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A New Approach for the Modification of Paper Surface Properties Using Polyoxometalates

Saraiva, Mikhail S.; Gamelas, José A. F.; Sousa, António P. Mendes de; Reis, Bruno M.; Amaral, José L.; Ferreira, Paulo J.
Fonte: Molecular Diversity Preservation International Publicador: Molecular Diversity Preservation International
Tipo: Artigo de Revista Científica
ENG
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A new approach for the chemical modification of the surface of paper based on the application of colloidal mixtures containing cationic starch and polyoxometalates on uncoated base paper is presented. Polyoxometalates with the Keggin-type structure and physical properties similar to those presented by coating pigments, namely H3PW12O40·23H2O, H4SiW12O40·24H2O, and K7PW11O39·9H2O, have been used in order to improve the quality of inkjet printing. The analysis of the different samples by FTIR-ATR spectroscopy showed the presence of the polyoxometalates (and the cationic starch) on the top surface of the paper. In addition, the determination of surface energy parameters, namely the polar component (σsp) and the dispersive component (σsd) of the surface energy, by contact angle measurements revealed that, for the new samples, the polar component level was much higher than that of the uncoated base paper. The quality of inkjet printing, evaluated by parameters such as the gamut area and the optical density, was considerably improved by these surface treatments

Filmes híbridos orgânico-inorgânicos formados pela técnica da automontagem eletrostática camada-por-camada contendo polioxometalatos do tipo Keggin; Hybrid self assembled layer-by-layer films containing Keggin type polyoxometalates

Souza, Adriano Lopes de
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Tese de Doutorado Formato: application/pdf
Publicado em 19/04/2010 PT
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Neste trabalho, filmes híbridos produzidos pela técnica da automontagem eletrostática camada-por-camada foram preparados usando-se Polioxometalatos do tipo Keggin, ácido fosfotúngstico (HPW) e o complexo monolacunar K(TPA)4[PW11O39Mn(OH2)] alternados via um polímero catiônico, poli(cloreto de alilamônio) (PAH). O filme que continha uma pré-camada de adsorção de PDMS, juntamente com 5 bicamadas de PAH e HPW apresentou um melhor comportamento eletroquímico em filmes formados sobre óxido de índio e estanho (ITO). Em função disso, este filme foi caracterizado através de Espectroscopias de Absorção na região do Ultra-Violeta Visível (UV-vis), de Absorção-Reflexão na Região do Infra-vermelho (FT-IRRAS) e de Ressonância de Plásmons de Superfície (SPR). Foi constatado por FT-IRRAS que parte da camada de PDMS está se difundindo para a superfície quando as bicamadas de PAH e HPW vão sendo preparadas. Imagens de Microscopia Eletrônica de Varredura com Emissão de Campo (MEV-EC) confirmam esta hipótese. Espectroscopia de SPR indicou que tanto a adsorção de PAH quanto a de HPW ocorrem em tempos curtos. Experimentos de Voltametria Cíclica com [Fe(CN)6]3-mostraram que este filme é poroso. Resultados de Espectroscopia de Fotoelétrons Excitados por Raios X (XPS) comprovaram que PDMS protege o substrato contra corrosão. Esse mesmo filme pôde ser utilizado numa aplicação de caráter ambiental. Ele foi capaz de detectar melamina e atrazina em concentrações 4.10-8 mol.L-1 e 1.10-6 mol.L-1 respectivamente. Filmes contendo 5 bicamadas de PAH e K(TPA)4[PW11O39Mn(OH2)] mostraram comportamentos similares referentes à queda da eletroatividade para arquiteturas iniciadas com PAH e PDMS. O filme com 5 bicamadas de PAH e K(TPA)4[PW11O39Mn(OH2)] iniciado com PAH não mostrou comportamento eletrocatalítico para a oxidação de triazinas.; In this work...

