Study of Capillary Condensation within Ordered Mesoporous Materials

为了阐明胶体和界面科学领域长期存在的毛细凝聚现象，我们测量了简单气体在具有明确孔结构的有序介孔材料上的吸附-脱附等温线。首先，我们构建了一个高压吸附装置，该装置能够在20- 300 K和0-30 atm的温度和压力范围内进行吸附测量。在低温下，具有墨水瓶型孔结构的SBA-16对氮气、氧气、氩气和二氧化碳的吸附-脱附等温线表现出较大的滞后回线，属于IUPAC分类中的H2型。当温度升高时，滞后收缩并最终在滞后温度下消失，远低于体临界温度。上述四种气体的毛细冷凝和蒸发相对压力对降低的温度的曲线符合单一曲线。现象学 关于我们 在SBA-16球形孔中的气泡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，形成和消失的气泡在液体中的限制在孔的能量障碍是负责的外观的吸附滞后和滞后温度是不关心的所谓的毛细管临界。低温下，氮气和二氧化碳在具有圆柱孔的MCM-41和SBA-15上的吸附-脱附等温线表现出较小的滞后回线，属于IUPAC分类中的H1型。然而，在圆柱形孔中，氮气的滞后回线的温度依赖性不同于二氧化碳。这表明圆柱形孔中的滞后机制不同于墨水瓶孔中的滞后机制。MCM-48有序介孔吸附剂具有明确的三维网络的圆柱形孔的结果强烈表明，几乎相同的尺寸和几何形状的孔之间的互连不具有显着的影响吸附滞后和孔临界。少

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