TY - JOUR
T1 - Structural Strengthening of Metal-Organic Frameworks Owing to the Confinement Effect of Ionic Liquids in the Nanopores
AU - Koh, Sang Gyu
AU - Koide, Taiki
AU - Arai, Asahi
AU - Ohira, Ichiro
AU - Kinoshita, Kentaro
N1 - Funding Information:
We are grateful to Prof. M. Itoi, Dr. M. Yokota, and Dr. T. Yamasaki for fruitful discussions and valuable comments on X-ray diffraction analyses. This work was supported by JSPS KAKENHI Grant Number JP20J12046.
Publisher Copyright:
© 2022 The Authors. Published by American Chemical Society.
PY - 2022/4/21
Y1 - 2022/4/21
N2 - Understanding the atmospheric structural stability and mechanical strength of ionic liquid-loaded metal-organic frameworks (IL-loaded MOFs) is indispensable considering their device applications. We investigated the confinement effect of IL [bmim+][TFSI-] (1-butyl-3-methylimidazolium bis(trifluoromethane sulfonyl)imide) in the nanopores of MOF Cu3(btc)2 (btc; 1,3,5-benzenetricarboxylic acid) using X-ray diffraction and nanoindentation analyses with single-crystal samples. The structural stability against moisture and mechanical strength of the Cu3(btc)2 framework were found to drastically improve by loading [bmim+][TFSI-] into the nanopores. Coulomb interaction between [TFSI-] anions and Cu ions, because of the spatial restriction of constituent ions for [bmim+][TFSI-] with the nanopores of Cu3(btc)2, provides a capping effect on the unsaturated Cu metal sites of Cu3(btc)2, preventing water molecules from adsorbing. Furthermore, the interaction increases the hardness of the Cu3(btc)2 framework owing to additional cross-linkages among the Cu metal sites by [TFSI-] anions. The observed synergy, which is controllable by exploiting the designability of ILs and MOFs, can further accelerate the material development of IL-loaded MOFs for device applications. Simultaneously, our findings indicate that the MOFs that have been avoided for use due to poor stability against moisture and external force should be revisited in the study of IL-loaded MOFs.
AB - Understanding the atmospheric structural stability and mechanical strength of ionic liquid-loaded metal-organic frameworks (IL-loaded MOFs) is indispensable considering their device applications. We investigated the confinement effect of IL [bmim+][TFSI-] (1-butyl-3-methylimidazolium bis(trifluoromethane sulfonyl)imide) in the nanopores of MOF Cu3(btc)2 (btc; 1,3,5-benzenetricarboxylic acid) using X-ray diffraction and nanoindentation analyses with single-crystal samples. The structural stability against moisture and mechanical strength of the Cu3(btc)2 framework were found to drastically improve by loading [bmim+][TFSI-] into the nanopores. Coulomb interaction between [TFSI-] anions and Cu ions, because of the spatial restriction of constituent ions for [bmim+][TFSI-] with the nanopores of Cu3(btc)2, provides a capping effect on the unsaturated Cu metal sites of Cu3(btc)2, preventing water molecules from adsorbing. Furthermore, the interaction increases the hardness of the Cu3(btc)2 framework owing to additional cross-linkages among the Cu metal sites by [TFSI-] anions. The observed synergy, which is controllable by exploiting the designability of ILs and MOFs, can further accelerate the material development of IL-loaded MOFs for device applications. Simultaneously, our findings indicate that the MOFs that have been avoided for use due to poor stability against moisture and external force should be revisited in the study of IL-loaded MOFs.
UR - http://www.scopus.com/inward/record.url?scp=85128229510&partnerID=8YFLogxK
U2 - 10.1021/acs.jpcc.1c10629
DO - 10.1021/acs.jpcc.1c10629
M3 - Article
AN - SCOPUS:85128229510
VL - 126
SP - 6736
EP - 6744
JO - Journal of Physical Chemistry C
JF - Journal of Physical Chemistry C
SN - 1932-7447
IS - 15
ER -