Synthesis of ordered nanoporous carbon and its application in Li-ion battery

Ordered nanoporous carbon (ONC) was comprehensively tested for the first time as electrode material in lithium-ion battery. Structure characterization shows the order nanoporous structure and tiny crystallite structure of as-synthesized ONC. The electrochemical properties of this carbon were studied by galvanostatic cycling and cyclic voltammetry. Of special interest is that ONC gave no peak on its positive sweep of the cyclic voltammetry, which was different from other known anode materials. Besides, X-ray photoelectron spectroscopy (XPS) and XRD were also used to investigate the electrochemical characteristics of ONC. (c) 2006 Elsevier Ltd. All rights reserved.

Mechanisms of ion channel activation in primary cultured and clonal cell lines

The effects of hypotonic shock upon membrane C1 permeability of ROS 17/2.8 osteoblast-like cells was investigated using the patch-clamp technique. Hypotonic shock produced cell swelling that was accompanied by large amplitude, outwardly rectifying, currents that were active across the entire physiological range of membrane potentials (-80 to +100 mV). At strong depolarisations (> +50 mV) the currents exhibited time-dependent inactivation that followed a monoexponential time course. The currents were anion selective and exhibited a selectivity sequence of SCN- > I > Br- > Cl- > F- > gluconate. Current activation was unaffected by inhibitors of protein kinase (A (H-89) and tyrosine kinase (tyrphostin A25), and could not be mimicked by elevation of intracellular Ca2+ or activation of protein kinase C. Similarly, disruption of actin filaments by dihydrocytochalsin B, or generation of membrane tension by dipyridamole failed to elicit significant increases in cell chloride permeability. The mechanism of current activation is as yet undetermined. The currents were effectively inhibited by the chloride channel inhibitors NPPB and DIDS but resistant to DPC. A Cl- conductance with similar characteristics was found to be present in mouse primary cultured calvarial osteoblasts. The volume-sensitive Cl- current in ROS 17/2.8 cells was inhibited by arachidonic acid in two distinct phases. A rapid block that developed within 10 s, preceding a slower developing inhibitory phase that occurred approximately 90 s after onset of arachidonate superfusion. Arachidonic acid also induced kinetic modifications of the current which were evident as an acceleration of the time-dependent· inactivation exhibited at depolarised potentials. Inhibitors of cyclo-oxygenases, lipoxygenases and cytochrome P-4S0 were ineffectual against arachidonic acid's effects sugtgesting that arachidonic acid may elicit it's effects directly. Measurements of cell volume under hypotonic conditions showed that ROS 17/2,8 cells could effectively regulate their volume, However, effective inhibitors of the volume-sensitive CI" current drastically impaired this response suggesting that physiologically this current may have a vital role in cell volume regulation, In L6 skeletal myocytes, vasopressin was found to rapidiy hyperpolarise cells. This appears to occur as the result of activation of Ca2+ -sensitive K+ channels in a process dependent upon the presence of extracellular Ca2+.

Ion plating

Under ideal conditions ion plating produces finely grained dense coatings with excellent adhesion. The ion bombardment induced damage initiates a large number of small nuclei. Simultaneous coating and sputtering stimulates high rates of diffusion and forms an interfacial region of graded composition responsible for good adhesion. To obtain such coatings on components far industrial applications, the design and construction Of an ion plater with a 24" (O.6rn) diameter chamber were investigated and modifications of the electron beam gun were proposed. A 12" (O.3m) diameter ion plater was designed and constructed. The equipment was used to develop surfaces for solar energy applications. The conditions to give extended surfaces by sputter etching were studied. Austenitic stainless steel was sputter etched at 20 and 30 mTorr working pressure and at 3, 4 and 5 kV. Uniform etching was achieved by redesigning the specimen holder to give a uniform electrostatic field over the surfaces of the specimens. Surface protrusions were observed after sputter etching. They were caused by the sputter process and were independent of grain boundaries, surface contaminants and inclusions. The sputtering rate of stainless steel was highly dependent on the background pressure which should be kept below 10-5 Torr. Sputter etching improved the performance of stainless steel used as a solar selective surface. A twofold improvement was achieved on sputter etching bright annealed stainless steel. However, there was only slight improvement after sputter etching stainless steel which had been mechanically polished to a mirror finish. Cooling curves Were used to measure the thermal emittance of specimens.The deposition rate of copper was measured at different levels of power input and was found to be a maximum at 9.5 kW. The diameter of the copper feed rod was found to be critical for the maintenance of a uniform evaporation rate.