Polyoxometalates as promoters of laccase-assisted reactions

Carneiro, Andrea; Abreu, Ana; Evtuguin, D. V.; Neto, C. Pascoal; Gübitz, Georg M.; Paulo, Artur Cavaco
Fonte: Elsevier Publicador: Elsevier
Tipo: Artigo de Revista Científica
Publicado em /01/2000 ENG
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A synergistic effect of polyoxometalate and laccase benzenediol:oxygen oxidoreductase, EC 1.10.3.2 has been observed in the aerobic oxidation of a hydrazonaphthalene type colorant. The considerable increase in the decolorization rate of Solophenyl Blue GL dye with the new catalytic system composed by laccase and heptamolybdopentovanadophosphate heteropolyanion, when compared with the treatment with enzyme or heteropolyanion alone, was tentatively explained by the redox mediation action of the heteropolyanion.

Luminescent polyoxotungstoeuropate anion-pillared layered double hydroxides

Sousa, Filipa L.; Pillinger, Martyn; Ferreira, Rute A. Sá; Granadeiro, Carlos M.; Cavaleiro, Ana M. V.; Rocha, João; Carlos, Luís D.; Trindade, Tito; Nogueira, Helena I. S.
Fonte: WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim Publicador: WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Tipo: Artigo de Revista Científica
ENG
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Novel luminescent polyoxometalate anion-pillared layered double hydroxides (LDHs) were prepared by aqueous ion exchange of a Zn–Al LDH precursor in nitrate form with the europium-containing polyoxotungstate anions [EuW10O36]9–, [Eu(BW11O39)(H2O)3]6– and [Eu(PW11O39)2]11–. The host– guest interaction has a strong influence on the nature of the final intercalated species, as evidenced by elemental analy- Introduction Layered double hydroxides are an important class of ionic lamellar solids with the general formula [M2+ 1–xM3+ x(OH)2](Am–)x/m·nH2O (M2+ = Mg2+, Zn2+, Ni2+ etc., M3+ = Al3+, Cr3+, Ga3+ etc).[1] The positively charged layers, containing divalent and trivalent cations in octahedral positions, are separated by charge balancing anions and water molecules. The water molecules are connected to both the metal hydroxide layers and the interlayer anions through extensive hydrogen bonding. A range of organic or inorganic guests may be incorporated into LDHs by either ion exchange, direct synthesis or hydrothermal reconstruction of calcined precursors.[2,3] In particular, intercalation chemistry has been explored with the aim of introducing catalytically active sites and photo- and electroactive species. Many different types of metal coordination compounds and oxometalates have been immobilized in LDHs...

Iron(III)-substituted polyoxotungstates immobilized on silica nanoparticles: novel oxidative heterogeneous catalysts

Sousa, JLC; Santos, ICMS; Simoes, MMQ; Cavaleiro, JAS; Nogueira, HIS; Cavaleiro, AMV
Fonte: Elsevier Publicador: Elsevier
Tipo: Artigo de Revista Científica
ENG
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Silica nanoparticles supporting polyoxometalates (POMs), namely an iron(III) mono-substituted Keggin-type polyoxotungstate of formula alpha-[PW(11)Fe(III)(H(2)O)O(39)](4-) and a sandwich-type tungstophosphate with the formula B-alpha-[(PW(9)O(34))(2)Fe(4)(III)(H(2)O)(2)](6-) were synthesized. The POM/SiO(2) nanocomposites were obtained by alkaline hydrolysis of tetraethoxysilane using a reverse micelle and sol-gel technique. The spectroscopic studies suggest that the POMs were successfully immobilized on the silica nanoparticles. The catalytic activity of POM/SiO(2) nanomaterials was tested in the epoxidation of geraniol using H(2)O(2) as oxygen donor. The alpha-[PW(11)Fe(III)(H(2)O)O(39)](4-)/SiO(2) nanocomposite was the most efficient catalyst with high geraniol conversion and good regioselectivity for 2,3-epoxygeraniol. (C) 2010 Elsevier B.V. All rights reserved.; Supplementary materials related to this article can be found online at doi:10.1016/j.catcom.2010.11.005.; FCT/FEDER for funding CICECO and QOPNA

Pharmacokinetics of antiviral polyoxometalates in rats.

