Metallic oxides nanoparticles are stably adsorbed on silicate clay (such as nanosilicate platelets, NSPs) to form the metallic oxide/silicate clay nano-composite. The metallic oxides nanoparticles may be ZnO, CuO, Fe3O4, MgO or CaO. Optionally, silver nanoparticles are also adsorbed on the silicate clay for applications. Different from polymer dispersants, the silicate clay has high surface area and charge density so that the metallic oxides are not wrapped and thus perform better bactericidal efficacies.