Sandwich-type Polyoxometalate Research Articles

Enhanced performance of a Na3.5Co4[Bi2Co2W19.75O70(H2O)6]/porous graphitic carbon nitride heterojunction based photocatalyst realized by the addition of copper sulfide nanoparticles.

Photocatalytic hydrogen (H2) evolution can effectively solve the global energy problem, in which the key factor is the synthesis of efficient photocatalytic materials. In this study, we successfully synthesized a novel photocatalyst, BiWCo/CuS/PGCN, by functionalizing porous graphitic carbon nitride (PGCN) with sandwich-type polyoxometalate Na3.5Co4[Bi2Co2W19.75O70(H2O)6]·39.5H2O (BiWCo) and introducing copper sulfide (CuS) nanoparticles as a cocatalyst. This approach was aimed at enhancing the built inner electric field between interfaces, resulting in a significant improvement in photocatalytic H2 evolution performance. This research adopts a step-by-step method to synthesize BiWCo/CuS/PGCN composites with p-n heterojunctions, which has high visible light absorption and a synergistic effect of multiple elements. PGCN with a high specific surface area contributes to the uniform distribution of active sites. In addition, the nano-CuS cocatalyst provides abundant active sites and more electron transfer pathways for photocatalysis. Therefore, the H2 production efficiency of BiWCo/CuS/PGCN is 6.3 times that of PGCN, 4.5 times that of BiWCo and 2.5 times that of BiWCo/PGCN under visible light. The H2 production rate of BiWCo/CuS/PGCN reaches 3477.58 μmol g-1 h-1. At the same time, the ternary photocatalyst shows high stability after 30 hours and 5 cycles. This work demonstrates that BiWCo/CuS/PGCN has good application prospects in H2 evolution, and provides a new strategy for the design of efficient ternary photocatalytic materials.

Synthesis, Characterization and Catalytic Application of Inorganic–Organic Nanohybrids Consisting of Sandwich-Type Polyoxometalates and Diethylenetriamine

Synthesis, Characterization and Catalytic Application of Inorganic–Organic Nanohybrids Consisting of Sandwich-Type Polyoxometalates and Diethylenetriamine

Facile synthesis of new hybrid nanocomposite sandwich‐type polyoxometalate@lead (II) oxide@polyvinyl alcohol as an efficient and reusable amphiphilic nanocatalyst for ODS of real fuel

In order to obtain the clean gasoline, a new heterogeneous organic/inorganic nanocatalyst FWF@PbO@PVA was synthesized and utilized in the catalytic oxidative desulfurization (CODS) processes. The nanocatalyst was synthesized by combining iron-substituted sandwich-type polyoxometalate (Na9K[Fe4(H2O)2(FeW9O34)2]·32H2O abbreviated as FWF), Lead (II) oxide (PbO), and polyvinyl alcohol (PVA). The obtained nanocomposite (FWF@PbO@PVA) was characterized via FT-IR, XRD, SEM, and EDX techniques. The spectroscopic characterization revealed that the Na9K[Fe4(H2O)2(FeW9O34)2 was immobilized on the surface of PbO@PVA. According to the results of XRD analysis, the average crystal size of FWF@PbO@PVA nanocomposite particles was estimated to be about 15 nm, which was confirmed by SEM results. FWF@PbO@PVA nanocomposite catalyzed the CODS reactions of actual/model fuel by H2O2-CH3COOH as an oxidant. FWF@PbO@PVA nanocatalyst displayed marvelous efficiencies with examined optimum conditions (0.1 g of FWF@PbO@PVA, for 1 h at 35 ˚C, H2O2/acetic acid 1:2 vol ratio oxidation system, and the ambient pressure) as the results depicted up to 99% efficiencies. Also, FWF@PbO@PVA as a heterogeneous nanocatalyst could be quickly recovered and reused multiple times by filtration with no noticeable loss of activity. This research shows that FWF@PbO@PVA nanocomposite can represent a promising new class of organic–inorganic hybrid nanocatalysts for the CODS system.

