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.

Trace removal of benzene vapour using double-walled metal-dipyrazolate frameworks.

In principle, porous physisorbents are attractive candidates for the removal of volatile organic compounds such as benzene by virtue of their low energy for the capture and release of this pollutant. Unfortunately, many physisorbents exhibit weak sorbate-sorbent interactions, resulting in poor selectivity and low uptake when volatile organic compounds are present at trace concentrations. Herein, we report that a family of double-walled metal-dipyrazolate frameworks, BUT-53 to BUT-58, exhibit benzene uptakes at 298 K of 2.47-3.28 mmol g-1 at <10 Pa. Breakthrough experiments revealed that BUT-55, a supramolecular isomer of the metal-organic framework Co(BDP) (H2BDP = 1,4-di(1H-pyrazol-4-yl)benzene), captures trace levels of benzene, producing an air stream with benzene content below acceptable limits. Furthermore, BUT-55 can be regenerated with mild heating. Insight into the performance of BUT-55 comes from the crystal structure of the benzene-loaded phase (C6H6@BUT-55) and density functional theory calculations, which reveal that C-H···X interactions drive the tight binding of benzene. Our results demonstrate that BUT-55 is a recyclable physisorbent that exhibits high affinity and adsorption capacity towards benzene, making it a candidate for environmental remediation of benzene-contaminated gas mixtures.

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.

Rapid Cs+ Capture via Multiple Supramolecular Interactions in Anionic Metal-Organic Framework Isomers.

Metal-organic frameworks (MOFs) provide an ideal platform for ion exchange due to their high porosity and structural designability; however, developing MOFs that have the essential characteristics for ion exchange remains a challenge. These crucial features include fast kinetics, selectivity, and stability. We present two anionic isomers, DGIST-2 (2D) and DGIST-3 (3D), comprising distinctly arranged 5-(1,8-naphthalimido)isophthalate ligands and In3+ cations. Interestingly, in protic solvents, DGIST-2 transforms into a hydrolytically stable crystalline phase, DGIST-2'. DGIST-2' and DGIST-3 exhibit rapid Cs+ adsorption kinetics, as well as high Cs+ affinity in the presence of competing cations. The mechanism for rapid and selective sorption is explored based on the results of single-crystal X-ray diffraction analysis of Cs+-incorporated DGIST-3. In Cs+-containing solutions, the loosely incorporated dimethylammonium countercation of the anionic framework is replaced by Cs+, which is held in the hydrophobic cavity by supramolecular ion-ion and cation-π interactions.

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.

A Practice of Reticular Chemistry: Construction of a Robust Mesoporous Palladium Metal-Organic Framework via Metal Metathesis.

Constructing stable palladium(II)-based metal-organic frameworks (MOFs) would unlock more opportunities for MOF chemistry, particularly toward applications in catalysis. However, their availability is limited by synthetic challenges due to the inertness of the Pd-ligand coordination bond, as well as the strong tendency of the Pd(II) source to be reduced under typical solvothermal conditions. Under the guidance of reticular chemistry, herein, we present the first example of an azolate Pd-MOF, BUT-33(Pd), obtained via a deuterated solvent-assisted metal metathesis. BUT-33(Pd) retains the underlying sodalite network and mesoporosity of the template BUT-33(Ni) and shows excellent chemical stability (resistance to an 8 M NaOH aqueous solution). With rich Pd(II) sites in the atomically precise distribution, it also demonstrates good performances as a heterogeneous Pd(II) catalyst in a wide application scope, including Suzuki/Heck coupling reactions and photocatalytic CO2 reduction to CH4. This work highlights a feasible approach to reticularly construct noble metal based MOFs via metal metathesis, in which various merits, including high chemical stability, large pores, and tunable functions, have been integrated for addressing challenging tasks.

In Situ Porphyrin Substitution in a Zr(IV)-MOF for Stability Enhancement and Photocatalytic CO2 Reduction.

