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In modern laser technologies, there is a need for coatings that would be compatible with flexible substrates while retaining the advantages of inorganic compounds in terms of robustness. As a first step in this direction, we developed here thin films of lanthanide oxysulfide, of optical quality, prepared by low-temperature dip coating. As a model compound in the family of oxysulfides, (Gd,Ce)

International audience; Rebuilding biological environments is crucial when facing the challenges of fundamental and biomedical research. Thus, preserving the native state of biomolecules is essential. We use electrospinning (ES), which is an extremely promising method for the preparation of fibrillar membranes to mimic the ECM of native tissues. Here, we report for the first time (1) the ES of pure and native collagen into a self-supported membrane in absence of crosslinker and polymer support, (2) the preservation of the membrane integrity in hydrated media in absence of crosslinker and (3) the preservation of the native molecular structure and recovery of the hierarchical assembly of collagen. We use a multiscale approach to characterize collagen native structure at the molecular level using circular dichroism, and to investigate collagen hierarchical organization within the self-supported membrane using a combination of multiphoton and electron microscopies. Finally, we show that the membranes are perfectly suited for cell adhesion and spreading, making them very promising candidates for the development of biomaterials and finding applications in biomedical research.

"Ce travail a bénéficié d'une aide de l'Etat gérée par l'Agence Nationale de la Recherche au titre du programme Investissements d'Avenir portant la référence ANR-11-IDEX-0004-02, dans le cadre du Laboratoire d'Excellence MATISSE porté par Sorbonne Universités". "This work was supported by French state funds managed by the ANR within the Investissements d'Avenir programme under reference ANR-11-IDEX-0004-02, and more specifically within the framework of the Cluster of Excellence MATISSE led by Sorbonne Universités".; International audience; The recent tendency in the battery field toward the use of aqueous electrolytes stimulated several studies searching for compatible electrode materials and charge carriers. Still, another aspect to forge ahead is the fundamental understanding of interfacial processes occurring at electrode/electrolyte interface. To this end, we investigated interfacial properties of a model LiCoO2 composite electrode in Li2SO4 aqueous electrolyte through extensively exploiting operando electrochemical quartz crystal microbalance (EQCM) and its coupling with electrochemical impedance spectroscopy (ac-electrogravimetry). EQCM revealed a global cation-exchange behavior, which is decoded by ac-electrogravimetry into multispecies contribution with different proportions/kinetics, benefiting from the capacity of the latter to study interfacial dynamics. Li+ plays the major role in the charge-compensation mechanism, but a strong interaction with H2O has been revealed with close interfacial transfer kinetics, which provides experimental evidence on the essential character of H2O assisting the Li+ insertion in layered materials due to the weakened charge density by screening the electrostatic interactions between the Li+ ions and the host lattice of cathode materials.

Anatase TiO2 structure has been widely studied as an electrode for Li-ion battery and as electrocatalyst for water splitting. Inserting guest species into TiO2 has been demonstrated as an effective approach to tune the electronic structure and consequently improves the hydrogen evolution reaction (HER) catalytic activity. In this work, by using mesoporous TiO2 electrodes, we have demonstrated the interplays between HER and Li-ion insertion in Water-in-Salt Electrolyte (WISE). Low C-rates favor the electro-catalytic reaction (HER), but the latter does also depend on the amount of Li in the electrode. Finally, this study guides the experimental conditions for an optimum functioning either in battery environment or in electro-catalysis.

Electrospinning (ES) is an extremely promising method for the preparation of self-supported membranes for tissue engineering by mimicking the 3D fibrillar structure of the extracellular matrix. Conflicting results about collagen ES in the literature concern the conditions of collagen solubilization to improve electrospinnability, and the use of co-polymers and chemical cross-linkers to stabilize the structure of collagen membranes. Here we report for the first time (1) the ES of pure and native collagen into a self-supported membrane in absence of polymer support and (2) the preservation of the membrane integrity in hydrated media in absence of crosslinker. We use a multiscale approach to characterize collagen native structure at the molecular level using synchrotron radiation circular dichroism, and to investigate collagen hierarchical organization within the self-supported membrane using electron and multiphoton microscopies. Finally, we show that the membranes are perfectly suited for cell adhesion and spreading, making very promising candidates for the development of advanced biomaterials.

