Search

Synthesizing efficient and environment–friendly visible–light photocatalyst with simple methods is becoming attractive in these years in the field of photocatalysis. We report the preparation of Au@SbW9Co3 nanostructures, an environment-friendly visible–light catalyst, by coating Au0 with Polyoxometalate (POM) in a green and convenient way, the photocatalytic activities of which were investigated under visible light. The prepared Au@POM nanostructures showed the photocatalytic active in visible light region, which indicates a synergistic effect between POM and Au0. In addition, the morphology of Au@POM nanostructures, species of POM, the proportion of POM in catalyst and the concentration of Au@POM all affect the photocatalytic effect of catalysts. When the used POM was SbW9Co3, the molar ratio of Au3+:SbW9Co3 was 2:1.0 and the catalyst concentration was 0.15 mM, the highest photocatalytic effect was obtained, and the removal efficiency for EY reached 99% after catalyzing 60 min in visible light. [ABSTRACT FROM AUTHOR]

A nanocomposite of tungstophosphoric acid (PW12), metal-organic framework (MOF), and graphene oxide (GO) (PW12/MOF/GO) was electrodeposited at −1.5 V by amperometry technique from a suspension of PW12/MOF/GO nanocomposite in 0.01 M H3PO4. The synthesized PW12/MOF/GO was characterized by Fourier-transform infrared spectroscopy, X-ray powder diffraction, Transmission electron microscopy, inductively coupled plasma-optical emission spectrometry, and Brunauer-Emmett-Teller analytical techniques. The morphology of PW12/MOF/P@ERGO/GCE was evaluated by FE-SEM images and energy dispersive spectroscopy. The modified GCE was an electrochemical sensitive surface for IO3− sensing. The PW12/MOF/P@ERGO/GCE had a higher reductive current in the electro-reduction of IO3− than bare GCE. The proposed sensor by amperometric experiments displayed a linear range of 10–2000 μM with a limit of detection (LOD) of 3.86 μΜ, a sensitivity of 20.0 μA mM−1, and excellent selectivity for IO3− detection in the presence of other potential interfering species. Moreover, the modified GCE was successfully applied for IO3− detection in mineral water and commercial table salt.

In this study, a new {Co9} cluster-added polyoxometalate (POM) Cs3K4Na5H6[BO(OH)2Co9O(OH)(H2O)3(GeW6O26)(B-α-GeW9O34)2]·22H2O (1) was successfully synthesized in the presence of inorganic boron sources under hydrothermal conditions. Its structural characterizaiton is realized using single-crystal X-ray diffraction, infrared spectroscopy, thermogravimetric analysis, and powder X-ray diffraction. Compound 1 represents the first Co-added POM bonded by a B atom, and its polyoxoanion is constructed by fusing together with one hexalacunary GeW6O26 and two trilacunary B-α-GeW9O34 fragments in an unprecedented V-shaped {Co9} cluster. Additionally, compound 1 is an efficient catalyst for accelerating the Knoevenagel condensation of various aldehydes with malonitrile.

Herein, the aim of this work was to investigate the intermolecular interactions between polyoxometalate (POMs) as a drug‐delivery system with nitrosourea at different sites: CH3, COOH, NH2, NO2 and OCH3 using density functional theory (DFT) at the M062X/LanL2DZ level of theory. The result showed that, the lowest bond lengths recorded for the adsorbate and the nanocage were 1.40Å, 1.64Å, 1.40Å and 1.57Å for NU/POM(CH3), NU/POM(NH2), NU/POM(NO2) and NU/POM(OCH3) respectively. The NU/POM(NO2) system had the highest adsorption energy in the three phases: −32.039, −26.95, and −29.38 kcal/mol for gas, solvent, and benzene respectively and the lowest was shown in NU/POM(OCH3) with −14.10, −10.33, −12.29 kcal/mol. The energy gap was found to be the highest in NU/POM(NO2) with 5.061eV followed by NU/POM and NU/POM(COOH) 4.020eV and 4.003eV respectively. It has been clearly shown that NU/POM(NO2) density peak in the Highest occupied molecular orbital and Lowest unoccupied molecular orbital (HOMO/LUMO) plot was above 5 and this go in line with the electronic properties possessing a stable nature. In the NBO analysis, after adsorption of the nitrosourea (NU), the NU/POM(NO2) system recorded the highest energy with 1309.42 kcal/mol and the lowest in NU/POM(OCH3) with 921.75 kcal/mol. The system with NO2 possess more stability, chemical hardness, electrophilicity index and strong interactions. It has a better surface interaction than other compounds found in Nitrosourea. [ABSTRACT FROM AUTHOR]