Ni, L; Boudinot, F D; Boudinot, S G; Henson, G W; Bossard, G E; Martellucci, S A; Ash, P W; Fricker, S P; Darkes, M C; Theobald, B R
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /03/1994 EN
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Polyoxometalates are soluble mineral compounds formed principally of oxide anions and early transition metal cations. The polyoxometalates K12H2[P2W12O48].24H2O (JM 1591), K10[P2W18Zn4(H2O)2O68].20H2O (JM 1596), and [(CH3)3NH]8[Si2W18Nb6O77] (JM 2820) demonstrate potent antiviral activity against human immunodeficiency virus types 1 and 2, herpes simplex virus, and cytomegalovirus in vitro. The preclinical pharmacokinetics of these three compounds were characterized after single-dose intravenous administration of 50 mg/kg to rats. Plasma, urine, and feces were collected for 168 h, and polyoxometalate concentrations were determined by atomic emission. Serum protein binding was measured by equilibrium dialysis. All three compounds were highly bound to serum proteins in a concentration-dependent manner. Total and unbound concentrations of the three compounds in plasma declined in a triexponential manner with terminal half-lives of 246.0 +/- 127.0, 438.4 +/- 129.4, and 32.2 +/- 5.37 h (mean +/- standard deviation) for JM 1591, JM 1596, and JM 2820, respectively. Systemic clearances based on total concentrations in plasma were low, averaging 0.016 +/- 0.002, 0.015 +/- 0.002, and 0.018 +/- 0.003 liter/h/kg for JM 1591, JM 1596, and JM 2820...

Surface charge of polyoxometalates modulates polymerization of the scrapie prion protein

Wille, Holger; Shanmugam, Maheswaran; Murugesu, Muralee; Ollesch, Julian; Stubbs, Gerald; Long, Jeffrey R.; Safar, Jiri G.; Prusiner, Stanley B.
Fonte: National Academy of Sciences Publicador: National Academy of Sciences
Tipo: Artigo de Revista Científica
EN
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Prions are composed solely of an alternatively folded isoform of the prion protein (PrP), designated PrPSc. N-terminally truncated PrPSc, denoted PrP 27–30, retains infectivity and polymerizes into rods with the ultrastructural and tinctorial properties of amyloid. We report here that some polyoxometalates (POMs) favor polymerization of PrP 27-30 into prion rods, whereas other POMs promote assembly of the protein into 2D crystals. Antibodies reacting with epitopes in denatured PrP 27-30 also bound to 2D crystals treated with 3 M urea. These same antibodies did not bind to either native PrPSc or untreated 2D crystals. By using small, spherical POMs with Keggin-type structures, the central heteroatom was found to determine whether prion rods or 2D crystals were preferentially formed. An example of a Keggin-type POM with a phosphorous heteroatom is the phosphotungstate anion (PTA). Both PTA and a Keggin-type POM with a silicon heteratom have low-charge densities and favor formation of prion rods. In contrast, POMs with boron or hydrogen heteroatoms exhibiting higher negative charges encouraged 2D crystal formation. The 2D crystals of PrP 27-30 produced by selective precipitation with POMs were larger and more well ordered than those obtained by sucrose gradient centrifugation. Our findings argue that the negative charge of Keggin-type POMs determines the quaternary structure adopted by PrP 27-30. The mechanism by which POMs function in competing prion polymerization pathways—one favoring 2D crystals and the other...

Fine-Tuning the Antimicrobial Profile of Biocompatible Gold Nanoparticles by Sequential Surface Functionalization Using Polyoxometalates and Lysine

Daima, Hemant K.; Selvakannan, P. R.; Shukla, Ravi; Bhargava, Suresh K.; Bansal, Vipul
Fonte: Public Library of Science Publicador: Public Library of Science
Tipo: Artigo de Revista Científica
Publicado em 17/10/2013 EN
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Antimicrobial action of nanomaterials is typically assigned to the nanomaterial composition, size and/or shape, whereas influence of complex corona stabilizing the nanoparticle surface is often neglected. We demonstrate sequential surface functionalization of tyrosine-reduced gold nanoparticles (AuNPsTyr) with polyoxometalates (POMs) and lysine to explore controlled chemical functionality-driven antimicrobial activity. Our investigations reveal that highly biocompatible gold nanoparticles can be tuned to be a strong antibacterial agent by fine-tuning their surface properties in a controllable manner. The observation from the antimicrobial studies on a gram negative bacterium Escherichia coli were further validated by investigating the anticancer properties of these step-wise surface-controlled materials against A549 human lung carcinoma cells, which showed a similar toxicity pattern. These studies highlight that the nanomaterial toxicity and biological applicability are strongly governed by their surface corona.

