and water were mixed in the following molar ratios of
H2O:TEOS, 4:1. During the sol-gel process, TEOS was
first hydrolyzed to silicic acid as shown in Eq. (1). Then,
condensation reaction has led to formation of Si-O-Si
bonds as shown in Eq. (2). The overall sol-gel reactions
employed in the production of the SiO2 by sol-gel method
are shown below