Despite numerous inherent merits of metal-organic frameworks (MOFs), structural fragility has imposed great restrictions on their wider involvement in many applications, such as in catalysis. Herein, a strategy for enhancing stability and enabling functionality in a labile Zr(IV)-MOF has been proposed by in situ porphyrin substitution. A size- and geometry-matched robust linear porphyrin ligand 4,4'-(porphyrin-5,15-diyl)dibenzolate (DCPP2- ) is selected to replace the 4,4'-(1,3,6,8-tetraoxobenzo[lmn][3,8]phenanthroline-2,7(1H,3H,6H,8H)-diyl)dibenzoate (NDIDB2- ) ligand in the synthesis of BUT-109(Zr), affording BUT-110 with varied porphyrin contents. Compared to BUT-109(Zr), the chemical stability of BUT-110 series is greatly improved. Metalloporphyrin incorporation endows BUT-110 MOFs with high catalytic activity in the photoreduction of CO2 , in the absence of photosensitizers. By tuning the metal species and porphyrin contents in BUT-110, the resulting BUT-110-50%-Co is demonstrated to be a good photocatalyst for selective CO2 -to-CO reduction, via balancing the chemical stability, photocatalytic efficiency, and synthetic cost. This work highlights the advantages of in situ ligand substitution for MOF modification, by which uniform distribution and high content of the incoming ligand are accessible in the resulting MOFs. More importantly, it provides a promising approach to convert unstable MOFs, which mainly constitute the vast MOF database but have always been neglected, into robust functional materials.

Alkali-Etched Ni(II)-Based Metal-Organic Framework Nanosheet Arrays for Electrocatalytic Overall Water Splitting.

The exploration of efficient electrocatalysts is the central issue for boosting the overall efficiency of water splitting. Herein, pertinently creating active sites and improving conductivity for metal-organic frameworks (MOFs) is proposed to tailor electrocatalytic properties for overall water splitting. An Ni(II)-MOF nanosheet array is presented as an ideal material model and a facile alkali-etched strategy is developed to break its NiO bonds accompanied with the introduction of extra-framework K cations, which contribute to creating highly active open metal sites and largely improving the electrical conductivity. As a result, the assembled defect-Ni-MOF||defect-Ni-MOF electrolyte cell delivers a lower and stable voltage of 1.50 V at 10 mA cm-2 in alkaline medium for overall water splitting, comparable to the combination of iridium and platinum as benchmark catalysts.

A Stable Zr(IV)-Based Metal-Organic Framework Constructed from C═C Bridged Di-isophthalate Ligand for Sensitive Detection of Cr2O72- in Water.

As the Cr2O72- anion is highly toxic, new sensors have been developing for its effective detection from water, among which metal-organic frameworks (MOFs) show distinct superiority over many other materials. Herein, a new fluorescent Zr(IV)-based MOF, [Zr6O4(OH)8(H2O)4(sbtc)2] (referred to as BUT-28), based on the di-isophthalate ligand with a central CH═CH moiety, trans-stilbene-3,3',5,5'-tetracarboxylate (sbtc4-), has been prepared and structurally determined. The MOF shows excellent stability in neutral, highly acidic, and weakly basic aqueous solutions. Moreover, no essential uptake loss in three cycles of water vapor adsorption-desorption measurements was observed for BUT-28, suggesting the robustness of the porous framework and its great potential for long-term use. Fluorescent measurements were carried out for BUT-28 and an isostructural MOF, Zr-abtc, which is constructed from the di-isophthalate ligand with a central N═N moiety, azobenzene-3,3',5,5'-tetracarboxylate (abtc4-). Interestingly, Zr-abtc shows very weak fluorescent emission. In contrast, BUT-28 exhibits relatively strong fluorescence and serves as a promising sensory material for the detection of trace Cr2O72- (limit of detection: 36 ppb) in aqueous solutions by selective and sensitive fluorescence quenching effect.

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.

Maximakinin reduced intracellular Ca2+ level in vascular smooth muscle cells through AMPK/ERK1/2 signaling pathways.

We detect the antihypertensive effects of maximakinin (MK) on renal hypertensive rats (RHRs) and further research the influence of MK on vascular smooth muscle cells (VSMCs) to explore its hypotensive mechanism. The effects of MK on arterial blood pressure were observed in RHRs. 3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazoliumbromide (MTT) assays were performed to detect the effect of MK on VSMC viability. Western blot and flow cytometry were used to investigate the influence of MK on intracellular Ca2+ levels and protein expression changes in VSMCs. In addition, specific protein inhibitors were applied to confirm the involvement of Ca2+-related signaling pathways induced by MK in VSMCs. MK showed a more significant antihypertensive effect than bradykinin in RHRs. MK significantly decreased intracellular Ca2+ concentrations. Furthermore, MK significantly induced the phosphorylation of signaling molecules, including extracellular signal-regulated kinase 1/2 (ERK1/2), P38, AMP-activated protein kinase (AMPK) and Akt in VSMCs. Moreover, only ERK1/2 inhibitor U0126 and AMPK inhibitor Compound C completely restored the decreased intracellular Ca2+ level induced by MK, and further research demonstrated that AMPK functioned upstream of ERK1/2 following exposure to MK. Finally, HOE-140, an inhibitor of the bradykinin B2 receptors (B2Rs), was applied to investigate the potential targets of MK in VSMCs. HOE-140 significantly blocked the AMPK/ERK1/2 pathway induced by MK, suggesting that the B2Rs might play an important role in MK-induced AMPK and ERK1/2 activation. MK significantly reduces blood pressure in RHRs. MK exerts its antihypertensive effect by activating the B2Rs and downstream AMPK/ERK1/2 pathways, leading to significantly reduced Ca2+ levels in VSMCs.

