Fast-Geomimicking using Chemistry in Supercritical Water.

Herein we introduce a powerful and fast method to produce nanominerals using a bottom up approach. The supercritical hydrothermal flow synthesis is exploited to produce model nanominerals by mimicking natural environments at high temperatures under pressure. This innovative concept is demonstrated with the talc synthesis; this represents a major technical breakthrough since it allows decreasing the mineral-synthesis time from tens of hours to tens of seconds. Through this example, we show these nanominerals exhibit new crystal-chemistry signals and new properties. This approach provides a means to reproduce the early stages of formation of minerals in different natural environments from sedimentary environments (low temperature and pressure) to hydrothermal/metamorphic environments (high temperature and high pressure).

Effect of Thermal Treatment on the Textural Properties of CeO2 Powders Synthesized in Near- and Supercritical Alcohols.

CeO2 nanocrystals (NCs) have attracted increasing interest over the past few years, in particular for their use in catalytic reactions. Syntheses mediated by near- and supercritical alcohols have proven to be innovative ways to obtain CeO2 NCs with controlled crystallite sizes (from 3 to 8 nm depending on the alcohol) and surface functionalities, with alcohol moieties. When submitted to a thermal treatment at 500 °C, required to desorb/degrade surface organic species, these powders displayed different behaviors depending on the alcohol used during the synthesis. Cerium oxide powders synthesized in sc-MeOH, sc-EtOH and sc-iPrOH undergo sintering during treatment at 500 °C, with a decrease of their specific surface area. Conversely, those synthesized in sc-BuOH, nc-PentOH and nc-HexOH keep their initial crystallite sizes and morphology, but show a great enhancement of their specific surface area (up to 200 m(2) g(-1)), which is unprecedented after such a thermal treatment.

CeO2 nanocrystals from supercritical alcohols: new opportunities for versatile functionalizations?

The fast and controlled synthesis of surface-modified cerium oxide nanoparticles was carried out in supercritical {ethanol + alcohol derivative} mixtures. The newly found ability of supercritical alcohols to graft onto cerium oxide nanocrystals (CeO2 NCs) during their synthesis was exploited to control their surface chemistry via the addition of three aminoalcohols: ethanolamine, 3-amino-1-propanol and 6-amino-1-hexanol. Although the ethanol to aminoalcohol ratio was consistent (285:1), the successful grafting of these alcohol derivatives onto CeO2 NCs was identified based on Fourier transform infrared (FTIR) and thermogravimetric analysis-mass spectrometry (TGA-MS) measurements. Smaller crystallite size of CeO2 NCs synthesized in the presence of aminoalcohols, compared to those synthesized in supercritical ethanol alone, were also noticed and attributed to a possible intervention of amine groups helping the grafting of the alcohols, allowing one to stop the growth of the CeO2 NCs faster. The use of supercritical alcohol mixture-ethanol with hexanol, dodecanol, or octadecanol, with a 285:1 ratio-was also investigated. Such mixtures allow accessing a finer control in CeO2 NCs crystallite size compared to pure alcohols, according to calculation made from X-ray diffraction measurements. Finally, fluorescent molecules (fluorescein isothiocyanate) were grafted onto amine-modified CeO2 NCs. The powders displayed a fluorescent behavior under UV light, confirming the suitability and interest of CeO2 NCs surface modification by such technique.

Near- and supercritical alcohols as solvents and surface modifiers for the continuous synthesis of cerium oxide nanoparticles.

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.