Polyoxometalate-based Inorganic Organic Hybrid Research Articles

Exploring the semiconductor characteristics of a polyoxometalate-based organic-inorganic hybrid dimer and its photocatalytic applications

Polyoxometalate-based organic-inorganic hybrid compounds have been widely used in the field of photocatalysis, photoelectrocatalysis, interfacial materials of semiconductor device. However, their intrinsic semiconductor characteristics such as carrier diffusion lengths and carrier mobility are still unclear. Herein, we first unravel the carriers diffusion length and carrier mobility of the novel POM-based dimeric compound, {(HBW12O40)[Cu(2,2′-bipy)2]2[CuO(2,2′-bipy)(H2O)]}2·2H2O (1), which is successfully synthesized through co-assembly of binuclear Cu(II)-complex and BW12 in hydrothermal reaction. Space charge-limited currents (SCLC) method shows that the holes carriers mobility (μh) of this compound reached 0.84 cm2V−1s−1, which is more 30 times than that of raw BW12 (2.6 × 10−2 cm2V−1s−1). The calculated carrier diffusion lengths of compound 1 is 82 nm, which is almost 3 time higher than that of BW12 (25 nm), indicating that photogenerated carriers are more easily separated and diffused in compound 1. Furthermore, the semiconductor properties of compound 1 have been demonstrated by the measurements of photocurrent response, VB-XPS spectrum and band gap (Eg) values. In addition, its applications of photocatalysis indicate the excellent activities of compound 1 with 71 % degradation rate for photodegradation of methylene blue (MB) and 67 % degradation rate for photocatalytic reduction of Cr(VI).

Efficient room-temperature oxidation of dibenzothiophene over mesoporous WO3@ZrO2-TiO2 composites derived from polymer-oriented self-assembly strategy

Deep removal of thiophenic sulfur compounds in fuel oil remains an enormous challenge to achieve ultra-clean diesel production. Herein, a polyoxometalate-based inorganic-organic hybrid derived mesoporous WO3@ZrO2-TiO2 composites has been prepared by a simple polymer-oriented self-assembly strategy using polyethyleneimine (PEI) as the structure-directing agent. It exhibits that the existence of mesoporous pore channels, Zr doped TiO2 matrix, and highly dispersed WO3 active sites on the ZrO2-TiO2 framework can facilitate the adsorption-oxidation process of thiophene-type sulfide and provide more accessible active sites. The as-prepared mesoporous WO3@ZrO2-TiO2 composite shows good catalytic activity for dibenzothiophene (DBT) at room temperature, removing 500 ppm of DBT from simulated oil within 80 min, making it a suitable alternative catalyst for deep oxidative desulfurization.

Insights into the Structure of Keggin-Type Polyoxometalate-Based Organic-Inorganic Hybrid Materials: The Actual Ratio of Organic Cations to Heteropolyanions.

Polyoxometalate (POM)-based organic-inorganic hybrid materials possess versatile properties and applications; however, the ratios of organic cations to POM anions still remain to be solved. In this work, 14 POM-based organic-inorganic hybrid materials were synthesized by the precipitation, hydrothermal, and solvent-evaporation methods. These hybrid materials consisted of a wide range of quaternary ammonium and imidazolium cations with different alkyl chains and different Keggin-type heteropolyanions [i.e., phosphotungstic ([PW12O40]3-), phosphomolybdic ([PMo12O40]3-), silicotungstic ([SiW12O40]4-), and silicomolybdic ([SiMo12O40]4-) anions]. Their compositions and structures were characterized complementarily by elemental analysis, powder X-ray diffraction, single-crystal X-ray diffraction, and Fourier transform infrared spectroscopy. The actual ratios of organic cations to heteropolyanions of [PW12O40]3-, [PMo12O40]3-, [SiW12O40]4-, and [SiMo12O40]4- were found to always be 3:1, 3:1, 4:1, and 4:1, respectively, independent of the organic cations, synthesis methods, and reaction parameters. This finding demonstrates that the organic cations completely substituted the protons of the heteropolyacid precursors in the hybrid materials, which thus hardly possessed Brønsted acidity probed by the pyridine adsorption and cellulose hydrolysis reaction. Such complete substitution of the protons arose apparently from the strong noncovalent interactions between the organic cations and heteropolyanions (such as electrostatic and C-H···O interactions) in the POM-based hybrid materials.

