In situ growth of ZnO nanoparticles in precursor-insensitive water-in-oil microemulsion as soft nanoreactors

Zinc oxide (ZnO) nanostructures of uniform shapes and sizes (spherical, needle-like, and acicular) were directly synthesized using a relatively precursor-insensitive water-in-n-heptane microemulsion system stabilized by a mixture of cationic and non-ionic surfactants. With this colloidal system, the synthesized ZnO possesses the highest reported surface area (76 m(2) g(-1)) among the published reports utilizing other microemulsion systems. Such precursor insensitivity allowed studying the effect of Zn precursor:precipitating agent molar ratio (as high as 1:8) on the particle size, specific surface area, porosity, and morphology of the synthesized nanoparticles. The interaction of the cationic surfactant head groups and their Br(-) counter ions with Zn(2+) and OH(-) ions is believed to play a major role in controlling the ZnO characteristics. Due to such interactions, it is believed that the nucleation processes are retarded while the growth is more dominating if compared with other microemulsion systems.