Ion interactions with the carbon nanotube surface in aqueous solutions:understanding the molecular mechanisms

We study the molecular mechanisms of alkali halide ion interactions with the single-wall carbon nanotube surface in water by means of fully atomistic molecular dynamics simulations. We focus on the basic physical-chemical principles of ion–nanotube interactions in aqueous solutions and discuss them in light of recent experimental findings on selective ion effects on carbon nanotubes.

Transition metal ion co-ordination in hydrophilic polymer membrane

This thesis is concerned with the investigation of transition metal (TM) ion complexation with hydrophilic membranes composed of copolymers of 4-vinyl pyridine & 4-methyl-4'vinyl- 2,2'-bipyridine with 2-hydroxyethyl methacrylate. The Cu(II), CoCII) & Fe(II) complexes with these coordinating membranes were characterised by a variety of techniques, in order to assess the effect of the polymer on the properties of the complex, and vice versa. A detailed programme of work was instigated into the kinetics of formation for the polymer-bound tris(bipyridyl) iron(II) complex; the rate and extent of complex formation was found to be anion-dependent. This is explained in terms of the influence of the anion on the transport properties and water content of the membrane, the controlling factor in the development of the tris-complex being the equilibrium concentration of Fe(II) in the gel matrix. A series of transport studies were performed with a view to the potential application of complexing hydrogel membranes for aqueous TM ion separations. A number of salts were studied individually and shown to possess a range of permeabilities; the degree of interaction between particular metal-ion:ligand combinations is given by the lag-time observed before steady-state permeation is achieved. However, when two TM salts that individually display different transport properties were studied in combination, they showed similar lag-times & permeabilities, characteristic of the more strongly coordinating metal ion. This 'anti-selective' nature thus renders the membrane systems unsuitable for TM ion separations. Finally, attempts were made to synthesise and immobilise a series of N ,0-donor macrocyclic ligands into hydrogel membranes. Although the functionalisation reactions failed, limited transport data was obtained from membranes in which the ligands were physically entrapped within the polymer matrix.

Development of an enantiomer selective microsampling assay for the quantification of ketorolac suitable for paediatric pharmacokinetic studies

Background: Ketorolac, a potent nonsteroidal anti-inflammatory drug used for pain control in children, exists as a racemate of inactive R (+) and active S (-) enantiomers. Aim: To develop a microsampling assay for the enantioselective analysis of ketorolac in children. Methods: Ketorolac enantiomers were extracted from 50 µl of plasma by liquid–liquid extraction and separated on a ChiralPak AD-RH. Detection was by a TSQ quantum triple quadrupole mass spectrometer with an electrospray ionisation source operating in a positive ion mode. Five children (age 13.8 (1.6) years, weight 52.7 (7.2) kg), were administered intravenous ketorolac 0.5 mg/kg (maximum 10 mg) and blood samples were taken at 0, 0.25, 0.5, 1, 2, 4, 6, 8 and 12 h post administration. CL, VD and t1/2 were calculated based on non-compartmental methods. Results: The standard curves for R (+) and S (-) ketorolac were linear in the range 0–2000 ng/ml. The LLOQs of the method were 0.15 ng on column and 0.31 ng on column for R (+) and S (-) ketorolac, respectively. The median (range) VD and CL of R (+) and S (-) ketorolac were 0.12 l/kg (0.07–0.17), 0.017 l/h/kg (0.12–0.29) and 0.17 (0.09–0.31) l/kg, 0.049 (0.02–0.1) l/h/kg, p = 0.043), respectively. The median (range) elimination half-life (t1/2) of the R (+) and S (-) ketorolac was 5.0 h (2.5–5.8) and 3.1 h (1.8–4.4), p = 0.043), respectively. Conclusion: The development of a simple, rapid and reliable ketorolac assay suitable for paediatric PK studies is reported. Copyright © 2013 John Wiley & Sons, Ltd.

