François Senocq

Synthesis of tin and tin oxide nanoparticles of low size dispersity for application in gas sensing.

Nanocomposite core-shell particles that consist of a Sn0 core surrounded by a thin layer of tin oxides have been prepared by thermolysis of [(Sn(NMe2)2)2] in anisole that contains small, controlled amounts of water. The particles were characterized by means of electronic microscopies (TEM, HRTEM, SEM), X-ray diffraction (XRD) studies, photoelectron spectroscopy (XPS), and Mossbauer spectroscopy. The TEM micrographs show spherical nanoparticles, the size and size distribution of which depends on the initial experimental conditions of temperature, time, water concentration, and tin precursor concentration. Nanoparticles of 19 nm median size and displaying a narrow size distribution have been obtained with excellent yield in the optimized conditions. HRTEM, XPS, XRD and Mossbauer studies indicate the composite nature of the particles that consist of a well-crystallized tin beta core of approximately equals 11 nm covered with a layer of approximately equals 4 nm of amorphous tin dioxide and which also contain quadratic tin monoxide crystallites. The thermal oxidation of this nanocomposite yields well-crystallized nanoparticles of SnO2* without coalescence or size change. XRD patterns show that the powder consists of a mixture of two phases: the tetragonal cassiterite phase, which is the most abundant, and an orthorhombic phase. In agreement with the small SnO2 particle size, the relative intensity of the adsorbed dioxygen peak observed on the XPS spectrum is remarkable, when compared with that observed in the case of larger SnO2 particles. This is consistent with electrical conductivity measurements, which demonstrate that this material is highly sensitive to the presence of a reducing gas such as carbon monoxide.

Novel, Spongelike Ruthenium Particles of Controllable Size Stabilized Only by Organic Solvents

Soluble ruthenium nanoparticles of uniform size (see picture) with a porous spongelike structure were obtained by the reaction of [Ru(C(8)H(10))(C(8)H(12))] with H(2) in methanol or THF/methanol. The particle size can be controlled in the range 15-100 nm by varying the MeOH/THF ratio. The particles catalyze benzene hydrogenation without modification of their size or structure. Their formation is proposed to occur in the droplets of a nanosized emulsion, which act as nanoreactors.

Synthesis and use of a novel SnO2 nanomaterial for gas sensing

Abstract Decomposition of the organometallic precursor [Sn(NMe 2 ) 2 ] 2 in a controlled water/anisol mixture leads to the formation of monodisperse nanocomposite particles of Sn/SnO x . Full oxidation of the particles into SnO 2 occurs at 600°C without size or morphology change. These particles can be deposited onto silicon nitride covered microelectronic platforms and used as sensitive layers of gas sensors. Doping of the sensors with palladium can be achieved either by co-decomposition of organometallic precursors (doping in volume) or by deposition of palladium on preformed SnO 2 nanoparticles (doping in surface). The doped sensors display an unusually high sensitivity for CO sensing.

Homogeneous catalysis in water Part III. The catalytic hydrogenation of propionaldehyde with (RuCl2L2)2, RuHClL3, RuH(OAc)L3, RuH2L4, RuHIL3, RuCl2(CO)2L2 and [Ru(OAc)(CO)2L]2, (LP(C6H4–mSO3Na)3·3H2O): A kinetic investigation of the salt effect in water

Abstract Seven water-soluble ruthenium complexes (RuCl2L2)2 1, RuHClL3 2, RuH(OAc)L3 3, RuH2L4 4, RuHIL3 5, RuCl2(CO)2L2 6 and [Ru(OAc)(CO)2L]2 7 (LP(C6H4–mSO3Na)3·3H2O) have been tested in the catalytic hydrogenation of propionaldehyde. Their catalytic performances have been compared to those of their organosoluble analogues (1′–7′, LPPh3). The non-carbonylated complexes 1–5 exhibit comparable rates of propionaldehyde hydrogenation in water at 100 °C, as determined by their first-order rate constants. In contrast, the rates observed with 1′–4′ are different from one another and extremely solvent dependent. With 1, the reaction is first order in aldehyde, catast and hydrogen pressure, as is found for the organosoluble complex RuH(CO)Cl(PPh3)3. Starting with 1–4, various equilibria have been observed which lead to the same complex RuH2L3(H2O). These equilibria suggest that the real catalyst precursor in water is RuH2L3. Whatever the precursor (1–5) used, addition of alkaline, alkaline-earth and ammonium salt dramatically increases the activity without any loss of selectivity. The rate equation is drastically modified in the presence of salt. It has been established that the salt acts by both its cation and its anion. For a given anion, the rate increases in the order: NR4+ (REt, n-Bu)

Homogeneous catalysis in water Part II. Synthesis and characterization of ruthenium water-soluble complexes

Abstract Seven water-soluble complexes of ruthenium and TPPTS have been prepared and characterized (TPPTS is the trisodium salt of the tri( m -sulfophenyl)phosphine):[RuCl 2 (TPPTS) 2 ] 2 1 , RuHCl(TPPTS) 3 2 , RuH(OAc)(TPPS) 3 3 , RuH 2 (TPPTS) 4 4 , RuHI(TPPTS) 3 5 , RuCl 2 (CO) 2 (TPPTS) 2 6 and [Ru(OAc)(CO) 2 (TPPTS)] 2 7 . Spectroscopic investigations have shown that in solution they have the same structures as their organosoluble analogues containing the ligand PPh 3 .