Reserving the right to stretch Retractable antennae or certain spider silks can stretch well beyond their apparent length because they have a reserve of material that lets them expand and contract over much longer distances. Grandgeorge et al. made nonwoven fibrous membranes by electrospinning a block copolymer with varying ratios of two components. They infused these membranes with a liquid that let the fibers buckle and fold without changing the apparent surface area. When the membranes were stretched, this material could unbuckle and slide along the membrane surface, allowing it to extend without breakage. Science , this issue p. 296

Photoelectrochemical devices are a promising approach to produce scalable and sustainable carbon-free energy. One of the challenges is to find the adequate Earth abundant semiconducting photoelectrodes able to harvest light, store it and convert it into electricity. To design efficient electrodes, there is a need to understand the physicochemical properties of the semiconductor, the chemical and the structure of the interfaces and the transfer mechanisms at these interfaces. The aim of this review is to summarize recent progress and open challenges in i) the bulk physicochemical properties of the semiconductor, ii) the chemical and energetic dynamics of the electrode/electrolyte interfaces and iii) the development and relevant use of operando techniques to understand transfer mechanism at these interfaces.

Aqueous lithium–air batteries have very high theoretical energy densities, which potentially makes this technology very interesting for energy storage in electric mobility applications. However, the aqueous electrolyte requires the use of a watertight layer to protect the lithium metal, typically a thick NASICON glass–ceramic layer, which adds ohmic resistance and penalizes performance. This article deals with the replacement of this ceramic electrolyte by a hybrid organic–inorganic membrane. This new membrane combines an ionically conducting inorganic phase for Li ion transport (Li1.3Al0.3Ti1.7(PO4)3 (LATP) and a poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF–HFP) polymer for water tightness and mechanical properties. The Li ion transport through the membrane is ensured by an interconnected 3-D network of crystalline LATP fibers obtained by coupling an electrospinning process with the sol–gel synthesis followed by thermal treatment. After an impregnation step with PVDF–HFP, hybrid membranes with ...

International audience; One of the most fundamental assets of natural polysaccharides is their water storage capacity. Analogically, materials able to regulate water hydration in energetic systems (e.x.: fuel-cells) are of paramount interest. In light of this key characteristic, chitosan, an aminocarbohydrate derived from shellfish waste, was structurally conjugated using sulfosuccinic acid to afford CS-SO3H. The resulting polymeric material appears well suitable for enhancing proton conduction and tuning the hydrophilic-hydrophobic balance of the proton exchange membranes (PEM). Consequently, Nafion membrane modified with CS-SO3H presented σH+ values almost 2 times higher than that of pristine Nafion at every % RH level exposed (30 °C - 80 °C and 30% - 90%). The σH+ enhancement is in agreement with the lower activation energy indicating that the proton transport is facilitated in the presence of -SO3H modified chitosan. We have found indications that –SO3H modified chitosan polymer, as a sustainable additive to Nafion is able to control the proton conduction mechanism and keep the activation energy for proton conduction at lower values as compared to pristine Nafion.

International audience; Li-ion batteries need to be charged by being plugged into the grid, limiting their autonomy. Charging a battery consists of applying an external load to reverse the spontaneous electrochemical reactions during discharge. A strategy to improve their autonomy is to design nanostructured electrodes whose composition and architecture allow for these reactions to be driven by light. Classical electrochemical experiments (in the dark and under light) demonstrate that light promotes the de-insertion reaction of 3D LixTiO2 mesoporous thin films due to the participation of photogenerated holes (h+). These holes allow the oxidation of Ti3+ into Ti4+, simultaneously giving rise to Li-ion extraction. Galvanostatic experiments performed on Li-rich TiO2 mesoporous films show that competition between ion insertion and de-insertion occurs, leading to electrodes with potentially infinite capacity. This work constitutes a proof of concept that low potential Li-ion batteries (TiO2//Li0) can solely be recharged by exposure to light.

