Synthesis and formation mechanism of amorphous silica particles via sol–gel process with tetraethylorthosilicate

Silica microspheres with narrow particle size distribution and average diameter of 80–200 nm were prepared by hydrolysis and condensation of tetraethylorthosilicate (TEOS) in ethanol solution. Effects of TEOS, ammonia, water concentration, and temperature on particle size and morphology were investigated by laser particle size analysis and field emission scanning electron microscopy (FESEM), in conjunction with energy-dispersive X-ray spectroscopy (EDS), Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD) spectroscopy. Monomer addition model was employed to analyze the stability of intermediate, as well as the direction in which the reaction of silica particles proceeds. The analysis was carried out by Materials Studio. Results demonstrated that particle size of Nano-silica increases with increasing concentrations of H2O, NH3·H2O, and TEOS in ethanol, whereas the size decreases with increasing temperature. In addition, when proper amount of H2O was added into NH3·H2O at suitable temperature, silicic acid can act as a nucleus for amorphous Nano-silica particles, forming microspheres with round and smooth surfaces. By contrast, when TEOS was used, resultant nanoparticles have poor surfaces. During nucleation process of Nano-silica, silicic acid can also acts as nucleating agent providing a platform for the growth of nanoparticles with symmetric structure. Findings further indicated that the reaction proceeds by first silicic acid participates in the reaction, and the dimer and trimer molecules then react with the surface of silicic acid molecules; the same products could be produced by different reactions.