Showing papers by "Jean-Marie Nedelec published in 2017"
TL;DR: Uniaxial compression of the obtained ultra-lightweight ductile nf-DCC aerogels down to 5% of their original volume intriguingly preserves nematic orientation and transparence as discussed by the authors.
Abstract: Dissolving pulp has been subjected to consecutive periodate/chlorite treatments to afford 2,3-dicarboxyl cellulose (DCC, 1.02 mmol g–1 COOH). Subsequent nanofibrillation afforded stable nematic nf-DCC dispersions (average particle size 2.1 nm × 525 nm) at significantly lower energy input compared to TEMPO-oxidation. Acid-induced gelation triggered by extensive hydrogen bonding sets the ordered state and affords free-standing hydrogels that can be converted to highly transparent birefringent aerogels by scCO2 drying. Uniaxial compression of the obtained ultra-lightweight ductile nf-DCC aerogels down to 5% of their original volume intriguingly preserves nematic orientation and transparence. Simultaneously, strain hardening translates into exceptionally good mechanical properties, such as toughness at nearly zero Poisson’s ratio. Uniaxial compression has been furthermore demonstrated to be a facile and efficient means for converting nf-DCC aerogels of broad, multiscale pore size distribution into entirely mi...
65 citations
TL;DR: A general overview of the doping mechanisms of BCP samples using cations from the first-row transition metals (from manganese to zinc), with respect to the applied sintering temperature is presented.
Abstract: Doped calcium phosphate bioceramics are promising materials for bone repair surgery because of their chemical resemblance to the mineral constituent of bone. Among these materials, BCP samples composed of hydroxyapatite (Ca10(PO4)6(OH)2) and β-TCP (Ca3(PO4)2) present a mineral analogy with the nano-multi-substituted hydroxyapatite bio-mineral part of bones. At the same time, doping can be used to tune the biological properties of these ceramics. This paper presents a general overview of the doping mechanisms of BCP samples using cations from the first-row transition metals (from manganese to zinc), with respect to the applied sintering temperature. The results enable the preparation of doped synthetic BCP that can be used to tailor biological properties, in particular by tuning the release amounts upon interaction with biological fluids. Intermediate sintering temperatures stabilize the doping elements in the more soluble β-TCP phase, which favors quick and easy release upon integration in the biological environment, whereas higher sintering temperatures locate the doping elements in the weakly soluble HAp phase, enabling a slow and continuous supply of the bio-inspired properties. An interstitial doping mechanism in the HAp hexagonal channel is observed for the six investigated cations (Mn2+, Fe3+, Co2+, Ni2+, Cu2+ and Zn2+) with specific characteristics involving a shift away from the center of the hexagonal channel (Fe3+, Co2+), cationic oxidation (Mn3+, Co3+), and also cationic reduction (Cu+). The complete crystallochemical study highlights a complex HAp doping mechanism, mainly realized by an interstitial process combined with calcium substitution for the larger cations of the series leading to potentially calcium deficient HAp.
55 citations
TL;DR: The present paper scrutinizes in detail the incorporation of ferric cation in order to correctly interpret the behavior of the iron-doped bioceramic in biological fluid and clearly appears that temperature can be used to design the doping according to desired medical application.
38 citations
TL;DR: This paper presents the first experimental evidence of pronounced electrification effects upon reversible cycle of forced water intrusion-extrusion in nanoporous hydrophobic materials and opens a perspective to increase the efficiency of numerous energy applications based on such systems taking advantage of electricity generation during operational cycle.
Abstract: This paper presents the first experimental evidence of pronounced electrification effects upon reversible cycle of forced water intrusion–extrusion in nanoporous hydrophobic materials. Recorded generation of electricity combined with high-pressure calorimetric measurements improves the energy balance of {nanoporous solid + nonwetting liquid} systems by compensating mechanical and thermal energy hysteresis in the cycle. Revealed phenomena provide a novel way of “mechanical to electrical” and/or “thermal to electrical” energy transformation with unprecedented efficiency and additionally open a perspective to increase the efficiency of numerous energy applications based on such systems taking advantage of electricity generation during operational cycle.
29 citations
TL;DR: The proposed sol-gel synthesis of Ca CO3 proved to create unprecedented size of CaCO3 nanoparticles with striking size uniformity, and clearly demonstrate their ability to incorporate hydrophobic components in a nanocomposite matrix converting them into amorphous nano sized particles, building stable colloids via release in acidic medium.
