Wang Rui, Bukowski Brandon C, Duan Jiaxin, Zhang Kun, Snurr Randall Q, Hupp Joseph T
Department of Chemistry, Northwestern University, Evanston, Illinois 60208, United States.
Department of Chemical and Biological Engineering, Northwestern University, Evanston, Illinois 60208, United States.
ACS Appl Mater Interfaces. 2023 Nov 8;15(44):51854-51862. doi: 10.1021/acsami.3c08861. Epub 2023 Oct 26.
Postsynthetic modification (PSM) of metal-organic frameworks (MOFs) enables incorporation of diverse functionalities in pores for chemical separations, drug delivery, and heterogeneous catalysis. However, the effect of PSM on molecular transport, which is essential for most applications of MOFs, has been rarely studied. In this paper, we used perfluoroalkane-functionalized Zr-MOF NU-1008 as a platform to systematically interrogate transport processes and mechanisms in solvated pores. We anchored perfluoroalkanes onto NU-1008 nodes by solvent-assisted ligand incorporation (, with = 3, 5, 7, and 9 denoting the number of fluorinated carbons). Transport of a luminescent molecule, BODIPY, through individual crystallites of four versions of methanol-filled was monitored by confocal fluorescence microscopy as a function of time and location. In comparison with the parent NU-1008, the diffusivity of the probe molecules within declined by 2- to 7-fold depending on chain length and loading, presumably due to the reduction in pore diameter or adsorptive interactions with perfluoroalkyl chains. Atomistic simulations were performed to uncover the microscopic behavior of the BODIPY diffusion in . The perfluoroalkyl chains are observed to stay close to the pore walls, instead of extending toward the pore center. BODIPY molecules, which preferably interact with linkers, were pushed to the interior of the channels as the chain length increased, resulting in solvated diffusion and minor differences in the short-time mobility of BODIPY in . This suggested that the observed decline of transport diffusivity in mainly stemmed from the reduction in the pore size when these flexible chains are present. We anticipate that this proof of concept will assist in understanding how pore functionalization can physically and chemically affect mass transport in MOFs and will be useful in further guiding the design of PSM to realize the optimal performance of MOFs for various applications.
金属有机框架材料（MOFs）的合成后修饰（PSM）能够在其孔道中引入多种功能，用于化学分离、药物递送和多相催化。然而，PSM对分子传输的影响——这对MOFs的大多数应用至关重要——却鲜有研究。在本文中，我们以全氟烷烃功能化的锆基MOF材料NU-1008为平台，系统地探究溶剂化孔道中的传输过程和机制。我们通过溶剂辅助配体引入法将全氟烷烃锚定在NU-1008的节点上（其中n = 3、5、7和9表示氟化碳的数量）。利用共聚焦荧光显微镜监测发光分子BODIPY在四种填充甲醇的变体的单个微晶中的传输情况，并将其作为时间和位置的函数。与母体NU-1008相比，根据链长和负载量的不同，探针分子在变体中的扩散系数下降了2至7倍，这可能是由于孔径减小或与全氟烷基链的吸附相互作用所致。进行了原子模拟以揭示BODIPY在变体中的扩散微观行为。观察到全氟烷基链靠近孔壁，而不是伸向孔中心。随着链长增加，BODIPY分子（其更倾向于与连接体相互作用）被推到通道内部，导致溶剂化扩散以及BODIPY在变体中的短时间迁移率存在微小差异。这表明在存在这些柔性链时，观察到的变体中传输扩散系数的下降主要源于孔径减小。我们预计这一概念验证将有助于理解孔功能化如何在物理和化学上影响MOFs中的质量传输，并将有助于进一步指导PSM的设计，以实现MOFs在各种应用中的最佳性能。
