Mechanism of nanoparticle formation in hydrolysis and condensation of tetraethyl orthosilicate

The mechanism of nanoparticle formation in hydrolysis and condensation of tetraethyl orthosilicate (TEOS) was studied. The reaction was carried out over 0.01-0.2 mole/cu dm TEOS, 5-20 mole/cu dm water, and 0.2-1.5 mole/cu dm in the absence and in the presence of LiCl and KCl as electrolytes. Nanoparticles with 23-100 nm avg dia were formed at the lower ammonia concentration of 0.2 mole/cu dm in the absence of the electrolytes. The effect of electrolyte concentration on particle diameter and the measurement of electric conductivity of the reaction system suggested that electrostatic repulsion between particles precipitated in the reaction system is the main factor determining final particle size. The formation of nanoparticle in the reaction was due to the increase in the electrostatic repulsion caused by a decrease in ionic strength.