UNC-CH APPLIED PHYSICAL SCIENCES DEPARTMENT
Yunzhao Xing, UNC-CH
“New NMR Methods for Characterizing Nanoporous Structures and Nanoconfined Shale Gas”
Porous materials, such as activated carbons and gas shale rocks, are playing crucial roles in our daily life and industry areas. However, both accurate determination of micropore size distribution in activated carbons and reliable evaluation of nature gas storage capability in gas shale rocks are challenging problems. First, a simple room temperature method is introduced for determining micropore size distribution of activated carbons based on 1H nuclear magnetic resonance (NMR) of adsorbed water under magic angle spinning (MAS). The observed NMR peak shift is determined by the mechanism of nucleus independent chemical shift (NICS). Density functional theory computation of NICS yields a quantitative relationship between the observed peak shift and the micropore size. This relationship provides a direct link between the 1H MAS NMR lineshape and micropore size distribution. Such NICS NMR porometry technique is shown to be useful for characterizing micropore structures of highly carbonized activated carbons. Second, a novel method based on NMR T2 contrast and Hahn Echo pulse sequence for evaluation of the gas storage capability of gas shale is introduced. The spectra signature of gas stored inside pores is also observed by experiments. The combined information from spectra, longitudinal relaxation and transverse relaxation not only offers more direct evidence for the stored gas, but also provides valuable information for gas storage mechanism and a foundation for further research.