Synthesis of Colloidal Mesoporous Silica Spheres with Large Through-Holes on the Shell

Colloidal silica spheres with controllable large through-holes and mesopores on the shell were synthesized by using polystyrene (PS) spheres as a hard template and cationic surfactant hexadecyl trimethylammonium bromide (CTAB) as a soft template. Through modulating the synthetic conditions, including the volume ratio of ethanol (EtOH)/water, the amount of ammonia hydroxide, and the dosage of CTAB, SiO₂ spheres can transform among hollow structure, through-hole structure, and no large pore structure. The investigation suggests that the hydrolysis rate of the silica source and the interaction strength between the PS sphere template and SiO₂ may determine the large pore structure of the final product. The moderate hydrolysis rate of tetraethyl orthosilicate (TEOS) and strong interaction between the PS sphere template and SiO₂ is conductive to the formation of large through-holes in SiO₂ spheres. To further investigate the pore structure of through-holes of SiO₂ spheres, the lysozyme (Lz) was selected as a model molecule for adsorption experiments. The Lz adsorption experiments show that SiO₂ spheres with through-hole structure exhibit a much faster adsorption rate than SiO₂ spheres with hollow structure and higher adsorption capacity than SiO₂ with no large pore structure. Such a behavior could find interesting applications in the fields that require a fast-loading characteristic.