Synthesis of monodispersed mesoporous silica spheres (MMSSs) with controlled particle size using gemini surfactant

A series of mesoporous silica spheres with tunable particle size were synthesized by the self-assembly of cationic gemini surfactant and silica source under basic condition. By varying the initial synthesis conditions, such as molar composition, temperature and addition of co-solvent, the particle sizes of the MMSSs with radially oriented pore structure were controlled in a range of 120-490 nm, and the pore sizes changed from 2.2 to 3.4 nm. The MMSSs have been obtained under different conditions when ethanol was used as co-solvent. With increasing the concentration of ethanol, the sphere diameter varied from 70 to 460 nm. The increasing of reaction temperature from 0 to 90 °C led to the average diameter of the mesoporous silica spheres changing from 90 to 410 nm. Higher NaOH concentration and lower surfactant concentration have been found to facilitate the formation of MMSSs with larger particle size. MMSSs with diameter of 180-380 nm were also synthesized with the addition of the co-solvents such as isopropanol, acetone, acetonitrile, dimethyl sulfoxide and methanol. The possible mechanism responsible for the shape and structure of MMSSs was discussed.