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Development of mesoporous materials by solid-liquid reactions within gel network

通过凝胶网络内的固液反应开发介孔材料

基本信息

批准号：
09555190
负责人：
NAKANISHI Kazuki
金额：
$ 1.47万
依托单位：
KYOTO UNIVERSITY
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (B)
财政年份：
1997
资助国家：
日本
起止时间：
1997 至 1998
项目状态：
已结题

来源：
https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-09555190/
关键词：
Metal Alkoxide Sol-Gel Transition Phase Separation Porous Structure Mesopores Chromatography Aging Process

项目摘要

The mesopore formation behavior in alkoxy-derived wet silica gels having co-continuous macropores has been investigated under varied conditions of aging. The starting gels were prepared via sol-gel route which include phase separation, and were aged under neutral to weakly basic conditions either by external addition or internal generation of ammonium hydroxide. The pH values of mother liquor of gels prepared in the presence of urea increased up to 10 by the thermal decomposition. Under non-hydrothemal conditions, the mesopore evolution depended only on pH values and temperatures during aging, and no substantial differences were recognized in the drying shrinkage and heat-evolution between the external and internal methods. In the additional hydrothermal aging performed with urea-containing gels, a significant acceleration of mesopore evolution rate was observed with an increase of aging temperature. At 200。C, the final size of mesopores reached 50nm with a marked decrease of their volume fraction. Above 200。C, the inner part of columnar gel skeletons eluted out and reprecipiated on their outer surface, thus resulted in the hollow columns with their walls consisting of granular building units less densely aggregated. The crystallization of the gel sample, however, was never observed possibly due to high purity of the gel samples. In contrast, the amorphous titania gels crystallized more easily under hydrothermal conditions.

研究了具有双连续大孔的烷氧基硅凝胶在不同老化条件下的中孔形成行为。起始凝胶通过溶胶-凝胶路线制备，其包括相分离，并且通过外部添加或内部生成氢氧化铵在中性至弱碱性条件下老化。在尿素存在下制备的凝胶母液的pH值通过热分解升高至10。在非水热条件下，中孔演化仅取决于老化过程中的pH值和温度，外部和内部方法之间的干燥收缩和放热没有实质性差异。在用含脲凝胶进行的另外的水热老化中，观察到随着老化温度的增加，中孔形成速率显著加快。在200 C时，介孔的体积分数明显降低，孔径达到50 nm。超过200 C时，柱状凝胶骨架的内部被洗脱出来，并在其外表面重新沉淀，从而形成中空柱，其壁由不太密集聚集的颗粒状结构单元组成。然而，可能由于凝胶样品的高纯度，从未观察到凝胶样品的结晶。相比之下，无定形二氧化钛凝胶在水热条件下更容易结晶。