Polyoxometalates (POMs) are a class of metal oxide complexes with a large structural diversity. Effective control of the final chemical and physical properties of POMs could be provided by fine-tuning chemical modifications, such as the inclusion of other metals or non-metal ions. In addition, the nature and type of the counterion can also impact POM properties, like solubility. Besides, POMs may combine with carbon materials as graphene oxide, reduced graphene oxide or carbon nanotubes to enhance electronic conductivity, with noble metal nanoparticles to increase catalytic and functional sites, be introduced into metal-organic frameworks to increase surface area and expose more active sites, and embedded into conducting polymers. The possibility to design POMs to match properties adequate for specific sensing applications turns them into highly desirable chemicals for sensor sensitive layers. This review intends to provide an overview of POM structures used in sensors (electrochemical, optical, and piezoelectric), highlighting their main functional features. Furthermore, this review aims to summarize the reported applications of POMs in sensors for detecting and determining analytes in different matrices, many of them with biochemical and clinical relevance, along with analytical figures of merit and main virtues and problems of such devices. Special emphasis is given to the stability of POMs sensitive layers, detection limits, selectivity, the pH working range and throughput.

The monolacunary Keggin-type [PW11O39]7− (PW11) heteropolyanion was immobilized on porous framework of mesoporous silicas, namely SBA-15 and an ethylene-bridged periodic mesoporous organosilica (PMOE). The supports were functionalized with a cationic group (N-trimethoxysilypropyl-N, N, N-trimethylammonium, TMA) for the successful anchoring of the anionic polyoxometalate. The PW11@TMA-SBA-15 and PW11@TMA-PMOE composites were evaluated as heterogeneous catalysts in the oxidative desulfurization of a model diesel. The PW11@TMA-SBA-15 catalyst showed a remarkable desulfurization performance by reaching ultra-low sulfur levels (

Through the use of two kinds of imidazole derivatives containing different O-functional units, three new Keggin- and one Wells-Dawson-polyoxometalate (POM)-based compounds, namely [Cu2La4(HPW12O40)] (1), [CuLa4(H2O)2(HPMo12O40)] (2), [Cu2La7(H2O)(H2P2W18O62)]·La(3), [Ag2(Lb4)(HPMo12O40)]·Lb·H2O (4)(La= (4-(2,5-dihydro-1H-imidazol-1-yl)benzaldehyde), and Lb=(4-(2,5-dihydro-1H-imidazol-1-yl)benzoic acid), were synthesized and characterized using single-crystal X-ray diffraction, elemental analyses, and infrared spectroscopy. The polyoxoanions occupy holes framed by two symmetrically oriented CuLa2 units in 1. In compound 2, the square-planar CuLa4 units form a two-dimensional (2D), supramolecular grid through π···π stacking interactions. The POMs occupy vacancies in this grid. In compound 3, the CuLa3 subunits connect the neighboring P2W18 units and an "S"-type chain is formed. Through hydrogen bonding interactions, the chains are connected to form a layer. In compound 4, the POM anions are linked by AgLb2 subunits to form a chain. All the chains are tied together to construct a layer structure with weak hydrogen bonding interactions between the terminal carboxylic acid functional groups of ligands Lb. The electrocatalytic and photocatalytic activities of all these four compounds were also studied. [ABSTRACT FROM AUTHOR]