Transition metal ion-substituted polyoxometalates entrapped into polypyrrole as electrochemical sensor for hydrogen peroxide

Anwar, Nargis; Vagin, Mikhail; Laffir, Fathima R.; Armstrong, Gordon; Dickinson, Calum; McCormac, Timothy
Fonte: Royal Society of Chemistry Publicador: Royal Society of Chemistry
Tipo: info:eu-repo/semantics/article; all_ul_research; ul_published_reviewed
ENG
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peer-reviewed; A conducting polymer was used for the immobilization of various transition metal ion-substituted Dawson-type polyoxometalates (POMs) onto glassy carbon electrodes. Voltammetric responses of films of different thicknesses were stable within the pH domain 2-7 and reveal redox processes associated with 10 the conducting polymer, the entrapped POMs and incorporated metal ions. The resulting POM doped polypyrrole films were found to be extremely stable towards redox switching between the various redox states associated with the incorporated POM. An amperometric sensor for hydrogen peroxide detection based upon the POM doped polymer films was investigated. The detection limits were 0.3 and 0.6 uM, for the Cu2+- and Fe3+-substituted POM-doped polypyrrole films respectively, with a linear region from 15 0.1 up to 2mM H2O2. Surface characterization of the polymer films was carried out using atomic force microscopy, x-ray photoelectron spectroscopy and scanning electron microscopy.

Encapsulation of polyoxometalates within layered metal-organic frameworks with topological and pore control

He, Z.; Pang, Q.; Rankine, D.; Sumby, C.; Zhang, L.; Doonan, C.; Li, Q.
Fonte: Royal Society of Chemistry Publicador: Royal Society of Chemistry
Tipo: Artigo de Revista Científica
Publicado em //2013 EN
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Organic links of varied structure metrics and functionalities connect with Cu₂(COO)₄ clusters to afford layered metal–organic frameworks. Through topological and pore control, polyoxometalates could be synthetically encapsulated within the cavities. The templating effects of polyoxometalates and specific link functionalizations provide two strategies for controllably incorporating these active species into frameworks.; Zhi He, Qingqing Pang, Damien Rankine, Christopher J. Sumby, Lijuan Zhang, Christian J. Doonan and Qiaowei Li; First published online 28 Aug 2013

Molecule-Based Water-Oxidation Catalysts (WOCs): Cluster-Size-Dependent Dye-Sensitized Polyoxometalates for Visible-Light-Driven O2 Evolution

Gao, Junkuo; Cao, Shaowen; Tay, Qiuling; Liu, Yi; Yu, Lingmin; Ye, Kaiqi; Mun, Peter Choon Sze; Li, Yongxin; Rakesh, Ganguly; Loo, Say Chye Joachim; Chen, Zhong; Zhao, Yang; Xue, Can; Zhang, Qichun
Fonte: Nature Publishing Group Publicador: Nature Publishing Group
Tipo: Artigo de Revista Científica
Publicado em 16/05/2013 EN
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From atomic level to understand the cluster-size-dependant behavior of dye-sensitized photocatalysts is very important and helpful to design new photocatalytic materials. Although the relationship between the photocatalytic behaviors and particles' size/shape has been widely investigated by theoretical scientists, the experimental evidences are much less. In this manuscript, we successfully synthesized three new ruthenium dye-sensitized polyoxometalates (POM-n, n relate to different size clusters) with different-sized POM clusters. Under visible-light illumination, all three complexes show the stable O2 evolution with the efficient order POM-3 > POM-2 > POM-1. This cluster-size-dependent catalytic behavior could be explained by the different numbers of M = Ot (terminal oxygen) bonds in each individual cluster because it is well-known that Mo = Ot groups are the catalytically active sites for photooxidation reaction. The proposed mechanism of water oxidation for the dye-sensitized POMs is radical reaction process. This research could open up new perspectives for developing new POM-based WOCs.