Sodium iron fluorophosphate Na2FePO4F is a candidate positive electrode material for both lithium-ion batteries and sodium-ion batteries. We report the synthesis of Na2FePO4F/carbon powders by the simple and easily up-scalable technique of spray-drying. An aqueous solution containing citric acid as a carbon source was sprayed in a pilot-scale spray-dryer. Heat treatment at 600 °C in argon for 12 h was found appropriate to obtain single-phase Na2FePO4F; only 1.8% of Fe (III) was detected by iron-57 Mossbauer spectroscopy. When cycled against lithium, the discharge capacity reached 110 mA h/g at C/15 rate.

The intercalation and de-intercalation of lithium cations in electrochromic tungsten oxide thin films are significantly influenced by their structural and surface characteristics. In this study, we prepared two types of amorphous films via the sol-gel technique: one dense and one mesoporous in order to compare their response upon lithium intercalation and de-intercalation. According to chronoamperometric measurements, Li+ intercalates/de-intercalates faster in the mesoporous film (24s/6s) than in the dense film (48s/10s). The electrochemical measurements (cyclic voltammetry and chronoamperometry) also showed worse reversibility for the dense film compared to the mesoporous film, giving rise to important Li+ trapping and remaining coloration of the film. Raman analysis showed that the mesoporous film provides more accessible and various W-O surface bonds for Li+ intercalation. On the contrary, in the first electrochemical insertion and de-insertion in the dense film, Li+ selectively reacts with a few surface W-O bonds and preferentially intercalates into pre-existing crystallites to form stable irreversible LixWO3 bronze.

A key issue in the commercialization of dye-sensitized solar cells is to maintain high efficiency and long lifetime. As reported in the literature, dye-sensitized solar cells are stable under visible light soaking but thermal stress and UV exposure lead to efficiency degradation. However, all the stability studies published so far have been performed on cells whose TiO2 electrodes were prepared by tape casting or screen printing of nanoparticle pastes/inks. The present study concerns cells based on highly porous templated TiO2 electrodes, whose larger surface area could enhance the negative effects of thermal stress, light soaking and UV exposure. The long-term stability of these cells is compared with a classical nanoparticle-based cell using current-voltage measurements (I-V curves) and electrochemical impedance spectroscopy. Due to their higher active interface, templated cells are more sensitive than nanoparticle cells to UV illumination, although this can be easily solved in both cases by the use of a UV filter. The templated cells are as stable as the nanoparticle cells under visible light soaking (UV filtered). However, we showed that templated cells are more stable under thermal stress. Moreover, as evidenced by electrochemical impedance spectroscopy, templated cells show lower transfer resistance, as well as lower recombination resistance compared to nanoparticle cells. The crystallite connectivity promoted by the templating route seems to favor the electron transfers inside the porous layer. Using templated films in dye-sensitized solar cells is therefore really promising because higher conversion efficiencies are reached without promoting cell degradation.

Research in the field of lithium-ion batteries favours electrode materials with high surface area. In this context, this paper is dedicated to mesoporous thin films (MTFs) and compares the electrochemical performance of γ-LiV2O5 MTFs with post-synthesis electrochemical lithium intercalation in α-V2O5 MTFs. Formation of vanadium oxide MTFs by soft-chemistry is notoriously difficult. However, it is shown that wormlike vanadium oxide (V–O) and lithium vanadium oxide (Li–V–O) MTFs can be obtained on silicon substrates by a direct sol–gel soft-templating route (evaporation-induced micelle assembly) using a polystyrene-block-poly(ethylene oxide) (PS-b-PEO) structuring agent. Heat treatment for 1 minute at 400 °C (Li–V–O system) or 30 minutes at 350 °C (V–O system) leads to the crystallization of γ-LiV2O5 or α-V2O5, respectively. These calcination conditions ensure the degradation of the structuring agent while preventing the collapse of the mesostructure, yielding MTFs with pore size diameter in the 30–35 nm range. Using the same set of synthesis conditions, films can be deposited on conductive glass substrates for electrochemical investigation: the α-V2O5 films display better specific capacities, while the cyclability is good for both compositions, even at a current density as high as 30 C-rate.

