Facile synthesis of Fe3O4/SiO2 composite nanoparticles from primary silica particles

A facile method was developed for preparation of Fe3O4/SiO2 composite nanoparticles by direct introduction of Fe3O4 nanoparticles into the Stöber process upon formation of the primary silica particles. When the Fe3O4 nanoparticles were added into the reaction mixture at appropriate time, the primary particles can quickly aggregate with the Fe3O4 nanoparticles, thus suppressing the dipole–dipole interactions among the magnetic nanoparticles effectively and allowing the synthesis of Fe3O4/SiO2 composite nanoparticles with defined structure by further deposition of silica layer. Such a method can also be applied for coating silica layer on other water soluble nanoparticles with surface affinity to silica, such as 3-mercaptopropionic acid (MPA) capping ZnS:Mn and citrate modified Au nanoparticles.