Polyoxometalates as photoelectrochemical models for quantum-sized colloidal semiconducting oxides

Gómez-Romero, P.
Fonte: Elsevier Publicador: Elsevier
Tipo: Artículo Formato: 579917 bytes; image/jpeg
ENG
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Full-text version available Open Access at: http://www.cienciateca.com/POMs_Photo_SSI_97_101_243.pdf; A comparative analysis is made of the photoredox, electrochemical and electron storage properties of polyoxotungstate and polyoxomolybdate clusters in comparison with those of colloidal WO3 particles. Both species can harvest light and act as photocatalysts, but polyoxotungstates present a smaller size, wider gap, lower reduction potentials and greater tunability. Furthermore, WO3 colloids are structurally ill-characterized and tend to coagulate whereas polyoxometalate structures are well characterized, controllable and stable in solution. These characteristics and the confinement of injected electrons in a zero-dimensional nanometre-sized polynuclear molecule make of polyoxometalates remarkable models for colloidal quantum-sized semiconducting oxides.; Financial support by the former Spanish Ministry of Education and Science (presently Education and Culture) is gratefully acknowledged (DGICYT project PB93-0122).; Peer reviewed

Photoredox Chemistry in Oxide Clusters. Photochromic and Redox Properties of Polyoxometalates in Connection with Analog Solid State Colloidal Systems

Gómez-Romero, P.; Casañ Pastor, Nieves
Fonte: American Chemical Society Publicador: American Chemical Society
Tipo: Artículo Formato: 579917 bytes; image/jpeg
ENG
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Data on the electrochemical and photoredox chemistry of polyoxometalates of formula H4[SiW12O40] and H3[PMo12O40] are reported and analyzed in relation to those of related extended solids (WO3 and colloidal WO3 particles). These soluble multinuclear anions show reversible single-electron and multielectron reduction processes to yield blue mixed valent species. Similar reduced species can be obtained photochemically, with a concomitant oxidation of organic substrates. The reported photochromic behavior is similar to that of colloidal WO3 particles. On the other hand, electrochemical potentials differ substantially from the flat band potential of WO3 colloids. Finally, the title compounds are more stable and present the added advantage of having well-characterized monodisperse and controllable structures and tunable electrochemical properties; We thank the DGICYT (PB93-0122) (Spain) for financial support.; Peer reviewed

Nanocomposite hybrid molecular materials for application in solid-state electrochemical supercapacitors

Cuentas Gallegos, A. K.; Lira-Cantú, Monica; Casañ Pastor, Nieves; Gómez-Romero, P.
Fonte: John Wiley & Sons Publicador: John Wiley & Sons
Tipo: Artículo Formato: 579917 bytes; image/jpeg
ENG
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Texto completo en: http://www.cienciateca.com/SupercapPAniPOMs_Adv_Mater_2005_15_7_1125.pdf; Molecular hybrid materials formed from polyoxometalates dispersed in conducting polymers represent an innovative concept in energy storage. This work reports in detail the first practical realization of electrodes based on these materials for energy storage in electrochemical supercapacitors. The molecular hybrids PAni/H4SiW12O40, PAni/H3PW12O40, and PAni/H3PMo12O40 (PAni: polyaniline) have been prepared electrochemically on platinum or carbon substrates, with PAni/H3PMo12O40 being the prototypical example presenting the best energy-storage performance in the series. This hybrid displays the combined activity of its organic and inorganic components to store and release charge in solid-state electrochemical capacitor cells, leading to a promising value of 120 Fg-1 and good cyclability beyond 1000 cycles.; Peer reviewed

