Neimark Alexander V, Coudert François-Xavier, Boutin Anne, Fuchs Alain H
Chimie ParisTech (École nationale supérieure de chimie de Paris), CNRS and Université Pierre et Marie Curie, 11 rue Pierre et Marie Curie, 75005 Paris, France.
Department of Chemical and Biochemical Engineering, Rutgers, The State University of New Jersey, 98 Brett Road, Piscataway, New Jersey 08854-8058.
J Phys Chem Lett. 2010 Jan 7;1(1):445-9. doi: 10.1021/jz9003087. Epub 2009 Dec 17.
Gas adsorption in pores of flexible metal-organic frameworks (MOF) induces elastic deformation and structural transitions associated with stepwise expansion and contraction of the material, known as breathing transitions between large pore (lp) and narrow pore (np) phases. We present here a simple yet instructive model for the physical mechanism of this enigmatic phenomenon considering the adsorption-induced stress exerted on the material as a stimulus that triggers breathing transitions. The proposed model implies that the structural transitions in MOFs occur when the stress reaches a certain critical threshold. We showcase this model by drawing on the example of Xe adsorption in MIL-53 (Al) at 220 K, which exhibits two consecutive hysteretic breathing transitions between lp and np phases. We also propose an explanation for the experimentally observed coexistence of np and lp phases in MIL-53 materials.
气体在柔性金属有机框架材料（MOF）的孔隙中吸附会引发弹性变形和结构转变，这与材料的逐步膨胀和收缩相关，被称为大孔（lp）相和窄孔（np）相之间的呼吸转变。我们在此提出一个简单却具启发性的模型，用于解释这一神秘现象的物理机制，该模型将吸附作用于材料的应力视为触发呼吸转变的刺激因素。所提出的模型表明，当应力达到某个临界阈值时，MOF中的结构转变就会发生。我们以220K下Xe在MIL-53（Al）中的吸附为例展示了该模型，其在lp相和np相之间呈现出两个连续的滞后呼吸转变。我们还对MIL-53材料中实验观察到的np相和lp相共存现象提出了解释。