Highly selective Pd/titanate nanotube catalysts for the double-bond migration reaction

Pd(II) and Pd(0) catalysts supported onto titanate nanotubes (H2Ti3O7) were prepared by an ion-exchange technique. The catalysts are characterised by narrow size distribution of metal nanoparticles on the external surface of the nanotubes. Pd(II) catalysts show high selectivity toward double-bond migration reaction versus hydrogenation in linear olefins. The catalytic activity exhibits a volcano-type dependence on the metal loading, with the maximum activity observed at ca. 8 wt%. The Pd(II) was shown to be rapidly reduced to Pd(0) by appropriate choice of solvent. Prereduced Pd(0) catalysts were found to be less active toward double-bond migration and more selective toward hydrogenation. The DBM reaction was faster in protic solvents, such as methanol or ethanol. © 2006 Elsevier Inc. All rights reserved.

Estudo de métodos de tratamento de efluentes (troca iônica e eletroquímico) separados e sequenciais para eliminação de derivados de petróleo

The produce of waste and the amount of the water produced coming from activities of petroleum production and extraction has been a biggest challenge for oil companies with respect to environmental compliance due to toxicity. The discard or the reuse this effluent containing organic compounds as BTEX (benzene, toluene, ethylbenzene and xylene) can cause serious environmental and human health problems. Thus, the objective this paper was study the performance of two process (separately and sequential) in one synthetic effluent for the benzene, toluene and xylene removal (volatile hydrocarbons presents in the produced water) through of electrochemical treatment using Ti/Pt electrode and exchange resin ionic used in the adsorption process. The synthetic solution of BTX was prepared with concentration of 22,8 mg L-1, 9,7 mg L-1 e 9,0 mg L-1, respectively, in Na2SO4 0,1 mol L-1. The experiments was developed in batch with 0.3 L of solution at 25ºC. The electrochemical oxidation process was accomplished with a Ti/Pt electrode with different current density (J = 10, 20 e 30 mA.cm-2). In the adsorption process, we used an ionic exchange resin (Purolite MB 478), using different amounts of mass (2,5, 5 and 10 g). To verify the process of technics in the sequential treatment, was fixed the current density at 10 mA cm-2 and the resin weight was 2.5 g. Analysis of UV-VIS spectrophotometry, chemical oxygen demand (COD) and gas chromatography with selective photoionization detector (PID) and flame ionization (FID), confirmed the high efficiency in the removal of organic compounds after treatment. It was found that the electrochemical process (separate and sequential) is more efficient than absorption, reaching values of COD removal exceeding 70%, confirmed by the study of the cyclic voltammetry and polarization curves. While the adsorption (separately), the COD removal did not exceed 25,8%, due to interactions resin. However, the sequential process (electrochemical oxidation and adsorption) proved to be a suitable alternative, efficient and cost-effectiveness for the treatment of effluents petrochemical.

Application of Numerical Methods to Study Arrangement and Fracture of Lithium-Ion Microstructure

The focus of this work is to develop and employ numerical methods that provide characterization of granular microstructures, dynamic fragmentation of brittle materials, and dynamic fracture of three-dimensional bodies.

We first propose the fabric tensor formalism to describe the structure and evolution of lithium-ion electrode microstructure during the calendaring process. Fabric tensors are directional measures of particulate assemblies based on inter-particle connectivity, relating to the structural and transport properties of the electrode. Applying this technique to X-ray computed tomography of cathode microstructure, we show that fabric tensors capture the evolution of the inter-particle contact distribution and are therefore good measures for the internal state of and electronic transport within the electrode.

We then shift focus to the development and analysis of fracture models within finite element simulations. A difficult problem to characterize in the realm of fracture modeling is that of fragmentation, wherein brittle materials subjected to a uniform tensile loading break apart into a large number of smaller pieces. We explore the effect of numerical precision in the results of dynamic fragmentation simulations using the cohesive element approach on a one-dimensional domain. By introducing random and non-random field variations, we discern that round-off error plays a significant role in establishing a mesh-convergent solution for uniform fragmentation problems. Further, by using differing magnitudes of randomized material properties and mesh discretizations, we find that employing randomness can improve convergence behavior and provide a computational savings.

The Thick Level-Set model is implemented to describe brittle media undergoing dynamic fragmentation as an alternative to the cohesive element approach. This non-local damage model features a level-set function that defines the extent and severity of degradation and uses a length scale to limit the damage gradient. In terms of energy dissipated by fracture and mean fragment size, we find that the proposed model reproduces the rate-dependent observations of analytical approaches, cohesive element simulations, and experimental studies.