Bismuth vanadate (BiVO 4), as an appropriate semiconducting material with a narrow band gap and high light-harvesting, suffers from a high charge recombination rate and low photoactivity. To address these issues, in this work, the embedded cobalt polyoxometalate (POM) within the network of polypyrrole (PPy) coated on BiVO 4 has been proposed to promote charge injection and separation. The photoanode based on BiVO 4 was fabricated by electrophoretic deposition (EPD) under the optimized conditions. Conducting a comprehensive and fundamental study, we also implemented experiments to achieve the best conditions for BiVO 4 preparation and the creation and optimization of PPy heterojunction with and without POM. The photoelectrochemical and physical analysis results revealed that the simultaneous incorporation of PPy and POM makes BiVO 4 experience an impressive current enhancement, a 900% increase relative to bare BiVO 4. Moreover, the hole extraction efficiency was enhanced to 93.7% from 15.12% (BiVO 4), and charge separation yielded 33.83% from 24.47% (BiVO 4). This study inspires promising studies on heterojunction formation through inorganic/organic semiconductor hybridization, achieved by molecular water oxidation co -catalysts like POM. [Display omitted] • A novel Inorganic/Organic heterojunction strategy using polyoxometalate was designed for solar water oxidation. • A layer of polypyrrole was introduced within whose network POM particles were inserted. • PEC results explicitly show the light-harvesting, charge separation, and charge injection improvement. • This drastic amelioration is mainly derived from the hole extraction (catalytic activity) improvement due to POM existence. • The elucidated PEC results suggest that the applied configuration is highly effective for solar water oxidation. [ABSTRACT FROM AUTHOR]

Two novel polyoxometalate-based catalysts were prepared by modifying Keggin POM H 4 PMo 11 VO 40 with a coumarin-surfactant through electrostatic interactions. The results indicate that (Coumarin) 3 HPMo 11 VO 40 exhibits excellent catalytic activity in the selective oxidation of benzyl alcohol using air as the oxidant, where the conversion of benzyl alcohol is 99%, and the selectivity for benzaldehyde is 100%. The excellent catalytic performance can be attributed to π-π* conjugate effects with the reactant, and the structural characteristics of the large BET specific surface area and pore size of the catalyst. [ABSTRACT FROM AUTHOR]

The molecular nanocluster HxPMo12O40⊂H4Mo72Fe30(O2CMe)15O254(H2O)98-y(EtOH)y (FeMoC), was the first molecular catalyst precursor (pro-catalyst) that promised controlled growth of carbon nanotubes (CNTs); however, temperatures in excess of ~ 900 °C or the addition of excess iron were required as catalyst promoters for CNT growth. To understand these disappointing results the “activation” of FeMoC for CNT growth was studied by systematic investigation of H2 gas concentration and growth temperature. The pathway for “activation” of FeMoC occurs through the sufficient reduction of both metal oxide components in the pro-catalyst. By ensuring pro-catalyst reduction prior to introduction of growth gases, we demonstrate for the first time, growth of CNTs at temperatures as low as 600 °C without the use of catalyst promoters using the single molecular precursor, FeMoC. To understand the role of catalyst promoters used in prior work, thermogravimetric analysis experiments were performed. The addition of an iron catalyst promoter is observed to play two key roles in the “activation” of FeMoC: (1) to replenish sublimated metal atoms, and (2) to reduce the reduction temperature required for reduction of FeMoC into an “active” catalyst. These results caution the conditions employed in many earlier studies for CNT growth, and create new possibilities for molecular pro-catalysts. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Shanghai University / Shanghai Daxue Xuebao is the property of Journal of Shanghai University (Natural Sciences) Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Adsorption of tungstophosphoric acid (H 3 PW 12 O 40 ) as a polyoxometalate (POM) on graphene oxide (GO) and two reduced graphene oxide supports (RGO-a/RGO-b) for producing supported catalysts was studied using an equilibrium adsorption technique by ultraviolet–visible spectroscopy analysis. The surface properties of supports were analyzed by XPS to interpret their different adsorption properties. The samples were characterized by XRD, RAMAN, FTIR, SEM-EDX, and TEM analyses. The three most determinant parameters in adsorption phenomena are presence of oxygen functional groups on the support, the polarization of surface functional groups in accordance to the suspension pH, and the solvent type. The supported polyoxometalate on GO (GO/POM) prepared by adsorption in a suspension of 1:1 water/methanol mixture with pH = 3.5 yielded the highest adsorption capacity of 427 mg/g while the adsorption capacities of supported polyoxometalate on reduced samples were 74 mg/g and 54 mg/g, respectively. The pH-dependent behavior of ionizable surface oxygen functional groups was investigated and results revealed that also played a key role in the adsorption capacity. The highest POM adsorption was obtained in the pHs below isoelectric point of GO where POM anions can establish chemical bonds with the positive net surface charge. The highest adsorption capacity was obtained in the water-methanol mixture. The kinetics of adsorption mechanism was best described by a pseudo-second-order model. [ABSTRACT FROM AUTHOR]

