A copper hydroxynitrate of stoichiometry Cu 2 (OH) 3 NO 3 , analogous to the layered double hydroxide family, was synthesized by the so-called controlled double jet precipitation technique, and by hydrolysis of urea in the presence of copper nitrate. Special attention has been focused on the size, morphology and agglomeration tendency of the particles. The aim of this work is to define the optimum precipitation conditions in terms of quality and dispersability of the recovered product. Such platelet-like particles can be used as anisotropic fillers in nanocomposite materials. Several reaction parameters such as flow and concentration of the reactant solutions, design of the reactor and addition of a growth modifier were studied. r
Synthetic lamellar silica and hybrid lamellar silicas have been prepared by liquid crystal templating, template extraction and silanization. The samples have been characterized by thermogravimetric analysis (TGA), carbon analysis, spectroscopy, X-Ray diffraction (XRD) and nitrogen adsorption. The XRD analyses have shown that the lamellar periodic stacking is preserved for all samples. The quantity and type of organic molecules at the silica surface have been evaluated by carbon analysis, TGA and spectroscopy. The covalent grafting of the solvent used for extraction of the initial surfactant has been highlighted by these analyses. The nitrogen adsorption analyses have revealed three categories of pores and two types of samples. The initial lamellar silica exhibits a very low specific surface area and plate-like type of pores. The second type of samples is made up of the hybrid samples and the initial substrate from whom the surfactant has been extracted. These samples show a significantly higher specific surface area with interlamellar spaces corresponding to narrow slit -like mesopores around 4 nm. The nitrogen adsorption data analysis has highlighted the presence of micropores within the silica sheets. The difference of specific surface is due to pore blocking by the surfactant impeding the access to nitrogen into interlamellar spaces and by the silanes covering the pores once the surface modified. The presence of micro and mesopores combined to a high BET specific surface of 612 m²/g make these lamellar silicas interesting materials for catalysis applications.
The covalent grafting of low-molecular weight poly(ethylene glycol) (PEG) onto high surface silica nanoparticles (Cab-O-Sil EH5) has been accomplished by a multi-step reaction. Reaction involved PEG attachment by epoxide-terminated ring opening of a sylilation agent previously grafted. A maximum grafting density of 0.42 PEG per nm≤ has been determined by thermogravimetric analysis (TGA). Differential scanning (DSC) calorimetry confirmed the modification of silica after reaction. Infra-Red (IR) analysis and Carbon-13 Magic Angle Spinning Nuclear Magnetic Resonance ( 13 C MAS NMR) confirmed PEG fixation and opening of the epoxide ring. EXPERIMENTAL DETAILSCab-O-Sil EH5 fumed silica (Cabot Corporation) has a specific surface of 380 m≤/g, 4 OH groups / nm≤ and is made of nanoparticles arranged in a non-porous three-dimensional branched chain aggregates. Tetrahydrofuran (THF) and toluene used for reaction were dried over sodium for a night. Methoxypoly(ethylene glycol) 350 (PEG, M w = 350, Aldrich) was dried by three successive azeotropic distillations with toluene. 3-glycidoxypropyl trimethoxysilane (GPS, Gelest) and dry sodium hydride 95% (Aldrich) were used as received. Technical grade toluene and isopropanol were used for washing procedure. Glassware was heated under vacuum to remove moisture and all reactions were carried out under nitrogen atmosphere.
This paper is focused on the preparation and characterization of different lamellar silica prepared by liquid crystal templating and silanisation. The initial template can be removed and replaced in the interlamellar spaces by different types of silane, being covalently grafted to the solid by reaction with the surface silanols. The lamellar stacking periodicity remains after this modification. The surfactant extraction can lead in significant grafting of isopropanol if the solid is simply refluxed in isopropanol, which have the effect of preserving the periodicity of the lamellar stacking. The surfactant extraction in an Soxhlet equipment avoid this reaction, with the effect of platelets organization collapsing. The lamellar silica studied exhibit great specific surface and combination of meso and microporosity, making them interesting materials for nanocomposite or catalysis applications.
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