Fabrication of heterogeneous Zr-containing polyoxometalate as an efficient catalyst for the synthesis of a broad range of 1,5-benzodiazepine derivatives

As an extension of our interest in polyoxometalate (POM) as catalysts, one heterogeneous catalyst TBA8[Zr(W5O18)2]·17H2O (Zr(W5)2) (TBA+: tetrabutylammonium) was synthesized and fully characterized by multiple spectroscopic techniques. In this catalyst, zirconium ion connected to two mono-lacunary Lindqvist [W5O18]4− anions to create anionic sandwich-type POM and this anionic unit was encapsulated by TBA+ cations to form heterogeneous catalyst with hydrophobic nature. It is assumed that alkyl chains of TBA+ can trap reactants on the surface of catalyst, thus in this regard, the probability of the interaction between reactants and POM center can increase which lead to the higher catalytic efficiencies of above catalysts. Using Zr(W5)2 as a heterogeneous and efficient catalyst, a series of 1,5-benzodiazepines were synthesized via four mild and solvent-free reactions such as reaction of 1,2-phenylenediamine with ketones, chalcones, 1,3-diketones and aldehydes. According to the results, the presented protocol is superior to the previously reported methodologies in terms of reaction time and product yield. The facile work-up procedure and the reusability of this catalyst are other advantages of this protocol.

A Cyclen-Functionalized Cobalt-Substituted Sandwich-Type Tungstoarsenate with Versatility in Removal of Methylene Blue and Anti-ROS-Sensitive Tumor Cells.

Oxidative degradation by using reactive oxygen species (ROS) is an effective method to treat pollutants. The synthesis of artificial oxidase for the degradation of dyes is a hot spot in molecular science. In this study, a nanoscale sandwich-type polyoxometalate (POM) on the basis of a tetra-nuclear cobalt cluster and trivacant B-α-Keggin-type tungstoarsenate {[Co(C8H20N4)]4}{Co4(H2O)2[HAsW9O34]2}∙4H2O (abbreviated as CAW, C8H20N4 = cyclen) has been synthesized and structurally examined by infrared (IR) spectrum, ultraviolet–visible (UV–Vis) spectrum, X-ray photoelectron spectrum (XPS), single-crystal X-ray diffraction (SXRD), and bond valence sum (Σs) calculation. According to the structural analysis, the principal element of the CAW is derived from modifying sandwich-type polyanion {Co4(H2O)2 [HAsW9O34]2}8– with four [Co(Cyclen)]2+, in which 1,4,7,10-tetraazacyclododecane (cyclen) is firstly applied to modify POM. It is also demonstrated that CAW is capable of efficiently catalyzing the production of ROS by the synergistic effects of POM fragments and Co–cyclen complexes. Moreover, CAW can interfere with the morphology and proliferation of sensitive cells by producing ROS and exhibits ability in specifically eliminating methylene blue (MB) dyes from the solution system by both adsorption and catalytic oxidation.

A hexa-Cu cluster sandwiched silicotungstate with reactive oxygen species catalytic ability and anti-tumor activity in PC12 cells

A sandwich-type polyoxometalate (POM) based on a hexa-nuclear copper cluster and trivacant B-α-Keggin-type silicotungstate [Cu(en)2][Cu(en)2H2O]2{[Cu(en)2][Cu6(en)2(H2O)2(SiW9O 34)2]}·8H2O (SCW) (ethylenediamine = en) has been synthesized and structurally featured by X-ray photoelectron spectrum (XPS), IR and UV spectra, and single-crystal X-ray diffraction (SXRD). According to the structural analysis, the principal element of the SCW is a 1-D linear polyoxoanion that is alternately joined by {[Cu6(en)2(H2O)2(SiW9O34)2]}8– fragments and [Cu(en)2]2+ complexes. The cations of SCW are present in two forms: [Cu(en)2H2O]2+ and [Cu(en)2]2+. Notably, the Cu ions have been shown to coexist in the SCW with quad-coordination, penta-coordination, and hexa-coordination, which is rare in polyoxometalates. It is also demonstrated that SCW can efficiently catalyze the production of reactive oxygen species (ROS) by the synergistic action between copper complexes and POM fragments. Furthermore, SCW exhibits ability in anti ROS-sensitive tumor cells, such as PC12 cells.

