Hi Saied

The Stober method, or base-catalyzed hydroysis of tetraethylorthosilicate (TEOS), is a very simple and cost effective approach for synthesizing batches of monodisperse SiO2 colloids of different size. The size of the SiO2 colloids obtained depends on the synthesis conditions, including [TEOS], [NH3], [H2O], solvent (usually ethanol) and temperature.

In a typical synthesis, you would mix the aqueous NH3, H2O and ethanol at room temperature, and then add a certain volume of TEOS quickly under vigorous stirring. Then you would stir overnight at room temperature. The resulting monodisperse SiO2 colloids are then collected by centrifugation and washed repeatedly with ethanol.

The attached papers will give some useful concentration ranges for preparing monodisperse SiO2 colloids of different sizes.

Best regards

Really, Stöber process is the best one. However, there are a lot of other ways to make  silica beads having near-spherical habitus. For example, when TEOS is absent, the simples precursor is sodium silicate - dry or solution. There are chemical methods (see enclosed "Synthesis of silica nanoparticles from sodium silicate under alkaline conditions") or semi-chemical using cation-exchange resin (see china patent CN1268545C "Nano-silicon dioxide used for nanometer standard granule")

Best regards

http://jhs.pharm.or.jp/data/56(6)/56_632.pdf

https://link.springer.com/article/10.1007/s10971-015-3950-7

Yes, the stober process. Good luck