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Study of Capillary Condensation within Ordered Mesoporous Materials

有序介孔材料内毛细管凝聚的研究

基本信息

批准号：
12440201
负责人：
MORISHIGE Kunimitsu
金额：
$ 6.27万
依托单位：
Okayama University of Science
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (B)
财政年份：
2000
资助国家：
日本
起止时间：
2000 至 2002
项目状态：
已结题

项目摘要

In order to elucidate s capillary condensation phenomenon, which is one of the long-standing problems in the field of colloid and interface science, we performed measurements of adsorption-desorption isotherms of simple gases on ordered mesoporous materials with well-defined porous structures. First, we constructed a high-pressure adsorption apparatus that enables adsorption measurements in the temperature and pressure ranges of 20-300K and 0-30 atm. At low temperature, the adsorption-desorption isotherms of nitrogen, oxygen, argon, and carbon dioxide on SBA-16 with ink-bottle type pore exhibited large hysteresis loops of type H2 in the IUPAC classification. When the temperature was increased, the hysteresis shrank and eventually disappeared at a hysteresis temperature, well below the bulk critical temperature. The plots of the relative pressures of capillary condensation and evaporation against the reduced temperature for the above four gases conform to a single curve. A phenomenologi … More cal model of a gas bubble in a liquid confined to the spherical pore of SBA-16 explains well the temperature dependence of adsorption hysteresis observed experimentally. This clearly indicates that the energy barrier for formation and disappearance of vapor bubbles in the liquid confined to the pores is responsible for the appearance of the adsorption hysteresis and the hysteresis temperature is not concerned with the so-called capillary criticality. At low temperatures, the adsorption-desorption isotherms of nitrogen and carbon dioxide on MCM-41 and SBA-15 with cylindrical pores exhibited relatively small hysteresis loops of type H1 in the IUPAC classification. In the cylindrical pores, however, the temperature dependence of the hysteresis loop for nitrogen was different from that for carbon dioxide. This indicates that the mechanism of the hysteresis in the cylindrical pores differs from that in the ink-bottle pores. The results for MCM-48 ordered mesoporous adsorbent with well-defined three-dimensional networks of cylindrical pores strongly suggests that interconnections among pores of almost the same size and geometry do not have a significant effect on the adsorption hysteresis and pore criticality. Less

为了解释毛细管冷凝现象，这是胶体和界面科学领域长期存在的问题之一，我们测量了简单气体在具有明确多孔结构的有序介孔材料上的吸附-解吸等温线。首先，我们构建了一个高压吸附装置，可以在20-300K和0-30 atm的温度和压力范围内进行吸附测量。低温条件下，具有墨水瓶型孔的SBA-16对氮气、氧气、氩气和二氧化碳的吸附-解吸等温线表现出IUPAC分类中较大的H2型滞回线。当温度升高时，迟滞缩小，并最终在远低于体临界温度的迟滞温度下消失。上述四种气体的毛细冷凝和蒸发相对压力随降低温度的变化曲线符合一条曲线。一个局限于SBA-16球形孔内的液体气泡的现象模型很好地解释了实验观察到的吸附滞后的温度依赖性。这清楚地表明，限制在孔隙内的液体中蒸汽泡形成和消失的能量垒是导致吸附滞后现象的原因，而滞后温度与所谓的毛细临界无关。低温条件下，具有圆柱孔的MCM-41和SBA-15对氮气和二氧化碳的吸附-解吸等温线在IUPAC分类中表现出相对较小的H1型滞回线。然而，在圆柱形孔隙中，氮气的滞回线与二氧化碳的滞回线的温度依赖性不同。这表明圆柱孔的滞回机理与墨水瓶孔的滞回机理不同。MCM-48有序介孔吸附剂具有良好定义的圆柱形孔三维网络，结果强烈表明，几乎相同大小和几何形状的孔之间的相互连接对吸附滞后和孔临界性没有显著影响。少