Transformation of Discrete Amorphous Aluminosilicate Nanoparticles into Nanosized Zeolites
Résumé
The effect of amorphous aluminosilicate precursor nanoparticles on the formation the nanosized zeolites with Faujasite (FAU) and Sodalite (SOD) type frameworks is illustrated using a new synthetic strategy to prepare nanosized zeolites with tailored particle size distribution, morphology and structure. This two-steps synthesis procedure includes: (1) the formation of colloidal suspensions followed by separation of the amorphous precursor nanoparticles, (2) their subsequent transformation into nanosized crystals by treatment with alkali suspensions (NaOH) solutions only. The selective transformation of the amorphous nanoparticles into FAU and SOD nanosized crystals is studied at atomistic and microscopic levels using 29Si and 23Na NMR spectroscopy, XRD and N2 physisorption, respectively. The presence of sodalite cages occluding highly mobile sodium in the amorphous nanoparticles is confirmed by 23Na-1H D-HMQC NMR spectroscopy. The subsequent treatment of these amorphous precursor particles with aqueous sodium hydroxide illustrates that the cations are not only charge compensators but also inorganic templates stabilizing sodalite cages during the long-range ordering in the amorphous particles.
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