Lastly, the Thick Level-Set model is implemented in three dimensions to describe the dynamic failure of brittle media, such as the active material particles in the battery cathode during manufacturing. The proposed model matches expected behavior from physical experiments, analytical approaches, and numerical models, and mesh convergence is established. We find that the use of an asymmetrical damage model to represent tensile damage is important to producing the expected results for brittle fracture problems.

The impact of this work is that designers of lithium-ion battery components can employ the numerical methods presented herein to analyze the evolving electrode microstructure during manufacturing, operational, and extraordinary loadings. This allows for enhanced designs and manufacturing methods that advance the state of battery technology. Further, these numerical tools have applicability in a broad range of fields, from geotechnical analysis to ice-sheet modeling to armor design to hydraulic fracturing.

Transient Receptor Potential Vanilloid 4 Ion Channel Functions as a Pruriceptor in Epidermal Keratinocytes to Evoke Histaminergic Itch.

TRPV4 ion channels function in epidermal keratinocytes and in innervating sensory neurons; however, the contribution of the channel in either cell to neurosensory function remains to be elucidated. We recently reported TRPV4 as a critical component of the keratinocyte machinery that responds to ultraviolet B (UVB) and functions critically to convert the keratinocyte into a pain-generator cell after excess UVB exposure. One key mechanism in keratinocytes was increased expression and secretion of endothelin-1, which is also a known pruritogen. Here we address the question of whether TRPV4 in skin keratinocytes functions in itch, as a particular form of "forefront" signaling in non-neural cells. Our results support this novel concept based on attenuated scratching behavior in response to histaminergic (histamine, compound 48/80, endothelin-1), not non-histaminergic (chloroquine) pruritogens in Trpv4 keratinocyte-specific and inducible knock-out mice. We demonstrate that keratinocytes rely on TRPV4 for calcium influx in response to histaminergic pruritogens. TRPV4 activation in keratinocytes evokes phosphorylation of mitogen-activated protein kinase, ERK, for histaminergic pruritogens. This finding is relevant because we observed robust anti-pruritic effects with topical applications of selective inhibitors for TRPV4 and also for MEK, the kinase upstream of ERK, suggesting that calcium influx via TRPV4 in keratinocytes leads to ERK-phosphorylation, which in turn rapidly converts the keratinocyte into an organismal itch-generator cell. In support of this concept we found that scratching behavior, evoked by direct intradermal activation of TRPV4, was critically dependent on TRPV4 expression in keratinocytes. Thus, TRPV4 functions as a pruriceptor-TRP in skin keratinocytes in histaminergic itch, a novel basic concept with translational-medical relevance.

UVB radiation generates sunburn pain and affects skin by activating epidermal TRPV4 ion channels and triggering endothelin-1 signaling.

At our body surface, the epidermis absorbs UV radiation. UV overexposure leads to sunburn with tissue injury and pain. To understand how, we focus on TRPV4, a nonselective cation channel highly expressed in epithelial skin cells and known to function in sensory transduction, a property shared with other transient receptor potential channels. We show that following UVB exposure mice with induced Trpv4 deletions, specifically in keratinocytes, are less sensitive to noxious thermal and mechanical stimuli than control animals. Exploring the mechanism, we find that epidermal TRPV4 orchestrates UVB-evoked skin tissue damage and increased expression of the proalgesic/algogenic mediator endothelin-1. In culture, UVB causes a direct, TRPV4-dependent Ca(2+) response in keratinocytes. In mice, topical treatment with a TRPV4-selective inhibitor decreases UVB-evoked pain behavior, epidermal tissue damage, and endothelin-1 expression. In humans, sunburn enhances epidermal expression of TRPV4 and endothelin-1, underscoring the potential of keratinocyte-derived TRPV4 as a therapeutic target for UVB-induced sunburn, in particular pain.

