Polyoxometalate-based Metal Organic Framework Research Articles

A lindquist-type polyoxometalate-based metal-organic framework as electrochemical sensor and efficient catalyst for selective oxidation of thioether

A new polyoxometalate-based metal-organic framework, [Co(Mo6O19)(9,10-BIMA)3] (MOF-1) has been prepared under hydrothermal conditions by selecting 9,10-bis(imidazol-1-ylmethyl)anthracene (9,10-BIMA) as bidentate N-donor ligand. In the structure of the MOF-1, the coordination of 9,10-BIMA ligands and Co(II) ions resulted in a three-dimensional 6-connected cationic framework containing a kind of one-dimensional channels, in which the Lindquist-type polyoxoanions [Mo6O19]2− as templates were assigned. The electrochemical and catalyticpropertystudiesshowed that the MOF-1 could be employed not only as electrochemical sensor for detecting bromate and ascorbic acid, but also efficient heterogeneous catalyst for the selective oxidation of thioether to sulfoxide with satisfying conversion and selectivity.

Ag Nanoparticle-Modified Polyoxometalate-Based Metal–Organic Framework for Enhanced CO2 Photoreduction

The photoreduction deposition method is employed to fabricate a family of silver nanoparticle (Ag NP)-modified polyoxometalate-based metal-organic framework (NENU-5) photocatalysts, named Ag/NENU-5. The title photocatalysts, Ag/NENU-5, can be used for the photocatalytic reduction of CO2 and are observed to efficiently reduce CO2 into CO, in which the highest reduction rate is 22.28 μmol g-1 h-1, 3 times greater than that of NENU-5. Photocatalytic reduction performances of CO2 have been extremely improved after the incorporation of Ag NPs as the cocatalyst. The enhancement of the photocatalytic reduction of CO2 has been attributed to the synergistic effects of Ag NPs and NENU-5, inhibiting the charge recombination during the photocatalytic process and increasing the reaction active sites. Furthermore, the influence of Ag NPs on the photocatalytic activity has also been investigated. The experimental results clearly reveal that the size of Ag NPs could exert a main effect on the photocatalytic activity, and the reasonable size of Ag NPs is able to enhance the photocatalytic reduction activity toward CO2 significantly.

A new 3D POMOF built upon Keggin clusters and flexible n-heterocycle carboxylate ligands for catalytic and antimicrobial properties

A new Keggin-based 3D framework with 1D U-shaped channels, [Ag 3 (H 2 O)(L) 2 ](H 2 PMo 12 O 40 )·H 2 O ( 1 ) (HL = 4-(1H-1,2,4-triazole-1-methyl) benzoic acid), was synthesized under hydrothermal conditions, which displays good properties of photocatalytic degradation of MB and electrocatalytic reduction of BrO 3 - and NO 2 – ions. Moreover, it also has the antimicrobial activities against Escherichia coli , Monilia albican and Xanthomonas axonopodis pv. Citri . • A new 3D framework constructed from Keggin clusters and 4-(1H-1,2,4-triazole-1-methyl) benzoic acid was synthesized by hydrothermal reaction. • 1D U-shaped channels exist in compound 1 . • Compound 1 displays good properties of photocatalytic degradation of MB and electrocatalytic reduction of BrO 3 - and NO 2 – ions. • The antimicrobial activities against Escherichia coli , Monilia albican and Xanthomonas axonopodis pv. Citri have also been investigated. A novel polyoxometalate-based metal–organic framework (POMOF), [Ag 3 (H 2 O)(L) 2 ](H 2 PMo 12 O 40 )·H 2 O ( 1 ) (HL = 4-(1H-1,2,4-triazole-1-methyl) benzoic acid), was synthesized under hydrothermal conditions. The structure was characterized by single crystal X-ray diffraction, elemental analysis, IR and TGA. In compound 1 , Ag ions are connected by organic ligands into a 1D U-shaped channel, and the 1D U-shaped channels are further linked into a 3D framework by {PMo 12 }. Compound 1 displays good properties of photocatalytic degradation of MB and electrocatalytic reduction of BrO 3 - and NO 2 – ions. Moreover, the antimicrobial activities against Escherichia coli , Monilia albican and Xanthomonas axonopodis pv. Citri have also been investigated.

