Preparation of hierarchical porous silica and its optical property

Inverse opal having mesoporous silica walls has been synthesized using close-packed polystyrene beads and octadecyltrimethylammonium chloride as a templates, and tetramethoxysilane as a silica precursor. The synthesized bimodal porous silica was characterized by XRD, N2 sorption, SEM and TEM. Hollow silica with inverted opaline structure had a macroporous diameter of 390 nm and a wall thickness of approximately 30 nm, and the mesoporous silica walls had a specific surface area of 367 m2/g, a mesopore diameter of 2.9 nm and a wall thickness of 1.8 nm. The refractive index (n) of this material was found be 1.05, which is lower than that of silica (n = 1.44) and also close to that of the air.