TY - JOUR
T1 - Thermodynamic Evidence of Structural Transformations in CO2-Loaded Metal-Organic Framework Zn(MeIm)2 from Heat Capacity Measurements
AU - Rosen, Peter F.
AU - Dickson, Matthew S.
AU - Calvin, Jason J.
AU - Ross, Nancy L.
AU - Friščić, Tomislav
AU - Navrotsky, Alexandra
AU - Woodfield, Brian F.
N1 - Funding Information:
The heat capacity work was financially supported by a grant from the U.S. Department of Energy under grant DE-SC0016446. A.N. acknowledges grant DE-SC0016573 from the U.S. Department of Energy. T.F. acknowledges the support of an NSERC Strategic Grant (Grant no. NSERC STPGP 463405-14) and the NSERC E.W.R. Steacie Memorial Fellowship. We would also like to thank Grace Neilsen for her assistance with sample preparation.
Publisher Copyright:
Copyright © 2020 American Chemical Society.
PY - 2020/3/11
Y1 - 2020/3/11
N2 - Metal-organic frameworks are a class of porous compounds with potential applications in molecular sieving, gas sequestration, and catalysis. One family of MOFs, zeolitic imidizolate frameworks (ZIFs), is of particular interest for carbon dioxide sequestration. We have previously reported the heat capacity of the sodalite topology of the zinc 2-methylimidazolate framework (ZIF-8), and in this Article we present the first low-temperature heat capacity measurements of ZIF-8 with various amounts of sorbed CO2. Molar heat capacities from 1.8 to 300 K are presented for samples containing up to 0.99 mol of CO2 per mol of ZIF-8. Samples with at least 0.56 mol of CO2 per mol of ZIF-8 display a large, broad anomaly from 70 to 220 K with a shoulder on the low-temperature side, suggesting sorption-induced structural transitions. We attribute the broad anomaly partially to a gate-opening transition, with the remainder resulting from CO2 rearrangement and/or lattice expansion. The measurements also reveal a subtle anomaly from 0 to 70 K in all samples that does not exist in the sorbate-free material, which likely reflects new vibrational modes resulting from sorbate/ZIF-8 interactions. These results provide the first thermodynamic evidence of structural transitions induced by CO2 sorption in the ZIF-8 framework.
AB - Metal-organic frameworks are a class of porous compounds with potential applications in molecular sieving, gas sequestration, and catalysis. One family of MOFs, zeolitic imidizolate frameworks (ZIFs), is of particular interest for carbon dioxide sequestration. We have previously reported the heat capacity of the sodalite topology of the zinc 2-methylimidazolate framework (ZIF-8), and in this Article we present the first low-temperature heat capacity measurements of ZIF-8 with various amounts of sorbed CO2. Molar heat capacities from 1.8 to 300 K are presented for samples containing up to 0.99 mol of CO2 per mol of ZIF-8. Samples with at least 0.56 mol of CO2 per mol of ZIF-8 display a large, broad anomaly from 70 to 220 K with a shoulder on the low-temperature side, suggesting sorption-induced structural transitions. We attribute the broad anomaly partially to a gate-opening transition, with the remainder resulting from CO2 rearrangement and/or lattice expansion. The measurements also reveal a subtle anomaly from 0 to 70 K in all samples that does not exist in the sorbate-free material, which likely reflects new vibrational modes resulting from sorbate/ZIF-8 interactions. These results provide the first thermodynamic evidence of structural transitions induced by CO2 sorption in the ZIF-8 framework.
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U2 - 10.1021/jacs.9b13883
DO - 10.1021/jacs.9b13883
M3 - Article
C2 - 32070102
AN - SCOPUS:85081944588
SN - 0002-7863
VL - 142
SP - 4833
EP - 4841
JO - Journal of the American Chemical Society
JF - Journal of the American Chemical Society
IS - 10
ER -