Self-assembly of Keggin-type polyoxometalates (POMs) with diammonium ions containing oligo(ethylene oxide) units form parallelepiped or octahedral nanocrystals. These structures are tunable depending on the chemical structure of the ammonium ions and preparative conditions. The ether linkages in these ammonium ions exert conformational flexibility, which is essential to achieve long-range regular molecular alignments in the nanocrystals. [ABSTRACT FROM AUTHOR]

[Display omitted] • Proposed a strategy for controlled alcoholysis by solubilization. • Synthesized POM catalysts with high thermal stability and limited catalytic activity. • 72.1 % oligomer products were obtained in 10 min under optimal conditions. • Multilayer alcoholysis with solubilization effect is the key to achieve controllable. • Oligomer was directly applied to the preparation of PET-PLA successfully. Controlled degradation of macromolecules or natural macromolecules is important for their subsequent utilization. Normally, it is easier to degrade them to monomers than to oligomers in designated molecular weight range, the controlled degradation is much difficult to achieve and has been challenge for the utilization of macromolecules. Here, we proposed a strategy for simultaneous degradation of the inner and outer layers of PET, which avoid the degradation of polymers from the outside to the inside and achieved the controlled degradation. Under high temperature and micro-pressure conditions, PET is transformed from dense to flocculent structure by the swelling effect, which satisfies the need for simultaneous degradation of the inner and outer layers. In addition, a stable "Dawson" type Polyoxometalates (POMs) α 2 -K 8 P 2 W 17 O 61 X(H 2 O)‧16H 2 O (X = Zn, Mn, Co, Ni, Cu) with limited number of catalytic activity center was synthesized and applied to PET alcoholysis to obtain oligomer with given molecular weight range. Under the optimal conditions, PET: EG: POM catalyst = 1.0: 4.0: 0.02 (wt%), 240 °C, 10 min, PET was completely degraded and obtained the oligomer products (Mn < 2000 g/mol) with 72.1 % yield. By investigating the mechanism of the controlled alcoholysis, the formation of flocculent PET was be the key factor in achieving controlled degradation; hydrogen bonding and coordination of POMs are the key interactions to achieve rapid alcoholysis. Finally, oligomers were applied in the preparation of PET-PLA copolymers to follow sustainable route. The incorporation of bio-based polymers demonstrates better inclusiveness to the environment and contributes to harmonious development. [ABSTRACT FROM AUTHOR]

The ion-pairing interaction for the ionic liquids (ILs)-based polyoxometalate (POM) salts in the aqueous solution is critical to the chemistry of the ILs-POM hybrid. Herein, for the first time, molecular dynamics simulations have been performed to investigate the aqueous solutions of the representative α-PW 12 O 40 3− Keggin anion (PW 3− ), neutralized by three different types of alkyl-functionalized imidazole-typed IL cations (1-alkyl-3-methylimidazolium cations, alkyl: n-ethyl, n-butyl, and n-octyl). The simulations provide a direct visual observation on the aggregate morphology for the POM anions in aqueous solution. Meanwhile, distinctive ion-pairing interaction mechanism and interfacial solvation behavior have been revealed. Our simulation results indicate that the alkyl-functionalized imidazole cations can affect the effective interaction between the charged POM anions, that is, the alkyl chain length in imidazolium cation could be applied to regulate the aggregation behavior among the negative POM anions. The unique ion-pairing phenomena can be ascribed to the variable modulating effects from neutralizing IL-typed cations, which not only acts as the screening counterions of electrostatic repulsion, but also induces the alkyl chain-anion interaction and overcomes the anion-anion repulsion. [ABSTRACT FROM AUTHOR]

This study is aimed at proposing a practical green procedure for the synthesis of octahydroquinazolinone derivatives using benzaldehyde, dimedone and urea under microwave irradiation in water. A surfactant type polyoxometalate-based organic-inorganic hybrid was able to efficiently catalyze this synthesis. The catalyst was prepared and characterized by Fourier transform infrared, UV-Vis, X-ray diffraction, and thermogravimetric analysis. The employed catalyst exerted a synergistic effect; the anion part acted as a catalyst while the cation part acted as a surfactant in order to increase the concentration of organic reactants in water. The main advantage of this method is its remarkable yield in short reaction periods, which results in the rendering of products with high purity. Moreover, this heterocatalyst is capable of being easily recovered and reused several times. The influences of reaction conditions were studied systematically, and a possible catalysis mechanism was proposed for understanding the highly efficient heterogeneous catalytic behavior. [ABSTRACT FROM AUTHOR]