Polyoxometalates: from inorganic chemistry to materials science

Gómez-Romero, P.; Casañ Pastor, Nieves
Fonte: Frontiers in Bioscience Publications Publicador: Frontiers in Bioscience Publications
Tipo: Artículo Formato: 579917 bytes; image/jpeg
ENG
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Full-text available Open Access at: http://www.cienciateca.com/POMs%20Frontiers%20in%20Bioscience2004.pdf; Polyoxometalates have been traditionally the subject of study of molecular inorganic chemistry. Yet, these polynuclear molecules, reminiscent of oxide clusters, present a wide range of structures and with them ideal frameworks for the deployment of a plethora of useful magnetic, electroionic, catalytic, bioactive and photochemical properties. With this in mind, a new trend towards the application of these remarkable species in materials science is beginning to develop. In this review we analyze this trend and discuss two main lines of thought for the application of polyoxometalates as materials. On the one hand, there is their use as clusters with inherently useful properties on themselves, a line which has produced fundamental studies of their magnetic, electronic or photoelectrochemical properties and has shown these clusters as models for quantum-sized oxides. On the other hand, the encapsulation or integration of polyoxometalates into organic, polymeric or inorganic matrices or substrates opens a whole new field within the area of hybrid materials for harnessing the multifunctional properties of these versatile species in a wide variety of applications...

Electrochemical supercapacitors based on novel hybrid materials made of carbon nanotubes and polyoxometalates

Cuentas Gallegos, A. K.; Martínez-Rosales, Rosa; Baibarac, Mihaela; Gómez-Romero, P.; Rincón, Marina E.
Fonte: Elsevier Publicador: Elsevier
Tipo: Artículo Formato: 579917 bytes; image/jpeg
ENG
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We have characterized symmetric solid-state supercapacitors in swagelok cells using film electrodes made of novel hybrid materials based on multiwalled carbon nanotubes (CNT) and phosphomolybdate polyanion (Cs-PMo12) with PVA as binder. These hybrid materials were carried out by Cs-PMo12 adhesion onto previously functionalized CNT, in order to disperse both components at a molecular level and use Cs-PMo12 as energy density enhancer in supercapacitor cells. Our results show high capacitance values (up to 285 F/g at I = 200 mA/g) due to the contribution of Cs-PMo12, which was revealed on the higher energy density values compared to pure CNT electrodes. Additionally, good stability was observed during 500 charge–discharge cycles for most hybrid electrodes. These preliminary results show a new approach to enhance energy density of double layer supercapacitor cells through the introduction of Cs-PMo12, whereas from a material science point of view these materials are innovative, and open the way to search for diverse applications aside from supercapacitors (sensors, catalysts, photovoltaic cells, etc.); UNAM-MEXICO, Projects IN111106-3 and CVA06000004; Peer reviewed

Hybrid nanocomposite materials for energy storage and conversion applications

Gómez-Romero, P.; Cuentas Gallegos, A. K.; Lira-Cantú, Monica; Casañ Pastor, Nieves
Fonte: Springer Publicador: Springer
Tipo: Artículo Formato: 579917 bytes; image/jpeg
ENG
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Functional Hybrid materials based on conducting polymers and inorganic photo-electroactive species provide a wealth of opportunities for the development of novel materials with improved properties. Polyoxometalates are one type of well-known inorganic species with most interesting photo-electrochemical activity. They are perfect models for nanometer-sized oxide quantum-dots both concerning structure, topology and electrochemical and photochemical properties. Yet, they have not been applied as materials because of their molecular nature (i.e., soluble in most solvents or electrolytes). In our group we have recently developed a research line dealing with the integration of these fascinating clusters in conducting polymer matrices to yield functional hybrid materials. Our past emphasis was on electroactivity for energy-storage applications but these materials can also be used, as it is shown here, for photoelectrochemical applications.; The authors acknowledge partial financial support from the Ministry of Science and Technology (Spain) (Grant MAT2002-04529-C03) and express his deep gratitude for the total dedication of his Ph.D. students; Peer reviewed

Materiales híbridos moleculares orgánicos-inorgánicos: síntesis y aplicación como electrodos en baterías recargables de litio; Molecular Organic-Inorganic Hybrid Materials : Synthesis and Application as Electrodes in Lithium Rechargeable Batteries

