**3. Silica nanoparticles**

Here we focus on a metalloid and the use of microemulsion method to obtain silica NPs. Yamauchi et al. [26] reported the synthesis of ultramicroparticles of silica by means of *w/o* microemulsion method.

Shantz et al. reported [27] synthesis of silicalite-1 nanocrystals in AOT-based microemulsion. They demonstrated that anionic microemulsions drive to essentially distinct crystal patterns than the nonionic [28] or cationic microemulsions formerly explored. The authors concluded that AOT and SDS anions synthesized by microemulsion method were employed to crystallize silicalite-1 nanocrystals with well-defined shapes and structures. Box, disk-like, spherical, and twinned nanocrystals were found under distinct experiential circumstances. It was also shown that tensioactive

uniqueness, TPAOH content, and the presence of salts and co-surfactant influence the morphology and crystallinity of silicalite-1. The crystal size and shape contrasted in all cases than those prepared in default of the microemulsion. The crystal morphology could be regulated by adjusting the interplay among surfactant and zeolite surfaces.