Cobalt-based sandwich-type polyoxometalate supported on amino-silane decorated magnetic graphene oxide: A recoverable catalyst for extractive-catalytic oxidative desulfurization of model oil

In order to produce ultra-low sulfur fuel, a sandwich-type polyoxometalate (K10[Co4(H2O)2(PW9O34)2]10- (Co4-POM) was covalently immobilized on amino-modified magnetic graphene oxide, and employed as a novel heterogeneous catalyst in an extractive- catalytic oxidative desulfurization system (ECODS). The (Co4-POM@APTES-(Fe3O4/GO)) nanocomposites with various Co4-POM content were prepared. The obtained samples were characterized by XRD, FT-IR, SEM, EDX, N2 adsorption, and VSM techniques. Meanwhile, the effects of Co4-POM load percentage, reaction temperature, catalyst dosage, and H2O2/DBT molar ratio on desulfurization efficiency of the prepared catalyst were investigated. The highest catalytic activity was observed for the sample with 30 wt% Co4-POM content. Dibenzothiophene (DBT) could be completely removed within at 50 ℃ using 4 g catalyst L−1 fuel, and H2O2/DBT molar ratio of 4. In addition, BT and 4,6-DMDBT could be completely removed under the optimized conditions, which suggested a promising prospect of the catalyst for industrial applications. The nanocomposite could be easily separated and reused by utilizing an external magnetic field without any substantial decline in its catalytic activity even after five runs. The kinetic data were fitted to a pseudo-first-order model. Finally, a reaction mechanism for the catalytic oxidation of DBT in the presence of Co4-POM@APTES-(Fe3O4/GO) was proposed.

Revisiting the Three Vanadium Sandwich-Type Polyoxometalates: Structures, Solution Behavior, and Redox Properties.

It is well known that the trivacant anions α-B-[XW9O33]9- react with vanadyl ions to give the sandwich-type polyoxometalates [(VIVO)3(XW9O33)2]12- with X = AsIII or SbIII. Nevertheless, the oxidized derivatives have been obtained selectively by electrochemical oxidation from the fully reduced derivatives [(VIVO)3(XW9O33)2]12- allowing full characterization both in solution using UV-vis and multinuclear (17O, 51V, and 183W) NMR spectroscopies and in the solid state by single-crystal X-ray diffraction. Structural analysis of the oxidized [(VVO)3(XW9O33)2]9- polyanions is consistent with the idealized D3h symmetry, while solution studies reveal a fair hydrolytic stability in a wide pH range from 0 to 6. Besides, the D3h polyanions either as reduced or oxidized forms [(VO)3(AsW9O33)2]9/12- have been identified as the thermodynamic product that results from the conversion of the C2v polyanion [(H2O)(VO)3(AsW9O33)2]9/12- through moderate heating. Conversely, the SbIII-containing derivative gives exclusively the D3h polyanion, probably either due to the extended lone pair of the trigonal SbIII heterogroup that prevents the formation of the C2v arrangement or the lability of the oxo-metalate bonds that favor chemical exchange. The electrochemical studies of sandwich-type polyoxometalates revealed that each {V═O} group gives rise to a one-electron transfer process. At last, the redox properties appear strongly altered in the 0.3-5 pH range, consistent with proton-coupled electron transfers.

The TiO2 films with sandwich-type polyoxometalates in dye sensitized solar cells with electron recombination decreasing and dye adsorption increasing

Unfavorable electron recombination, which hinders the efficiency of dye-sensitized solar cells (DSSCs), usually occurs at the TiO2/dye/electrolyte interface on a photoanode. Polyoxometalates (POMs), as good electron acceptors, can be used as electron-transfer materials in DSSCs to improve electron transport in TiO2 and reduce electron recombining on the interface of a photoanode. In this paper, the pure inorganic sandwich-type POM Na9[Na3(H2O)6Cu3(H2O)3(SbW9O33)2]·40H2O (Cu3Na3POM) was mixed with TiO2 to form nanocomposites by simple sol-gel method. X-ray photoelectron spectroscopy (XPS) proved that Cu3Na3POM and TiO2 combined. Then the nanocomposite was doped with P25 to form Cu3Na3POM@TiO2/P25 photoanodes which were applied to the DSSCs. The Cu3Na3POM improved the transfer and recombination of electrons in the photoanode, proved by open circuit voltage decay (OCVD) and electrochemical impedance spectroscopy (EIS). Scanning electron microscopy (SEM) and ultraviolet-visible (UV-vis) absorption spectra showed that Cu3Na3POM optimized the morphology of the photoanode and the adsorption capacity of dye. The electrochemical test showed that the photoelectric conversion efficiency of DSSCs with Cu3Na3POM@TiO2/P25 photoanodes was enhanced to 6.91%, which was 13.66% higher than the DSSCs without Cu3Na3POM.