Crystal structure of hexa-sodium tetra-serinolium paratungstate B deca-hydrate, [Na6{(CH2OH)2CHNH3}4][W12O40(OH)2]·10H2O.

The title polyoxometalate-based organic-inorganic hybrid compound, [Na6(C3H10NO2)4][W12O40(OH)2]·10H2O, consists of a di-μ 3-hydroxido-tetra-μ 3-oxido-octa-deca-μ-oxido-octa-deca-oxidododeca-tungstate (para-do-deca-tungstate B) anion, [W12O40(OH)2]10-, and six sodium cations coordinated by the oxygen ions of the polyanions, serinol ligands protonated at the N atom, and water mol-ecules. The centrosymmetric paratungstate B anion shows characteristic features in terms of bond lengths and angles. The three-dimensional framework structure is established by bonding of the sodium cations with oxygen ions of the paratungstate B anions and a network consisting of N-H⋯O and O-H⋯O hydrogen bonds of medium strength between the protonated serinol cations, water mol-ecules and the paratungstate B anions. The title compound was also characterized by means of elemental analysis, IR spectroscopy and thermogravimetric analysis.

Capped Keggin Type Polyoxometalate-Based Inorganic-Organic Hybrids Involving In Situ Ligand Transformation as Supercapacitors and Efficient Electrochemical Sensors for Detecting Cr(VI).

To construct polyoxometalate-based complexes as electrode materials for supercapacitors and electrochemical sensors, we intentionally used in situ ligand transformation during the reaction. Two complexes based on polyoxometalates capped by zinc ions, H{Zn4(DIBA)4[(DIBA)(HPO2)]2(α-PMoVI8MoV4O40Zn2)} (1) and [ε-PMoV8MoVI4O37(OH)3Zn4(HDBIBA)2]·6H2O (2) [DIBA = 3,5-di(1H-imidazol-1-yl)benzoic acid, and DBIBA = 3,5-bis(1H-benzoimidazol-1-yl)benzoic acid], have been prepared successfully. The DIBA and DBIBA ligands were generated in situ from initial materials 3,5-di(1H-imidazol-1-yl)benzonitrile and 3,5-di(1H-benzoimidazol-1-yl)benzonitrile. The three-dimensional structure of 1 consisted of two-dimensional interpenetrating layers and polyoxometalate-based chains composed of bicapped α-PMo12Zn2 polyoxoanions and phosphite-modified DIBA ligands. In 2, a kind of tetracapped ε-PMo12Zn4 polyoxoanion exists, which was further linked by DBIBA ligands into a one-dimensional chain. Two complexes could be employed as not only electrode materials for supercapacitors with specific capacitances of 171.17 F g-1 for 1 and 146.77 F g-1 for 2 at 0.5 A g-1 but also efficient electrochemical sensors for detecting Cr(VI) with excellent limits of detection of 0.026 μM for 1 and 0.035 μM for 2, which represents a hopeful approach for exploiting polyoxometalate-based complexes as supercapacitor and electrochemical sensor materials.

Exploring the Coordination Modes of a Keggin-Type [ZnW12O40]6- Anionic Cluster: Bonding Patterns, Crystal Structure, and Semiconducting Properties.