Ionic Conduction Mechanism and Design of Metal-Organic Framework Based Quasi-Solid-State Electrolytes.

We report the theoretical and experimental investigation of two polyoxometalate-based metal–organic frameworks (MOFs), [(MnMo6)2(TFPM)]imine and [(AlMo6)2(TFPM)]imine, as quasi-solid-state electrolytes. Classical molecular dynamics coupled with quantum chemistry and grand canonical Monte Carlo are utilized to model the corresponding diffusion and ionic conduction in the two materials. Using different approximate levels of ion diffusion behavior, the primary ionic conduction mechanism was identified as solvent-assisted hopping (>77%). Detailed static and dynamic solvation structures were obtained to interpret Li+ motion with high spatial and temporal resolution. A rationally designed noninterpenetrating MOF-688(one-fold) material is proposed to achieve 6–8 times better performance (1.6–1.7 mS cm–1) than the current state-of-the-art (0.19–0.35 mS cm–1).

Enhanced Carrier Separation in Visible-Light-Responsive Polyoxometalate-Based Metal-Organic Frameworks for Highly Efficient Oxidative Coupling of Amines.

Photocatalytic technology is widely studied, while it comes with drawbacks such as low sunlight utilization efficiency and high carrier recombination rates. Herein, for the first time, we present two crystalline polyoxometalate (POM)-based metal-organic frameworks (POMOFs), {[Cd(DMF)2Ru(bpy)2(dcbpy)]2(POMs)(DMF)2} xDMF (PMo-1, POMs = [PMoVI11MoVO40]4-, x = 5; SiW-2, POMs = [SiW12O40]4-, x = 4) through assembling the photosensitizer [Ru(bpy)2(H2dcbpy)]Cl2 and POMs into a single framework. The assembly not only enhances light absorption in the visible light regime but also improves carrier separation efficiency; atop of that, both POMOFs demonstrate activities in the photocatalytic oxidative coupling of amines. Particularly, PMo-1 enables the quantitative completion of oxidative coupling of benzylamine reaction within 30 min (yield = 99.6%) with a high turnover frequency (TOF = 6631.6 h-1). To our knowledge, the PMo-1 catalyst outperforms any other photocatalysts previously reported in similar use cases where TOF values were usually obtained <2000 h-1.

Copper-Containing Polyoxometalate-Based Metal-Organic Frameworks as Heterogeneous Catalysts for the Synthesis of N-Heterocycles.

Three new polyoxometalate-based metal-organic frameworks (POMOFs) [Cu4(μ3-OH)2(tba)3(H2O)5(SiW12O40)0.5](H2SiW12O40)0.5·2.5H2O (CuSiW), [Cu3(μ3-OH)(tba)3(Htba)(H2O)2(HPMo12O40)]·7H2O (CuPMo), and [Cu4(μ3-OH)2(tba)3(H2O)3(PW12O40)0.5]2(PW12O40)·0.5H2O (CuPW) were constructed using multinuclear copper clusters, 3-(4H-1,2,4-triazol-4-yl)benzoic acid (Htba), and Keggin polyoxometalates (POMs). Different POMs regulate the formation of different multinuclear copper clusters ("boat" tetranuclear clusters in CuSiW, trinuclear clusters in CuPMo, and "chair" tetranuclear clusters in CuPW) and different topological structures of CuSiW, CuPMo, and CuPW (3-connected two-dimensional (2D) network for CuSiW, 4-connected 2D network for CuPMo, and (4,6)-connected three-dimensional network for CuPW). CuSiW, CuPMo, and CuPW as heterogeneous catalysts combine the high stability of MOFs in polar solvents and excellent catalytic activity of POMs and could be used for the synthesis of nitrogen-heterocycle compounds. The condensation cyclization reactions of 2-aminophenols/benzenesulfonyl hydrazines with 1,3-diketones produce benzoazoles and pyrazoles in good to excellent yields under the catalysis of CuPMo. Moreover, the catalyst could be reused at least for 7 runs, and this protocol was suitable for gram-scale reactions.