The microporous, sodalite-like zeolite imidazolate framework ZIF-8 [Zn(MeIM); MeIM = 2-methylimidazole] has been selected as a host matrix for stabilization of guest H3PW12O40 (PW12) in this study. To modify ZIF-8 by H3PW12O40 (PW12), a one-pot hydrothermal synthesis strategy has been developed and used in the chemoselective oxidation of sulfides to the corresponding sulfoxides (and sulfones) in the presence of 30 % H2O2 in ethanol (and CH3CN) as solvent. Some of the advantages of our method include excellent yields, heterogeneous conditions, simplicity, compatibility with a variety of functionalities, and ease of isolation of the products. X-ray diffraction, scanning electron microscopy, energy-dispersive analysis X-ray spectroscopy, ultraviolet/visible rays, and Brunauer-Emmett-Teller have been used to characterize the samples prepared. Large-sized pores and cavities of ZIF-8 become occupied by PW12 units on modification with PW12, as shown by analysis results. This method might bring light to new opportunities in the development of high-performance polyoxometalate catalysts using rapidly growing ZIFs as supports. [ABSTRACT FROM AUTHOR]

Ethyl lactate is a promising green solvent, which can be produced via esterification of biomass derived lactic acid and ethanol. Herein, we report the development of highly active and stable polyoxometalates (POMs) supported on zeolite catalysts for synthesis of ethyl lactate. Repetitive stability tests were performed using the developed catalysts, and comparative characterization of the fresh and used catalysts was performed to understand the changes in the physicochemical properties of the catalysts. It was found that low-silica Y zeolites (silicon-to-aluminum ratio, SAR, of 2 and 5) are prone to be dealuminated (by lactic acid) under the reaction conditions, and thus being not suitable to be used as the catalyst support. Direct support of 12-tungstophosphoric acid (by impregnation) on high-silica Y zeolite (SAR40) led to deactivation during catalysis due to 12-tungstophosphoric acid leaching. This issue was solved by surface modification of the high-silica Y zeolite using cesium (Cs) ions before impregnation of 12-tungstophosphoric acid because the formed cesium phosphotungstate is insoluble in the reaction. As a result, a stable composite catalyst of Cs exchanged 12-tungstophosphoric acid supported on high-silica mesoporous Y was developed, which showed good reusability. In detail, after seven cyclic tests, the physiochemical properties of the catalyst and the catalytic performance remained relatively stable, e.g., the yield of ethyl lactate remained at around 29.6%. Findings of the study show that the stability of the zeolitic support and the support heteropolyacid are equally important for obtaining a stable catalyst for ethyl lactate synthesis via esterification. • Low-silica Y zeolites are prone to be dealuminated (by lactic acid) under the conditions. • High-silica mesoporous Y zeolite showed the good stability in the system. • Direct support of HPW on high-silica Y led to deactivation during catalysis due to HPW leaching. • Cs exchanged HPW supported on high-silica mesoporous Y shows good activity and stability. [ABSTRACT FROM AUTHOR]

The development of catalysts with high thermal stability, high catalytic activity and high cycling performance has been an important challenge in PET alcoholysis research. PET degradation is a surface interface controlled process, but PET as a dense solid with lower specific surface area severely reduces its degradation rate. Here, the high specific surface area (0.4–3.3 m2/g) and the large number of pores (0–17.5 nm) formed by the swelling of PET at high temperature were used to break the interfacial confinement between the reactants; then the rapid and complete degradation of PET was achieved under the multi-hydrogen bonding microenvironment formed by the multi-active site polyoxometalate (POM) catalysts K 10 [M 4 (H 2 O) 2 (PW 9 O 34) 2 ]-H 2 O (M = Zn, Mn, Cu, Ni, Co) and EG. Finally, accompanied by the attack of the transition metal active site on C O of PET, 1.0 g of PET could be completely degraded in 5 min under the optimal reaction conditions (2.0 wt% of catalyst to PET, 240 °C) and the bis(hydroxyethyl) terephthalate (BHET) yield of 92.8% was achieved within 8 min. Moreover, the catalyst could be recycled more than 30 times, which is very meaningful. In the same time, the mechanism of PET alcoholysis was investigated and proposed a mechanism of PET alcoholysis. [Display omitted] • The swelling effect changes the morphology of PET and promoted its alcoholysis. • The POM catalyst has excellent cycling performance (> 30) with high stability and activity. • The catalyst forms a highly active microenvironment with EG to promote rapid alcoholysis of PET. • PET can be completely degraded within 5 min and 92.8% BHET yield can be obtained in 8 min [ABSTRACT FROM AUTHOR]

