Boric acid assisted formation of mesostructured silica: from hollow spheres to hierarchical assembly

A boric acid assisted assembly approach has been provided to prepare mesostructured silica with various morphologies and porosities. The hollow siliceous spheres with ultrasmall size (similar to 15 nm) can be synthesized under an ultra-dilute CTAB/P123 surfactant concentration, with TEOS as the silica source in a weak acid system. It was also found the ratio of CTAB/P123, the concentration of boric acid and surfactant, the amount of TEOS and the addition of MgSO4 had key roles in controlling the morphologies and porosities. The obtained mesostructure silica possessed ordered structure, uniform morphologies (hollow sphere, tubular and cage-like mesoporous silica), high surface area (304.2-742.0 m(2) g(-1)), tunable large pore volume (0.55-2.07 cm(3) g(-1)) and pore size distribution (2.2- 11.8 nm).