Proton diffusion in hybrid materials of CsHSO4 and silica nanoparticles as studied by H 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.