Solid-State NMR Characterization of Phenylbenzimidazolesulfonic Acid Coencapsulated with Cetyltrimethylammonium in Mesoporous Silica Materials

Abstract

The hydrophilic molecule phenylbenzimidazolesulfonic acid (PBSA) has been coencapsulated with cetyltrimethylammonium chloride (CTAC), an amphiphilic surfactant, via an in situ method in a mesoporous silica matrix. The effect of coencapsulation on texture and structure of the mesoporous silica host has been studied by X-ray diffraction (XRD), transmission electron microscopy (TEM), nitrogen sorption experiments, and 29Si magic-angle spinning (MAS) NMR spectroscopy. It was clearly observed that the presence of PBSA led to different characteristics compared to the reference MCM-41 type organized mesoporous silica (OMS), which suggests that the active molecules perturb the silica network formation. The encapsulation of the hydrophilic PBSA molecule was found to be stable in aqueous media, indicating that strong interactions exist between PBSA and its environment (surfactant and silica framework). 1H−29Si and 1H−13C MAS NMR experiments evidenced their spatial proximity and confirmed the presence of interaction between PBSA and both CTA+ molecules and silanol of the silica framework. This NMR study gave an overall picture of the organic/inorganic interface.