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 reactions of Si(OC2H5)4 (TEOS) in the presence of a fixed concentration of acetic acid and water (TEOS ∶ CH3COOH ∶ H2O = 1 ∶ 4 ∶ 4) were studied by FTIR absorption spectroscopy, particle size measurement by dynamic light scattering 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 absorbance decrease of an alkoxide peak at 792 cm−1 (SiO4 asymmetric stretch + CH2 rock) during the hydrolysis–condensation process followed a first order reaction with the rate constant (k) within the range 6–10 × 10−3 s−1. The formation of silica particles and their growth in the sol via condensation reactions of silanols and subsequent molecular addition were monitored by measuring the particle size profile with respect to time. This study confirmed 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 investigations.