Nanocrystals and Ultrafine Particles

Zeolite Bulk source Linuid nhase Crystallization Maximun 

In general, molecular sieve nanocrystals and ultra-fine powders( 200 nm)are prepared by the following methods  

The above rules are consistent with the assumptions about the crystallization process of nanocrystals proposed by Van Grieken et al.[123] These rules provide useful guidance for the best conditions in the synthesis of nanozeolites and ultra-fine particles. 

High-quality molecular sieve nanocrystals can be prepared by hydrothermal crystallization in the initial reaction gel system. The key point is the strict control of the reaction conditions. In 2003, Yan and colleagues[126] investigated the influence of [TMA+] concentration and anion [Br ] and [OH-] concentrations on the formation and yield of zeolite Y nanocrystals in the 1.00 A1203 4.35 Si02 2.4 (TMA)20(2 OH-) (1 1.2) (TMA)20(2 Br ) 0.048, a20 249.0 H20 system at 100°C. When TMABr was added to the reaction system as a second SDA, the nanocrystal size decreased (generally stable under 40 nm), and a yield improvement of zeolite Y could be observed due to the increase of nucleation rate. Furthermore, the effect of the TMABr/TMAOH ratio in the reaction system on the nanocrystal sizes and yield of as-made product was also studied, and, based on this, zeolite Y nanocrystals with controllable particle sizes of 32 120 nm were synthesized. 

Ultra-fine particles of molecular sieves (0.2 0.5 pm) can also be synthesized by hydrothermal crystallization in a suitable reaction gel system. The key to this synthesis is again the study of the crystallization process and the control of crystallization conditions. 

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