Supercritical fluids offer fast and facile routes toward well-crystallized tailor-made cerium oxide nanoparticles. However, the use of surfactants to control morphology and surface properties remains essential. Therefore, although water, near-critical (nc) or supercritical (sc), is a solvent of choice, the poor water solubility of some surfactants could require other solvent systems such as alcohols, which could themselves behave as surface modifiers. In here, the influence of seven different alcohols, MeOH, EtOH, PrOH, iPrOH, ButOH, PentOH, and HexOH, in alcothermal conditions (300 °C, 24.5 MPa) over CeO(2) nanocrystals (NCs) size, morphology, and surface properties was investigated. The crystallite size of the CeO(2) nanocrystals can be tuned in the range 3-7 nm depending on the considered alcohol, and their surface has been modified by these solvents without the use of surfactants. Mechanisms are proposed for the interaction of primary and secondary alcohols with CeO(2) surface and its functionalization during the synthesis based on FTIR and TGA-MS studies. This study allows apprehending the role of alcohols during the synthesis and may lead to an informed choice of solvent as a function of the required size and surface properties of CeO(2) NCs. It also opens new route to CeO(2) functionalization using supercritical alcohol derivatives.

Solid‐sate monolithic macrocellular foams are synthesized by mineralizing the continuous phase of oil‐in‐water Pickering emulsions, used as templates, with the sol–gel process. For the first time, taking advantage of the limited coalescence phenomenon occurring in emulsions stabilized by solid particles, concentrated emulsions with calibrated drop size are produced, leading to the synthesis of monolithic foams with nearly monodisperse macroscopic voids. Such a strategy allows independent tuning of the macrocellular void diameters from 20 to 800 μm and the diameter of the windows connecting adjacent cells. The obtained macrocellular foams also bear micro‐ and mesoporosity, leading to Brunauer, Emmet and Teller (BET) surface area values between 700 and 900 m2 g−1 with a good mesopores monodispersity.

No abstract

Hydrolysis and condensation of (CH3COCHCOCH3)2SnF(Otert-Am) and (CF3COCHCOCH3)2Sn(Otert-Am)2 gave soluble stannic oxo-oligomers or -polymers including fluorine and β-diketonate groups. Under thermal treatment in air at 550 °C, they yielded nanocrystalline fluorine-doped tin dioxide powders. The amount of remaining ligands in the xerosols depends on the hydrolysis ratio and on the nature of the solvent used, dimethylformamide (DMF) favoring ligand removal. The thermolytic reactions have been investigated by thermogravimetry coupled to mass spectrometry: (1) the β-diketonate ligands pyrolyze in two stages, at 200 and 320 °C, involving two different processes; (2) elimination of polar solvents of high boiling point, such as DMF, occurs up to 300 °C; (3) fluorine is lost as fluorhydric acid from 230 °C. The best strategy to prepare F-doped SnO2 materials by the sol−gel route is thus to start from precursors including Sn−F bonds and to use a polar aprotic solvent of low boiling point such as acetonitrile. It led to nanocrystalline, highly conductive F-doped tin dioxide materials with resistivities 1 order of magnitude lower than that reported for Sb-doped tin dioxide powders.

The elaboration of organo-silica-based hybrid monoliths exhibiting a hierarchical trimodal porous structure (micro-, meso-, and macroporosity) with tunable functionality have been synthesized for the first time via high internal phase emulsion (HIPE) process and lyotropic mesophases. Through one-pot synthesis, many organic functionalities that can act as network modifiers (methyl, dinitrophenylamino, benzyl, and mercaptopropyl) or co-network formers (pyrrol) have been anchored to the amorphous silica porous network. The resulting materials have been thoroughly characterized via a large set of techniques: SEM, TEM, SAXS, mercury porosimetry, nitrogen adsorption isotherms, FTIR, 29 Si MAS NMR, and XPS. These sol-gel-derived hierarchical open-cell functional hybrid monoliths exhibit macroscopic void spaces ranging from 5 µm up to 30 µm and their accessible micro-and mesoporosities reveal hexagonal organization for the dinitrophenylamino-, benzyl-, and pyrrol-based hybrids. The average condensation degree for these hybrid networks ranges between 86 and 90%, yielding shaped monoliths with both good integrity and sufficient mechanical properties to be usable as functional catalytic or chromatographic supports. Also, function accessibility has been demonstrated through heterogeneous nucleation of Pd metallic nanoparticles.

No abstract

Photocatalytic activities of mesoporous RuO 2 /TiO 2 heterojunction nanocomposites for organic dye decomposition and H 2 production by methanol photoreforming have been studied as a function of the RuO 2 loading in the 1−10 wt % range. An optimum RuO 2 loading was evidenced for both kinds of reaction, the corresponding nanocomposites showing much higher activities than pure TiO 2 and commercial reference P25. Thus, 1 wt % RuO 2 /TiO 2 photocatalyst led to the highest rates for the degradation of cationic (methylene blue) and anionic (methyl orange) dyes under UV light illumination. To get a better understanding of the mechanisms involved, a comprehensive investigation on the photogenerated charge carriers, detected by electron spin resonance (ESR) spectroscopy in the form of O − , Ti 3+ , and O 2 − trapping centers, was performed. Along with the key role of superoxide paramagnetic species in the photodecomposition of organic dyes, ESR measurements revealed a higher amount of trapped holes in the case of the 1 wt % RuO 2 /TiO 2 photocatalyst that allowed rationalizing the trends observed. On the other hand, a maximum average hydrogen production rate of 618 μmol h −1 was reached with 5 wt % RuO 2 /TiO 2 photocatalyst to be compared with 29 μmol h −1 found without RuO 2 . Favorable band bending at the RuO 2 /TiO 2 interface and the key role of photogenerated holes have been proposed to explain the highest activity of the RuO 2 / TiO 2 photocatalysts for hydrogen production. These findings open new avenues for further design of RuO 2 /TiO 2 nanostructures with a fine-tuning of the RuO 2 nanoparticle distribution in order to reach optimized vectorial charge distribution and enhanced photocatalytic hydrogen production rates.

No abstract