TY - JOUR
T1 - New Insights into the Cs Adsorption on Montmorillonite Clay from 133Cs Solid-State NMR and Density Functional Theory Calculations
AU - Ohkubo, Takahiro
AU - Okamoto, Takuya
AU - Kawamura, Katsuyuki
AU - Guegan, Regis
AU - Deguchi, Kenzo
AU - Ohki, Shinobu
AU - Shimizu, Tadashi
AU - Tachi, Yukio
AU - Iwadate, Yasuhiko
PY - 2018/12/6
Y1 - 2018/12/6
N2 - The adsorption sites of Cs on montmorillonite clays were investigated by theoretical 133Cs chemical shift calculations, 133Cs magic-angle-spinning nuclear magnetic resonance (MAS NMR) spectroscopy, and X-ray diffraction under controlled relative humidity. The theoretical calculations were carried out for structures with three stacking variations in the clay layers, where hexagonal cavities formed with Si-O bonds in the tetrahedral layers were aligned as monoclinic, parallel, alternated; with various d-spacings. After structural optimization, all Cs atoms were positioned around the center of hexagonal cavities in the upper or lower tetrahedral sheets. The calculated 133Cs chemical shifts were highly sensitive to the tetrahedral Al (AlT)-Cs distance and d-spacing, rather than to the Cs coordination number. Accordingly, three peaks observed in our theoretical spectra were interpreted to be adsorbed Cs around the center of hexagonal cavity with or without AlT and on the surface in the open nanospace. In a series of 133Cs MAS NMR spectral changes for partial Cs substituted samples, the Cs atoms are preferentially adsorbed at sites near AlT for low Cs substituted montmorillonites. The presence of nonhydrated Cs was also confirmed in partially Cs substituted samples, even after being hydrated under high relative humidity.
AB - The adsorption sites of Cs on montmorillonite clays were investigated by theoretical 133Cs chemical shift calculations, 133Cs magic-angle-spinning nuclear magnetic resonance (MAS NMR) spectroscopy, and X-ray diffraction under controlled relative humidity. The theoretical calculations were carried out for structures with three stacking variations in the clay layers, where hexagonal cavities formed with Si-O bonds in the tetrahedral layers were aligned as monoclinic, parallel, alternated; with various d-spacings. After structural optimization, all Cs atoms were positioned around the center of hexagonal cavities in the upper or lower tetrahedral sheets. The calculated 133Cs chemical shifts were highly sensitive to the tetrahedral Al (AlT)-Cs distance and d-spacing, rather than to the Cs coordination number. Accordingly, three peaks observed in our theoretical spectra were interpreted to be adsorbed Cs around the center of hexagonal cavity with or without AlT and on the surface in the open nanospace. In a series of 133Cs MAS NMR spectral changes for partial Cs substituted samples, the Cs atoms are preferentially adsorbed at sites near AlT for low Cs substituted montmorillonites. The presence of nonhydrated Cs was also confirmed in partially Cs substituted samples, even after being hydrated under high relative humidity.
UR - http://www.scopus.com/inward/record.url?scp=85057821297&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=85057821297&partnerID=8YFLogxK
U2 - 10.1021/acs.jpca.8b07276
DO - 10.1021/acs.jpca.8b07276
M3 - Article
C2 - 30383382
AN - SCOPUS:85057821297
VL - 122
SP - 9326
EP - 9337
JO - Journal of Physical Chemistry A
JF - Journal of Physical Chemistry A
SN - 1089-5639
IS - 48
ER -