A hybrid borotungstate-coated metal-organic framework with supercapacitance, photocatalytic dye degradation and H2O2 sensing properties

The compounding of polyoxometalates (POMs) with structurally well-defined and porous metal-organic frameworks (MOFs) has become a hot research topic. Here, a core-shell type hybrid, {Ag₅BW₁₂O₄₀}@[Ag₃(μ-Hbtc)(μ-H₂btc)]_n (called {Ag₅BW₁₂O₄₀}@Ag-BTC-2, where BTC = 1,3,5-benzyl carboxylic acid), was successfully prepared via a simple grinding method. IR, XRD, SEM, TEM, and XPS analysis was used to confirm the structure. The specific capacitance is 179.1 F g^-1 when the current density is 1 A g^-1, using nickel foam as the collector, and the capacitance retention is 97.4% after 5000 cycles. The resulting aqueous-based symmetric supercapacitor has a power density of 496 W kg^-1 and an energy density of 12.4 W h kg^-1. In addition, the degradation rates using {Ag₅BW₁₂O₄₀}@Ag-BTC-2 toward methylene blue (MB), rhodamine B (RhB), and methyl orange (MO) exceeded 90% in 140 min and remained essentially unchanged over five replicate experiments, showing high photocatalytic activity. Meanwhile, when {Ag₅BW₁₂O₄₀}@Ag-BTC-2 acts as a H₂O₂ biosensor, it has a low detection limit (0.19 μM), a wide linear range (0.4 μM-0.27 mM) and high anti-interference properties. This shows that the synthesis of POMOFs via a grinding method is an effective strategy to improve the performance.

Efficient visible-light-driven reduction of hexavalent chromium catalyzed by conjugated organic species modified hourglass-type phosphomolybdate hybrids

Four conjugated-organic-species modified hourglass-type phosphomolybdate hybrids with a 0-D + 1-D → 3-D supramolecular structure exhibited favorable photocatalytic activity and stability towards Cr(vi) reduction.

{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 [{Cu^I₅(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.

Two three-dimensional polyanionic clusters [M(P4Mo6)2] (M = Co, Zn) exhibiting excellent photocatalytic CO2 reduction performance

Two captivating {P4Mo6}-based compounds, formulated as (H2bbi)2{[Co2(bbi)][Co2.33(H2O)4][H9.33CoP8Mo12O62]}·4H2O (1) and (H2bbi){[Zn(Hbbi)]2[Zn0.75(bbi)][K2Zn(H2O)4][H8.5ZnP8Mo12O62]} (2) [bbi = 1,1'-(1,4-butanediyl)bis(imidazole)], were successfully synthesized under hydrothermal conditions. Structural analysis demonstrates that compounds 1 and 2 are constructed from hourglass-shaped structures [M(P4Mo6O31)2]n- (M = Co, Zn), which are all made up of molybdophosphates and one transition metal ion as the central connecting node. Compounds 1 and 2 feature three-dimensional (3D) frameworks, which are all connected to form a 3D structure by metal ions and bbi ligands. More interestingly, compound 1 exhibits higher catalytic activity than 2 in CO2 photoreduction due to the suitable energy band structure of Co species in {P4Mo6} clusters. The CO yield was 3261 μmol g-1 with high selectivity in 8 h for compound 1 in photocatalytic CO2 reduction, which is highly promising in the photocatalytic field. Additionally, the photoluminescence properties of 2 were investigated.

Assembling [M(P4Mo6)2] (M = Na, Mn, Na/Cu) dimeric clusters via transition metal/sodium ions into 0D to 3D phosphomolybdates

Six novel molybdenum(v) phosphates with structures ranging from a zero-dimensional cluster to three-dimensional frameworks have been solvothermally synthesized.

Crystal structures of hybrid completely reduced phosphomolybdates and catalytic performance applied as molecular catalysts for the reduction of chromium(VI)

The exploration of highly efficient and low-cost catalysts for the treatment of hexavalent chromium Cr^VI in environmental remediation is currently one of the most challenging topics. Here, three phosphomolybdate hybrid compounds have been successfully isolated by the hydrothermal method and been applied as supramolecular catalysts for the reduction of Cr^VI. Single-crystal X-ray diffraction revealed their formulae as (H₂bpp)₂[Fe(H₂O)][Sr(H₂O)₄]₂{Fe[Mo₆O₁₂(OH)₃(H₂PO₄)(HPO₄)(PO₄)₂]₂}·5H₂O (1), (H₂bpp)₂[Na(H₂O)(OC₂H₅)][Fe(H₂O)₂][Ca(H₂O)₂]₂{Fe[Mo₆O₁₂(OH)₃(H₂PO₄)(HPO₄)(PO₄)₂]₂}·4H₂O (2) and (H₂bpe)₃{Fe[Mo₆O₁₂(OH)₃(HPO₄)₃(H₂PO₄)]₂}·8H₂O (3) [bpp is 1,3-bis(pyridin-4-yl)propane (C₁₃H₁₄N₂) and bpe is trans-1,2-bis(pyridin-4-yl)ethylene (C₁₂H₁₀N₂)]. The three hybrids consist of supramolecular networks built up by noncovalent interactions between {Fe[P₄Mo₆^VO₃₁]₂}^22- polyanions and protonated organic cations. This kind of hybrid polyoxometalate could be applied as heterogeneous molecular catalysts for the reduction of Cr^VI. It was found that the organic moiety plays a vital role in influencing the catalytic activity of the polyanions. Organic bpp-containing hybrids 1 and 2 are highly active in the catalytic reduction of heavy metal Cr^VI ions using HCOOH as reductant, while bpe-containing hybrid 3 is inactive to this reaction. This work is significant for the design of new catalysts, as well as the exploration of reaction mechanisms at a molecular level.

Novel fully reduced phosphomolybdates for highly efficient removal of inorganic hexavalent chromium and the organic dye methylene blue

New Na-bridged phosphomolybdates as heterogeneous catalysts exhibit efficient catalytic performance on the reduction of hexavalent chromium and photodegradation of methylene blue.

Efficient and robust photocatalysts based on {P2W18} modified by an Ag complex

Ag⁺ and the flexible ligand bimb were introduced into Dawson phosphomolybdate systems as linkage units to induce two fascinating 3-D inorganic–organic networks, which exhibit excellent electro- and photo-catalytic behavior.

The basket-type dimer layers based on tetra-electron reduced heteropoly blue directed by copper/nickel and strontium linkers

Two basket-type dimer layers have been prepared, which exhibit highly efficient catalytic ability for the degradation of typical dyes and bifunctional electrocatalytic behaviors.

Construction of two novel borotungstates modified by different ligands connected with single/double bridges

Unusual copper complex units modified by two types of ligands are introduced into the {BW₁₂} systems, leading to the assembly of intricate borotungstate networks, which exhibit good photo-/electro-catalytic activities.