Polyoxometalate-based organic-inorganic hybrid compounds (POIHCs) have been greatly developed due to their wide application prospects, but the pursuit of their directed synthesis via molecular design still remains a challenge. Herein, we demonstrate that the coordination modes of the Keggin-type [ZnW12O40]6- anion can be tuned, which leads to different semiconductor characteristics. Using the same building block, ligand, and metal ion (ZnW12, phen, Cu2+), we synthesized three new POIHCs with different bonding patterns by means of different coordination modes of ZnW12. The three POIHCs (H2phen){ZnW12O40[Cu(phen)2]2}·3H2O (1), {ZnW12O40[Cu(phen)(H2O)2]2[Cu(phen)(H2O)]}n·3H2O (2), and (Me4N)2{ZnW12O40[Cu(phen)(H2O)]2}n·5H2O (3) (phen = 1,10-phenanthroline) have been structurally characterized by single-crystal X-ray diffraction. Compound 1 appears as a zero-dimensional coordination complex cluster, while compounds 2 and 3 are both 1D chain structures with different Cu2+ bridge linkages. Although these three POIHCs possess the same chemical components, their semiconductor properties are different, which is demonstrated by measurements of transient photocurrent and band gap (Eg) values. Furthermore, we carried out comparative experiments on the photoconductivity performance of compounds 1-3 and their photocatalytic reduction from O2 to H2O2, indicating the significant influence of the energy level matching on the photocatalytic activity.

Synthesis and Characterization of New Substituted Sandwich-Type Polyoxometalate-Based Inorganic–Organic Hybrid Nanocomposites for Catalytic Oxidative Desulfurization of Real Gasoline

Synthesis and Characterization of New Substituted Sandwich-Type Polyoxometalate-Based Inorganic–Organic Hybrid Nanocomposites for Catalytic Oxidative Desulfurization of Real Gasoline

Preyssler-type polyoxometalate-based crystalline materials for the electrochemical detection of H2O2

Four Preyssler-type polyoxometalate-based organic–inorganic hybrid materials were synthesized as non-enzymatic H2O2 electrochemical sensors, with high sensitivity and low detection limit.

Introducing of a novel polyoxometalate-based organic–inorganic hybrid: Insights into electochemical property-photoactivity relationship

Herein a new visible photocatalyst by TiO2 and nanosized polyoxometalate-based inorganic–organic hybrid material, NaH8[PDA]3[PW9Co3O37]·13H2O (PDA = p-phenylenediamine) (PDA-Co3W9), were successfully synthesized by an new straight forward method. Prepared powder was characterized by, FT-IR, PL, XRD, UV–Vis, DRS, and FE-SEM techniques. The FE-SEM images of the nanocomposite showed spherical-like nanoparticles with the mean size particle of 20–30 nm. The resulting materials were evaluated in the photodegradation of dye, using different light illuminations. Under optimized conditions, 100% dye removal was obtained. Tauc plots showed different bandgaps for different PDA-Co3W9 weight percentages on TiO2 (PDA-Co3W9/TiO2). The amplified photodegradation properties would be owing to the synergetic effect of PDA, Co3W9 and TiO2 as components. Optimization of conditions were studied by response surface methodology. Also, relationship between effective factors and electrochemical properties of photocatalyst was investigated by Mott-Schotcky, Nyqist, and Bode plots. Vfb, ND, and lifetimes of photogenerated electron–hole separation were calculated and compared with each other according to the photoactivity of different kinds of the catalysts. Specific capacitance of the best photocatalyst was calculated. Mechanism of photodegradation and reusability of the catalyst were also investigated.

Synthesis and investigation of two new crystalline organic inorganic nano-hybrids based on Wells-Dawson vanadotungstates and 1H-1, 2, 4-triazole as electro- and photocatalysts