18 citations
TL;DR: In this article, the morphology and structural properties of Ca(10−3x)Eu2x(PO4)6F2 were determined using TEM (transmission electron microscopy) and XRPD (X-ray powder diffraction) techniques, as well as the IR (infrared) and Raman spectroscopy.
Abstract: Eu3+ doped fluorapatite nanopowders were synthesized by a microwave assisted hydrothermal technique and annealed in the 500–1000 °C temperature range for 3 h. The europium ion concentration was determined to be in the 0.5–10 mol% concentration range. The morphology and structural properties of Ca(10−3x)Eu2x(PO4)6F2 were determined by using TEM (transmission electron microscopy) and XRPD (X-ray powder diffraction) techniques, as well as the IR (infrared) and Raman spectroscopy. The average nanoparticle sizes were calculated by Rietveld refinement to be in the range from 30 nm for the as-prepared samples to above 100 nm for the materials thermally treated at 1000 °C. The particles developed into rectangular prism nanorods. The spectroscopic properties of the obtained materials were observed to be dependent on the dopant concentration and annealing temperature and were studied in detail. The Judd–Ofelt theory was applied and correlated with structural and optical properties to get detailed insight into the fluorapatite structures.
16 citations
03 Jan 2017
TL;DR: In this article, mesoporous nanostructured pure tantalum pentoxide and Eu-doped Ta2O5 were produced by facile and reproducible one-pot procedure not involving structure directing agents.
Abstract: Mesoporous nanostructured pure tantalum pentoxide and Eu-doped Ta2O5 were produced by facile and reproducible one-pot procedure not involving structure directing agents. The as-produced material is poorly crystalline and catalytically inactive. Photoluminescence behavior of the doped oxide indicates that it is formed by quick nucleation of pure Ta2O5, leaving the Eu-dopant only on the surface of the formed material. Further thermal treatment leads to crystallization and structural transformation as revealed by in situ X-Ray Diffraction (XRD) and Rietveld refinement used to identify and quantify the emerging phases as well as Diffuse Reflectance UV-vis Spectroscopy (DR-UV-Vis) and Raman Spectroscopy studies. The thermally induced transformation results in generation of surface oxygen vacancies that provide the material with pronounced photocatalytic activity in selective oxidation of aromatic amine compounds. The processes of generation and curing of the vacancies have been followed and quantified by temperature programmed oxidation and reduction and photoluminescence studies, offering in depth insight into the reaction mechanism.
12 citations
TL;DR: In this paper, the nano-biphasic calcium phosphate co-doped with 1 mol% Er3+ and 5 mol% Yb3+ ions was prepared using Pechini's technique.
Abstract: The nano-biphasic calcium phosphate co-doped with 1 mol% Er3+ and 5 mol% Yb3+ ions was prepared using Pechini's technique. The preparation of the biphasic calcium phosphate showed the removal of fluorine ions from the matrix. The structural properties and morphology of the particles were studied by means of XRD (X-ray powder diffraction), TEM (Transmission Electron Microscopy), and SEM (Scanning Electron Microscopy) techniques. The spectroscopic properties of Ca10(PO4)6F2/Ca3(PO4)2:Er3+,Yb3+ nano-biphasic calcium phosphate were investigated in detail using emission spectra, power dependence and emission kinetics. This material demonstrated intense green up-conversion depending on laser power. Additionally, the luminescence lifetimes for Er3+ ions were calculated from the measured decays. Power dependence of the green and red emissions was found to result from a temperature increase of nano-biphasic calcium phosphate that opens potential applications in theranostics.
10 citations
TL;DR: In this paper, a reversible wetting process of a liquid in nanopores provoked by a temperature variation can be used to develop systems with the necessary thermal expansion behavior, which can be controlled in an unprecedentedly wide range of both negative and positive values.
Abstract: In this work a general thermodynamic grounds as well as experimental verification are given to demonstrate how a reversible wetting process of a liquid in nanopores provoked by a temperature variation can be used to develop systems with the necessary thermal expansion behavior. Thermal expansion coefficients of such nanoporous heterogeneous lyophobic systems can be controlled in the unprecedentedly wide range of both negative and positive values. Perspectives as well as challenges on the full potential use of the proposed mechanism are identified.
8 citations
TL;DR: The findings highlight that the strong affinity of GFs with the ceramic surfaces, demonstrated by a slow GFs release, is enhanced by the large surface area, confinement into mesopores of ceramics and high difference of surface charge between ceramic surfaces and GFs.
7 citations