Cobalt-Based Sandwich-Type Polyoxometalate Supported on Amino-Silane Decorated Magnetic Graphene Oxide: A Beneficial and Recoverable Catalyst for Extractive-Catalytic Oxidative Desulfurization of Model Oil

Cobalt-Based Sandwich-Type Polyoxometalate Supported on Amino-Silane Decorated Magnetic Graphene Oxide: A Beneficial and Recoverable Catalyst for Extractive-Catalytic Oxidative Desulfurization of Model Oil

Decorating MOF-74-derived nanocarbons with a sandwich-type polyoxometalate to enhance their OER activity: Exploring the underestimated bulk-deposition approach

Ternary nanocomposites consisting of cobalt phosphotungstate, metal nanoparticles and a carbon matrix (Co4(PW9)2@NP@C) were synthesized by decorating four different MOF-74-derived nanocarbons with the sandwich-type polyoxometalate [Co4(H2O)2(PW9O34)2]10−, Co4(PW9)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 Co4(PW9)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 Co4(PW9)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 Co4(PW9)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.

Synthesis of polyoxometalates (POM)/TiO2/Cu and removal of nitrate nitrogen in water by photocatalysis

Nitrate nitrogen is one of the vital issues needed to be addressed in the water purification process utilizing groundwater as a drinking water source. In this study, a sandwich-type polyoxometalate Na [α-SiW9O34] has been synthesized and SiW9/TiO2/Cu composite has been prepared by sol-gel method. Samples have been characterized by XRD, BET, FTIR, SEM, ED-Mapping, UV–Vis, XPS. The catalytic reduction of nitrate was performed in the presence of SiW9/TiO2/Cu composite as photocatalyst. The effects of catalyst loading, initial nitrate concentration, sandwich-type polyoxometalate loading, dissolved O2, and concentration of formic acid on nitrate removal have been investigated. The results showed that the prepared composite catalyst had better photocatalytic activity than the TiO2. 76.53% of nitrate removal with 82.09% of N2 selectivity was obtained under the following conditions: catalyst dosage 0.8 g/L, initial nitrate concentration of 30 mg/L, SiW9/Cu loading percentage of 10%, 30 mmol/L of formic acid, in presence of N2, and 6 h reaction time.

Ultra-deep oxidative desulfurization of real fuels by sandwich-type polyoxometalate immobilized on copper ferrite nanoparticles, Fe6W18O70 ⊂ CuFe2O4, as an efficient heterogeneous nanocatalyst

In order to obtain the clean gasoline, we report on the synthesis and characterization of a new heterogeneous nanocatalyst comprised of the sandwich-type polyoxotungstate [(FeW9O34)2Fe4(H2O)2]−10 (Fe6W18O70) clusters and copper ferrite (CuFe2O4) nanoparticles. The materials were characterized by powder X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), ultraviolet-visible (UV–vis), and scanning electron microscopy (SEM). The Fe6W18O70⊂CuFe2O4 nanocatalyst catalyzed the oxidative desulfurization (ODS) reactions of hazardous sulfur-containing compounds by H2O2-CH3COOH as oxidant. The nanocatalyst exhibited an exceptionally high catalytic performance in the ultra-deep ODS of simulated fuels and real gasoline. The experimental results revealed that the oxidation reaction efficiencies were up to 95% at the temperature of 35 °C and the contact time of 1 h. Particularly, the removal (%) of thiophene (C4H4S), benzothiophene (C8H6S), and dibenzothiophene (C12H8S) from simulated fuels over Fe6W18O70⊂CuFe2O4 nanocatalyst could reach 98%, 99%, and 99%, respectively. Moreover, the heterogeneous nanocatalyst could be easily recovered and reused multiple times by filtration with no obvious loss of activity. The present study will lead to the widespread catalytic application of Fe6W18O70⊂CuFe2O4 material in the efficient and feasible ODS of petroleum fractions.

Comparative NMR Relaxivity Study of Polyoxometalate-Based Clusters [Mn4(H2O)2(P2W1SO56)2]16\u2212 and [{Dy(H2O)6}2Mn4(H2O)2(P2W15O56)2]10\u2212 from 20\xa0MHz to 1.2\xa0GHz

