关键词: 核磁共振光谱, 双量子, 过冷水, MCM-41

Abstract: Dynamics of water adsorbed on MCM-41 has been investigated by ²H double quantum filtered (DQF) NMR and T₁ inversion-recovery NMR. The modified cone model is employed in this study. From temperature dependent studies with various water loadings on MCM-41, it is found that there are different sites for water adsorption on MCM-41. The signal of water molecules in the slow site dominates in the observed DQF NMR. The influence of silanol groups on the MCM-41 surface strongly affects the motion of water molecules in the slow site, resulting in a residual quadrupolar interaction. As the signal of water in fast site dominates that observed in single quantum spectra, it also appears in DQF spectra through an exchange process. It is found that the single SiOH group is the major adsorption site on MCM-41 surface and the ratio is one water molecule to on SIOH group. The wobbling motion of the water in slow site is also influenced by the translation diffusion of the second monolayer water through collision. The phase transitions of water in fast motion site are also found. The results indicate that the phase transition temperature varies with different hydration. Higher hydration sample may cause the more serious structure distortion in the pore. Therefore, the lower phase transition temperature is found in the higher hydration sample. Moreover, with the low hydration MCM-41 sample, it shows that there is only single layer of water molecules on the surface. Alternative pulse sequence for DQF NMR, which is called spinlock double quantum filtered (SLDQF) NMR, and reorientation mediated by 2D jump diffusion model have also been developed in this study.

Key words: NMR, double quantum, surpercoal water, MCM-41