Two new Wells–Dawson polyoxometalate-based organic-inorganic hybrid materials, namely, {[O]2.75[trz]7[α2-P2W17VO62]•12H2O}2(1) and {[O]11.5[trz]7[α2-P2W14.4V3.6O62]}2(2) (trz=1-H-1,2,4-triazole) were synthesized under mildconditions, and characterized by FT-IR, 1H NMR and 31P NMR spectroscopy, powder X-ray diffraction, TGA, field emission SEM and cyclic voltammetry. These hybrids constructed from trz ligand and Wells–Dawson polyoxoanions, in which trzis connected to a mono-vanadium substituted [α2-P2W17VO62]7− in 1 and a hexa-vanadium substituted [P2W12V6O62]12−in 2 by hydrogen bonding interactions. The structures of 1 and 2 were determined by single-crystal X-ray diffraction. Electrocatalytical activities of compounds 1 and 2 in the form of modified carbon paste electrode (MCPE) towards the reduction of nitrite ion have been studied in different pH values at acidic buffer solutions. Compounds 1-MCPE and 2-MCPE exhibit good electrocatalytical activity for reduction of NO2−. Also, the photocatalytical properties of the compounds 1 and 2 for the degradation of methylene blue have been studied.

A Keggin-Type Tungstovanadate-Based Hybrid Compound: Synthesis, Crystal Structure, and Electrocatalytic Oxidation of Ascorbic Acid

A new V-centered Keggin polyoxometalate-based inorganic-organic hybrid (HPpz)3[VW12O40] (I) (Ppz = piperazine) has been hydrothermal synthesized and characterized by IR spectroscopy, UV−Vis spectroscopy, elemental analysis and single-crystal X-ray diffraction (CIF file CCDC no. 1835683). Compound I belongs to the rhombohedral space group $$R\bar {3}c$$ and displays a three-dimensional supramolecular structure. The band gap energy value calculated for compound I was observed to be 1.30 eV using UV−Vis-NIR absorption spectrum. Furthermore, electrocatalytic performance of I has also been investigated in details.

A new 2D silver(I) inorganic-organic hybrid constructed from in situ decarboxylation reaction: Synthesis, structure and properties

A polyoxometalate-based inorganic-organic hybrid, [Ag(Hpi)(Mo3O10)] (1) (pi = 2-(pyridine-3-yl)-1H-imidazole), has been synthesized and characterized. In 1, adjacent [Mo3O10]2− chains are linked by Ag+ to form a 2D layer structure. The organic ligand pi is formed through hydrothermal in situ decarboxylation reaction of H2pidc (H2pidc = 2-(pyridine-3-yl)-1H-imidazole-4,5-dicarboxylic acid). The luminescence property, photocatalytic activity and antibacterial activity were also investigated.

Polyoxometalate-based inorganic-organic hybrids based on a half rigid N-heterocyclic carboxylate ligand: Syntheses, structures and properties

Three new inorganic-organic hybrids constructed from a half rigid N-heterocyclic carboxylate ligand, K[Ag3(HL1)4](Mo8O26) (1), [Ag4(HL1)2(HL2)2(SiMo12O40)] (2) and (H3O)[Ag(L1)2]·2H2O (3) [HL1 = 1-(4-carboxylbenzyl)-3-(pyrazine-2-yl)pyrazole; HL2 = 3-(2-pyrazine)pyrazole], were hydrothermally synthesized and characterized. In compound 1, {K[β-Mo8O26]}n3n− chains fill in the channels of the 3D supramolecular network. In compound 2, HL1 and HL2 coordinate to Ag(I) ions into left- (L) and right-handed (R) helical chains, and (SiMo12O40)4- anions link two neighboring helical chains into a 2D layer structure. The crystal structure of compound 3 is stabilized by hydrogen bonds and π … π interactions, forming a 3D supramolecular network. The luminescent properties of the three compounds have been investigated. In addition, the electrochemical properties of compound 2 have also been investigated.

