| Popis: |
The diffusion of water and small organic molecules in the pores of Na-MCM-41 with diameters between 2.8 and 6.5 nm has been studied by H-NMR relaxation times T 1 and T 2 and the pulsed field gradient technique. The translational diffusion of all organic molecules (benzene, cyclohexane, 1,4-dioxane, n-pentane, neopentane and n-dodecane) is comparable to the bulk liquids. But no freezing has been observed down to 135 K. Only benzene in samples hydrolized at pH = 12 and 373 K showed freezing, as confirmed by DSC, with a freezing point depression of 60-70 K. The water diffusion in Na-MCM-41, only obtained from T 1 and T 2 , is 1000 times slower than in bulk water and comparable with water sorbed in zeolites. No freezing has been found, too. |