Graphical abstract: - Highlights: • Li{sub 4}Ti{sub 5}O{sub 12} is prepared by a method involving self-ignition of a freeze-dried gel. • Addition of NH{sub 4}NO{sub 3} modifies the self-ignition propagation mode. • Well-crystallized Li{sub 4}Ti{sub 5}O{sub 12} phase is obtained after only 2 h at 800 °C. • Li{sub 4}Ti{sub 5}O{sub 12} powder has 161 mAh g{sup −1} capacity and good retention at C/4 rate. - Abstract: Crystalline Li{sub 4}Ti{sub 5}O{sub 12} is synthesized by a method involving the freeze-drying and self-ignition of a gel prepared from titanium isopropoxide, lithium nitrate and hydroxypropylmethylcellulose (HPMC). This synthesis route yields crystalline Li{sub 4}Ti{sub 5}O{sub 12} particles after calcination at 800 °C for 2 h. In an alternative route, addition of ammonium nitrate shifts the self-ignition mode from wave-like propagation to simultaneous. Powders with different microstructures are thereby obtained. Electrochemical characterization shows that the best results for Li{sup +} intercalation/desintercalation are obtained for the powder prepared without ammonium nitrate addition. These results highlight the necessity for a control of the self-ignition mode to obtain adequate properties.

This work investigates the possibility to prepare mesoporous thin films of Li–Ti, Li–Nb, Li–Nb–V and Li–V oxides through a direct sol–gel EISA route by dissolving a lithium salt in the precursor solution. Experimental conditions involve a hydrolysis molar ratio H 2 O/TM ∼ 10 (TM = Ti, Nb, V) and the common Pluronic structuring agent P123 (EO 20 –PO 70 –EO 20 ). Systematic formation of lithium-containing oxides as first-crystallizing phases points to a significant intermixture of lithium and transition metal ions in the inorganic network. In the case of Ti-based and Nb-based oxide films, addition of lithium to the precursor solution is compatible with the formation of amorphous mesoporous films at 350 °C. On the contrary, addition of lithium has a detrimental effect on the notoriously difficult formation of vanadium-based mesostructured films: even when replacing half of the vanadium by niobium as a stabilizer, formation of mesostructured films has not been possible in the investigated range of experimental conditions.

This study quantifies the highest perturbation encountered by the first layer of a TiO2 12 layers-mesoporous coating, which is submitted to a multistep calcination process. Besides, we propose an alternative thermal treatment in order to limit the degradation induced by repeated calcinations. This paper reports and compares the modifications in film thickness, surface area, anatase crystallite size and global crystallinity of films obtained from different thermal treatments. It defines the maximum crystal size compatible with the preservation of the mesoarchitecture initially induced by templating. Differences in microporosity and rate of crystallization are also discussed.

SiO2/TiO2 xerogel ultrathin protective coatings, with tunable refractive index between 1.45 and 2.20, have been prepared by dip-coating sol−gel solutions of TiCl4 and tetraethyl orthosilicate with various molar compositions. In situ thermal ellipsometry analysis is used to follow the modifications of optical properties of these binary oxide systems upon thermal treatment up to 820 °C. Involved phenomena, such as dehydration, condensation, viscous sintering, crystallization, and diffusive sintering have been clearly identified and studied with respect to the Ti/Si atomic proportion and the treatment conditions. Due to the influence of the crystal size on the semiconducting properties of titania nanoparticles, its crystallization kinetic has been specifically investigated. We show that the crystallization of TiO2 is globally taking place between 300 and 600 °C depending on the silica to titania ratio and on the heating rate. Films containing more than 40% of silica remain amorphous at 820 °C. Poor silica co...

Sol-gel processing of TiO2, ZrO2 and mixed Ti/Zr oxide thin films has been studied as application of these coatings in electrochromic devices. Their structural transformations as a function of annealing temperatures were analyzed by XRD and FTIR techniques. Electrochromic behavior of the three kind materials was investigated by cyclic voltammetry and the basic electrochromic characteristics were determined.

Nb 2 x V 2 − 2 x O 5 (0 ≤ x ≤ 1) powders were prepared by a synthetic route based on the inorganic polymerization of alkoxy-choride precursors and characterized by a combination of X-ray diffraction, 51 V and 93 Nb NMR and Raman spectroscopy. Amorphous mesoporous thin films of similar compositions were successfully prepared by a modified Evaporation Induced Self Assembly method using polystyrene- b -polyethyleneoxide diblock copolymer as structuring agent. The electrochemical properties of the mesoporous films upon lithium insertion–deinsertion are investigated by cyclic voltammetry. This study highlights the advantages of such nanoarchitecture in terms of increased capacity to insert lithium.

