| Autor: |
Rosen PF; Department of Chemistry and Biochemistry, Brigham Young University, Provo, Utah 84602, United States., Dickson MS; Department of Chemistry and Biochemistry, Brigham Young University, Provo, Utah 84602, United States., Calvin JJ; Department of Chemistry and Biochemistry, Brigham Young University, Provo, Utah 84602, United States., Ross NL; Department of Geosciences, Virginia Tech, Blacksburg, Virginia 24061, United States., Friščić T; Department of Chemistry, McGill University, Montreal H3A 0B8, Canada., Navrotsky A; School of Molecular Sciences and Center for Materials of the Universe, Arizona State University, Tempe, Arizona 85281, United States., Woodfield BF; Department of Chemistry and Biochemistry, Brigham Young University, Provo, Utah 84602, United States. |
| Abstrakt: |
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 CO 2 . Molar heat capacities from 1.8 to 300 K are presented for samples containing up to 0.99 mol of CO 2 per mol of ZIF-8. Samples with at least 0.56 mol of CO 2 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 CO 2 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 CO 2 sorption in the ZIF-8 framework. |