Highlights: [•] Self-assembled films of [Ru(bpy)3]2γ*-[W18O54(SO4)2] were prepared at Pt electrodes. [•] Low electrolyte concentrations are required to maintain film integrity. [•] Photocatalysis by [W18O54(SO4)2]4− is sensitized by the ruthenium centres. [•] Photocatalytic performance of the film was optimised under low electrolyte conditions. [•] The highest photocurrent response from POM films under visible irradiation is reported. [ABSTRACT FROM AUTHOR]

Highlights: [•] Overview of basic concepts, seminal studies, recent progress and breakthroughs in dendritic catalysis. [•] Locations of catalytic entities include core, periphery, nanoparticles and building block. [•] Metallodendritic catalysts, dendrimer-stabilized nanoparticle catalysts and dendritic organocatalysts. [•] Essential new concepts have emerged with various positive and negative dendritic effects. [Copyright &y& Elsevier]

Abstract: We demonstrate that electron injection in single-layer polyfluorene based polymer light-emitting diodes (PLEDs) can be significantly enhanced by inserting a thin (<10nm) inorganic polyoxometalate (POM) molecular oxide layer between the polymer layer and an aluminum cathode. Hydrophilic POM was spin-cast from methanol, an orthogonal solvent with regard to the hydrophobic polymer layer underneath, to form the thin cathode interfacial/electron injection layer. A lower turn-on and operating voltage and a higher luminance and current density was obtained in the POM-modified hybrid LEDs (HyLEDs) which are associated with the electron injection barrier reduction in the modified polymer/Al interface, evidenced by the increased open circuit voltage from photovoltaic measurements. These results demonstrate the potential of polyoxometalates as novel, stable cathode interfacial layers for efficient electron injection/transport in high performance HyLEDs. [Copyright &y& Elsevier]

The kinetics of the oxidation of a series of substituted phenols by polyoxometalate (POM), K5[SiVW11O40] · 12H2O were investigated. Under all conditions studied second-order kinetics were observed. Electron-transfer from neutral phenols (k1) was slower than that from the corresponding phenoxide anions (k2), and the reaction rate was highly dependent on the nature of the substituent groups. The observed rate constants decreased in the order: p-methoxyphenol (1)>p-methylphenol (2)>m-methylphenol (4)>m-methoxyphenol (3)>phenol (5)>p-chlorophenol (6)>p-bromophenol (7)>m-chlorophenol (8)>m-nitrophenol (9). A Hammett plot of the data revealed a better correlation with σ+ than with σ, suggesting a reaction involving the formation of an electron-deficient radical intermediate with the rate-determining step being an electron-transfer from a neutral substrate. Depending on the concentration of POM, oxidized phenolic and oxidative coupling products were detected. [ABSTRACT FROM AUTHOR]

The chemical structural changes of Lodgepole pine milled wood lignin (MWL) before and after polyoxometalate (POM) oxidation were investigated using gel permeation chromatography (GPC), Fourier Transform infrared spectroscopy (FTIR), and solution-state nuclear magnetic resonance spectroscopy (NMR). 13C NMR spectroscopic data revealed an approximately 28% decrease in α-OH/β-O-4 inter-unit linkages after POM treatment. This was accompanied by an increase in carbonyl and phenolic hydroxyl content. These results suggest POM oxidation involved side chain (such as α-OH/β-O-4) oxidation and/or degradation of some of the inter-unit linkages. Quantitative 13C NMR along with GPC analysis revealed an increase in the degree of condensation of the MWL as a result of POM treatment, suggesting radical coupling as a major reaction pathway. [ABSTRACT FROM AUTHOR]

