Facile synthesis of hierarchically mesoporous silica particles with controllable cavity in their surfaces.

Novel and uniform mesoporous silica particles with controllable cavities in their surface have been fabricated using PAA and CTAB as dual templates in a mild reaction system. Herein, a series of hierarchically distinct silica particles can be obtained by simply adjusting the mass ratios (R) of PAA to CTAB. When the R value continues to decrease, the corresponding number and opening size of these cavities are also increased. However, if no PAA added, only unique monodisperse mesoporous silica spheres with uniform size of approximately 400 nm can be obtained. These specific silica particles were characterized by means of small-angle X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscope (TEM), Fourier-transform infrared (FT-IR) spectra, and nitrogen adsorption-desorption measurements. Results show that these unique mesoporous silica particles totally behave as an hexagonally ordered mesophase. The maximum BET surface area can be as high as 891 m(2)/g, and the maximum pore volumes can be as large as 0.27 cm(3)/g. Notably, the specific cavity features including opening size and cavity number almost do not change after calcination treatment. Moreover, a possible formation mechanism of the hierarchically distinct silica particles has been put forward, considering that the specific interface instability effect, the reduction in the surface free energy, and the synergic self-assembly of PAA and CTAB in solution can play a key role in mediating the formation of the hierarchical silica nanostructures. In general, the synthesis route is simple and straightforward for the preparation of the other biomineral nanostructures and may play an important role in microencapsulation.