Dantas Silvio, Neimark Alexander V
Department of Chemical and Biochemical Engineering, Rutgers, The State University of New Jersey, 98 Brett Road, Piscataway, New Jersey 08854, United States.
ACS Appl Mater Interfaces. 2020 Apr 1;12(13):15595-15605. doi: 10.1021/acsami.0c01682. Epub 2020 Mar 20.
Metal-organic frameworks (MOFs) attract a rapidly growing attention across the disciplines due to their multifarious pore structures and unique ability to selectively adsorb, store, and release various guest molecules. Pore structure characterization and coupling of adsorption and structural properties are imperative for rational design of advanced MOF materials and their applications. The pore structure of MOFs represents a three-dimensional network comprised of several types of pore compartments: interconnected cages and channels distinguished by their size, shape, and chemistry. Here, we propose a novel methodology for pore structure characterization of MOF materials based on matching of the experimental adsorption isotherms to -generated fingerprint isotherms of adsorption in individual pore compartments of the ideal crystal. The proposed approach couples structural and adsorption properties, determines the contributions of different types of pores into the total adsorption, and estimates to what extent the pore structure of the sample under investigation is different from the ideal crystal. The MOF pore structure is characterized by the pore type distribution (PTD), which is more informative than the traditional pore size distribution that is based on oversimplistic pore models. The method is illustrated on the example of Ar adsorption at 87 K on hydrated and dehydrated structures of Cu-BTC, one of the most well-known MOF materials. The PTD determined from the experimental isotherm provides an estimate of the crystal fraction in the sample and the accessibility and degree of hydration of different types of pore compartments. In addition, the PTD determined from the experimental adsorption isotherm is used to predict the isosteric heat of adsorption that provides important information on the specifics of adsorption interactions. The results are found to be in excellent agreement with experimental data. Such detailed information about the pore structure and adsorption properties of practical MOF samples cannot be obtained with currently available methods of adsorption characterization.
金属有机框架材料（MOFs）因其多样的孔结构以及选择性吸附、存储和释放各种客体分子的独特能力，在各学科领域正迅速吸引着越来越多的关注。对于先进MOF材料的合理设计及其应用而言，孔结构表征以及吸附与结构性质的耦合至关重要。MOFs的孔结构代表了一个三维网络，它由几种类型的孔腔组成：相互连接的笼状结构和通道，它们通过尺寸、形状和化学性质加以区分。在此，我们提出一种新颖的方法来表征MOF材料的孔结构，该方法基于将实验吸附等温线与理想晶体各个孔腔中生成的吸附指纹等温线进行匹配。所提出的方法将结构和吸附性质相结合，确定不同类型的孔对总吸附的贡献，并估计所研究样品的孔结构与理想晶体的差异程度。MOF孔结构由孔类型分布（PTD）来表征，它比基于过于简单化孔模型的传统孔径分布更具信息量。以87K下氩气在最著名的MOF材料之一Cu-BTC的水合和脱水结构上的吸附为例，对该方法进行了说明。从实验等温线确定的PTD可估计样品中的晶体分数以及不同类型孔腔的可及性和水合程度。此外，由实验吸附等温线确定的PTD用于预测等量吸附热，这提供了有关吸附相互作用细节的重要信息。结果与实验数据高度吻合。利用目前可用的吸附表征方法无法获得关于实际MOF样品孔结构和吸附性质的如此详细的信息。
