Organically Modified SiO₂−B₂O₃ Gels Displaying a High Content of Borosiloxane (B−O−Si⋮) Bonds

Hybrid SiO 2 −B 2 O 3 gels have been synthesized from cohydrolysis of modified silicon alkoxides (R−Si(OE) 3 R = Me, Vi, Et) and triethylborate, B(OEt) 3 . The structure of these gels was investigated by Fourier-transformed infrared (FT-IR) spectroscopy, 29 Si and 11 B solid-state nuclear magnetic resonance (NMR), X-ray diffraction (XRD), and chemical analysis. The results show, for the first time, the possibility of obtaining a SiO 2 −B 2 O 3 gel in which trigonal boron atoms are homogeneously dispersed in the siloxane network via B−O−Si bonds. The identification of such bonds was mainly based on the FT-IR and 11 B MAS NMR results. The formation of the borosiloxane bonds is favored by increasing the pH of hydrolysis water and by the use of Et− or Vi−Si(OR) 3 rather than Me−Si(OEt) 3 . Some hypotheses to rationalize the experimental results are also presented.