The structural conversion from α-AgVO3 to β-AgVO3: Ag nanoparticle decorated nanowires with application as cathode materials for Li-ion batteries

The majority of electrode materials in batteries and related electrochemical energy storage devices are fashioned into slurries via the addition of a conductive additive and a binder. However, aggregation of smaller diameter nanoparticles in current generation electrode compositions can result in non-homogeneous active materials. Inconsistent slurry formulation may lead to inconsistent electrical conductivity throughout the material, local variations in electrochemical response, and the overall cell performance. Here we demonstrate the hydrothermal preparation of Ag nanoparticle (NP) decorated α-AgVO3 nanowires (NWs) and their conversion to tunnel structured β-AgVO3 NWs by annealing to form a uniform blend of intercalation materials that are well connected electrically. The synthesis of nanostructures with chemically bound conductive nanoparticles is an elegant means to overcome the intrinsic issues associated with electrode slurry production, as wire-to-wire conductive pathways are formed within the overall electrode active mass of NWs. The conversion from α-AgVO3 to β-AgVO3 is explained in detail through a comprehensive structural characterization. Meticulous EELS analysis of β-AgVO3 NWs offers insight into the true β-AgVO3 structure and how the annealing process facilitates a higher surface coverage of Ag NPs directly from ionic Ag content within the α-AgVO3 NWs. Variations in vanadium oxidation state across the surface of the nanowires indicate that the β-AgVO3 NWs have a core–shell oxidation state structure, and that the vanadium oxidation state under the Ag NP confirms a chemically bound NP from reduction of diffused ionic silver from the α-AgVO3 NWs core material. Electrochemical comparison of α-AgVO3 and β-AgVO3 NWs confirms that β-AgVO3 offers improved electrochemical performance. An ex situ structural characterization of β-AgVO3 NWs after the first galvanostatic discharge and charge offers new insight into the Li+ reaction mechanism for β-AgVO3. Ag+ between the van der Waals layers of the vanadium oxide is reduced during discharge and deposited as metallic Ag, the vacant sites are then occupied by Li+.

Effect of the Electrolyte Formulation on the Performances of Edlc and Li-Ion Batteries

One of the most important components in electrochemical storage devices (batteries and supercapacitors) is undoubtedly the electrolyte. The basic function of any electrolyte in these systems is the transport of ions between the positive and negative electrodes. In addition, electrochemical reactions occurring at each electrode/electrolyte interface are the origin of the current generated by storage devices. In other words, performances (capacity, power, efficiency and energy) of electrochemical storage devices are strongly related to the electrolyte properties, as well as, to the affinity for the electrolyte to selected electrode materials. Indeed, the formulation of electrolyte presenting good properties, such as high ionic conductivity and low viscosity, is then required to enhance the charge transfer reaction at electrode/electrolyte interface (e.g. charge accumulation in the case of Electrochemical Double Layer Capacitor, EDLC). For practical and safety considerations, the formulation of novel electrolytes presenting a low vapor pressure, a large liquid range temperature, a good thermal and chemical stabilities is also required.

This lecture will be focused on the effect of the electrolyte formulation on the performances of electrochemical storage devices (Li-ion batteries and supercapacitors). During which, a summary of the physical, thermal and electrochemical data obtained by our group, recently, on the formulation of novel electrolyte-based on the mixture of an ionic liquid (such as EmimNTf2 and Pyr14NTf2) and carbonate or dinitrile solvents will be presented and commented. The impact of the electrolyte formulation on the storage performances of EDLC and Li-ion batteries will be also discussed to further understand the relationship between electrolyte formulation and electrochemical performances. This talk will also be an opportunity to further discuss around the effects of additives (SEI builder: fluoroethylene carbonate and vinylene carbonate), ionic liquids, structure and nature of lithium salt (LiTFSI vs LiPF6) on the cyclability of negative electrode to then enhance the electrolyte formulation. For that, our recent results on TiSnSb and graphite negative electrodes will be presented and discussed, for example 1,2.

1-C. Marino, A. Darwiche1, N. Dupré, H.A. Wilhelm, B. Lestriez, H. Martinez, R. Dedryvère, W. Zhang, F. Ghamouss, D. Lemordant, L. Monconduit “ Study of the Electrode/Electrolyte Interface on Cycling of a Conversion Type Electrode Material in Li Batteries” J. Phys.chem. C, 2013, 117, 19302-19313

2- Mouad Dahbi, Fouad Ghamouss, Mérièm Anouti, Daniel Lemordant, François Tran-Van “Electrochemical lithiation and compatibility of graphite anode using glutaronitrile/dimethyl carbonate mixtures containing LiTFSI as electrolyte” 2013, 43, 4, 375-385.

