A facile route to synthesis of hollow SiO2/Al2O3 spheres with uniform mesopores in the shell wall

The hollow SiO2/Al2O3 spheres with uniform mesopores in the shell wall have been successfully synthesized by a sol–gel process in an oil/water/oil (O/W/O) microemulsion. The intact hollow spheres are obtained by washing the as-synthesized solid produces with boiling water to remove the organic components. A large amount of silanol groups are retained in the hollow spheres by this facile route without calcination, and the possible agglomeration of the spheres and collapse of hollow structures are effectively avoided. The diameter and shell thickness of the spheres are measured by scanning electron microscope (SEM) and transmission polarized light microscope, which are ca. 10 and 2 μm, respectively. TEM image and N2 adsorption–desorption isotherms suggest that uniform mesopores are present in the shell wall of hollow SiO2/Al2O3 spheres after treatment with boiling water. 27Al NMR spectrum indicates almost all of aluminium species of hollow SiO2/Al2O3 spheres are in the four-coordinated environment.