CVD Germania on Pyrogenic Silica

Abstract

Germania on a pyrogenic silica surface (GS) has been synthesized by chemical vapor deposition (CVD) and investigated by infrared (IR), optical, and dielectric relaxation (DRS) spectroscopies and quantum chemical ab initio and semiempirical MNDO, AM1, and PM3 methods. The GS synthesis was carried out via GeCl 4 vapor chemisorption and subsequent hydrolysis of the Ge-Cl bonds in the O-GeCl 3 groups bound to the surface. In the IR spectra of GS, absorption bands of ?SiO-H at 3750 cm -1 , ?GeO-H at 3682 cm -1 , and the strained rings =GeOOSi= at 885 cm -1 were observed. According to the dielectric relaxation and optical spectra of water and n-dimethylaminoazobenzene (DMAAB) adsorbed on GS, the new surface sites are generated on GS having more acidic properties compared with those for the parent silica. Their concentration depends on the germania content, GS hydration degree, and pretreatment temperature. Structures ofthese sites and adsorption complexes have been simulated by quantum chemical ab initio and semiempirical methods.