Intercumulus titanian phlogopite occurs in leuco- and gabbro-noritic cumulates from the Suwalki anorthosite massif, NE Poland. The degree of Ti enrichment in the micas ranges from 2.59 to 9.41 wt.% TiO2. The chemical composition is highly variable for several other elements: Al 2O3 (13.07-16.75 wt.%), K2O (7.90-10.16 wt.%), FeOtot (6.92-16.69 wt.%), Fe2O3 (0.82-2.95 wt.%), and MgO (9.86-19.54 wt.%), with a Mg/(Fe + Mg) ratio ranging from 0.47 to 0.83. Substitution mechanisms for Ti are proposed, which suggest the presence of exchange vectors involving octahedral and tetrahedral cations. In samples characterized by low Ti contents (0.147-0.239 Ti a.p.f.u.), the Ti incorporation mechanism is: [6]Ti4+ + [6]□ = 2( [6]Mg2+, [6]Fe2+, [6]Mn2+), where [6]□ corresponds to a vacancy in octahedral coordination (Ti-vacancy). In the two groups with intermediate (0.164-0.326 Ti a.p.f.u.) and high Ti contents (0.477-0.532 Ti a.p.f.u.), the Ti substitution mechanism corresponds to the reaction: [6]Ti4+ + 2([4]A13+, [4]Fe3+) = ([6]Mg2+, [6]Fe2+, [6]Mn2+) + 2 [4]Si4+ (Ti-Tschermak). The Mössbauer spectral investigation shows that 0.046-0.167 a.p.f.u. Fe3+ occur on the octahedral sites of the structure. The substitution mechanism responsible for the incorporation of Fe3+ in phlogopites from Suwalki is 3( [6]Mg2+, [6]Fe2+) = 2( [6]Al3+, [6]Fe3+) + [6](M3+-vacancy). The use of the Ti content of phlogopite as geothermometer reveals crystallization temperatures from 729 ± 15 to 874 ± 15 °C for the phlogopites. © 2009 E. Schweizerbart'sche Verlagsbuchhandlung. ispartof: EUROPEAN JOURNAL OF MINERALOGY vol:21 issue:2 pages:397-406 status: published

LiMn 2− x Ti x O 4 compounds with 0 ≤ x ≤ 1 were prepared by solid state reaction and Pechini technique. Powder X-ray diffraction showed that all samples crystallize with the spinel crystal structure (S.G. Fd3¯m ). The cubic unit-cell parameter increases with the Ti content. The influence of the Ti content and cationic distribution on the magnetic properties of the compounds was studied by measuring the temperature and magnetic field dependences of the magnetization: substitution by non-magnetic d 0 Ti 4+ ions appeared to weaken the magnetic interactions between the manganese ions. The electrical properties of LiMnTiO 4 were studied by AC impedance spectroscopy and DC polarisation measurements, which revealed the electronic character of the conduction process.

A novel method to prepare thick, crack-free, and fully transparent nanocrystalline TiO2 mesoporous layers from pure aqueous solution is described. This method is easy to scale up, and can be generalized to most of transition metal oxides.

We report the formation of ZnO/SiO2 nanocomposite thin films. They are composed of 5 nm sized-wurtzite ZnO nanoparticles nucleated within vitreous SiO2 which was in the form of either an ordered mesoporous or a dense matrix. Mesoporous thin films were obtained by evaporation induced self-assembly from the chemical solution deposition of solutions containing TEOS, ZnCl2, and Pluronic-type block copolymers as structuring agent. Direct thermal treatment in air was applied to achieve the desired film characteristics. Dense or highly ordered mesoporous (pore size = 6 nm and pore volume = 60%) films can be achieved with high optical quality. When 50 mol% ZnO is used, the mesoporous films exhibit a very low refractive index of 1.17, which suggests a high accessible porosity that is ideal for molecular diffusion towards ZnO nanoparticles. In these films, the similar intensity of the UV and visible emission bands reveals a high amount of oxygen defects, making them well suited for applications in stimulated emitters, actuators, lasing cavities, or optical sensors. The present results are supported by in situ time-resolved grazing incident small angle X-ray scattering/wide angle X-ray scattering/thermal ellipsometry analysis experiments, which allow for the study of the crystallization kinetics of ZnO within amorphous matrices. The present work constitutes an example of a one-pot synthesis of divalent oxide nanoparticles dispersed in mesoporous silica that can virtually be extended to most divalent metal oxides, but also to other processing such as aerosol pulverisation of powders.

