Hydrothermal crystallization of clathrasils in acidic medium: energetic aspects
Résumé
A series of clathrasils, including AST, DOH, MTN, and DDR topologies, were synthesized in an acidic medium. The general composition of the initial system was 1 SiO 2 : 0.3-0.5 SDA: 0.1-0.5 HF/NH 4 F: 0-0.3 HBr: 10-50 H 2 O in the pH range of 2-6, where SDA stands for organic amines or ammonium ions as the structure-directing agents. And the hydrothermal syntheses were performed in the 150-200°C temperature range. Besides elaborating the synthesis recipes and product characterizations, the study also attempted to elucidate the origins of slow crystallization kinetics. It was found that the thermodynamic stabilities of the SDA@Framewrok-SiO 2 compounds play an overwhelming role in the crystalline phase selection. The finding of this study can be used as a guidance of silica-based porous materials synthesis under acidic conditions.
Domaines
Matériaux
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