High resolution Thomson Parabola Spectrometer for full spectral capture of multi-species ion beams

We report on the experimental characterisation of laser-driven ion beams using a Thomson Parabola Spectrometer (TPS) equipped with trapezoidally shaped electric plates, proposed by Gwynne et al. [Rev. Sci. Instrum. 85, 033304 (2014)]. While a pair of extended (30 cm long) electric plates was able to produce a significant increase in the separation between neighbouring ion species at high energies, deploying a trapezoidal design circumvented the spectral clipping at the low energy end of the ion spectra. The shape of the electric plate was chosen carefully considering, for the given spectrometer configuration, the range of detectable ion energies and species. Analytical tracing of the ion parabolas matches closely with the experimental data, which suggests a minimal effect of fringe fields on the escaping ions close to the wedged edge of the electrode. The analytical formulae were derived considering the relativistic correction required for the high energy ions to be characterised using such spectrometer.

Síntese e estudo de polioxotungstatos do tipo Keggin com interesse catalítico

O objectivo principal deste trabalho foi estudar as propriedades e comportamento de polioxotungstatos (POM) do tipo Keggin com interesse em catálise oxidativa. Os estudos efectuados centraram-se no comportamento electroquímico dos aniões em meio não aquoso, na estabilidade das suas estruturas em diferentes meios, na sua capacidade de catalisar a oxidação de diferentes substratos orgânicos e na sua eficácia em oxidar, de forma selectiva, um modelo não fenólico da lenhina. Efectuou-se, igualmente, o estudo estrutural de diversos aniões pela técnica de EXAFS. Neste trabalho, prepararam-se e caracterizaram-se alguns dos sais de tetra-n-butilamónio (TBA) dos polioxotungstatos estudados: compostos de Keggin, TBAx[XW12O40], lacunares, TBAxHy[XW11O39], mono-substituídos, TBAxHy[XW11M(H2O)O39]·nH2O, com X= P e Si e M = CoII, NiII, ZnII, CuIl, RuIII, MnIII e FeIII e os compostos com mistura de átomos adenda TBAx[XW11VO40]·nH2O (X = P e Si). Seleccionou-se este conjunto de polioxotungstatos de forma a efectuar-se um estudo comparativo da influência da natureza do heteroátomo central (P e Si) e dos metais de transição M nas propriedades estudadas. O conjunto de sais de TBA dos silicotungstatos estudados mostraram ser isoestruturais, apresentando a mesma estrutura dos fosfotungstatos análogos. O comportamento electroquímico dos polioxotungstatos foi estudado em soluções de acetonitrilo por voltametria cíclica e electrólise a potencial controlado. Verificou-se a ocorrência de vários processos mono-electrónicos de oxi-redução, reversíveis ou quasi-reversíveis, associados aos átomos de WVI/V e a alguns dos metais de transição. Os metais em estado de oxidação +3 reduziram-se mais facilmente do que os átomos de WVI. O metal CuII apresentou um comportamento diferente dos outros metais de transição. Este metal, na estrutura do POM, reduziu-se a CuI, proporcionando a observação do anião [PW11CuIO39]6- pela primeira vez. A redução posterior do CuI conduziu à formação de Cu0, que se depositou na superfície do eléctrodo. A re-oxidação do cobre a CuII conduziu à reconstituição da estrutura do POM, nas condições estudadas. Constatou-se que a ocorrência de protões na fórmula molecular dos POMs influenciou o seu comportamento electroquímico. Para os compostos que apresentam protões, a redução dos átomos de tungsténio ocorreu a potenciais menos negativos do que para aqueles que não apresentam protões na sua fórmula. Para os primeiros observou-se a transferência global de um maior número de electrões no mesmo intervalo de potencial, originando soluções fortemente azuladas. Quando os catiões tetra-n-butilamónio foram substituídos por catiões de menor dimensão, como Li+ e Na+, ocorreu a formação de pares iónicos com os polianiões [PW12O40]3- e [SiW11VO40]5-, originando um aumento do potencial de redução. Não houve evidência da formação de pares iónicos com os catiões TBA+. Este foi o primeiro estudo sistemático