Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, 2-1-1, Katahira, Aoba-ku, Sendai, 980-8577 (Japan), Fax: (+81) 22-217-5626; Advanced Materials Laboratory, Nissan Research Center, Nissan Motor Co., Ltd. 1,Natsushima-cho, Yokosuka-shi Kanagawa 237-8523 (Japan), Fax: (+81) 46-866-5336.
Chemistry. 2013 Sep 23;19(39):13009-16. doi: 10.1002/chem.201301806. Epub 2013 Aug 28.
Nanoporous materials, such as zeolites, activated carbons, and metal-organic frameworks (MOFs), are peculiar platforms in which a variety of guest molecules are stored, reacted, and/or separated. The size of the nanopores is essential to realize advanced functions. In this work, we demonstrate a very simple but innovative method for the control of nanopore size, that is, reversible and continuous control by mechanical force loaded to soft nanoporous materials. The elastic properties of several microporous materials, including zeolites, zeolite-templated carbon (ZTC), activated carbon, and MOFs (e.g., ZIF-8), are examined and it is found that ZTC is a material that is suitable for the aforementioned idea thanks to its extraordinary soft properties compared to the others. The original pore size of ZTC (1.2 nm) can be contracted to 0.85 nm by using a relatively weak loading force of 135 MPa, whereas the other microporous materials barely contracted. To demonstrate the change in the physical properties induced by such artificial deformation, in situ gas adsorption measurements were performed on ZTC with and without loading mechanical force, by using CO2, CH4, and H2, as adsorbates. Upon the contraction by loading 69 or 135 MPa, CO2 adsorption amount is increased, due to the deepening of the physisorption potential well inside the micropores, as proved by the increase of the heat of adsorption. Moreover, the adsorption amount is completely restored to the original one after releasing the mechanical force, indicating the fully reversible contraction/recovery of the ZTC framework against mechanical force. The experimental results are theoretically supported by a simulation using Grand Canonical Monte Carlo method. The similar adsorption enhancement is observed also on CH4, whereas H2 is found as an exception due to the weak interaction potential.
纳米多孔材料，如沸石、活性炭和金属有机骨架（MOF），是储存、反应和/或分离各种客体分子的特殊平台。纳米孔的大小对于实现先进功能至关重要。在这项工作中，我们展示了一种非常简单但具有创新性的纳米孔尺寸控制方法，即通过加载到软纳米多孔材料上的机械力实现可逆和连续控制。我们考察了几种微孔材料（包括沸石、沸石模板碳（ZTC）、活性炭和 MOF（例如 ZIF-8））的弹性性质，发现与其他材料相比，ZTC 是一种适合上述想法的材料，因为它具有非凡的柔软特性。通过使用相对较弱的 135 MPa 加载力，ZTC 的原始孔径（1.2nm）可以收缩到 0.85nm，而其他微孔材料几乎没有收缩。为了证明这种人为变形引起的物理性质变化，我们对加载机械力前后的 ZTC 进行了原位气体吸附测量，使用 CO2、CH4 和 H2 作为吸附剂。在加载 69 或 135 MPa 时，由于微孔内物理吸附势阱的加深，CO2 吸附量增加，这一点通过吸附热的增加得到证明。此外，在释放机械力后，吸附量完全恢复到原始状态，表明 ZTC 框架可以完全可逆地抵抗机械力进行收缩/恢复。实验结果得到了 Grand Canonical Monte Carlo 模拟的理论支持。在 CH4 上也观察到了类似的吸附增强，而 H2 则是一个例外，因为其相互作用势较弱。
