TY - JOUR

T1 - Probing Gas Adsorption in Metal-Organic Framework ZIF-8 by EPR of Embedded Nitroxides

AU - Sheveleva, A. M.

AU - Anikeenko, A. V.

AU - Poryvaev, A. S.

AU - Kuzmina, D. L.

AU - Shundrina, I. K.

AU - Kolokolov, D. I.

AU - Stepanov, A. G.

AU - Fedin, M. V.

N1 - Publisher Copyright: © 2017 American Chemical Society.

PY - 2017/9/14

Y1 - 2017/9/14

N2 - Metal-organic frameworks (MOFs) are being increasingly considered as promising materials for gas separation and storage, yet specific interactions between gas molecules and the inner surface of pores are still not well understood. In this work, we propose a new approach for investigation of such interactions by Electron Paramagnetic Resonance (EPR). We use stable nitroxide radicals as multifunctional agents embedded into the pores of a MOF prior to the gas sorption. They act as EPR-active reporters, and simultaneously as competitor molecules during the gas adsorption process. We exemplify this approach using a ZIF-8 framework, nitroxide TEMPO ((2,2,6,6-tetramethylpiperidin-1-yl)oxyl), and CO2, N2, and O2 gases. The mobility of nitroxide monitored by continuous wave EPR behaves differently upon adsorption of each of these gases. In particular, a noticeable increase of mobility in the presence of CO2 reveals the weakening of guest-host interactions TEMPO-MOF induced by CO2, which was qualitatively supported by molecular dynamic calculations. The nitroxides can be embedded in MOFs postsynthetically, and their negligible amounts (≤1 per 1000 cells) are required due to a high sensitivity of EPR. Therefore, the proposed approach is sufficiently versatile and might find broad applications for various MOFs.

AB - Metal-organic frameworks (MOFs) are being increasingly considered as promising materials for gas separation and storage, yet specific interactions between gas molecules and the inner surface of pores are still not well understood. In this work, we propose a new approach for investigation of such interactions by Electron Paramagnetic Resonance (EPR). We use stable nitroxide radicals as multifunctional agents embedded into the pores of a MOF prior to the gas sorption. They act as EPR-active reporters, and simultaneously as competitor molecules during the gas adsorption process. We exemplify this approach using a ZIF-8 framework, nitroxide TEMPO ((2,2,6,6-tetramethylpiperidin-1-yl)oxyl), and CO2, N2, and O2 gases. The mobility of nitroxide monitored by continuous wave EPR behaves differently upon adsorption of each of these gases. In particular, a noticeable increase of mobility in the presence of CO2 reveals the weakening of guest-host interactions TEMPO-MOF induced by CO2, which was qualitatively supported by molecular dynamic calculations. The nitroxides can be embedded in MOFs postsynthetically, and their negligible amounts (≤1 per 1000 cells) are required due to a high sensitivity of EPR. Therefore, the proposed approach is sufficiently versatile and might find broad applications for various MOFs.

KW - ELECTRON-PARAMAGNETIC-RESONANCE

KW - CARBON-DIOXIDE

KW - FORCE-FIELD

KW - MOLECULAR-DYNAMICS

KW - IMIDAZOLATE

KW - CO2

KW - MEMBRANES

KW - HYDROGEN

KW - H-2

KW - SELECTIVITY

UR - http://www.scopus.com/inward/record.url?scp=85029536713&partnerID=8YFLogxK

U2 - 10.1021/acs.jpcc.7b06884

DO - 10.1021/acs.jpcc.7b06884

M3 - Article

AN - SCOPUS:85029536713

VL - 121

SP - 19880

EP - 19886

JO - Journal of Physical Chemistry C

JF - Journal of Physical Chemistry C

SN - 1932-7447

IS - 36

ER -