Proton diffusion in hybrid materials of CsHSO4 and silica nanoparticles as studied by 1H solid-state NMR

Hybrid materials of CsHSO4 and silica nanoparticles were prepared by mechanical milling, and hydrogen bond states and proton dynamics were studied by means of 1H solid-state NMR. 1H MAS NMR spectra demonstrated that three types of domains are present in the milled materials. Domain A has hydrogen bond states similar to those in the bulk compound. With respect to hydrogen bonds, domains A-II and A-III are similar to phases II and III of CsHSO4, respectively. Protons in domain A-II undergo translational diffusion, and the diffusion is faster than in phase II of bulk CsHSO4. Domain B is originated by mixing of CsHSO4 with silica nanoparticles, presumably locating at the boundary region. Protons in this domain also undergo translational diffusion. The motional rate is faster than in phase II of bulk CsHSO4 but is slower than in domain A-II. In domain C protons are contained as OH groups on the surface of silica nanoparticles. Protons are immobile in this domain.

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