Mechanism of zeolite A nanocrystal growth from colloids at room temperature.
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.
- SourceAvailable from: Jean-Pierre Gilson[Show abstract] [Hide abstract]
ABSTRACT: Nanosized faujasite (FAU) crystals have great potential as catalysts or adsorbents to more efficiently process present and forthcoming synthetic and renewable feedstocks in oil refining, petrochemistry and fine chemistry. Here, we report the rational design of template-free nanosized FAU zeolites with exceptional properties, including extremely small crystallites (10-15 nm) with a narrow particle size distribution, high crystalline yields (above 80%), micropore volumes (0.30 cm(3) g(-1)) comparable to their conventional counterparts (micrometre-sized crystals), Si/Al ratios adjustable between 1.1 and 2.1 (zeolites X or Y) and excellent thermal stability leading to superior catalytic performance in the dealkylation of a bulky molecule, 1,3,5-triisopropylbenzene, probing sites mostly located on the external surface of the nanosized crystals. Another important feature is their excellent colloidal stability, which facilitates a uniform dispersion on supports for applications in catalysis, sorption and thin-to-thick coatings.Nature materials. 01/2015;
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ABSTRACT: Abstract A novel confined-space synthesis method has been developed to synthesize zeolite nanocrystals from colloidal silica nanoparticles. The silica nanoparticles function as a silica source as well as a hard template for zeolite nanocrystals. The synthetic zeolite nanocrystals possess similar size distribution corresponding to that of colloidal silica nanoparticles. As an example, zeolite NaA nanocrystals were produced from colloidal silica particles with a size range of 70-250 nm. Firstly, mesoporous silica-carbon composite was prepared by carbonization of a nanocomposite of silica particle, polyfurfuryl alcohol (FA)) and triblock copolymer surfactant (P123). Secondly, colloidal silica particles enclosed in the mesoporous carbon matrix were transformed into zeolite NaA nanocrystals in alkaline Na2O-Al2O3 aqueous solution under hydrothermal conditions. X-ray diffraction (XRD), scanning electron microscopy (SEM), and N2 sorption were used to characterize the mesoporous carbon-silica composite and NaA nanocrystals. The amount of FA, aging time and hydrothermal time showed significant effects on the morphology and crystal size of NaA. NaA nanocrystals in a size range of 80-240 nm were prepared from the carbon-silica composite with a weight composition of 1 SiO2: 2 P123: 5 FA, which was treated in an alkaline solution with a final molar ratio of 5.85 Na2O: 1.00 Al2O3: 182 H2O (on a basis of 1 SiO2) at 80C for 7h. The zeolite nanocrystals produced in this study would be useful for fabricating zeolite-polymer nancomposite membranes. Furthermore, the as-synthesized carbon-zeolite nanocomposite would be served as a new type hierarchical nanostructured adsorbent for wastewater treatment.2008 AIChE Annual Meeting; 11/2008
Conference Paper: Chapter 1: Structural Chemistry and Properties of Zeolites[Show abstract] [Hide abstract]
ABSTRACT: Zeolites in the strict sense are highly porous crystalline aluminosilicates that comprise tetrahedrally-connected three dimensional frameworks and extra-framework charge balancing cations. The frameworks contain pores that are able to take in molecules of up to 1 nm in size (depending on the structure type) and the pore geometry can include cages and/or channels, and be one-, two-, or three-dimensionally connected. The chemical composition of both framework and extra-framework components can extend very widely whilst retaining „zeolitic‟ character. This chemical variation can arise directly during synthesis, or postsynthetically: changes include exchange of both charge-balancing and framework cations, inclusion of organic groups into the framework and replacement of framework oxygen. This chapter introduces the current diversity of framework structure types and also describes some of the structural chemistry that zeolite structures undergo, emphasising that the properties of zeolites, which make them so widely applicable, are directly related to both periodic and defect structures.5th International FEZA Conference; 07/2011