Torres-Gómez, G.; Lira-Cantú, Monica; Gómez-Romero, P.
Fonte: Sociedad Española de Cerámica y Vidrio Publicador: Sociedad Española de Cerámica y Vidrio
Tipo: Artículo Formato: 291755 bytes; application/pdf
SPA
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[ES] Se describe la síntesis y aplicación como electrodos para el almacenamiento o conversión de energía de materiales híbridos basados en la dispersión de especies inorgánicas electroactivas en el seno de polímeros orgánicos conductores. Polianilina y polipirrol son dopados con polioxometalatos electroactivos ([PMo12O40]3-) o aniones ferricianuro ([(FeCN)6]3-) como únicas especies dopantes. La elevada carga y tamaño de estos aniones evitan, en la mayoría de los casos, su desintercalación durante la reducción. Estos híbridos se han sintetizado por métodos químicos y electroquímicos, siendo la relación anillos de anilina o de pirrol por anión de [PMo12O40]3- de nueve, de manera que el anión permanece en el interior de la matriz polimérica incluso después de reducir el material a -0.4V (vs Ag/AgCl, 2.6V vs Li). En el caso del híbrido Polipirrol/Fe(CN)6 la relación anillos de pirrol/anión oscila entre 10 y 12 dependiendo de la temperatura de síntesis. La temperatura también afecta a su conductividad eléctrica, oscilando los valores más elevados alrededor de 60 Scm-1 (preparado a 0ºC). El anión permanece en el interior de la matriz polimérica cuando se reduce en medio orgánico. Los híbridos con PMo12 pueden intercalar hasta 5.3 Li+ durante la descarga (52Ah/Kg). El híbrido con Fe(CN)6 intercala 2.7 iones litio por fórmula unidad (69Ah/Kg).; [EN] A novel family of molecular hybrid materials based on electroactive inorganic species dispersed in conducting organic polymers is reported as electrodes for energy storage or conversion. Polyaniline and polypyrrole are effectively doped with electroactive polyoxometalates ([PMo12O40]3-) or ferricyanide ([(FeCN)6]3-) anions as the only doping species. The high charge and size of these anions prevents their deintercalation during reduction in most cases. The synthesis of these hybrids can be made by chemical (bulk powders) and electrochemical (films) methods. For [PMo12O40]3-...

Molybdenum-Based Polyoxometalates as Highly Active and Selective Catalysts for the Epimerization of Aldoses

Ju, Feifei; VanderVelde, David; Nikolla, Eranda
Fonte: American Chemical Society Publicador: American Chemical Society
Tipo: Article; PeerReviewed Formato: application/pdf
Publicado em /05/2014
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In this contribution, we report on the high activity and selectivity of Keggin structure molybdenum-based polyoxometalates (POMs) in catalyzing the epimerization of aldoses. Near-equilibrium conversions and selectivities were obtained within the first hour of operation under aqueous conditions at relatively low temperatures and a wide range of pHs. Characterization of the molybdenum-based POM catalysts using X-ray diffraction and FTIR studies before and after the reaction showed no evidence of their decomposition. Our studies suggest that the active sites for the reaction are the molybdenum oxide octahedra on the surface of the Keggin structure of the molybdenum-based POMs (H_3PMo_(12)O_(40), Ag_3PMo_(12)O_(40), Sn_(0.75)PMo_(12)O_(40)). Further characterization of the system using ^(31)P NMR and X-ray photoelectron spectroscopy experiments showed that the interaction between the aldose (e.g., glucose) and the molybdenum oxide octahedra in the POM results in electron transfer from the aldose to molybdenum, leading to the formation of the reduced form of the POM (also known as heteropoly blue). Isotope labeling experiments demonstrated that the epimerization of glucose using molybdenum-based POMs proceeds via an intramolecular C1–C2 shift mechanism with an activation barrier of as low as 96 kJ/mol...

Towards an understanding of the bonding in polyoxometalates through bond order and bond energy analysis

Bridgeman, Adam; Cavigliasso, German
Fonte: Royal Society of Chemistry Publicador: Royal Society of Chemistry
Tipo: Artigo de Revista Científica
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The molecular and electronic structures of transition metal complexes, [MOCl5]n- (n = 2 for M = V,Nb,Ta and n = 1 for Mo,W) and mixed-metal polyoxometalates, [M′M5O19] 3- (M′ = V,Nb,Ta, M = Mo,W) containing a single terminal oxo group on each metal, a