TY - JOUR
T1 - Multi-Lorentzian representation of deuterium spectrum to study water spin magnetization exchange in MCM-41
AU - Hassan, J.
AU - Reardon, E.
AU - Peemoeller, H.
PY - 2012/7
Y1 - 2012/7
N2 - Water behavior on the pore surface of nano-silica MCM-41, at a hydration level corresponding to one water molecule per OH group, is studied using 2H NMR spectra in the temperature range 213 to 313 K. In an earlier study [J. Hassan, E. Reardon, H. Peemoeller, Microporous Mesoporous Materials, 122 (2009) 121-127] it was shown that at this hydration level, deuterons of water at single OH sites exhibit a Lorentzian line shape and deuterons of water at hydrogen-bonded OH sites exhibit a powder pattern. Here it is shown that magnetization exchange occurs between these two deuteron spin groups. This exchange cannot be described using the common, two-site exchange model, involving two Lorentzians. We successfully apply a multi-Lorentzian exchange model, prompted by Woessners work [D. E. Woessner, Mol. Phys. 34, 4, (1977) 899-920] on the effects of motion on the shape of water spin resonance lines exhibiting doublet splitting. For this low hydration sample the rate of magnetization exchange out of the hydration site, where the water deuterons exhibit a Lorentzian line in the 2H spectra, is 1.3 ms -1 and the activation energy for the exchange is found to be 3.4±0.1 kcal/mole.
AB - Water behavior on the pore surface of nano-silica MCM-41, at a hydration level corresponding to one water molecule per OH group, is studied using 2H NMR spectra in the temperature range 213 to 313 K. In an earlier study [J. Hassan, E. Reardon, H. Peemoeller, Microporous Mesoporous Materials, 122 (2009) 121-127] it was shown that at this hydration level, deuterons of water at single OH sites exhibit a Lorentzian line shape and deuterons of water at hydrogen-bonded OH sites exhibit a powder pattern. Here it is shown that magnetization exchange occurs between these two deuteron spin groups. This exchange cannot be described using the common, two-site exchange model, involving two Lorentzians. We successfully apply a multi-Lorentzian exchange model, prompted by Woessners work [D. E. Woessner, Mol. Phys. 34, 4, (1977) 899-920] on the effects of motion on the shape of water spin resonance lines exhibiting doublet splitting. For this low hydration sample the rate of magnetization exchange out of the hydration site, where the water deuterons exhibit a Lorentzian line in the 2H spectra, is 1.3 ms -1 and the activation energy for the exchange is found to be 3.4±0.1 kcal/mole.
KW - MCM-41
KW - Multi-Lorentzian representation of line shapes
KW - Powder pattern and Lorentzian line shapes
KW - Spin exchange
UR - http://www.scopus.com/inward/record.url?scp=84864584388&partnerID=8YFLogxK
U2 - 10.1016/j.ssnmr.2012.04.004
DO - 10.1016/j.ssnmr.2012.04.004
M3 - Article
AN - SCOPUS:84864584388
SN - 0926-2040
VL - 45-46
SP - 23
EP - 29
JO - Solid State Nuclear Magnetic Resonance
JF - Solid State Nuclear Magnetic Resonance
ER -