Facile synthesis of hollow silica microspheres

Hollow silica microspheres were synthesised at room temperature from a vortexed mixture of water and droplets of tetraethoxysilane (TEOS) containing 10 mol% aminopropyltriethoxysilane: droplets stabilized with the surfactant cetyltrimethylammonium bromide produced silica shells, 30.6 µm in mean diameter, whereas replacing the Br− counterion with [Co(B9C2H11)2]− gave an approximately hundred-fold decrease in the size of the hollow spheres. Organo-functionalized hollow microspheres containing a covalently linked dye moiety were prepared by replacing 5 mol% of TEOS with dinitrophenylaminotriethoxysilane in the reaction mixture, and encapsulation of TEOS-soluble additives within the silica shells was demonstrated by incorporating porphyrin molecules and particles into the ethoxysilane droplets.