Organic Inorganic Hybrid Polyoxometalate Research Articles

Efficient Removal of Methylene Blue Using an Organic–Inorganic Hybrid Polyoxometalate as a Dual-Action Catalyst for Oxidation and Reduction

Efficient Removal of Methylene Blue Using an Organic–Inorganic Hybrid Polyoxometalate as a Dual-Action Catalyst for Oxidation and Reduction

An organic-inorganic hybrid based on bicapped Keggin polyoxometalate as a heterogeneous catalyst for MB removal via Fenton-like/photo-Fenton-like degradation or reduction

An organic-inorganic hybrid polyoxometalate (POM) [CuI(phen)2]4[PMoVI8VIV6O42{CuI(phen)}2]•H5O2 (CuPMoV) was explored as heterogeneous Fenton-like catalyst for methylene blue (MB) degradation in the absence/presence of visible light at neutral pH. CuPMoV was characterized by XRD, SEM, FT-IR and UV–vis DRS techniques. The effect of initial pH, the concentrations of H2O2 and dye, and CuPMoV dosage on the degradation was evaluated. The possible mechanism for the Fenton-like/photo-Fenton-like was proposed. Under the optimum conditions, the MB degradation rates were 85.3 % (Fenton-like reaction) and 95.2 % (photo-Fenton-like reaction) in 12 min, respectively. CuPMoV also exhibited excellent catalytic performance for MB reduction in the presence of NaBH4, with the reduction rate of 98.6 % in 90 s. The pseudo-first-order rate constant of the reduction was estimated as 0.0246 s−1. The high reusability and stability of CuPMoV enabled it to undergo five cycles of usage without significant loss of catalytic activity. The multi-metal composition of CuPMoV and the bicapped Keggin unit were the root of its excellent catalytic activities. CuPMoV may be a potential candidate for the practical treatment of MB contaminated wastewater via oxidation or reduction.

Multi-Electron Visible Light Photoaccumulation on a Dipyridylamine Copper(II)-Polyoxometalate Conjugate Applied to Photocatalytic Generation of CF3 Radicals.

This article describes the synthesis and characterization of an organic-inorganic hybrid polyoxometalate functionalized by a short link with a tripodal N-based ligand and its copper complex. Upon visible light irradiation, the latter is able to store up to three reducing equivalents. The locus of the reduction is discussed based on physicochemical measurements and DFT calculations. In the presence of Togni's reagent, this complex allows for the photocatalytic generation of CF3 radicals, opening the road to valuable synthetic applications.

Dy-incorporated organic-inorganic hybrid polyoxometalates with photoluminescence property

Two new organic-inorganic hybrid polyoxometalate [N(CH3)4]3K2[Dy(C7H5O2)(H2O)2(α-PW11O39)]·13H2O (1) and [N(CH3)4]3K2[Dy(C7H5O3)(H2O)2(α-PW11O39)]·13H2O (2) were prepared via the reaction of K14[P2W19O69(H2O)]·24H2O, DyCl3·6H2O and organic ligands, which were further characterized by IR spectrum, TG analysis, and X-ray single-crystal diffraction. Structural analysis reveals that 1 and 2 consist of polyanion [Dy(L)(H2O)2(α-PW11O39)]5– (L = C7H5O2 (1a), C7H6O3 (2a)), three [N(CH3)4]+ cations, two K+ cations for the charge balance, and thirteen water molecules. The excitation and emission spectra and decay time curves prove the existence of different potential energy transfer pathways, and the decay time curves indicate POM components can sensitize the emission of Dy3+ ion and lifetimes were prolonged.

Supramolecular assemblies of organo-functionalised hybrid polyoxometalates: from functional building blocks to hierarchical nanomaterials.

This review provides a comprehensive overview of recent advances in the supramolecular organisation and hierarchical self-assembly of organo-functionalised hybrid polyoxometalates (hereafter referred to as hybrid POMs), and their emerging role as multi-functional building blocks in the construction of new nanomaterials. Polyoxometalates have long been studied as a fascinating outgrowth of traditional metal-oxide chemistry, where the unusual position they occupy between individual metal oxoanions and solid-state bulk oxides imbues them with a range of attractive properties (e.g. solubility, high structural modularity and tuneable properties/reactivity). Specifically, the capacity for POMs to be covalently coupled to an effectively limitless range of organic moieties has opened exciting new avenues in their rational design, while the combination of distinct organic and inorganic components facilitates the formation of complex molecular architectures and the emergence of new, unique functionalities. Here, we present a detailed discussion of the design opportunities afforded by hybrid POMs, where fine control over their size, topology and their covalent and non-covalent interactions with a range of other species and/or substrates makes them ideal building blocks in the assembly of a broad range of supramolecular hybrid nanomaterials. We review both direct self-assembly approaches (encompassing both solution and solid-state approaches) and the non-covalent interactions of hybrid POMs with a range of suitable substrates (including cavitands, carbon nanotubes and biological systems), while giving key consideration to the underlying driving forces in each case. Ultimately, this review aims to demonstrate the enormous potential that the rational assembly of hybrid POM clusters shows for the development of next-generation nanomaterials with applications in areas as diverse as catalysis, energy-storage and molecular biology, while providing our perspective on where the next major developments in the field may emerge.

