphenyl). In 1, 10-connected [Co5(µ3-OH)2(COO)8] clusters are extended by the µ4-1,4-ndc(2-) and trans-bix ligands to construct a rare, self-penetrating ile framework that can interestingly be regarded as the cross-link of two interpenetrating 6-connected pcu networks. While for 2, [Co8(µ3-OH)4(COO)12] clusters serve as the 8-connected nodes, which are bridged by the µ4/µ5-1,4-ndc(2-) and trans-btp ligands to afford the highest-connected uninodal self-penetrating (4(20).6(8)) network based on octacobalt clusters. A synthetic and structural comparison of 1 and 2 demonstrates that the features of auxiliary N-donor ligands play a key role in governing the in situ formed clusters and the final 3-D coordination frameworks. Magnetic susceptibility measurements indicate that complex 1 shows an antiferromagnetic interaction between the adjacent Co(II) ions, whereas 2 displays the dominant antiferromagnetic exchanges in 300-50 K and a ferrimagnetic-like behavior at lower temperatures.