do comportamento electroquímico dos aniões lacunares e mono-substituídos em meio não aquoso. Estudou-se a estrutura dos polioxotungstatos em sais de TBA e em soluções de acetonitrilo. A aplicação da técnica de EXAFS ao estudo deste tipo de compostos em solução foi realizada pela primeira vez. Pela análise estrutural nos sólidos verificou-se que, a natureza do metal de transição M e do átomo central X, na estrutura do POM, influenciam o tamanho dos vários octaedros que o constituem. Não se observaram diferenças significativas nas estruturas dos polianiões em solução. A estabilidade da estrutura dos polioxometalatos na presença de um excesso de H2O2, em soluções de acetonitrilo/H2O foi analisada por espectroscopia de absorção de EXAFS, RMN de 31P, IV e espectrofotometria de absorção no UV-Vis. De uma forma geral, os POMs em que o átomo central da estrutura é o Si apresentaram maior estabilidade do que os POMs correspondentes com átomo de P no centro. Em solução de acetonitrilo, na ausência de H2O2, todos os aniões mostraram ser estáveis durante vários dias. Em solução, na presença de H2O2 em excesso (H2O2/POM = 1300), o anião lacunar [PW11O39]7- não é estável, transformando-se no anião de Venturello, {PO4[W(O)(O2)2]4}3-, após a formação de [PW12O40]3-, como produto intermediário. Em relação aos aniões substituídos [PW11M(H2O)O39]p-, M = MnIII, RuIII, FeIII, CoII e ZnII, verificou-se o seguinte na presença de H2O2: os aniões com MnIII e CoII transformaram-se no anião de Keggin, [PW12O40]3-. Os aniões de RuIII e FeIII mantiveram as suas estruturas e o anião de ZnII decompôs-se em {HPO4[W(O)(O2)2]2}2- e fosfato. Para estes casos de não estabilidade estrutural, o processo de decomposição foi mais rápido na presença de maiores conteúdos de água. Pela análise de EXAFS, na presença de um menor excesso de H2O2 (H2O2/POM = 70) e apenas 8% de parte aquosa, verificou-se que os aniões substituídos por MnIII mantiveram a sua estrutura, embora o ligando H2O, coordenado ao Mn, tivesse sido substituído por um grupo oxo no polianião [SiW11Mn(H2O)O39]5-, e por um grupo peroxo no polianião [PW11Mn(H2O)O39]4-. O anião com RuIII, nestas condições, também mostrou substituir o seu ligando H2O por um grupo peroxo ou hidrogenoperoxo. Os polioxotungstatos mono-substituídos e lacunares mostraram ser catalisadores eficientes para a oxidação de cis-cicloocteno, geraniol e ciclooctano com H2O2. A maior novidade deste trabalho residiu na actividade catalítica apresentada pelos silicotungstatos estudados, contrariando o que é referido na literatura. Outro aspecto inovador foi o elevado valor de conversão obtido para a oxidação de ciclooctano. Este substrato foi oxidado com 74% de conversão, após 2h de reacção e com 80% de selectividade para o hidroperóxido de ciclooctilo, na presença do anião [PW11Fe(H2O)O39]4-. Os restantes produtos de reacção foram o ciclooctanol e a ciclooctanona. Os silicotungstatos apresentaram maior selectividade para o hidroperóxido de ciclooctilo do que os fosfotungstatos. O geraniol foi completamente oxidado após 3h de reacção, com 82% de selectividade para o 2,3-epoxigeraniol, na presença do anião [PW11Mn(H2O)O39]4-. O cis-cicloocteno foi oxidado ao seu epóxido, com 92% de conversão ao fim de 5h de reacção, na presença do anião lacunar [PW11O39]7-. O estudo da capacidade oxidativa do anião [SiW11VO40]5- foi analisada utilizando-se um modelo não fenólico da lenhina, a anisoína. Estudaram-se as condições favoráveis à obtenção de uma reacção selectiva para o anisilo, de forma a poder estudar-se a cinética da reacção. A estequiometria da reacção mostrou ser de 1:2 anisoína/POM. As ordens de reacção foram determinadas pelo método das velocidades iniciais e, a partir destes resultados, conheceu-se que o POM não estava envolvido no passo que limita a velocidade da reacção, sendo esta limitada pela transformação da anisoína. O estudo realizado sobre o efeito isotópico sugeriu que o passo que limitou a velocidade de reacção correspondeu à enolação da anisoína. Desta forma, observou-se pela primeira vez, que o POM oxida um modelo não fenólico da lenhina por via de enolação.