In situ small-angle and wide-angle X-ray scattering investigation on nucleation and crystal growth of nanosized zeolite A
In situ small-angle and wide-angle X-ray scattering investigation on nucleation and crystal growth of nanosized zeolite A
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DOI：
10.1021/cm062827j
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发表时间：
2007-04-17
影响因子：
8.6
通讯作者：
Okubo, Tatsuya
中科院分区：
文献类型：
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作者：
Fan, Wei;Ogura, Masaru;Okubo, Tatsuya
从组成为11.25:1.8:13.4:x:700 SiO2:Al2O3:(TMA)(2)O:NaOH:H2O （x = 0.6, 0.9, 1.2）的四甲基铵阳离子透明溶液开始，从前体颗粒的形成开始，经过成核阶段，最终完全转变为林德A型（LTA）沸石纳米晶体并生长。通过同步原位小角x射线散射（SAXS）和广角x射线散射（WAXS）监测了1.5)。在结晶过程中形成尺寸约为0.5 nm的初级单位和尺寸约为4.5 nm的前驱体颗粒。尺寸为4.5 nm的前驱体颗粒在成核过程中起重要作用。通过改变合成溶液中Na+阳离子的浓度，研究了Na+对结晶的影响。发现Na+阳离子不仅影响成核过程，而且影响晶体生长过程。当x < 1.5时，前驱体粒子的数量密度随着Na+浓度的增加而增加，这是由于Na+的结构影响和电荷补偿作用。然而，当Na+浓度较高（x = 1.5）时，在合成开始时，在合成溶液中观察到6 nm大小的颗粒，这是由于Na+的盐出效应。另一方面，对前驱体颗粒结构的研究表明，前驱体颗粒不具有长程有序，而具有与晶体LTA结构相关的中程有序，这些中程有序在水热处理过程中变得有序。
The entire sequence of crystallization processes, starting with the formation of precursor particles, proceeding through the nucleation stage, and finishing with complete transformation into Linde type A (LTA) zeolite nanocrystals and crystal growth, from a clear solution using tetramethylammonium cation with the composition 11.25:1.8:13.4:x:700 SiO2:Al2O3:(TMA)(2)O:NaOH:H2O (x = 0.6, 0.9, 1.2, or 1.5) has been monitored by simultaneous in situ small-angle X-ray scattering (SAXS) and wide-angle X-ray scattering (WAXS). Primary units with a size of ca. 0.5 nm and precursor particles with a size of ca. 4.5 nm are formed during the crystallization. The precursor particles with a size of 4.5 nm play an important role during the nucleation process. The influences of Na+ on the crystallization are studied by varying the concentration of Na+ cations in the synthesis solution. It is found that the Na+ cations affect not only the nucleation process but also crystal growth process. When x < 1.5, the number density of the precursor particles increases with the concentration of Na+, which is due to the structure-making influence and charge-compensating role of Na+. However, when the concentration of Na+ is relatively high (x = 1.5), the 6 nm sized particles in the synthesis solution are observed at the beginning of the synthesis, which is due to the salt-outing effect of Na+. On the other hand, the studies on the structure of the precursor particles suggest that they do not contain long-range order, but some medium-range order related to the crystalline LTA structure, which become ordered during the course of hydrothermal treatment.