Five isomorphous polyoxometalate-based inorganic-organic hybrid materials comprising 2D metal-organic layers

Five new isomorphous inorganic-organic hybrid materials {[M2(btp)3(H2O)6] (α-SiW12O40)·3H2O}n (M ​= ​Co(1), Fe(2), Zn(3), Cd(4), Mn(5)) (btp ​= ​2,6-bis(1,2,4-triazol -1-yl)pyridine), have been hydrothermally synthesized and characterized by IR spectroscopy, single-crystal X-ray diffraction, powder X-ray diffraction (PXRD), elemental analysis and thermal gravimetric analysis (TGA). X-ray single crystal diffraction reveals that compounds 1–5 crystallize in trigonal system R3c acentric space group, featuring one 3D sandwich framework, in which the [α-SiW12O40]4‒ polyoxoanions are present between the metal-organic layers by electrostatic interaction. Moreover, compounds 1–5 display nonlinear optical (NLO) properties and luminescent behaviors at solid state; compound 1 shows the certain photocatalytic activities for the degradation of Rhodamine B (RhB); compounds 1, 4 and 5 exhibit significant electrochemical activities for the reduction of H2O2 and compounds 1, 2 and 5 display antiferromagnetic behaviors.

Octamolybdate-based hybrid constructed by flexible bis-triazole ligands: synthesis, photocatalytic and electrochemical properties

A novel polyoxometalate-based organic–inorganic hybrid compound was synthesized via a facile in situ hydrothermal reaction. 1 exhibits selective photocatalytic degradation of dyes and the great property to electrocatalytically reduce H2O2 and NaNO2.

Two polyoxometalate-based inorganic-organic hybrids and one coordination polymer assembled with a functionalized calix[4]arene: Catalytic and electrochemical properties

Self-assembly of 4-pyridyl-functionalized calix[4]arene ligand 5,11,17,23-tetrakis(1,1-dimethylethyl)-25,26,27,28-tetrakis[(4-pyridylmethyl)oxy]calix[4]arene (L), Ag(I)/Cd(II) cations and polyoxometalate obtained two inorganic-organic hybrids [Ag3(L)2][PMo12O40]·CH3CN·4H2O (1), [Ag3(L)2][PMo12O40]·2DMA·0.5EtOH (2) and one complex [Cd3(L)2Cl6]·4CH3CN·4H2O (3) (DMA = N,N-dimethylacetamide). Hybrids 1 and 2 have fascinating one-dimensional chains, which are linked by hydrogen bonds between the C atoms of L ligands and the O atoms of [PMo12O40]3− anions to generate supramolecular layers. 3 displays a thick layer containing trinuclear Cd(II) clusters. Noteworthy, hybrid 1 exhibits excellent heterogeneous catalytic activity for oxidative desulfurization reaction and obvious electrocatalytic activity for oxidize ascorbic acid and reduce NaBrO3. Complex 3 shows heterogeneous catalytic ability for Knoevenagel condensation reaction.

A 3D inorganic-organic hybrid constructed from Strandberg-type polyoxometalates and silver complexes: Synthesis, structure and properties

A 3D Strandberg-type polyoxometalate-based inorganic-organic hybrid, [Ag4(H3L)2(P2Mo5O23)]·H2O (1) (H2L = 2,6-dimethyl-3,5-bis(pyrazol-3-yl)pyridine), has been synthesized under hydrothermal conditions and structurally characterized by single crystal X-ray diffraction, elemental analysis, IR, TG and powder X-ray diffraction. In compound 1, the adjacent [P2Mo5O23]6− clusters are linked by Ag1 into a 2D layer with left- and right-handed helical chains. And the layers are further linked together through organic ligands H2L and Ag⋯Ag interactions into a 3D framework with 1D channels extended along c axis. The luminescence, electrochemical properties and photocatalytic activities of compound 1 have also been investigated.

