Host-guest inclusion compound from nitramine crystals exposed to condensed carbon dioxide.

HNIW or CL20 (2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane) is a nitramine, which is considered as the highest energetic molecular compound known to date, therefore, attracting increasing interest in propulsion applications. Additionally, CL20 is an interesting system for fundamental studies, exhibiting several polymorphs, which can behave as host lattices for trapping guest molecules. Herein, a new CL20 structure that contains inserted CO(2) molecules is reported. A combination of Fourier transform infra red (FTIR) spectroscopy, scanning electron microscopy (SEM), single-crystal X-ray diffraction, and thermal analyses (thermogravimetric analysis coupled with mass spectrometry and differential scanning calorimetry) was used to characterize this new material.

In situ IR spectroscopy and ab initio calculations to study polymer swelling by supercritical CO(2).

The CO(2) sorption and polymer swelling of hydroxytelechelic polybutadiene (HTPB) and poly(ethylene glycol) (PEG) have been investigated as a function of temperature and CO(2) pressure by combining in situ near-infrared spectroscopy with molecular modeling. The results reported here for the PEG-CO(2) system are in a very good agreement with literature data hence validating our experimental procedure. It has been found that CO(2) sorption and swelling effect is more important for PEG than for HTPB. For both polymers, an increase of temperature leads to a strong decrease of both the CO(2) sorption and swelling. In order to identify at a molecular level the nature and strength of intermolecular interaction occurring between CO(2) and the polymers, ab initio calculations have been performed on model structures, representative of the main functional group of the polymer, and their complex with CO(2). Trans-3-hexene (3-Hex), propyl methyl ether (PME) and methoxytrimethylsilane (MTMS) have been selected to mimic the functional groups of HTPB, PEG and polydimethyl siloxane (PDMS), respectively. The last system has been chosen since previous works on the swelling of PDMS by high pressure CO(2) have revealed the high ability of CO(2) to swell both uncrosslinked and crosslinked PDMS. The calculated stabilization energies of the MTMS-CO(2), PME-CO(2), and 3-Hex-CO(2) dimers indicate that CO(2) interacts specifically with the three moieties through a Lewis acid-Lewis base type of interaction with the energies displaying the following order: E(MTMS-CO(2)) = -3.59 > E(PME-CO(2)) = -3.43 > E(3-Hex-CO(2)) = -2.5 kcal/mol. Since the solubility of CO(2) in the corresponding homopolymers follows the same order, it is evidenced that the stronger the interaction between CO(2) and the polymer, the higher the CO(2) sorption. Therefore, even if one cannot exclude the influence of free volume and chain flexibility of the polymer, it appears that the solubility of CO(2) in the polymer is predominantly governed by the interaction between CO(2) and the polymer. Although the same trend is observed for the swelling of the polymer as a function of the CO(2) pressure, we have found that for a given value of CO(2) sorption, the swelling of the polymer depends on its nature, meaning that the swelling is not only governed by the CO(2)-polymer interaction but also by other intrinsic properties of the polymer.

Current and foreseeable applications of supercritical water for energy and the environment.

It is crucial to develop economical and energy-efficient processes for the sustainable transformation of biomass into fuels and chemicals. In this context, supercritical water biomass valorization (SCBV) processes are an alternative way to produce biogas, biofuels, and valuable chemicals. Supercritical water technology has seen much progress over the last fifteen years and an industrial application has merged: the supercritical water oxidation of wastes. The evolution from lab-scale to pilot-scale facilities has provided data on reaction mechanisms, kinetics, modeling, and reactor technology as well as an important know-how, which can now be exploited to use the reactivity in supercritical water to transform biomass into gases (CO, H(2), CO(2), CH(4), and N(2)) or into liquids (liquid fuel and valuable chemicals) with the supercritical water biomass gasification and liquefaction processes, respectively. This Review highlights the potential of SCBV processes to transform biomass into gas and liquid energy sources and highlights the developments that are still necessary to push this technology onto the market.

Preparation of functional hybrid palladium nanoparticles using supercritical fluids: a novel approach to detach the growth and functionalization steps.

We report a novel and versatile approach to control separately the growth and functionalization steps in preparing functional nanomaterials. The applicability of this method was demonstrated with the preparation of palladium nanoparticles capped with thiol or stabilized with ionic liquid.

Tailor-made surface properties of particles with a hydrophilic or hydrophobic polymer shell mediated by supercritical CO2.

Controlling the surface characteristics of inorganic materials with an organic shell is of great interest for control of the properties of the final material. A challenge is thus to be able to deposit a polymer shell with different solvation properties onto the surface of inorganic particles and to have a good control of the thickness of the organic layer without a prefunctionalization of surfaces. We demonstrate, in this paper, a method for coating silica particles (170-550 nm), used as model substrates, with either a hydrophilic (polyethylene glycol) or a hydrophobic polymer (polybutadiene hydroxy terminated) using a supercritical antisolvent process (precipitation from a compressed antisolvent). Several operating parameters were studied to control precisely the thickness of the deposited layer (from 2 to 30 nm), which was characterized using TEM, FESEM, XPS, and UV-visible techniques. This work demonstrates that supercritical antisolvent processes are powerful methods and good alternatives to conventional coating techniques toward the development of hybrid and/or core-shell nanomaterials.

General approach for the synthesis of organic-inorganic hybrid nanoparticles mediated by supercritical CO2.

We report in this paper novel chemistry that addresses the problem of surfactant solubility in supercritical CO2 for metal nanoparticle synthesis. This new approach for the preparation of organic-functionalized inorganic nanoparticles relies on the reduction of a metal precursor in a CO2-containing insoluble polymer. Reduction of the metal with H2 leads to small nanocrystals stabilized by the polymer with a relatively small polydispersity. The functionalized metal nanoparticles are recovered as a dry powder, free of any organic solvents, which can then be resuspended in an appropriate solvent. This approach limits the number of steps for the preparation of functional nanoparticles which are ready for use. To illustrate this, we report results of the preparation of palladium and silver nanoparticles of 3-5 nm size stabilized with hyperbranched polyamines, functionalized with perfluoroalkyl, perfluorooligoether, non-fluorinated alkyl, polysiloxane, or polyethylene glycol moieties.

Design at the nanometre scale of multifunctional materials using supercritical fluid chemical deposition.

Recent developments in multifunctional devices show the interest in combining different materials to obtain specific properties. Through supercritical fluid chemical deposition (SFCD), silica spheres, used as a model support, were coated with copper nanoparticles (5-17 nm) with a tuneable amount of coverage (40-80%). The coating process is based on the reduction of metal precursors with hydrogen in a supercritical CO(2)/isopropanol mixture in a temperature range between 100 and 150 °C at 24 MPa. Several parameters were studied such as temperature, residence time or mass ratio of precursor/silica spheres, allowing control of the size of the copper nanoparticles and of the amount of coverage from metal nanoparticles scattered onto the surface to a metal nanoparticle thin film.

Supercritical fluid technology of nanoparticle coating for new ceramic materials.

This work highlights, for the first time, the coating of ferroelectric nanoparticles with a chemical fluid deposition process in supercritical fluids. BaTiO3 nanoparticles of about 50 nm are coated with a shell of a few nanometers of amorphous alumina and can be recovered as a dry powder for processing. The sintering of these core-shell nanoparticles gives access to a ceramic material with very interesting ferroelectric properties, in particular, dielectric losses below 1%.