Argon adsorption at 77 K as a useful tool for the elucidation of pore connectivity in ordered materials with large cagelike mesopores
Argon adsorption at 77 K as a useful tool for the elucidation of pore connectivity in ordered materials with large cagelike mesopores
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DOI：
10.1021/cm021774c
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发表时间：
2003-07-29
影响因子：
8.6
通讯作者：
Jaroniec, M
中科院分区：
文献类型：
--
作者：
Kruk, M;Jaroniec, M
结果表明，77 K 下的氩吸附有助于阐明具有大笼状介孔的有序材料中的孔连通性，并且能够提供常用的 77 K 氮吸附中无法获得的有价值的结构信息。所讨论的方法是基于解吸时的孔堵塞现象。这种现象的本质是，来自特定孔隙的毛细管蒸发被延迟，直到该孔隙通过未填充孔隙的连续路径形成通向周围气体的通道，或者达到该孔隙的滞后压力下限。当观察到前一种行为时，毛细管蒸发压力提供有关连接给定孔隙与周围气体的孔隙入口的最宽连续路径的信息，即沿该最宽路径的最小孔隙入口尺寸的信息。在毛细管蒸发被延迟到滞后下限的情况下，可以仅确定可能的孔隙入口尺寸的上限。结果表明，从孔隙连通性阐明的角度来看，在 77 K 时，在圆柱形孔中观察到的滞后现象比在 77 K 时的氮气更广泛的孔径范围内，氩气的吸附通常更优越，允许人们探测孔径接近 4.0 nm（与 77 K 下氮气情况下的接近 5.0 nm 相比），这是使用具有圆柱形介孔的有序二氧化硅估计的。对于 FDU-1 二氧化硅，证明了在 77 K 下使用氩气的优点。进一步阐明了 FDU-1 中形成小孔入口尺寸的有利条件，揭示了孔入口尺寸均匀性随着初始合成温度的升高而降低，并揭示了在 373 K 或更高温度下长时间水热处理的样品中孔入口的双峰分布。 77 K 下的氩吸附对于表征许多其他大孔材料的孔连通性可能有用。
It is shown that argon adsorption at 77 K is convenient for the elucidation of pore connectivity in ordered materials with large cagelike mesopores and is capable of providing valuable structural information that may not be available from commonly used nitrogen adsorption at 77 K. The discussed approach is based on the phenomenon of pore blocking upon desorption. The nature of this phenomenon is that the capillary evaporation from a particular pore is retarded until either the pore develops an access to the surrounding gas through a continuous path of unfilled pores, or the lower pressure limit of hysteresis for the pore is reached. When the former of these behaviors is observed, the capillary evaporation pressure provides information about the widest continuous path of pore entrances connecting the given pore with the surrounding gas, that is, about the smallest pore entrance size along this widest path. In the case where the capillary evaporation is delayed to the lower limit of hysteresis, it is possible to determine only the upper boundary of the possible pore entrance size. It is shown that argon adsorption at 77 K, for which hysteresis in cylindrical pores is observed for a wider range of pore sizes than for nitrogen at 77 K, is often superior from the point of view of the pore connectivity elucidation, allowing one to probe pore entrance sizes down to similar to4.0 nm (compared to similar to5.0 nm in the case of nitrogen at 77 K), as estimated using ordered silicas with cylindrical mesopores. The merits of the use of argon at 77 K were demonstrated for the FDU-1 silicas. Conditions favorable for the formation of small pore entrance sizes in FDU-1 were further elucidated, and the lowering of the pore entrance size uniformity with the increase in the initial synthesis temperature was revealed, and bimodal distributions of pore entrances in the samples hydrothermally treated at or above 373 K for extended periods of time were uncovered. Argon adsorption at 77 K is potentially useful for the characterization of pore connectivity in many other large-pore materials.