One-Pot Synthesis of A Cubic Silicate Phase Functionalized With Phenyl Groups
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hexagonal silicate phases functionnalized with the organic R groups. By following this synthetic approach, a large amount of organic groups can be introduced (up to 25 mol% compared to the total Si amount) without alteration of the porous structure; however, the presence of the R groups at the silica surface, and therefore their accessibility for further reactants, has to be confirmed. One can think that the R groups could develop specific interactions with the surfactant molecules, and thus be pushed to react at the surfactant/silicate interface: indeed bromination reaction performed on vinyl-functionnalized systems have proved that the organic groups are accessible, and thus certainly at the silicate surface [6]. Most of the previous functionnalized porous silicates were prepared under basic conditions with CTAB, and hexagonal (2d, p6m) phases were obtained. We have chosen to work under acidic conditions, similar to those developed by Stucky et al. [13-15] to prepare the SBA series of silicates. Two main reasons for that: (i) trifunctionnal alkoxides are known to hydrolyze faster under acidic conditions, which could favor their reaction with TEOS; (ii) the interactions between the silicate species and the surfactant moieties are weak under acidic conditions: the surfactant can be simply extracted by reaction in ethanol [ 14]. This is a great advantage for these systems in order not to alter the R groups during the removal of the surfactant; solvent extraction represents thus a gentle alternative to calcination. Preparation of a series of organically modified porous silicates have already been reported with emphasis given to the phenyl containing system [12]. In this previous study, phenyltriethoxysilane 229 Mat. Res. Soc. Symp. Proc. Vol. 576 ©1999 Materials Research Society
(PhTES) and TEOS were first pre-hydrolyzed in ethanol before reaction with an acidic solution of CTAB: a microporous phenyl modified silicate with the hexagonal (2d p6m) symmetry was obtained after calcination at 350°C, characterized by a type I isotherm and a BET surface area of 1000 m2/g. In the present study, the synthetic procedure has been slightly modified: the two alkoxides were directly reacted with the CTAB solution without the pre-hydrolysis step. In this case, surprisingly, a cubic phase has been obtained. This paper will report on the characterization of this new organically modified porous phase. EXPERIMENTAL SECTION TEOS (Fluka) and PhTES (Fluka) in a 4:1 molar ratio were mixed with an acidic solution of CTAB (CTAB/Si = 0.12; HCIIIH 2 0/Si = 9.2/130/1), and stirred for several hours. The precipitate was then filtered, rinsed with distilled water and dried at 100°C. Removal of the surfactant wa•; performed by solvent extraction in ethanol at 65°C. Calcinations were done in tubular furnace under oxygen with a heating rate of 50°C/h. The low angle X-ray diffraction patterns were recorded either at LURE, the French synchroton facility, with a wavelength of X•= 1.2836 A•,or with a Philips diffractometer using the Cu Kcx wavelength.
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