Photocatalytic Multielectron Reduction of Nitroarenes to Anilines by Utilizing an Electron-Storable Polyoxometalate-Based Metal-Organic Framework.

A powerful approach to generate photocatalysts for the highly selective reduction of nitrobenzene using light as the driving force is a combination of photosensitizers and electron-storable components in a cooperative photocatalysis fashion. Herein, a new precious metal-free photocatalyst, {ZnW-TPT}, was prepared by incorporating a Zn-substituted monovacant Keggin polyanion [SiZnW11O39]6- and a photoactive organic bridging link 2,4,6-tri(4-pyridyl)-1,3,5-triazine (TPT) into a framework. In this structure, the direct coordination bond between [SiZnW11O39]6- and the TPT ligand and the π-π interactions between TPT molecules help separate and migrate photogenerated carriers, which improves the photocatalytic activity of {ZnW-TPT}. The photoelectrochemical properties of {ZnW-TPT} were well studied by solid UV-vis absorption, fluorescence, transient photocurrent response, and electrochemical impedance spectroscopy tests. {ZnW-TPT} efficiently converts using hydrazine hydrate with 99% conversion and 99% selectivity for anilines under mild conditions.

Designing a Polyoxometalate-Incorporated Metal-Organic Framework for Reduction of Nitroarenes to Anilines by Sequential Proton-Coupled Electron Transfers.

Developing new photocatalysts for reduction of nitroarenes to anilines under mild conditions is very significant. Herein, a new polyoxometalate-based metal-organic framework (POMOF), {[Co(H2O)]2[Co2(H2O)6(TPT)][Co(TPT)PW11O39]}·3H2O·TPT (namely, CoW-TPT, TPT = 2,4,6-tri(4-pyridyl)-1,3,5-triazine), was prepared by incorporating Co(II)-substituted Keggin-type anions [PCoW11O39]5- and a photosensitizer (TPT) into a framework. In this structure, the direct coordination bond between [PCoW11O39]5- and TPT ligand and π···π interactions between TPT molecules are beneficial for the separation and migration of photogenerated carriers, thus improving the photocatalytic activity of CoW-TPT. The combination of both photosensitizer TPT and the electron-storable component [PCoW11O39]5- in a cooperative photocatalysis fashion is conducive to the photocatalytic multielectron reduction of nitroarenes. CoW-TPT provided a high conversion of 94.71% in the photocatalytic reduction of nitroarenes to anilines utilizing triethanolamine as the proton source and electron donor by sequential proton-coupled electron transfers.

A Novel Anderson-Evans Polyoxometalate-based Metal-organic Framework Composite for the Highly Selective Isolation and Purification of Cytochrome C from Porcine Heart

Anderson-Evans type polyoxometalate group (Na6[TeW6O24]·22 H2O, TeW6) was combined with porous metal-organic framework ZIF-8 by electrostatic interaction to obtain a novel Anderson-Evans polyoxometalate-based metal-organic framework composite, TeW6 @ZIF-8. FT-IR, Raman, XRD, TG, DSC, SEM, and TEM were used to characterize the composite. It was proved that the Anderson-Evans type polyoxometalate group TeW6 was successfully hybridized with metal-organic framework ZIF-8, and the composite possesses good stability. Based on the potential interaction between TeW6 and proteins and the coordination between imidazole groups in ZIF-8 and proteins with a porphyrin ring structure, the adsorption selectivity towards different proteins on the TeW6 @ZIF-8 composite was studied in this work. The experiment results showed that the TeW6 @ZIF-8 composite was selectively adsorbed to cytochrome C. At pH 11.0, the adsorption efficiency of 94.01% was obtained for processing 1.0 mL 100 μg mL-1 cytochrome C with 3.0 mg TeW6 @ZIF-8 composite. The adsorption behavior of cytochrome C fits well with the Langmuir adsorption model, corresponding to a theoretical adsorption capacity of 232.56 mg g-1. The retained cytochrome C could be readily recovered by 1% SDS (m/m), giving rise to a recovery of 65.6%. Circular dichroism spectra indicate no conformational change for cytochrome C after the adsorption and desorption processes, demonstrating the favorable biocompatibility of TeW6 @ZIF-8 composite. In applying practical samples, SDS-PAGE results showed that cytochrome C was successfully isolated and purified by TeW6 @ZIF-8 composite from porcine heart protein extract, which is further identified with LC-MS/MS. Thus, a new strategy for separating and purifying cytochrome C from the porcine heart using TeW6 @ZIF-8 composite as an adsorbent was established.

