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The Effect of Methyl Functionalization on Microporous Metal‐Organic Frameworks' Capacity and Binding Energy for Carbon Dioxide Adsorption
Author(s) -
Liu Hui,
Zhao Yonggang,
Zhang Zhijuan,
Nijem Nour,
Chabal Yves J.,
Zeng Heping,
Li Jing
Publication year - 2011
Publication title -
advanced functional materials
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 6.069
H-Index - 322
eISSN - 1616-3028
pISSN - 1616-301X
DOI - 10.1002/adfm.201101479
Subject(s) - microporous material , adsorption , metal organic framework , ligand (biochemistry) , materials science , dimethylformamide , surface modification , metal , linker , pillar , inorganic chemistry , crystallography , polymer chemistry , organic chemistry , chemistry , structural engineering , engineering , biochemistry , receptor , solvent , computer science , metallurgy , composite material , operating system
The design, synthesis, and structural characterization of two new microporous metal‐organic framework (MMOF) structures is reported; Zn(BDC)(DMBPY) 0.5 ·(DMF) 0.5 (H 2 O) 0.5 (1; H 2 BDC = 1,4‐benzenedicarboxylic acid; DMBPY=2,2′‐dimethyl‐4,4′‐bipyridine) and Zn(NDC)(DMBPY) 0.5 ·(DMF) 2 (2; H 2 NDC = 2,6‐naphthalenedicarboxylic acid, DMF=N,N,‐dimethylformamide), which are obtained by functionalizing a pillar ligand with methyl groups. Both compounds are 3D porous structures of the Zn 2 ( L ) 2 ( P ) type and are made of a paddle‐wheel Zn 2 (COO) 4 secondary building unit (SBU), with the dicarboxylate and DMBPY as linker ( L ) and pillar ( P ) ligands, respectively. Comparisons are made to the parent structures Zn(BDC)(BPY) 0.5 ·(DMF) 0.5 (H 2 O) 0.5 (3; BPY = 4,4′‐bipyridine) and Zn(NDC)(BPY) 0.5 ·(DMF) 1.575 (4) to analyze and understand the effect of methyl functionalization. CO 2 ‐adsorption studies indicate substantially enhanced isosteric heats of CO 2 adsorption ( Q st ) for both compounds, as a result of adding methyl groups to the BPY ligand. The CO 2 uptake capacity, however, is affected by two opposing and competing factors: the enhancement due to increased MMOF–CO 2 interactions (higher Q st values) and detraction due to the surface area and pore‐volume reduction. For 1′ (the guest‐free form of 1), the positive effect dominates, which leads to a significantly higher uptake of CO 2 than that of its parent structure 3′ (the guest‐free form of 3). In 2′ (the guest‐free form of 2), however, the negative effect rules, which results in a slightly lower CO 2 uptake with respect to 4′ (the guest‐free form of 4). All four compounds exhibit a relatively high separation capability for carbon dioxide over other small gases, including CH 4 , N 2 , and O 2 . The separation ratios of CO 2 to O 2 and N 2 (at 298 K and 1 atm) are 39.8 and 23.5 for compound 1′, 57.7 and 40.2 for 2′, 25.7 and 29.5 for 3′, 89.7, and 20.3 for 4′, respectively. IR and Raman spectroscopic characterization of CO 2 interactions with 1′ and 2′ provides indirect support of the importance of the methyl groups in the interaction of CO 2 within these systems.