Two step, hydrolytic-solvothermal synthesis of redispersible titania nanocrystals and their gas-sensing properties

A titanium chloromethoxide solution was prepared by reacting TiCl₄ with methanol, followed by water addition. The starting solutions were characterized by Fourier Transform Infrared (FTIR) spectroscopy, evidencing that the in situ generated water results in early hydrolysis of the chloroalkoxide. The solution was reacted with molten dodecylamine at room temperature, obtaining a white slurry of amorphous titania nanoparticles. Stable, redispersible TiO₂ nanocrystals could be prepared by subsequent solvothermal treatment in oleic acid at 250???C. The use of oleic acid was essential for obtaining crystalline structures, while other surfactants prevented crystallization. The nanocrystals were characterized by X-ray Diffraction and Transmission Electron Microscopy, confirming the formation of anatase TiO₂ nanocrystals with a mean size of 3.3?nm. The TiO₂ nanocrystals were used for fabricating gas-sensing devices, which were tested towards ethanol vapors. The initial small size of the nanocrystals, and the limited size growth during the high-temperature sensor operation, result in remarkable sensing performances if compared with bulk titania sensors.     

Neutron crystallographic and molecular dynamics studies of the structure of ammonia-cellulose I: rearrangement of hydrogen bonding during the treatment of cellulose with ammonia

The hydrogen bond arrangement in a complex of cellulose with ammonia has been studied using neutron crystallography in combination with molecular dynamics simulations. The O6 atom of the hydroxymethyl group is donor in a highly occupied hydrogen bond to an ammonia molecule. This rotating ammonia molecule is donor in partially occupied and transient hydrogen bonds to the O2, O3 and O6 atoms of the hydroxyl groups of other chains. The hydrogen atom bound to the O3 atom is disordered but it is almost always involved in some type of hydrogen bonding. It is donated in a hydrogen bond most of the time to the O5 atom on the same chain. However, it also rotates away from this O5 atom to be donated to an ammonia molecule part of the time. On the other hand the hydrogen atom bound to the O2 atom is free from hydrogen bonding most of the time. It is donated in a hydrogen bond to the O6 atom on a neighboring chain only with a relatively small probability. These results provide new insights into how hydrogen bonds are rearranged during the conversion of cellulose I to cellulose III_I by ammonia treatment.     

Determination of the absolute configuration of the enantiomers of dihydroquinolines, isolated by chiral chromatography, by non empirical analysis of circular dichroism spectra and X-ray analysis

The enantiomers of racemic 3,4-dihydroquinolines with an acetal or thioacetal spiro ring and a quaternary stereogenic carbon have been isolated through semipreparative chiral chromatography using a polysaccharide-derived chiral stationary phase (Chiralpak AD) and n-hexane/ethanol as a mobile phase. The absolute configurations of the enantiomers of four compounds have been determined by a comparison of density functional theory (DFT) calculations of their electronic circular dichroism (ECD) spectra with the experimental ECD data. A detailed conformer population search to achieve a conformational average of these compounds was crucial, due to the flexibility of these molecules. The conformer distribution was evaluated by spartan 02 and the structure of each of the conformers found within 4 kcal/mol energy range was optimized with DFT. The final calculated ECD spectrum obtained after Boltzmann averaging was compared with the ECD spectrum of the less well retained enantiomer and the correlation (R)/(−) was established for all compounds. The monocrystals of both enantiomers of one compound were obtained from the HPLC eluates. Their absolute configurations were determined by X-ray crystallographic analysis and confirmed by ECD analysis. In all cases, the second-eluted enantiomer in chiral HPLC exhibits an (R)-configuration.     

