Synthesis of silica aerogel microspheres by a two-step acid-base sol-gel reaction with emulsification technique

Silica aerogel microspheres were synthesized by a two-step acid-base sol-gel reaction in water-in-oil emulsion systems, in which tetraethoxysilane was used as a precursor and ethanol as a solvent, and HCl and NH4OH as acid-base catalysts in two steps. The synthesis process and parameters of the emulsion process including viscosity, surfactant concentration and stirring rate have been investigated. In the emulsifying process, the viscosity of silica sol is vital to restrain the occurrence of flocculation phenomenon for forming monodisperse alcogel microspheres. The smooth silica aerogel microspheres can be formed from the silica sol with the viscosity of 107 mPa s. The resultant silica aerogel microspheres with similar surface areas above 650 m(2)/g, bulk densities in the range of 0.094-0.138 g/cm(3), and mean diameters ranging from 40.3 to 126.1 mu m can be formed by controlling these parameters of the emulsion process. The minimum of polydispersity and roundness of silica aerogel microspheres are 0.058 and 1.11, respectively. Furthermore, silica aerogel microspheres show a high capacity of uptaking bean oil, isopropanol, kerosene and n-hexane, highlighting the possibility to remove oils from water for oil spill cleanup.