Copper-Containing Polyoxometalate-Based Metal-Organic Framework as a Catalyst for the Oxidation of Silanes: Effective Cooperative Catalysis by Metal Sites and POM Precursor.

The oxidation of silanes into silanols is a very necessary transformation, and yet the rational fabrication of efficient catalysts for this reaction remains a challenging task. Here, a 3D polyoxometalate-based metal-organic framework (POMOF), [CuΙ3(pz)3{PMo12O40}]·H2O (HENU-8, HENU = Henan University; pz = pyrazine) was consciously prepared and first employed in the oxidation of dimethylphenylsilane with tert-butyl hydroperoxide (TBHP) as an oxidant, achieving 89% yield at a production rate of 132 mmol·g-1·h-1. Control experiments indicated that polyoxometalates and Cu atoms together affected the ultimate outcome in this catalytic system, and the designed catalyst followed a free radical mechanism.

Polyoxometalate-Based Metal-Organic Frameworks as the Solid Support to Immobilize MP-11 Enzyme for Enhancing Thermal and Recyclable Stability.

The immobilization of enzymes has received much attention. Metal-organic framework (MOF) as the adsorbent for enzyme encapsulation provides an effective strategy. However, the encapsulation efficacy is not dependent solely on the specific surface area. Though leading into appropriate substrate with negative charge would enhance the encapsulation efficacy. Polyoxometalates (POMs) as the electron sponge would donate electrons without any structural change. In this study, Keggin-type phosphotungstic acid (PW12) was encapsulated in Zirconium metal-organic framework (PW12@UiO-67) as a heterogeneous adsorbent for the encapsulation of enzyme. Our following data proved that this composite cluster could enhance the adsorption of enzyme and the stability of MP-11 was then significantly improved after immobilization.

Design of a Polyoxometalate-Based Metal-Organic Framework for Photocatalytic C(sp3)-H Oxidation of Toluene.

A powerful and promising route for developing novel photocatalysts for light-driven toluene oxidation in water under mild conditions is presented. Herein, a novel polyoxometalate-based metal-organic framework (POMOF), {Co4W22-DPNDI}, is prepared by incorporating the unusual Co4-sandwiched POM anion [Co4(μ-OH)2(SiW11O39)2]10- ({Co4W22}) and the photoactive organic bridging link N,N'-bis(4-pyridylmethyl)naphthalene diimide (DPNDI) into a framework. {Co4W22} is a good candidate for photocatalytic water oxidation. DPNDI is easily excited to form the radical species DPNDI* in the presence of an electron donor, which is beneficial for activation of the inert O2. Anion···π interactions and covalent bonds between {Co4W22} and DPNDI facilitate electron-hole separation and electron transfer. {Co4W22-DPNDI} displays high catalytic activity for the activation of the C(sp3)-H bond of toluene using light as a driving force and inexpensive water as an oxygen source under mild conditions. In particular, the yield and selectivity are improved by replacing oxygen with water, which may be ascribed to the release of protons during the water oxidation process that facilitate the generation of •OH.

