CVD GERMANIA ON PYROGENIC SILICA

Germania on a pyrogenic silica surface (GS) has been synthesized by ch emical vapor deposition (CVD) and investigated by infrared (IR), optic al, and dielectric relaxation (DRS) spectroscopies and quantum chemica l ab initio and semiempirical MNDO, AM1, and PM3 methods. The GS synth esis was carried out via GeCl4 vapor chemisorption and subsequent hydr olysis of the Ge-Cl bonds in the O-GeCl3 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) we re observed. According to the dielectric relaxation and optical spectr a of water and n-dimethylaminoazobenzene (DMAAB) adsorbed on GS, the n ew surface sites are generated on GS having more acidic properties com pared with those for the parent silica. Their concentration depends on the germania content, GS hydration degree, and pretreatment temperatu re. Structures of these sites and adsorption complexes have been simul ated by quantum chemical ab initio and semiempirical methods.