An intriguing tetranuclear Rh-based polyoxometalate for the reduction of nitroarene and oxidation of aniline.

An organic-inorganic hybrid polyoxometalate Na5H5.68 [Na0.17Rh0.83III(C6H8N2)2Cl2]2(C8H8N2)2[As4W40O140Rh4IV(C6H4N2S)2]·nH2O (1) containing 5.66 Rh atoms is prepared; to our knowledge, it owns the largest number of Rh atoms in the Rh-POM family. Compound 1 demonstrates good catalytic performance in the reduction of nitrobenzene to aniline and the oxidation of aniline to azobenzene under mild conditions. Moreover, catalyst 1 exhibits high activity, excellent stability and recyclability.

An organic–inorganic hybrid nanoscale phosphotungstate with reactive oxygen species catalytic ability

An organic-inorganic hybrid polyoxometalate (POM) based on bi-nuclear copper complexes and Dawson-type phosphotungstate (POT) [CuL(H2O)][CuL]2[P2W18O62]·3H2O (abbreviated as CPW) (L = 2-(1H-pyrazol-3-yl)pyridine) was synthesized and structurally characterized by IR spectrum, and single-crystal X-ray diffraction. Structural analysis indicated that CPW is nanoscale molecule and extends into a two-dimensional layer, in which three bi-nuclear copper complexes are substituted at different sites of Dawson-type POT and joined adjacent POT fragments together. Notably, CPW can efficiently catalyze the production of reactive oxygen species.

Ionic liquid polyoxometalate-enhanced Pd/N,P-codoped coal-based carbon fiber catalysts for formic acid electrooxidation

Direct formic acid fuel cells have great application potential in the energy field, but their commercialization is hindered by the CO poisoning and low performance of Pd-based anode catalysts. In this study, novel composite catalysts composed of Pd, organic-inorganic hybrid imidazole ionic liquid polyoxometalates, and N,P-codoped coal-based carbon fibers with good dispersion and smaller Pd nanoparticles were synthesized successfully. Physical and electrochemical characterizations revealed that the as-prepared Pd-based composite catalysts have excellent CO poisoning resistance and enhanced electrocatalytic activity in formic acid electrooxidation. Notably, the CO oxidation onset potential of a catalyst modified by imidazole ionic liquid polyoxometalate with long alkyl chain was 0.1 V lower than that of the unmodified catalyst. The mass activity of the as-prepared Pd catalyst in formic acid oxidation was 754.1 mA mg−1Pd. It is expected that organic-inorganic hybrid polyoxometalates can be further applied to fuel cell catalysts.

A PHBA-functionalized organic-inorganic hybrid polyoxometalate as a luminescent probe for selectively sensing chromium and calcium in aqueous solution

Detection of trace metal ions in drinking as well as irrigation water is crucial in understanding their roles among living humans and animals. Herein, an organic PHBA-functionalized polyoxometalate (POM) derivative [N(CH3)4]3K2Eu(PHBA)(H2O)2(α-PW11O39)]·7H2O (1) (PHBA = p-hydroxybenzoic acid) was successfully synthesized which acts as a luminescent probe for selective sensing of chromium and calcium in aqueous solution. The aqueous solution photoluminescence properties of 1 were carefully investigated, indicating PHBA ligand can sensitize the luminescence of Eu3+ ion in 1. The time-resolved emission spectroscopy was also performed to authenticate the energy transfer from π-π* transition of PHBA group to Eu3+ ion. The sensing properties of 1 were performed on Cd2+, Cr3+, Ba2+, K+, Li+, Pb2+, Zn2+, Al3+, Ag+, Hg2+, Co2+, Sr2+, Ca2+, Na+, Mg2+ ions in aqueous solution, and the photoluminescence intensity for Cr3+ ion display a quenching phenomenon, whereas, Ca2+ ion displays an enhancement signal in their photophysical behavior. The detection limits for detecting Cr3+ and Ca2+ ion were 1.423 μM and 0.676 mM, respectively. In the detection process of Cr3+ ion, the values of quenching rate constant (Kq) were varied from 4.34 × 106 L (mol s)−1 to 4.29 × 109 L (mol s)−1, which were lower than the value of the maximum scatter collision quenching constant (2.0 × 1010 L (mol s)−1). The results reveal that the quenching mechanism between 1 and Cr3+ ion can be attributed to dynamic collision quenching mechanism. Furthermore, the active sites for sensing Cr3+ and Ca2+ ions also have been investigated, determining the different interaction mechanisms exist in detection of Cr3+ and Ca2+ ions in solution.

