Reverse microemulsion-mediated synthesis of SiO(2)-coated ZnO composite nanoparticles: multiple cores with tunable shell thickness.

Monodispersed SiO(2)-shell/ZnO-core composite nanospheres have been prepared in an oil-in-water microemulsion system. By using cyclohexane as the oil phase and Triton X-100 as the surfactant, composite nanospheres with high core loading levels and tunable shell thickness were obtained. Utilization of PVP capping agent on ZnO allowed the synthesis of composite nanospheres without forming any coreless SiO(2) spheres or shell-less ZnO particles. The photoactivity of ZnO nanoparticles was greatly reduced by SiO(2)-coating, which enables their applications as durable, safe, and nonreactive UV blockers in plastics, coating, and other products.