Three Anderson-type POMOFs with bis(pyrimidine)-bis(amide) ligands: Synthesis, fascinating structures and performances of electrochemical sensing and dye adsorption

Three new Anderson-type polyoxometalate (POM)-based metal–organic frameworks (POMOFs) [Co3(L1)(TeMo6O24)(H2O)10]·8H2O (1), [Co3(L2)(TeMo6O24)(H2O)10]·8H2O (2) and [Cu3(L1)(TeMo6O24)(H2O)10]·6H2O (3) (L1 ​= ​N,N′-bis(4-pyrimidinecarboxamido)-1,2-ethane, L2 ​= ​N,N′-bis(4-pyrimidinecarboxamido)-1,4-butane) were obtained under 90 ​°C aqueous solution for two days. POMOFs 1–3 show fascinating 3D framework structures formed by transition metal linking bis(pyrimidine)-bis(amide) ligands and Anderson-type [TeMo6O24]6– anions. The carbon paste electrodes bulk-modified by POMOFs 1–3 (1-, 2-, 3-CPEs) have good bifunctional electrocatalytic performance towards the oxidation of ascorbic acid and the reduction of potassium bromate, potassium nitrite and heavy metal ions Cr(VI). 1-, 2-, 3-CPEs can be used as electrochemical sensors for the detection of Cr(VI), the limits of detection (LODs) are 0.389 ∼ 0.422 ​μM, which are lower than the 1.0 ​μM standard set by the WHO. In addition, the adsorption properties of POMOFs 1–3 on organic dyes gentian violet (GV) and methyl orange (MO) were investigated.

POM-based metal organic frameworks with a woven fabric structure for lithium storage

A novel POMOFs with fabric structure possesses high lithium storage capacity, and its long life cycle performance is further enhanced by CNTs.

N-Donor flexible ligands for constructing polyoxometalate-based metal–organic frameworks as multifunctional electrocatalysts

Two POMOFs,CUST-631andCUST-632, were synthesized by a hydrothermal method and then were directly prepared as electrode materials to explore the electrocatalytic properties for reduction of BrO3−and NO2−ions and oxidation properties towards AA.

Progress in the Preparation and Catalytic Performance Research of Encapsulated Polyoxometalate-based POMs@MOFs Materials

The composition, structure and size of the polyoxometalates are easy to be controlled in their synthetic process, and they have good electronic storage and redox capabilities. They are favored by chemists due to their broad application prospects in the development of clean, green and environmentally efficient catalysts. Encapsulating polyoxometalates into metal-organic framework materials can solve some problems such as deactivation due to agglomeration during the catalytic reaction process, difficulty in catalysts recycling in homogeneous system, and their low specific surface area. In this paper, the preparation methods of polyoxometalate-based metal-organic framework materials, namely, in-situ synthesis, immersion synthesis and mechanical grinding synthesis, are summarized, and the advantages and disadvantages of each method are discussed respectively. We further summarized the research progress of polyoxometalate-based metal-organic framework materials in the field of catalysis, and looked forward to their development trends in future.

A novel core-shell structured hybrid composed of zinc homobenzotrizoate and silver borotungstate with supercapacitor and photocatalytic dye degradation performance

Polyoxometalate-based metal-organic frameworks (POMOFs) are challenging as electrode materials for supercapacitors and catalysts for the photocatalytic degradation of organic pollutants. To this end, a novel core-shell structured zinc homobenzotrizoate and silver borotungstate ([Zn4(BTC)2(μ4-O)(H2O)2]@Ag5[BW12O40], abbreviated as Zn-BTC@Ag5[BW12O40], BTC = 1,3,5-benzylcarboxylic acid) was synthesized by wrapping polyoxometalate (POM) on metal-organic framework (MOF) by a simple grinding method. This unique synergy between the core (Zn-BTC) and shell (Ag5[BW12O40]) sets the compound more surface active sites. The composition, structure, and morphology of the title compound were discussed by infrared (IR), powder X-ray diffraction (XRD), scanning electron microscope (SEM), energy dispersive spectroscopy (EDS), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and other methods. In the three-electrode foam nickel system, the Zn-BTC@Ag5[BW12O40] electrode showed a higher specific capacitance (161.7 F g−1) than the Ag5[BW12O40] (97.7 F g−1) and Zn-BTC (118.4 F g−1), and the capacitance retention rate was 92.8% after 5000 cycles. Assembled into a symmetrical supercapacitor with an energy density of 9.3 Wh Kg−1 and a power density of 501.2 W Kg−1. The capacitance retention rate reached 91.4% after 5000 cycles. In addition, The photocatalytic degradation efficiency of Zn-BTC@Ag5[BW12O40] for Methylene Blue (MB), Methyl Orange (MO), and Rhodamine B (RhB) dyes are all greater than 90% in 140 min. The photocatalytic cycle test has been carried out 5 times, and the degradation effect remains the same. This indicates that the title compound has high activity in the direction of photocatalytic degradation of dyes.

