Experimental design applied to optimisation of silica nanoparticles size obtained by sonosynthesis

In this paper, the sonocatalysis has been successfully used to synthesise silica nanoparticles. The Stober method which implies silicon alkoxide, ammonia and aqueous alcohol solution with magnetic stirring followed by ultrasound bath was modified with the use of a high-power ultrasound probe. The factors considered to prepare silica nanoparticles were the amount of water, tetraethyl orthosilicate and ammonia concentrations, reaction temperature, energy applied by the ultrasound probe and insonation time. The synthesis time was significantly reduced (from 270 to 10 min compared to the traditional Stober method), and smaller nanoparticles have also been obtained. Statistical experimental design has allowed us to establish the most important factors and its interactions, which influence on the size and size distribution, with a reduced number of experiments. A central composite experimental design at two levels was selected. Dynamic light scattering (DLS) was used to characterise the silica nanoparticles. The sizes obtained for different conditions ranged from 6 to 153 nm. Zeta potential was also estimated to establish its stability. In some cases, transmission electron microscopy was used to evaluate the nanoparticle shape.