Seaweed-like phosphates/MOF heterostructures as a synergistic electrocatalyst for alcohol oxidation.

A series of seaweed-like heterogeneous Co3(PO4)2/Ni3(PO4)2/MOF-74-x electrocatalysts were synthesized via a hydrothermal method. The optimal composite exhibits excellent catalytic performance toward methanol/ethanol oxidation reactions (MOR/EOR) with peak current densities reaching 27.5 and 32.6 mA cm-2, respectively. This work heralds the advent of more efficient heterogeneous electrocatalysts for DAFCs and other energy conversion systems.

Ar plasma assists in enhanced oxygen evolution kinetics of MOG-derived multicomponent transition metal sulfides.

Transition metal sulfides are low-cost oxygen evolution reaction (OER) electrocatalysts that can potentially substitute noble metal catalysts. However, the adsorption process of their OER is impeded by their intrinsic poor catalytic activity. Constructing heterojunction and vacancy defects in transition metal sulfides is an efficient method to promote the process of oxygen evolution. Herein, a facile approach based on in situ sulfurization of metal-organic gels (MOGs) and a short-time plasma treatment was developed to fabricate vacancy-modified polymetallic sulfides heterojunction. The synergistic effect of the multi-component heterojunction and sulfur vacancy contributed greatly to improving the electron migration efficiency and OER ability of the electrocatalyst. As a result, the optimum oxygen evolution activity was achieved with appropriate surface vacancy concentrations by regulating the plasma radio frequency powers. The plasma-treated catalyst under 400 W showed the best OER performance (lower overpotential of 235 mV in 1 M KOH solution with the Tafel slope of 31 mV dec-1) and good durability over 11 h of chronopotentiometry testing. This work sheds new light on constructing multimetal-based heterojunction electrocatalysts with rich vacancy defects for oxygen evolution reactions.

Thermal treatment for promoting interfacial interaction in Co-BDC/Ti3C2Tx hybrid nanosheets for hybrid supercapacitors.

The design and synthesis of high-performance metal-organic frameworks (MOFs)-based electrodes are important for hybrid supercapacitors (HSC). Herein, enhanced interfacial interaction in Co-BDC/Ti3C2Tx (denoted as CoTC) hybrid nanosheets is achieved through thermal treatment, giving remarkably improved capacity performance compared with CoTC. The low temperature annealing treatment enables modulation of the bridging bonds content of CoTC and thus regulates the interfacial coupling effect between Co-BDC and Ti3C2Tx. Moreover, both the detailed XPS and XANES analysis reveal that the strong interfacial interactions between the two components promote a partial electron transfer from Ti3C2Tx to Co-BDC through the Ti-O-Co interfacial bonds. Consequently, it endows the Co-BDC with enhanced conductivity as well as the higher valence of Ti species in Ti3C2Tx, hence contributes a remarkable enhanced specific capacity. This work will provide a pathway to design advanced MOF/MXene materials for HSC.

π-Stacks of radical-anionic naphthalenediimides in a metal-organic framework.

Radical-ionic metal-organic frameworks (MOFs) have unique optical, magnetic, and electronic properties. These radical ions, forcibly formed by external stimulus-induced redox processes, are structurally unstable and have short radical lifetimes. Here, we report two naphthalenediimide-based (NDI-based) Ca-MOFs: DGIST-6 and DGIST-7. Neutral DGIST-6, which is generated first during solvothermal synthesis, decomposes and is converted into radical-anionic DGIST-7. Cofacial (NDI)2•- and (NDI)22- dimers are effectively stabilized in DGIST-7 by electron delocalization and spin-pairing as well as dimethylammonium counter cations in their pores. Single-crystal x-ray diffractometry was used to visualize redox-associated structural transformations, such as changes in centroid-to-centroid distance. Moreover, the unusual rapid reduction of oxidized DGIST-7 into the radical anion upon infrared irradiation results in effective and reproducible photothermal conversion. This study successfully illustrated the strategic use of in situ prepared cofacial ligand dimers in MOFs that facilitate the stabilization of radical ions.