Mesoporous thin films (MTFs) appear as an interesting architecture for positive electrodes in Li-ion energy storage systems because they offer high specific area and interconnected porosity presenting homogeneous pore size and wall thickness. However, it must be ascertained that the mesostructure survives template removal or/and crystallization and is retained on electrochemical cycling. In order to investigate the potentialities and limits of the soft-templating approach in the case of complex transition metal oxide networks, we deliberately selected a “difficult” compound: NbVO5 was chosen because it combines a challenging synthesis with reported severe structural distortions during the first lithium insertion in the bulk material. In this work, NbVO5 MTFs with different pore sizes were synthesized using the evaporation induced micelles packing (EIMP) method. PS-b-PEO diblock copolymers of different molar weights were used as structure directing agent in order to obtain wormlike porous networks with pore size and wall thickness ranging from 15 to 100 nm. Thermal ellipsometry analysis, used to track surfactant removal and crystallization of the layer, reveals that partial crystallization is possible while retaining the mesoporous architecture. Electron tomography complements result from environmental ellipsometric porosimetry, atomic force microscopy, and transmission electron microscopy to provide a comprehensive description of the structure. A multilayer process is also proposed to build crack-free thick mesoporous films. The mechanical stability of MTFs presenting three different pore sizes is tested by inserting Li+ in amorphous NbVO5 MTFs using cyclic voltammetry. Capacity retention data show that the mechanical stresses associated with Li+ insertion are better accommodated by MTFs compared to nonporous films, and this ability is enhanced as the pore size decreases.

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Mesoporous anatase thin films are very promising materials to act as electrode in dye-sensitized solar cell. Randomly oriented nanocrystalline TiO2 particles are usually used to prepare photoelectrodes with a thickness of 10–15 µm. Template-assisted dip-coating techniques are used to obtain thin films with ordered porosity. However, monolayer films prepared by dip-coating from a solution suffer from a low quantity of active material with a limited surface area, leading to poor photovoltaic performances. Therefore a multilayer deposition process is needed to increase the film thickness along with the surface area. Multilayer dip-coating procedures have already been reported but are usually characterized by a lack of linearity in the evolution of parameters (roughness, surface area, PV performances) as the number of layer increases. In this paper, a dip-coating-based multilayer deposition technique is reported. First, the influence of the template on the film organization and porosity is studied in terms of long-range order, percentage of porosity, pore size and pores connectivity. Different techniques such as transmission electron microscopy (TEM), atmospheric poroellipsometry (AEP) and UV-visible absorption spectroscopy (UV-vis) have been used to describe the microstructural features of the films with a thickness of 1 µm. The film exhibiting the highest dye loading was selected and its thickness gradually increased up to 4 µm. Finally, the photovoltaic performances of the thick films (1 to 4 µm) have been evaluated in combination with the N-719 dye and show excellent efficiency (6.1%) when compared to values reported in the literature. Such mesostructured films are compared in terms of photovoltaic performance with TiO2 nanoparticles films, generally used in DSSC.

The properties of mesoporous materials hinge on control of their composition, pore dimensions, wall thickness, and the size and shape of the crystallite building units. We create ordered mesoporous materials in which all of these parameters are independently controlled. Different sizes (from 4.5 to 8 nm) and shapes (spheres and rods) of ligand-stripped nanocrystals are assembled using the same structure-directing block copolymers, which contain a tethering domain designed to adsorb to their naked surfaces. Material compositions range from metal oxides (Sn-doped In(2)O(3) or ITO, CeO(2), TiO(2)) to metal fluorides (Yb,Er-doped NaYF(4)) and metals (FePt). The incorporation of new types of nanocrystals into mesoporous architectures can lead to enhanced performance. For example, TiO(2) nanorod-based materials withstand1000 electrochemical cycles without significant degradation.