Three novel polyoxometalate-based inorganic–organic hybrid materials based on 2,6-bis(1,2,4-triazol-1-yl)pyridine

Three novel inorganic–organic hybrid materials [Co(btp)2(W5O16)(H2O)]n (1), [Cd3(btp)6(PW12O40)2(H2O)6·6H2O]n (2), and [Ag3(btp)2(PMo12O40)·1.5H2O]n (3) (btp = 2,6-bis(1,2,4-triazol-1-yl)pyridine) have been hydrothermally synthesized and characterized by IR spectroscopy, single-crystal X-ray diffraction, powder X-ray diffraction (PXRD), elemental analysis and thermal gravimetric analysis (TGA). The most striking structure feature of compound 1 is a 3D polycatenation framework, interpenetrated by a 2D 4-connected sql topology layer and a 3D 6-connected rob topology framework. Compound 2 exhibits a rare meso-helices 3D network with different chiralities crossing coexistence. Compound 3 also holds a 3D framework formed by linking terminal oxygen atoms of [α-PMo12O40]3− anions and silver ions in a 2D metal–organic layer. Compound 1 displays antiferromagnetic behavior. The luminescence, electrochemical and photocatalytic properties of compounds 1–3 have also been investigated. Compound 3 exhibits significant electrochemical activity for the reduction of H2O2 while compounds 1 and 2 show efficient photocatalytic activities for the degradation of Rhodamine B (RhB). Furthermore, the three compounds display luminescence behaviors in the solid state.

Polyoxometalates decorated with metal-organic moieties as new molecular photo- and electro-catalysts

Three new polyoxometalate-based organic-inorganic hybrid compounds (POIHCs), [Cu(PBI)2(H2O)][{Cu(PBI)(OH)(H2O)}{PW12O40}]·5H2O (1), [Cu(PBI)2(H2O)][{Cu(PBI)2(H2O)}{SiW12O40}]·4H2O (2) and [Cu4(HPO4)(PO4)(H2O)2(PBI)4][PMo12O40]·H2O (3) (PBI =2-(pyridin-2-yl)-1H-benzo[d]imidazole), have been synthesized under hydrothermal conditions. All three compounds were characterized by elemental analysis, IR spectroscopy, thermogravimetric analysis, powder X-ray diffraction and single-crystal X-ray diffraction. In 1 and 2, the Keggin-type polyoxometalate (POM) units are decorated by the {Cu/PBI} metal-organic fragments, together with additional {Cu/PBI} isolated cations, which further stack into 3-D supramolecular frameworks with porous structural features. Compound 3 consists of a rare cationic cluster [Cu4(HPO4)(PO4)(H2O)2(PBI)4]3+ and the Keggin-type POM anion, forming a 3-D supramolecular framework with limited interspaces for the entry of guest molecules. Comparable photocatalytic properties of 1–3 were investigated by the use of methylene blue (MB) and Rhodamine B (RhB) degradation under UV light. All compounds showed good catalytic activity for the degradation of MB in contrast to RhB. The possible catalytic mechanism was discussed based on the size of dye molecules, the low adsorption ability and crystal packing mode of the as-synthesized compounds. Additionally, the electrochemical properties of 1–3 have also been investigated, exhibiting good electrocatalytic performance for nitrite reduction.

A 3D supramolecular architecture built from an Organic–Inorganic hybrid octamolybdate: Synthesis, characterization and Hirshfeld Surface Analyses

A novel polyoxometalate-based organic–inorganic hybrid compound, (C4H7N2)2(H3O)2 [β-Mo8O26]·2H2O (1), has been synthesized and structurally characterized by single-crystal X-ray diffraction methods, IR spectroscopy, UV–Vis absorption. Compound (1) crystallizes in the Triclinic system, space group P-1 with unit a = 8.379 (3) Å, b = 10.200 (5) Å, c = 10.861 (5) Å, α = 68.27° (3), β = 71.61° (2), γ = 78.40° (3), V = 814.5 (6) Å3, Z = 2. The refinement of the structure leads to a residual factor R = 0,050 for 3549 independent observed reflections [I > 2σ(I)] and 227 parameters. The structure of (1) consists of [β-Mo8O26]4- anions with [C4H7N2]+, H3O+ cations and water molecules connected to the mineral parts by hydrogen bonds. Furthermore, we report results of the thermogravimetric analysis, cyclic voltammetry measurement and Hirshfeld surface studies.