Preparation of silica nanoparticles from sodium orthosilicate in inverse microemulsions

Sodium orthosilicate has been used to synthesize nanometer silica particles (5-20 nm in water-in-oil microemulsion systems containing cyclohexane and a mixture of non-ionic surfactants, without using a cosurfactant. The particle sizes of silica formed in the microemulsion systems were affected by the pH and the concentration of sodium orthosilicate. Spherical silica particles formed in a wide range of pH (2-11) can easily be observed by transmission electron microscopy. Silica particles produced under basic conditions were more uniform in size, but larger specific surface areas (350-400 m(2) g(-1)) of the calcined silica powders were only obtained from samples prepared in an acidic medium.