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Magnesium silicates combining acidic and basic surface properties are known to be interesting as heterogeneous catalysts. Nevertheless, their catalytic performances are highly dependent on the synthesis method used. In this study, a series of magnesium silicates was synthesized for the first time using a coprecipitation method with a micromixer. It is first shown that changes in synthesis/precipitation pH led to magnesium silicates with different Mg/Si ratios: the higher the synthesis pH, the higher the Mg/Si ratio. Moreover, prepared silicates with a final Mg/Si ratio greater than 0.7, thus prepared at high pH, exhibit negligible specific surface area, whereas relatively high values (>180 m2/g) have been obtained for lower Mg/Si ratios. A set of experimental characterization data obtained by N2 physisorption, SEM, XRD, TGA-DTA as well as Raman and 29Si NMR spectroscopies are presented and discussed. They show the existence of two distinct families with a similar Magnesium Silicate Hydrate (MSH) phase, but they reveal different aggregation states and textural properties. Finally, the surface acid–base reactivity of the co-precipitated magnesium silicates was determined using the model reaction of 2-methylbut-3-yn-2-ol (MBOH) conversion. The results obtained suggest that it is possible to prepare silicates with a wide range of surface acid–base properties, from purely basic solids to those with both acidic and basic properties, by adjusting the final Mg/Si ratio via the control of the synthesis parameters. [ABSTRACT FROM AUTHOR]

A novel generation of drilling fluids based on the principle of Pickering emulsions was prepared in this work using three different types of commercial silica nanoparticles with various hydrophobicity and particle sizes. We demonstrated that a threshold of nanoparticles concentration was necessary to stabilize the emulsions which strongly depended upon the particles wettability (hydrophobicity) and sizes. Nonetheless, on increasing the water phase volume fraction, a catastrophic inversion from Water-in-Oil (W/O) to Oil-in-Water (O/W) was obtained for emulsions prepared using amphiphilic silica nanoparticles. Particles wettability has proven to be strongly affected by the pH of the aqueous phase. However, changing the salinity of the brine phase did not have remarkable effects neither on the stability to coalescence/sedimentation nor on the droplet size distribution of the emulsions prepared. Oscillatory rheology illustrates that addition of clay particles boosts fluids thixotropic properties which experienced full recovery of gel strength even after aging. The drilling fluids prepared were aged for 16 h at 350 °F (177 °C) and 500 psi (35 bar) and provided high stability contrary to surfactant stabilized Oil-Based-Mud (OBM) that failed completely after aging.

Green low-sensitivity energetic materials which can be stored under laboratory conditions and do not ignite spontaneously at room temperature are currently of high relevance due to their multiple energy applications in propulsion, pyrotechnics or civil engineering. In this context, we report a gram-scale synthesis of copper oxide (Cu2O) nanoparticles interfaced at the surface of 2D aluminum (Al) nanosheets. This synthesis is mild, cheap, and environmentally friendly, allowing us to obtain a stable and homogeneous product with high crystallinity. The burst heat released was estimated to be 6841 ± 272 J g−1 under air, and 2946 ± 306 J g−1 under a nitrogen (N2) atmosphere, which are the largest values reported so far. We attribute this superior performance to the intimate interfacing between Al and Cu2O nanoparticles. The complex reactivity of this material was thoroughly studied, permitting to account for the branching of reactions occurring in the material under different conditions, which is essential for the understanding of the factors governing the reactivity. [ABSTRACT FROM AUTHOR]

Spinodal decomposition in the TiO2- SnO2 system produces TiO2 rich/ SnO2 rich nano-wide lamellae. The high density of coherent interfaces is expected to reduce thermal conductivity of the ceramic without blocking electron transport. These semiconductors could therefore be candidates for environmental friendly oxide thermo-electrics. However, dense materials are difficult to obtain by conventional sintering from a mixture of TiO2 and SnO2 powders due to evaporation of tin oxide. The article presents a novel route to produce, by aqueous co-precipitation, Ti0.5 Sn0.5 O2 nanopowders as precursors for dense ceramics. The nanostructure developed by spinodal decomposition inside the grains of the as obtained dense Ti0.5 Sn0.5 O2 ceramic is shown to be comparable to that of porous Ti0.5 Sn0.5 O2 ceramic obtained by conventional method. [ABSTRACT FROM AUTHOR]

TiO2 aerogel–10 mol% TiO2 nanowire composite was prepared by a sol–gel technique with the addition of TiO2 nanowires to TiO2 sol, followed by supercritical drying in CO2. TiO2 nanowires (anatase with minor rutile phases) as dispersoid were prepared by a hydrothermal process followed by calcination in air at 600°C. The TiO2 nanowires were dispersed in a 2-propanol/H2O/HNO3 solution, and the mixture was added drop by drop to a tetrabutyl orthotitanate [i.e. Ti (IV) n-butoxide] solution in 2-propanol. After gelation, the TiO2 alcogel–TiO2 nanowire composite was dried in supercritical CO2 to obtain the final, TiO2 aerogel–TiO2 nanowire composite. TEM analysis revealed that a unique "nanowire network" structure was formed within the mesoporous aerogel matrix. The aerogel–TiO2 nanowire composite had a relatively large surface area 427 m2/g, with mesopores ~ 16 nm in diameter and a pore of volume of 1.63 cm3/g. [ABSTRACT FROM AUTHOR]

Abstract: Increasing the activity of a photocatalyst goes through the improvement of both its absorption (light) and adsorption (reactant) properties. For a given semiconducting material, the charge carrier separation is also a very important step. Properly combining chosen phases is one option to improve this separation (example of the commercial P25) and depositing platinum on the surface of the catalyst, another one. In some cases, coupling both may nevertheless lead to a decrease of photoactivity or at least limit the potentiality of the catalyst. A third option, consisting in modifying the morphology of the photoactive phase, has shown very promising results. In this study, we have elaborated, characterized and evaluated the hydrogen evolution potentiality (through methanol assisted water splitting) of different TiO2 morphologies: nanoparticles, nanotubes and aerogels. These materials have shown different behaviours depending on both their composition and morphology. Different types of separation processes have been claimed to account for the observed different photoactivities, with more or less pronounced synergetic effects, due to: the use of Pt as a co-catalyst, the mixture of different TiO2 phases (anatase and TiO2(B) or rutile) and the specific morphology of the samples (nanotubes or aerogels). Among all the tested samples, the TiO2 aerogel supported Pt one exhibited very promising performances, three times as active as P25 supported Pt, which is already much more active than pure P25 in our testing conditions. [Copyright &y& Elsevier]