Two Polymorphic Polyoxometalate-Based Metal–Organic Frameworks for the Efficient Synthesis of Functionalized Sulfoxides and Detoxification of Mustard Gas Simulants

Two Polymorphic Polyoxometalate-Based Metal–Organic Frameworks for the Efficient Synthesis of Functionalized Sulfoxides and Detoxification of Mustard Gas Simulants

A new ɛ-Keggin polyoxometalate-based metal-organic framework: From design and synthesis to electrochemical hydrogen evolution

A new ɛ-Keggin polyoxometalate based metal-organic framework, [TBA]3[H4PMo8VMo4VIO40Zn4](HTPT)2 (1) (H3TPT = 1,1′:4′,1″-terphenyl-3,4″,5-tricarboxylic acid, TBA+ = tetrabutylammonium ion) was synthesized under hydrothermal conditions. The tetrahedral Zn4-ε-Keggin is connected through angular HTPT2− to form a 2D entangled structure with 2-fold interpenetration. The whole network displays a staggered layer structure in AB/CD/EF/GH/AB/CD/EF/GH arrangement with extensive hydrogen bonding and intermolecular interactions. More interestingly, compound 1 exhibited good hydrogen evolution reaction (HER) activity in an acidic medium, with a Tafel slope of 68 mV·dec−1 and an η10 of 417 mV. It showed an excellent long-term stability, which could maintain its catalytic activity after 1000 cycles.

{BW12O40} Hybrids Modified by in Situ Synthesized Rigid Ligand with Supercapacitance and Photocatalytic Properties.

Organic rigid ligand-modified polyoxometalate-based materials possess complex and diverse structures, promising electrochemical energy storage properties and outstanding photocatalytic capabilities. Hence, two new [BW12O40]5-(abbreviated as {BW12O40})-based inorganic-organic hybrids [{Cu(en)2(H2O)}][{Cu(pdc)(en)}{Cu(en)2}(BW12O40)]·2H2O (1) and [{CuI5(pz)6(H2O)4}(BW12O40)] (2) (pdc = 2-picolinate, en = ethylenediamine, pz = pyrazine) were successfully synthesized through a hydrothermal method. Among them, pdc and pz were obtained by in situ transformation from 2,6-pyridinedicarboxylic acid (H2 pydc) and 2,3-pyrazinedicarboxylic acid (H2pzdc), respectively. In compound 1, the {BW12O40} clusters as an intermediate junction connect with {Cu(pdc)(en)}{Cu(en)2} and {Cu(en)2(H2O)} to form monomers, which in turn form supramolecular chains, sheets, and space network via hydrogen bonding. The {BW12O40} clusters are packed into copper-pyrazine frameworks in compound 2, and a unique polyoxometalate-based metal organic frameworks (POMOFs) structure with a new topology of {12}2{6.123.142}2{62.12.142.18}{62.123.16}{6}6 is formed via covalent bonds. When used as electrode materials for supercapacitors, the values of specific capacitance are 651.56 F g-1 for 1-GCE and 584.43 F g-1 for 2-GCE at a current density of 2.16 A g-1 and good cycling stability (90.94%, 94.81% of the initial capacity after 5000 cycles at 15.12 A g-1, respectively). The kinetic analysis reveals that surface capacitance plays a major role. Furthermore, both compounds can effectively degrade Rhodamine B (RhB) and Methylene blue (MB), showing the outstanding photocatalytic performance.