Free-solvent Synthesis and Properties of Higher Fatty Esters of Starch — Part 2

A solvent-free synthesis and the properties of esters of starch from different sources (maize, waxy maize, Eurylon 7, potato, wheat, rice, amylose, and amylopectin) and higher fatty acids are described. Higher fatty acid esters (C 8 -C 18 ) of potato starch were synthesized by chemical gelatinization using formic acid, followed by treatment with fatty acid chlorides. Esterification was readily carried out at 105 °C and a reaction time of 40 min. Formic acid permits esterification of starch by long-chain acid chlorides with minimum degradation. The results indicated that the degree of substitution of the starch esters diminishes with increase in fatty acid chain length. All starch esters have a hydrophobic character which rises with length of the fatty side chain. X-ray and Differential Scanning Calorimetry (DSC) showed that the fatty acid side 1 chains (C n > 16) grafted onto starch form cristallites between them. This phenomenon provokes the decrease of elongation at break for these starch esters. On the other hand, the tensile strength at break and thermal stability of fatty esters of starch increase both with a higher fatty chain grafted onto starch.

Iridium coatings grown by metal–organic chemical vapor deposition in a hot-wall CVD reactor

Abstract Deposition of uniform coatings on relatively large size and/or complex shaped pieces require generally isothermal rather than cold-wall chemical vapor deposition (CVD) reactor. After a review of the state-of-the-art of Ir CVD processes aiming the selection of the starting materials, Ir thin films were deposited on W substrates by thermal decomposition of Ir(COD)(MeCp) either in presence of H2 or O2. The growth was carried out in a horizontal hot-wall metal–organic chemical vapor deposition reactor under reduced pressure and low temperature (573–673 K). Using this CVD reactor the process is more difficult to control using H2 rather than O2 as co-reagent. The purity, the microstructure, the growth rate and the thickness uniformity depend on the deposition conditions. Oxygen avoids carbon incorporation in the layers and enhances significantly the growth rate. However, co-deposition of Ir and IrO2 was observed using a high excess of O2. Polycrystalline, compact, untextured and pure Ir coatings were deposited with a satisfactory thickness uniformity over a length of approximately 15 cm and with a typical thickness of 1–2 μm. These coatings have attractive properties to be used as oxidation barriers at high temperature. Optimal deposition conditions were found using the trends predicted by a kinetic model simulating the growth rate along the CVD reactor. A good thickness uniformity along the reactor requires a very short residence time of the reactive species. As a result, the conversion rate is low leading to a poor efficiency of the process.

Gold nanoparticles from self-assembledgold(I) amine precursors

The reaction of AuCl(THT) (1) with long chain primary amines (CnH2n+1NH2; n = 8, 12, 16) leads to the formation of the complexes AuCl(NH2R) (R = C8H17, 2; C12H25, 3; C16H33, 4) which are characterized by classical methods and shown to self-organize in the solid state into a fibrous material; decomposition of the complexes inside the supramolecular framework yields a monolayer of ordered gold nanoparticles.

Elucidating the crystal-chemistry of Jbel Rhassoul stevensite (Morocco) by advanced analytical techniques

Abstract The composition of Rhassoul clay is controversial regarding the nature of the puremineral clay fraction which is claimed to be stevensite rather than saponite. In this study, the raw and mineral fractions were characterized using various techniques including Fourier transform infrared spectroscopy and magic angle spinning nuclear magnetic resonance (MAS NMR). The isolated fine clay mineral fraction contained a larger amount of Al (>1 wt.%) than that reported for other stevensite occurrences. The 27Al MAS NMR technique confirmed that the mineral is stevensite in which the Al is equally split between the tetrahedral and octahedral coordination sites. The 29Si NMR spectrum showed a single unresolved resonance indicating little or no short-range ordering of silicon. The chemical composition of the stevensite from Jbel Rhassoul was determined to be ((Na0.25K0.20)(Mg5.04Al0.37Fe0.20⃞0.21)5.61(Si7.76Al0.24)8O20(OH)4). This formula differs from previous compositions described from this locality and shows it to be an Al-bearing lacustrine clay mineral.

Heterobimetallic d—f Metal Complexes as Potential Single‐Source Precursors for MOCVD: Structure and Thermodynamic Study of the Sublimation of [Ni(salen)Ln(hfa)3], Ln = Y, Gd

Heterobimetallic [Ni(salen)Ln(hfa)3] species [H2salen and Hhfa being N,N′-ethylenebis(salicylideneimine) and hexa-fluoroacetylacetone respectively], where Ni(salen) acts as a neutral chelating ligand towards LnIII, form a series of isostructural compounds for Ln = YIII and any lanthanideIII cation from La to Yb. They are also isostructural with some of the [Cu(salen)Ln(hfa)3] compounds. They sublime without decomposition under vacuum which makes them potential single-source precursors in MOCVD. Sublimation, thermal behaviour, pressure and composition of the vapour phase versus temperature have been studied for the yttrium derivative, by means of thermal analyses, and mass spectrometry using a Knudsen cell. The dissociation process [Ni(salen)Y(hfa)3] = Ni(salen) + Y(hfa)3 has been thermodynamically investigated. Information on the solid-state intermolecular interactions in relation with volatility was obtained through the crystal structure determination of the gadolinium derivative. A comparative structural study of [Ni(salen)Gd(hfa)3] and [Cu(saloph)Y(hfa)3], [H2saloph is N,N′-o-phenylenebis(salicylideneimine)], allows to under-stand why the latter is less volatile than the former despite similar molecular and solid-state structures.