Article

Mechanism of zeolite A nanocrystal growth from colloids at room temperature.

Department of Chemistry, Purdue University, West Lafayette, IN 47907, USA.
Science (Impact Factor: 31.48). 03/1999; 283(5404):958-60. DOI: 10.1126/science.283.5404.958
Source: PubMed

ABSTRACT The formation and growth of crystal nuclei of zeolite A from clear solutions at room temperature were studied with low-dose, high-resolution transmission electron microscopy in field emission mode and with in situ dynamic light scattering. Single zeolite A crystals nucleated in amorphous gel particles of 40 to 80 nanometers within 3 days at room temperature. The resulting nanoscale single crystals (10 to 30 nanometers) were embedded in the amorphous gel particles. The gel particles were consumed during further crystal growth at room temperature, forming a colloidal suspension of zeolite A nanocrystals of 40 to 80 nanometers. On heating this suspension at 80 degrees C, solution-mediated transport resulted in additional substantial crystal growth.

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    • "The increase in the chemical shift in the 29 Si MAS NMR spectrum demonstrates that the Si/Al ratio of the gel skeleton decreased as the geopolymerization process continued. These results confirm the same coordination in the Al 2 O 3 –2SiO 2 –Na 2 O geopolymer and the NaA zeolite structures and the existence of NaA zeolite seeds in the geopolymer, which can be grown into NaA zeolite crystals under proper crystallization conditions [15] [16] [22] [23] "
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    • "Although the physical and chemical properties of zeolites largely depend on their structures, the morphology and size distribution of zeolite crystals also have a significant effect on their properties and applications. Recently, a lot of work has been performed to investigate the nucleation mechanism [3] [4] and the hydrothermal synthesis parameters [5] that may influence the crystal size and morphology of NaA zeolites, such as the solvent [6], Si/Al ratio in the gel [7] [8], solid/ liquid ratio [9], alkalinity [9] [10] [11] [12], crystallization time [13] and temperature [14] used during synthesis. The results showed that the overall chemical composition of the reaction mixture, especially its alkalinity, determined the morphology of the crystalline end products. "
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