EaStChem, School of Chemistry, University of St. Andrews, St. Andrews, Fife KY16 9ST,United Kingdom.
J Am Chem Soc. 2009 Dec 16;131(49):17986-92. doi: 10.1021/ja907475z.
Microstructural analysis of the early stage crystal growth of zeolite A in hydrothermal synthetic conditions revealed a revised crystal growth route from surface to core in the presence of the biopolymer chitosan. The mechanism of this extraordinary crystal growth route is discussed. In the first stage, the precursor and biopolymer aggregated into amorphous spherical particles. Crystallization occurred on the surface of these spheres, forming the typical cubic morphology associated with zeolite A with a very thin crystalline cubic shell and an amorphous core. With a surface-to-core extension of crystallization, sodalite nanoplates were crystallized within the amorphous cores of these zeolite A cubes, most likely due to an increase of pressure. These sodalite nanoplates increased in size, breaking the cubic shells of zeolite A in the process, leading to the phase transformation from zeolite A to sodalite via an Ostwald ripening process. Characterization of specimens was performed using scanning electron microscopy and transmission electron microscopy, supported by other techniques including X-ray diffraction, solid-state NMR, and N(2) adsorption/desorption.
水热合成条件下沸石 A 早期晶体生长的微观结构分析表明，在生物聚合物壳聚糖存在的情况下，其晶体生长路径从表面到核心发生了修正。本文讨论了这种特殊晶体生长路径的机制。在第一阶段，前体和生物聚合物聚集形成无定形的球形颗粒。这些球体的表面发生了结晶，形成了与沸石 A 相关的典型立方形态，具有非常薄的结晶立方壳和无定形核心。随着结晶从表面向核心的扩展，方钠石纳米板在这些沸石 A 立方体内的无定形核中结晶，这很可能是由于压力的增加。这些方钠石纳米板的尺寸增大，在这个过程中打破了沸石 A 的立方壳，导致沸石 A 通过奥斯特瓦尔德熟化过程向方钠石的相转变。通过扫描电子显微镜和透射电子显微镜对样品进行了表征，并辅以 X 射线衍射、固态 NMR 和 N2 吸附/脱附等其他技术。
