Effects of silicon sources on the formation of nanosized LTA: An in situ small angle X-ray scattering and wide angle X-ray scattering study

Abstract

The formation of LTA nanocrystals from clear solutions containing different silicon sources, tetramethylammonium (TMA) silicate, tetraethylorthosilicate (TEOS), and colloidal silica (Ludox SM 30) was studied by in situ small angle X-ray scattering and wide angle X-ray scattering. The size of the precursor particles formed at the initial stage of the reaction appears to strongly dependent on the type of silicon sources employed. When TMA silicate was used, 4.5 nm sized precursor particles were formed after heating for 10 min at 110 °C, which were consumed during the crystallization and played an important role in the nucleation process. 13 nm sized particles were formed from the beginning of reaction when TEOS was used as a silicon source. On the other hand, 17 nm sized particles were observed from the synthesis solution containing Ludox SM 30. The 13 and 17 nm sized particles formed in the synthesis solutions with TEOS and Ludox SM 30, respectively, may not be the precursor particles in the crystallization, but the reservoir of silicon source. 29Si NMR spectra suggest the formation of the D4R in the initial stage of crystallization depends on the silicon source, and similarly 27Al NMR spectra indicate that, as the crystallization proceeds, the distribution of Al sites changes progressively from small aluminosilicate species to cage-like species. The synthesized crystals were characterized by X-ray diffraction and scanning electron microscopy. The morphology of the LTA crystals synthesized from the three different synthesis solutions was found to be different depending on the silicon sources.