Proton dynamics in CsHSO4 confined in mesoporous silica FSM-16 as studied by 1H solid-state NMR

Cesium hydrogen sulfate CsHSO4 was introduced in a nanospace of mesoporous silica FSM-16, and we have investigated proton dynamics of CsHSO4 confined in the mesopores by means of 1H solid-state NMR. X-ray powder diffraction patterns demonstrate accommodation of CsHSO4 in the mesopores and suggest that confined CsHSO4 is amorphous. Thermal analyses indicate that the confinement suppresses the transition from phases II to I and the melting. The motional narrowing in the 1H static NMR spectra takes place in the temperature range lower than that for bulk CsHSO4, and the spectral line shape indicates that the proton motional rate has a distribution. The proton mean residence times are estimated from the spectrum simulation assuming the distribution of the motional rate. The obtained central values are smaller by one order of magnitude than those for bulk CsHSO4 although the central values of the activation energies are comparable.