Porous aggregates of unidirectionally oriented microcrystallites of heteropoly compounds
Porous aggregates of unidirectionally oriented microcrystallites of heteropoly compounds
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DOI：
10.1016/s1387-1811(98)00010-9
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发表时间：
1998-05-01
影响因子：
5.2
通讯作者：
Misono, M
中科院分区：
文献类型：
--
作者：
Inumaru, K;Ito, T;Misono, M
用SEM、XRD、TEM、艾德能谱和N2吸附等方法对不同温度下沉淀的Cs3 PW 12 O 40和（NH 4）（3）PW 12 O 40的聚集体进行了表征。不同的沉淀温度和阳离子的种类，其微观结构有很大的不同。在298 K下析出的Cs_3PW_（12）O_（40）形成分散或松散聚集的Ca. 10 nm，具有随机晶体取向。当温度升高到368 K时，Cs3 PW 12 O 40自组装形成微孔聚集体，其中微晶的晶面是单向取向的，但彼此之间没有太多的外延连接。（NH_4）（3）在273 K沉淀的PW_（12）O_（40）形成了类似于在368 K沉淀的Cs_3 PW_（12）O_（40）的圆形聚集体，而在368 K沉淀的NH_4盐形成了十二面体聚集体，其中微晶相互外延连接（外延自组装）。这些观察结果表明，微观结构由沉淀条件下的溶解度控制;随着沉淀温度的升高或阳离子半径的减小，聚集体的微观结构由无规聚集体变为单向取向的微晶，微晶之间的外延连接发展。(C)1998 Elsevier Science B. V.保留所有权利。
The microstructures of aggregates of heteropoly compounds Cs3PW12O40 and (NH4)(3)PW12O40 precipitated at various temperatures were characterized by SEM, XRD, TEM, ED, and N-2 adsorption. The microstructures were remarkably different according to the precipitation temperature and the kind of cation. Cs3PW12O40 precipitated at 298 K formed dispersed or loosely aggregated fine particles of ca. 10 nm with random crystal orientation. As the temperature increased to 368 K, Cs3PW12O40 self-assembled to form microporous aggregates in which the crystal planes of microcrystallites were oriented unidirectionally, but were not much connected epitaxially with each other. (NH4)(3)PW12O40 precipitated at 273 K formed round aggregates similar to Cs3PW12O40 precipitated at 368 K, while the NH4 salt precipitated at 368 K formed dodecahedral aggregates in which microcrystallites were epitaxially connected with each other (epitaxial self-assembly).These observations indicate that microstructure is controlled by the solubility at the precipitating conditions; with increasing precipitation temperature or decreasing ionic radii of cation, the microstructure of aggregates varies from the random aggregates to unidirectionally oriented microcrystallites and the epitaxial connection between microcrystallites develops. (C) 1998 Elsevier Science B.V. All rights reserved.