Abstract: Three compounds, K2(H2O)4H2SiMo12O40 ·7H2O (1), K2Na2(H2O)4SiW12O40 ·4H2O (2), and Na4(H2O)8SiMo12O40 ·6H2O (3) have been synthesized and structurally characterized by single-crystal X-ray analysis, IR, and thermogravimetry. Compounds 1 and 2 both show the high symmetry trigonal space group P3221 and a novel 3D network structure. The Keggin anions [SiM12O40]4−(M=Mo, W) are linked by potassium or sodium cations to generate hexagon-shaped channels along the c-axis, in which water molecules are accommodated. Compound 3 is tetragonal, space group P4/mnc constructed from [SiMo12O40]4− anions and Na ions. [Copyright &y& Elsevier]

Polyoxometalates (POMs) are a class of metal oxide complexes with a large structural diversity. Effective control of the final chemical and physical properties of POMs could be provided by fine-tuning chemical modifications, such as the inclusion of other metals or non-metal ions. In addition, the nature and type of the counterion can also impact POM properties, like solubility. Besides, POMs may combine with carbon materials as graphene oxide, reduced graphene oxide or carbon nanotubes to enhance electronic conductivity, with noble metal nanoparticles to increase catalytic and functional sites, be introduced into metal-organic frameworks to increase surface area and expose more active sites, and embedded into conducting polymers. The possibility to design POMs to match properties adequate for specific sensing applications turns them into highly desirable chemicals for sensor sensitive layers. This review intends to provide an overview of POM structures used in sensors (electrochemical, optical, and piezoelectric), highlighting their main functional features. Furthermore, this review aims to summarize the reported applications of POMs in sensors for detecting and determining analytes in different matrices, many of them with biochemical and clinical relevance, along with analytical figures of merit and main virtues and problems of such devices. Special emphasis is given to the stability of POMs sensitive layers, detection limits, selectivity, the pH working range and throughput., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2022 Veríssimo, Evtuguin and Gomes.)

• We explore the bulk-deposition of POM nanocrystals —Co 4 (PW 9) 2 — on carbon supports. • Four MOF-74-derived nanocarbons Co@C, Co/Ni@C, N,S-Co@C and N,S-Co/Ni@C as supports. • The bulk-deposition of Co 4 (PW 9) 2 always improves the nanocarbon OER performances. • However, nanocarbon metal and doping features determine improvement magnitudes. • Co 4 (PW 9) 2 ↔Co/Ni@C synergy results in the highest intrinsic POM OER activity. Ternary nanocomposites consisting of cobalt phosphotungstate, metal nanoparticles and a carbon matrix (Co 4 (PW 9) 2 @NP@C) were synthesized by decorating four different MOF-74-derived nanocarbons with the sandwich-type polyoxometalate [Co 4 (H 2 O) 2 (PW 9 O 34) 2 ]10−, Co 4 (PW 9) 2. An unprecedented strategy based on the "bulk" deposition of the POM salt nanocrystals has been persecuted on purpose, avoiding the homogeneous dispersion of POM clusters across the nanocarbon surfaces. Thereby, virtually unaltered Co 4 (PW 9) 2 nanocrystals were supported on three of the four nanocarbons, but unexpectedly the combination of bimetallic undoped Co/Ni@C support with the POM induces partial structural modifications in both materials. Consequently, the derived Co 4 (PW 9) 2 @Co/Ni@C electrocatalyst undergoes a noteworthy electroactive surface area relative increase, but at the same time, its intrinsic OER activity declines. This is not an obstacle for this nanocomposite to exhibit (along with Co 4 (PW 9) 2 @N,S-Co@C) very significant nominal OER performances: low overpotentials (ca. 400 mV to develop 10 mA cm−2 of current density), fast kinetics at intermediate overpotentials (Tafel slopes ≤67 mV dec−1) and remarkable stability levels. Regardless of the specific results, this preliminary study demonstrates for the first time the POM "bulk" deposition strategy as a useful tool to prepare highly active OER catalysts, and it shows up the dramatic effect that the nanocarbon doping and metal composition has on the resultant POM loading, electrocatalytically active area and OER behavior. [Display omitted] [ABSTRACT FROM AUTHOR]