Nuclear Magnetic Resonance relaxivities are a measure for the sensitivity of a contrast agent (CA), i.e. the potential of a paramagnetic moiety to enhance longitudinal and transverse relaxation of molecules in its near neighbourhood. The underlying mechanism is called Paramagnetic Relaxation Enhancement (PRE). The relaxivity, characterizing PRE, depends not only on the external applied magnetic field but also depends on numerous factors, such as number of coordinated water molecules, water exchange rate, rotational diffusion, first and second coordination hydration sphere, electronic and magnetic properties of paramagnetic centers and the molecular shape/size of the CA. Relaxation rates are usually normalized to the concentration of the contrast agent to provide the relaxivities. To investigate the influence of these factors on PRE of newly synthesized potential CA, two paramagnetic metals containing polyoxometalates (POMs) [Mn4(H2O)2(P2W15O56)2]16− (Mn4-P2W15) and [{Dy(H2O)6}2Mn4(H2O)2(P2W15O56)2]10− (Dy2Mn4-P2W15) were selected as models to be studied at 1H Larmor frequencies from 20 MHz to 1.2 GHz. Structurally, the POM Dy2Mn4-P2W15 is similar to the tetra-nuclear manganese(II)-substituted sandwich-type POM Mn4-P2W15, with the two coordinated DyIII cations acting as linkers connecting Mn4-P2W15 units, thus forming a 1D ladder-like chain structure based on sandwich-type rungs strung together by the dysprosium cations. This study shows that POM (Dy2Mn4-P2W15) is a promising CA at high magnetic fields and proves that the use of heterometallic clusters is an effective strategy to increase PRE due to the synergistic effects from different metal ions.

Design and synthesis of {CaCo3}-based sandwich-type polyoxometalate

A {CaCo3}-containing sandwich-type polyoxometalate, Li2Na2Ca3(H2O)16{Co3(H2O)[Ca(H2O)5PW8O31](PW9O34)}·16.5H2O (1), was synthesized by using a trivacant phosphotungstate to react with Co2+ and Ca2+ by a conventional aqueous solution method. 1 was characterized by single crystal X-ray diffraction, powder X-ray diffraction, IR spectra, elemental analyses and TG analyses. Structural analysis reveals that 1 is composed of trivacant and a tetravacant phosphotungstates to trap a {Co3} cluster and a Ca2+ cation. The obtained sandwich-type polyoxoanion was further connected to form a two-dimensional expanded structure via the Ca2+ linkers. This work highlights an efficient method to simultaneously introduce both alkaline-earth and transition-metal cations into polyoxotungstates.

Chemical reactivity descriptors as a tool of prediction in the synthesis of sandwich type polyoxometalate organic–inorganic hybrid compounds

In the present study a predictive model aimed at the selection of organic ligands for the successful synthesis of Cobalt sandwich-type polyoxometalate (Co-STPs) organic–inorganic hybrid compounds in aqueous solution, has been introduced. The computations were performed using Gaussian09 and the results have been evaluated by the graphic interface program, GaussView05. Geometry optimization and frequency calculations have been performed at B3LYP level with 6-311G basis set. Dipole moment was recalled from optimization results and reactivity descriptors were calculated via Fukui function using atomic charges and frontier orbitals energies. Firstly the organic molecules with dipole moments more than water are filtered.Then, ligands with less electronegativity, hardness, global electrophilicity and energy bond gap and more softness, global softness and chemical potential found to be promoters for substitution reaction on the cobalt atoms. From the local reactivity descriptors, it is concluded when the fk+, Sk+, ωk+ >fk-, Sk-, ωk- and ωk+ is greater than Sk+, the ligand will undergo substitution reaction.2-Aminobenzimidazole (ABI), 4-nitroaniline (PNA), imidazole and pyridine were evolved in synthesis reaction to test the predicted results for a major product. Applying obtained rules from local Fukui descriptors has predicted ABI and PNA will engage in a substitution reaction, which indeed occurred and resulted in two new thermodynamic controlled and purple colored organic–inorganic hybrid sandwich type polyoxometalates, (PNA)2Na12[Co4(PW9O34)2] and (ABI)2Na12[Co4(PW9O34)2]. These hybrids were characterized by infrared spectroscopy, ICP-MS, TGA-DSC and EDX. Imidazole and pyridine were failed to perform substitution reaction and led to yellow disfavored kinetic controlled products.

