Complexation and Molecular Speciation in the Silica Sol−Gel Process Characterized by Electrospray Ionization Fourier Transform Ion-Cyclotron Resonance Mass Spectrometry

Abstract

The sol−gel reactions of tetraethyl orthosilicate have previously been characterized by various instrumental methods, each revealing different aspects of the reactions that eventually form glass, SiO2. In this paper, we use electrospray ionization Fourier transform ion-cyclotron resonance mass spectrometry (ESI FT-ICR MS) to characterize the hydrolysis and condensation intermediates based on alkali and transition metal ion attachment to ionize the intermediates. Sodium trifluoromethanesulfonate and nickel(II) nitrate hexahydrate were added to solutions containing tetraethyl orthosilicate, electrosprayed, and the resulting species observed. Sodium ion binds nonspecifically to silicates, whereas nickel produces a tris-tetraethyl orthosilicate nickel(II) complex. Sodium-bound dimers were also observed; they could be dissociated without damage to the silicate backbone by infrared multiphoton dissociation. It is thus possible to observe all of the hydrolysis products (OH exchanged for OCH2CH3) for a given silicate oligomer as well as different silicate oligomers.