Emmanuel Baudrin

Synthesis and Electrochemical Properties of Vanadium Oxide Aerogels Prepared by a Freeze-Drying Process

Vanadium oxide aerogels have received considerable interest as a reversible electrode material for lithium secondary batteries. The aerogel morphology is a critical factor in obtaining the electrochemical properties of these materials. The present paper reports on the synthesis of V 2 O 5 by freeze-drying, an alternative approach for producing a material with an aerogel-like morphology. In this synthesis, the sublimation of cyclohexane circumvents the capillary pressures which cause pore collapse during the normal solvent removal process. The resulting materials are very porous with specific surface areas as high as 250 m 2 /g. The electrochemical properties of the freeze-dried material are strongly influenced by both the specific surface area of the solid phase and crystallite size. The controlled heat-treatment of the aerogel produces a ω-Li x V 2 O 5 -type phase with improved capacity and reversibility.

Low temperature synthesis and electrochemical performance of crystallized FeVO4·1.1H2O

Abstract A wet synthesis method, which consists in a precipitation reaction occurring without pH control, is described to obtain a hydrated crystallized iron orthovanadate. Both reaction time and temperature parameters were used to reach the thermodynamic equilibrium formation conditions of FeVO4·1.1H2O. By means of several characterization techniques this compound was identified as similar to the fervanite mineral Fe4V4O16·5H2O. Like the other iron-based orthovanadates, this fervanite-type phase displays unusual electrochemical properties with respect to Li acceptance/removal at low average voltages. From the electrochemical data collected on the artificial fervanite and its dehydrated products, a linear correlation between the material water content and its electrochemical performances, namely in terms of irreversible and reversible capacities, has been found.

A Core–Corona Hierarchical Manganese Oxide and its Formation by an Aqueous Soft Chemistry Mechanism

One of the main challenges that still needs to be overcome in the design of nanotextured materials is the synthesis of uniform complex architectures. Indeed, many properties are known to be greatly modified by the size and shape of nanostructures. Other than size and shape tailoring, however, control of the ordering between nanostructures and the resulting texture is still difficult. Synthetic routes that make use of organic solvents and templates (i.e., surfactants) often require subsequent purification procedures which significantly increase production costs. The development of environmentally friendly, low-cost, and template-free synthetic methods that produce complex architectures is therefore key to enhancing both the control of the properties and the viability of such materials. In this context, porous manganese oxide materials are attracting great interest due to their applicability in domains such as ion-exchange, catalysis, and energy storage in Li batteries and supercapacitors. Indeed, layered birnessitelike manganese oxides (LMO) are particularly relevant due to their lamellar structure, which contain layers of MnO6 octahedra between which different species can be intercalated (see Figure S1 in the Supporting Information). However, the design of ordered LMO architectures remains a significant challenge as their synthesis usually takes place in an aqueous medium by sol–gel or precipitation methods, both of which result in fast and uncontrolled solid growth that hinders the synthesis of well-ordered nanostructures. Herein we present a low-temperature aqueous precipitation of potassium-intercalated LMO with a peculiar hierarchical core–corona architecture in the absence of both a template and an organic medium. Particle formation takes place in an easy “one-pot” process involving two distinct precipitation kinetic stages. The synthesis of similar inorganic/ inorganic core–corona morphologies generally requires two steps for core formation and shell growth, and there are very few reports concerning one-pot procedures that lead to fully inorganic core–shell particles. Furthermore, these methods are generally limited to metal–oxide structures. The approach presented herein, which uses in situ seeding to control the solid growth, significantly broadens the range of strategies available for the elaboration of hierarchical inorganic structures and can be extended to the design of new functional nanostructured materials, by taking advantage of the unique oxide properties, in areas such as catalysis, energy harnessing, and information storage. The synthesis of birnessite (see the Experimental Section and the Supporting Information) is based on the redox reaction between MnSO4 and an excess of KMnO4 [4f, 5b] (total Mn concentration of 0.2 molL ) in water according to Equation (1). Mixing the acidic (pH 2) solutions of the