Synthesis of Arylsulfonyl Benzenediols by Sandwich Type Polyoxometalate Intercalated MgAl-Layered Double Hydroxides in Water at Room Temperature

This paper reports on the preparation of simple and cost-effective nanocomposite that involved intercalation of sandwich-type polyoxometalate (STPOM) anion [(OCe)3(PW9O34)2]12− into Mg/Al layered double hydroxides (donated as Mg3Al–Ce3W18) using an ion-exchange method. The catalytic performance of nanocomposite catalyst was examined in green synthesis of aryl sulfonyl benzene diols via oxidative coupling between 1,2-benzenediols and sodium benzenesulfinates under mild green condition (; in water at room temperature) with good yields (63–75%). Besides, the nanocomposite catalyst exhibited excellent reusability up to five subsequent runs. SEM, EDX and BET were employed to characterize the as-fabricated nanocomposite.

Synthesis and characterization of new nanocomposite based on sandwich-type polyoxometalate and nanoceramic (Fe2W18Fe4@FeTiO3) as a nanocatalyst for germination of barley seeds

In this manuscript, a new nanocomposite Fe2W18Fe4@FeTiO3 was synthesized on the basis of sandwich-type polyoxometalate (Na9K[(FeW9O34)2Fe4(H2O)2]·32H2O, abbreviated as Fe2W18Fe4) and nanoceramic FeTiO3. The results of FT-IR, XRD, SEM and EDX analysis method indicated the successful composition of the materials. The XRD studies showed that the average crystallite size of the composite particles was estimated to be about 42 nm, which confirmed by the results of SEM. The influence of the new nanocomposite Fe2W18Fe4@FeTiO3 in the germination of barley seeds was investigated. In order to compare, several polyoxometalates with different concentrations were used to obtain their effects on growth factors of barley seeds. From the obtained results, it was found that by applying new nanocomposite Fe2W18Fe4@FeTiO3 with 10 µM and 100 µM concentrations achieved the most preferred results.

Solid-state rearrangement of sandwich-type polyoxometalate-dopamine nanohybrid to the nanoflower Keggin polyoxometalate: synthesis, characterization, and catalytic efficiency

Sponge-like inorganic-organic nanohybrid consisting of sandwich-type polyoxometalate of [P2W18Ce3(H2O)2O71]12− (P2W18Ce3) and dopamine (DA) was fabricated by a simple procedure. The DA/P2W18Ce3 sponge-like nanohybrid is turned into a nanoflower by calcination at 300 °C. The results showed a structure rearrangement of sandwich-type polyoxometalate to the Keggin-type polyoxometalate along with this morphology change. The nanomaterials were fully characterized by scanning electron microscopy (FE-SEM), energy dispersive X-ray analysis (EDX), thermogravimetric analysis (TGA), Fourier transform infrared (FT-IR) spectroscopy, texture analysis (BET), and X-ray powder diffraction (XPRD). The DA/P2W18Ce3 sponge-like nanohybrid and the Keggin nanoflower showed efficiency toward degradation of methylene blue (MB) and rhodamine B (RhB). Moreover, the catalytic activity of the Keggin nanoflower was examined in the oxidation of sulfides to sulfones with H2O2 as oxidant in water at room temperature. The catalyst was reused at least four times without loss of its catalytic activity.

Thin Films of Fully Noble Metal-Free POM@MOF for Photocatalytic Water Oxidation.

P2W18Co4@MOF-545, which contains the sandwich-type polyoxometalate (POM) [(PW9O34)2Co4(H2O)2]10- (P2W18Co4) immobilized in the porphyrinic metal-organic framework (MOF), MOF-545, is a "three-in-one" (porosity + light capture + catalysis) heterogeneous photosystem for the oxygen-evolution reaction (OER). Thin films of this composite were synthesized on transparent and conductive indium tin oxide (ITO) supports using electrophoretic (EP) or drop-casting (DC) methods, thus providing easy-to-use devices. Their electro- and photocatalytic activities for OER were investigated. Remarkably, both types of films exhibit higher turnover numbers (TONs) than the original bulk material previously studied as a suspension for the photocatalytic OER, with TONs after 2 h equal to 1600 and 403 for DC and EP films, respectively, compared to 70 for the suspension. This difference of catalytic activities is related to the proportion of efficiently illuminated crystallites, whereby a DC thin film offers the largest proportion of POM@MOF crystallites exposed to light due to its lower thickness when compared to an EP film or crystals in suspension. Such devices can be easily recycled by simply removing them from the reaction medium and washing them before reuse. The films were fully characterized with extended X-ray absorption fine structure (EXAFS) and X-ray absorption near edge structure (XANES) spectroscopies, Raman, scanning electron microscopy, and electrochemistry before and after catalysis. The combination of all of these techniques shows the stability of both the POM and the MOF within the composite upon water-oxidation reaction.