Hydrolysis-condensation reactions of TEOS in the presence of acetic acid leading to the generation of glass-like silica microspheres in solution at room temperature

The generation of dense silica microspheres (density 2.14 +/- 0.02 g cm(-3) ; 95-98% of theoretical value) from the hydrolysis and condensation reactio ns of Si(OC2H5)(4) (TEOS) in the presence of a fixed concentration of aceti c acid and water (TEOS : CH3COOH : H2O = 1 : 4 : 4) were studied by FTIR ab sorption spectroscopy, particle size measurement by dynamic light scatterin g and transmission electron microscopy. The growth of ethanol peaks at 1049 cm(-1) (C-O stretch) and 882 cm(-1) (C-C stretch), as well as the absorban ce decrease of an alkoxide peak at 792 cm(-1) (SiO4 asymmetric stretch + CH 2 rock) during the hydrolysis-condensation process followed a first order r eaction with the rate constant (k) within the range 6-10 x 10(-3) s(-1). Th e formation of silica particles and their growth in the sol via condensatio n reactions of silanols and subsequent molecular addition were monitored by measuring the particle size profile with respect to time. This study confi rmed the generation of nano-sized primary particles of dimensions about 50 nm, which gradually grew to 2000-3000 nm dense particles at the end of the reaction. The particle size data were further confirmed by TEM investigatio ns.