Facile fabrication method and characterization of hollow Ag/SiO2 double-shelled spheres

Hollow Ag/SiO2 double-shelled spheres with silver nanoparticle coating onto the interior wall of hollow silica have been successfully prepared via a novel and facile approach. In this method, negatively charged polystyrene (PS) beads were first modified by Sn2+ ions via electrostatic interaction, and then by Ag+ ions, which were reduced by Sn2+ ions and sodium-potassium tartrate to obtain PS/Ag composite spheres. When these spheres were coated by silica nanoparticles as shells from the hydrolysis and condensation reaction of tetraethoxysilane (TEOS) in isopropanol/ammonia mixture at 15 degrees C, the PS beads were "dissolved" in the same medium subsequently even synchronously, directly forming hollow Ag/SiO2 double-shelled spheres. Neither additional dissolution nor calcination process was used to remove polymer templates. This structure of hollow spheres not only has high catalytic activity, but also will decrease the loss of Ag nanoparticles due to frictional and/or other mechanical forces and the possible aggregations, and have controllable and selective catalytic activity compared to these common nanocomposite spheres with noble metal nanoparticles coating on the surfaces of supporting beads.