Effects of chain length on the size, stability, and electronic structure of redox-active organic–inorganic hybrid polyoxometalate micelles

Double-chain redox-active surfactants based on hybrid polyoxometalates show solvent-dependent assembly into nanoscale micellar architectures.

A silanol-functionalized polyoxometalate with excellent electron transfer mediating behavior to ZnO and TiO2 cathode interlayers for highly efficient and extremely stable polymer solar cells

A silanol-functionalized polyoxometalate improves the electron collecting interface.

Shining a light on the photo-sensitisation of organic-inorganic hybrid polyoxometalates.

Finding new ways of using visible light (or, more specifically, solar irradiation) to drive commercially significant and/or challenging chemical processes is an ongoing research goal. Polyoxometalates (POMs) are discrete, metal-oxide clusters which are cheap, robust and easily synthesised but can also act as versatile molecular building blocks, allowing for astonishing variety in their structures and properties. In particular, the rich redox chemistry and inherent photo-activity of POMs makes them attractive for use in a variety of photochemical applications, however POMs characteristically only absorb strongly in the UV region. In this perspective, we discuss the various strategies which have been employed in order to sensitise POMs to visible light, with a particular focus on hybrid inorganic-organic POM species. We will discuss the two clear photo-activation mechanisms which have been developed to date and provide an outlook on some of the possible future directions of the field.

A Simple Approach to the Visible-Light Photoactivation of Molecular Metal Oxides.

This study explores a new method to maximize the visible-light-driven photocatalytic performance of organic-inorganic hybrid polyoxometalates (POMs). Experimental and theoretical investigations of a family of phosphonate-substituted POMs show that modification of grafted organic moieties can be used to tune the electronic structure and photoactivity of the metal oxide component. Unlike fully inorganic polyoxotungstates, these organic-inorganic hybrid species are responsive to visible light and function as photocatalysts (λ > 420 nm) in the decomposition of a model environmental pollutant. The degree of photoactivation is shown to be dependent on the nature of the inductive effect exerted by the covalently grafted substituent groups. This study emphasizes the untapped potential that lies in an orbital engineering approach to hybrid-POM design and helps to underpin the next generation of bespoke, robust, and cost-effective molecular metal oxide photoactive materials and catalysts.

A New 2-D Inorganic–Organic Hybrid Polyoxometalate Based on Mono-Cu-Substituted [CuSiW11O39] n 6n− Chains and [Cu(en)2]2+ Bridges

A new organic–inorganic hybrid polyoxometalate H2[Cu(en)2(H2O)]2[Cu(en)2]{[Cu(en)2]3 (CuSiW11O39)2}·6H2O (1) (en = ethylenediamine) have been hydrothermally synthesized and characterized by IR spectrum, thermogravimetric analysis, power X-ray diffraction and single-crystal X-ray diffraction. Crystal data for 1: monoclinic, P21/c, a = 18.8077(3) A, b = 23.0703(5) A, c = 26.0723(6) A, β = 96.438(2)°, Z = 4. Single-crystal X-ray diffraction analysis revealed that 1 exhibits a 2-dimensional network constructed from mono-Cu-substituted [CuSiW11O39] 6− chains and [Cu(en)2]2+ bridges. A new organic–inorganic hybrid polyoxometalate H2[Cu(en)2(H2O)]2[Cu(en)2]{[Cu(en)2]3(CuSiW11O39)2}·6H2O (1) (en = ethylenediamine) have been hydrothermally synthesized and characterized, which exhibits a 2-dimensional network constructed from mono-Cu-substituted [CuSiW11O39] 6− chains and [Cu(en)2]2+ bridges.

Orbital Engineering: Photoactivation of an Organofunctionalized Polyoxotungstate.

