Abstract
The present study has been carried out to investigate the mechanisms of sol–gel reactions using TEOS as precursor in the presence of acid or base catalyst. The gels were prepared by hydrolysis of TEOS using hydrochloride acid or ammonium hydroxide catalyst. The obtained gels were also characterized by FTIR spectroscopy. The results of FTIR spectroscopy indicated the existence of silanol and siloxane bonds; due to the formation of hydrolyzed species as reactive intermediate compounds in initial stage converted by condensation reactions to gels as ultimate products. Accordingly, appropriate mechanisms have been proposed for sol – gel reaction using TEOS as precursor in the presence of acid or base catalyst. These mechanisms involve three-steps SN2 mechanisms for base catalyzed hydrolysis reaction of TEOS and SN1 mechanisms for acid catalyzed hydrolysis reaction of TEOS. Three mechanisms have been also proposed for condensation reaction as second stage in sol-gel process. These mechanisms include alcoxolation, oxolation and oltaion.
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