Pulsed Laser Deposition and Electrochemical Properties of LiFePO4 Thin Films

Well-crystallized and homogeneous LiFePO 4 films, of the order of 300 nm thick, have been grown by pulsed laser deposition on Pt-capped Si substrates in a one-step process. Their intrinsic lithium insertion properties have been evaluated both in aqueous and nonaqueous electrolytes. The films show the electrochemical fingerprint characteristic of pure triphylite LiFePO 4 , with, namely, equilibrium voltage at 3.42 V vs. Li + /Li. While carbon-free, the kinetic of the insertion/deinsertion process in such films compared favorably with those of optimized carbon-coated LiFePO 4 powders. Furthermore, we demonstrate sensor responses of these thin-film LiFePO 4 electrodes toward the quantitative detection of Li + ions in aqueous solutions as long as their concentration ranges from 10 - 4 to I M.

Structural and morphological control of manganese oxide nanoparticles upon soft aqueous precipitation through MnO4−/Mn2+ reaction

A low-temperature (60 or 95 °C) “one-pot” procedure for the aqueous precipitation of manganese oxide nanoparticles is developed through the MnO4−/Mn2+ reaction. Characterization of the particles is carried out using elemental analysis, mean oxidation state determination, powder XRD, FESEM, TEM and electron diffraction. Many synthesis parameters are investigated, such as acidity, reactant ratio, concentration and nature of the counter-cation, temperature and aging time. Speciation diagrams are drawn for the synthesis of five different pure phases (spinel-type Mn3O4, layered birnessite-type δ-MnO2, tunnel-based frameworks cryptomelane-type α-MnO2, γ-MnO2 and pyrolusite β-MnO2). The influence of synthetic parameters is rationalized and reaction pathways toward various structures and morphologies are discussed.

Selective heterogeneous oriented attachment of manganese oxide nanorods in water: toward 3D nanoarchitectures

MnOOH and MnO2 polymorphs are synthesized using a reaction between Mn2+and MnO4− in water at low temperature (95 °C). Nanoparticles are characterized using powder XRD, TEM and electron diffraction. Depending on the acidity of the aging medium, γ-MnO2 compounds are shown to be obtained as nanorods (final pH = 2.0) or hollow nanocones (3.6 ≤ final pH ≤ 4.5). The external faces of the cones originate from heterogeneous oriented attachment of α-MnOOH nanorods on early cones. The selective attachment between (−110)γ–MnO2 and (101)α–MnOOH faces is discussed by taking into account the surface charge of the primary particles and the reactivity of the Mn–OHx surface groups. This study underlines the role of the electrostatic repulsions and the surface reactivity in the oriented attachment mechanism in water for oxides.

Synthesis and antibacterial activity of catecholate-ciprofloxacin conjugates.

The development of an efficient route to obtain artificial siderophore-antibiotic conjugates active against Gram-negative bacteria is crucial. Herein, a practical access to triscatecholate enterobactin analogues linked to the ciprofloxacin along with their antibacterial evaluation are described. Two series of conjugates were obtained with and without a piperazine linker which is known to improve the pharmacokinetics profile of a drug. A monocatecholate-ciprofloxacin conjugate was also synthesized and evaluated. The antibacterial activities against Pseudomonas aeruginosa for some conjugates are related to the iron concentration in the culture medium and seem to depend on the bacterial iron uptake systems.

A new sensitive organic/inorganic hybrid material based on titanium oxide for the potentiometric detection of iron(III)

The formation of a new hybrid material based on titanium dioxide as inorganic support and containing an iron organochelator (ICL670) is described. An organophosphorous coupling agent was used to graft the organic molecule on the oxide surface. The attachment of the organic substrate was well-confirmed by FTIR (DRIFT), solid-state (31)P and (13)C CPMAS NMR, thermal analysis and the integrity of the structural and morphological parameters were verified using XRD and TEM analyses. The interaction between the material and dissolved iron(III) was also investigated through potentiometric measurements and demonstrated the interest of this new non-siliceous based hybrid material. The obtained linear evolution of the open circuit potential from 10(-2) to 10(-6) mol L(-1) can be used for the analytical detection of iron(III).