Tungsten-based polyoxometalates (POMs) have been employed as UV-driven photo-catalysts for a range of organic transformations. Their photoactivity is dependent on electronic transitions between frontier orbitals and thus manipulation of orbital energy levels provides a promising means of extending their utility into the visible regime. Herein, an organic-inorganic hybrid polyoxometalate, K6 [P2 W17 O57 (PO5 H5 C7 )2 ]⋅6 C4 H9 NO, was found to exhibit enhanced redox behaviour and photochemistry compared to its purely inorganic counterparts. Hybridization with electron-withdrawing moieties was shown to tune the frontier orbital energy levels and reduce the HOMO-LUMO gap, leading to direct visible-light photoactivation of the hybrid and establishing a simple, cheap and effective approach to the generation of visible-light-activated hybrid nanomaterials.

A new organic-inorganic hybrid tetrameric polyoxometalate assembled by monovacant Dawson [α2-P2W17O61]10 − and trivalent cerium cations

A novel octa-nuclear cerium(III)-containing organic-inorganic hybrid polyoxometalate [N(CH3)4]8H16[{Ce(η1-C6H5NO2)2(H2O)6[Ce(H2O)3(α2-P2W17O61)]}{Ce(η2-C6H5NO2)2(H2O)5[Ce(H2O)(α2-P2W17O61)]}]2·90H2O (C6H5NO2=isonicotinic acid) (1) was obtained, which had been hydrothermally synthesized and characterized by IR spectrum, thermogravimetric analysis (TGA), and X-ray single-crystal diffraction. Structural analysis indicated at 1 is composed of four lacunary Dawson-type units [α2-P2W17O61]10− joined together by eight cerium cations forming an uncommon zigzag tetrameric structure with eight isonicotinic acids as the organic pendants coordinating to the cerium cations. Magnetic property studies indicate that obvious antiferromagnetic interactions exist in eight Ce3+ cations.

Organic–inorganic hybrid polyoxometalate and its graphene oxide–Fe3O4nanocomposite, synthesis, characterization and their applications as nanocatalysts for the Knoevenagel condensation and the synthesis of 2,3-dihydroquinazolin-4(1H)-ones

Organic–inorganic hybrid of H6Cu2[PDA]6[SiW9Cu3O37]·12H2O (HybPOM), was synthesized and grafted on graphene oxide decorated with Fe3O4. The structures of HybPOM and GO@Fe3O4@HybPOM nanocomposites were characterized and their catalytic activities investigated.

Heterogeneous Catalysis of Polyoxometalate Based Organic-Inorganic Hybrids.

Organic–inorganic hybrid polyoxometalate (POM) compounds are a subset of materials with unique structures and physical/chemical properties. The combination of metal-organic coordination complexes with classical POMs not only provides a powerful way to gain multifarious new compounds but also affords a new method to modify and functionalize POMs. In parallel with the many reports on the synthesis and structure of new hybrid POM compounds, the application of these compounds for heterogeneous catalysis has also attracted considerable attention. The hybrid POM compounds show noteworthy catalytic performance in acid, oxidation, and even in asymmetric catalytic reactions. This review summarizes the design and synthesis of organic–inorganic hybrid POM compounds and particularly highlights their recent progress in heterogeneous catalysis.

Reversible photodimerization of coumarin-modified Wells–Dawson anions

The light-driven reversible dimerization of a coumarin-functionalized organic–inorganic hybrid polyoxometalate anion and the resulting changes in their aggregation and redox-behaviour are reported.

A novel organic-inorganic hybrid polyoxometalate for the selective adsorption/isolation of β-lactoglobulin.

A novel polyoxometalate (POM)-based organic-inorganic hybrid [C33H24O4]H3PMo12O40, namely, TPPA-PMo12, is prepared via a one-pot hydrothermal reaction between a Keggin POM (H3PMo12O40, PMo12) and a star-like N-donor ligand (tri(4-pyridylphenyl)amine, TPPA). The hybrid polyoxometalate is confirmed by characterization with XRD, FT-IR, TGA, SEM and EDS. It exhibits excellent adsorption performance towards β-lactoglobulin, and thus a solid-phase extraction procedure was established for the efficient and selective isolation of β-lactoglobulin from complex sample matrices. At pH 5.0, an adsorption efficiency of 99.2% is achieved for processing 100 μg mL-1β-lactoglobulin in 1.0 mL aqueous solution with 0.5 mg TPPA-PMo12 as an adsorbent. The adsorption behavior of β-lactoglobulin fits the Langmuir model, corresponding to a theoretical adsorption capacity of 1428 mg g-1. The retained β-lactoglobulin could be readily recovered by rinsing with 0.05 mol L-1 Tris-HCl buffer, facilitating a recovery of 91.5%. The hybrid polyoxometalate was practically applied to the selective isolation of β-lactoglobulin from milk whey, and SDS-PAGE assay results clearly indicate that β-lactoglobulin of high-purity is obtained.