• Fabrication an electrochemical sensor based on (bdpy)PW 11 Co/MWCNTs-COOH. • (bdpy)PW 11 Co/MWCNTs-COOH/GCE showed excellent electrocatalysis towards NO 2 –. • (bdpy)PW 11 Co/MWCNTs-COOH/GCE exhibited good selectivity and stability. • The LOD of NO 2 – is about 0.63 µmol L−1 with sensitivity of 17.9 µA mM−1. A nanocomposite modified glassy carbon electrode (GCE) based on K(1,1′-(1,4-Butanediyl) dipyridinium) 2 [PW 11 O 39 Co(H 2 O)]/carboxyl functionalized multi-walled Carbon Nanotubes ((bdpy)PW 11 Co/MWCNTs-COOH/GCE) was fabricated by electrodeposition method. TEM images demonstrated that ((bdpy)PW 11 Co nanoparticles were dispersed uniformly on the surfaces of MWCNTs-COOH or their interlayers with a diameter of 8.5 nm. The morphological, electrochemical, and electrocatalytic behaviors of the modified electrode were investigated by field emission scanning electron microscopy (FE-SEM) combined with energy-dispersive X-ray spectroscopy, cyclic voltammetry, and amperometry techniques. The FE-SEM images well showed immobilization of (bdpy)PW 11 Co/MWCNTs-COOH on GCE by deformation of the mirror surface to the rough surface. The electrochemical test results confirmed that (bdpy)PW 11 Co/MWCNTs-COOH/GCE has good stability and remarkable electrocatalytic behavior toward the reduction of nitrite ion. The proposed sensor displayed a linear range of 10–1600 µmol L−1 with LOD of 0.63 µmol L−1 (S/N = 3), and sensitivity 17.9 µA mM−1. Moreover, the results of the electrochemical experiments indicated that this sensor has an excellent selectivity, good reproducibility, and repeatability, high stability, as well as analytical performance in real samples. [ABSTRACT FROM AUTHOR]

The monolacunary Keggin-type [PW 11 O 39 ] 7- (PW 11 ) heteropolyanion was immobilized on porous framework of mesoporous silicas, namely SBA-15 and an ethylene-bridged periodic mesoporous organosilica (PMOE). The supports were functionalized with a cationic group ( N -trimethoxysilypropyl- N, N, N -trimethylammonium, TMA) for the successful anchoring of the anionic polyoxometalate. The PW 11 @TMA-SBA-15 and PW 11 @TMA-PMOE composites were evaluated as heterogeneous catalysts in the oxidative desulfurization of a model diesel. The PW 11 @TMA-SBA-15 catalyst showed a remarkable desulfurization performance by reaching ultra-low sulfur levels (<10 ppm) after only 60 min using either a biphasic extractive and catalytic oxidative desulfurization (ECODS) system (1:1 MeCN/diesel) or a solvent-free catalytic oxidative desulfurization (CODS) system. Furthermore, the mesoporous silica composite was able to be recycled for six consecutive cycles without any apparent loss of activity. The promising results have led to the application of the catalyst in the desulfurization of an untreated real diesel supplied by CEPSA (1,335 ppm S) using the biphasic system. The system has proved to be a highly efficient process by reaching desulfurization values higher than 90% for real diesel during three consecutive cycles., (Copyright © 2019 Ribeiro, Granadeiro, Corvo, Pires, Campos-Martin, de Castro and Balula.)

A method for the enrichment of phosphopeptides based on magnetic nanoparticles coated with polyoxometalate (POM) was developed. A layer-by-layer assembly technique was used to prepare magnetic nanoparticles (MNPs) coated with polyoxometalate and chitosan. The composites were used for phosphopeptide enrichment prior to analysis by matrix assisted laser desorption ionization time of flight mass spectrometry (MALDI-TOF MS). The composites exhibited advantages of rapid magnetic separation, hydrophilicity, positive electricity, and a high selectivity for enrichment of phosphopeptides. β -Casein was selected as a model phosphorylated protein to assess the performance of the enrichment technique. After the enrichment step, the limit of detection was determined to be 0.02 fmol. The prepared POM-based MNPs thus exhibit significant potential in the detection of low-abundance phosphoproteins.