Synthesis and crystal structure of poly[(3-amino-1,2,4-triazole)(µ3-1H-benzimidazole-5,6-di-carboxyl-ato)cobalt(II)].

The asymmetric unit of the title coordination polymer, [Co(C9H4N2O4)(C2H4N4)] n or [Co(L 1)(L 2)] n , consists of one crystallographically independent Co2+ centre, one L 1 2- ligand and one L 2 ligand (L 1 = 1H-benzimidazole-5,6-di-carb-oxy-lic acid, L 2 = 3-amino-1,2,4-triazole). The Co2+ centre is coordinated by two carboxyl-ato-O atoms from two independent L 1 2- ligands and two nitro-gen atoms from L 2 and another L 1 ligand. Thus, the metal center adopts a four-coordinate mode, forming a tetra-hedral geometry. Inter-estingly, through the combination of two L 1 2-, two L 2 ligands and two Co2+ ions, a basic repeating unit is constructed, resulting in the formation of a one-dimensional straight chain structure. These chains are further expanded to the final three-dimensional framework via N-H⋯O hydrogen-bonding inter-actions.

In Situ Synthesis of Surface-Mounted Novel Nickel(II) Trimer-Based MOF on Nickel Oxide Hydroxide Heterostructures for Enhanced Methanol Electro-Oxidation.

Engineering the heterogeneous interface fusing MOFs and inorganic active component is an effective strategy to improve the electrochemical performance. Herein, we report a new Ni3-based MOF (denoted as CTGU-24) with an infrequent two-fold interpenetrating 3D (3,8)-connected network constructed from Ni(II) trimer and mixed tripodal tectonics for the electrocatalytic methanol oxidation reaction (MOR). In order to improve its stability and activities, the heterogeneous hybrid CTGU-24@NiOOH has been fabricated successfully via the first preparation of the NiOOH nanosphere and then in situ formation of CTGU-24 decorated on the NiOOH surface. Moreover, the integration of CTGU-24@NiOOH and different additives [acetylene black (AB) and ketjen black (KB)], resulting in the optimized hybrid sample AB&CTGU-24@NiOOH (4:4). It attains better MOR performance with an area-specific peak current density of 34.53 mA·cm-2 than pure CTGU-24 (14.99 mA·cm-2) and improved durability in an alkali medium. The new findings indicate that the CTGU-24@NiOOH heterostructure formed in situ and the integration of moderate additives are critical to optimizing and improving electrocatalytic activity of pure MOF crystalline material.

[Online determination of pH in fresh pork by visible/near-infrared spectroscopy].

The present research was focused on determination of the pH value online by visible and near-infrared spectroscopy. In the part of data gathering, fresh pork longissimus dorsi was moving at the constant velocity of 0.25 m x s(-1) on the conveyor belt, and the visible and near-infrared diffuse reflectance spectrum (350-1 000 nm) was captured. In the part of data processing, band of 510-980 nm of the spectra was chosen to calibrate reflex distance, then to set up online detection model of pH value in fresh pork by partial least squares regression (PLSR). Kennard-stone algorithm was applied to divide the samples to the calibration set and validation set. The performances of several PLSR models employing various preprocessing methods including multiple scatter correction, derivative and both of them combined were compared. Further, the best performance model was optimized by interval PLSR to decrease the modeling variables of wavelength. The results indicated that the PLSR model based on preprocessing of multiple scatter correction (MSC) combined with first derivative gave the best performance with 0.905 of the correlation coefficient for validation set and 0.051 of the root of mean square errors for validation set. For the best PLSR model performance, the correlation coefficient of validation set increased to 0.926 and the root of mean square errors for validation set to 0.045 in the optimization interval PLSR model. However, only half of variables were used. The research demonstrates that using visible and near-infrared spectroscopy to determine fresh pork pH online is feasible.

Selective adsorption and separation of C2 hydrocarbons in a "flexible-robust" metal-organic framework based on a guest-dependent gate-opening effect.

The selective adsorption/separation of C2 hydrocarbons has been realized in a "flexible-robust" MOF, Zn2(Atz)2Ox. Owing to the distinctive guest-dependent multistep adsorption behaviors and suitable guest-framework interactions, this MOF shows outstanding separation performance for C2H2/C2H4 mixtures in a wide range of temperature confirmed by a column breakthrough experiment.