One-Pot Cooperation of Single-Atom Rh and Ru Solid Catalysts for a Selective Tandem Olefin Isomerization-Hydrosilylation Process

Realizing the full potential of oxide-supported single-atom metal catalysts (SACs) is key to successfully bridge the gap between the fields of homogeneous and heterogeneous catalysis. Here we show that the one-pot combination of Ru₁/CeO₂ and Rh₁/CeO₂ SACs enables a highly selective olefin isomerization-hydrosilylation tandem process, hitherto restricted to molecular catalysts in solution. Individually, monoatomic Ru and Rh sites show a remarkable reaction specificity for olefin double-bond migration and anti-Markovnikov α-olefin hydrosilylation, respectively. First-principles DFT calculations ascribe such selectivity to differences in the binding strength of the olefin substrate to the monoatomic metal centers. The single-pot cooperation of the two SACs allows the production of terminal organosilane compounds with high regio-selectivity (>95 %) even from industrially-relevant complex mixtures of terminal and internal olefins, alongside a straightforward catalyst recycling and reuse. These results demonstrate the significance of oxide-supported single-atom metal catalysts in tandem catalytic reactions, which are central for the intensification of chemical processes.     

Measurement of lithium diffusion coefficient in thin metallic multilayer by neutron depth profiling

Diffusion of Li ions in thin sandwich films with copper or lead encompassing layers (obtained by ion beam sputtering deposition technique) has been studied. These metals are promising candidates for electrodes in lithium-ion batteries. It is because they exhibit an ability to store and release Li ions during charging and discharging processes. Lithium diffusion was induced in samples by thermal annealing cycles. The lithium depth profile was measured using a nondestructive neutron depth profiling technique after each thermal annealing step. The analysis of experimental data allowed to evaluate the lithium depth profiles and directly calculate the diffusion coefficients.     

Flammability and morphology of HDPE/clay nanocomposites

High-density polyethylene/modified bentonite clay/polar compatibilizer nanocomposites were prepared through the melt intercalation process. The clay was organophilizated using different percentages of quaternary ammonium salt 100, 125, and 150 % based cation exchange capacity of the clay. The nanocomposites were prepared in a counter-rotating twin-screw extruder and then specimens were injection molded. For the evaluation of flammability of the test system was used for burning in the horizontal position according to the norm (Underwriters Laboratories, UL94HB) and to the method of cone calorimeter. The thermal behavior of nanocomposites was evaluated by thermogravimetry and X-ray diffraction techniques, and transmission electron microscopy were used to characterize the morphology and analyze the degree of expansion of the clays prepared and the degree of exfoliation of nanocomposites. It was observed that the percentage of ammonium salt and the compatibilizer polar influence on the final properties of the systems and consequently improving the thermal stability and reducing the flammability of the matrix.     

Time regularity of the solutions to second order hyperbolic equations

We consider the Cauchy problem for a second order weakly hyperbolic equation, with coefficients depending only on the time variable. We prove that if the coefficients of the equation belong to the Gevrey class g^s₀\gamma^{s_{0}} and the Cauchy data belong to g^s₁\gamma^{s_{1}}, then the Cauchy problem has a solution in  g^s₀([0,T^*];g^s₁(\mathbbR))\gamma^{s_{0}}([0,T^{*}];\gamma^{s_{1}}(\mathbb{R})) for some T ^*>0, provided 1≤s ₁≤2−1/s ₀. If the equation is strictly hyperbolic, we may replace the previous condition by 1≤s ₁≤s ₀.     

Riemannian 3-metrics with a generic Codazzi Ricci tensor

We determine a large family of explicit metrics, defined on open subsets of \mathbb R ³{\mathbb R ^3} , having a Codazzi Ricci tensor and three distinct Ricci eigenvalues.     

A column generation algorithm for the vehicle routing problem with soft time windows

The Vehicle Routing Problem with Time Windows consists of computing a minimum cost set of routes for a fleet of vehicles of limited capacity visiting a given set of customers with known demand, with the additional constraint that each customer must be visited in a specified time window. We consider the case in which time window constraints are relaxed into “soft” constraints, that is penalty terms are added to the solution cost whenever a vehicle serves a customer outside of his time window. We present a branch-and-price algorithm which is the first exact optimization algorithm for this problem.