Preparation and characterization of porous silica spheres by the sol-gel method in the presence of tartaric acid

Millimetre-sized mesoporous silica spheres, the sizes of which could be controlled by the mixing speed of the preparation solution, have been prepared directly from the reaction of tetraethoxysilane with tartaric acid in cyclohexanol by the sol-gel process. The silica gel spheres calcined at 400 degrees C showed specific surface areas of about 850 m(2) g(-1) and gave sharp pore size distribution curves in the narrow range around 2.3 nm radius. The peak of the pore size distribution curve shifted to smaller values as the calcination temperature increased from 400 to 900 degrees C. The gel retained a surface area of about 180 m(2) g(-1) and remained porous even after calcination at 1000 degrees C. The scanning electron microscope images showed that the spheres are basically composed of closely packed uniform primary particles of diameter ca. 20 nm. The high surface area of the spherical gel was considered to be caused by the micropores within the apparent primary particles.