Hierarchically porous silica monoliths with tuneable morphology, porosity, and mechanical stability

Colloids have been used as sacrificial templates to produce porous materials with controllable morphology and pore sizes. Ceramic particles were employed to prepare porous ceramics and strong composite materials by freeze-casting. However, highly porous monodisperse microspheres have been rarely used as building blocks to obtain hierarchically porous structures. In the present study, porous monodisperse silica microspheres were prepared by a modified Stober method and then used as building blocks to produce porous silica with meso-/micro-pores and macropores by a controlled freezing approach. The macropore morphologies could be tuned with the addition of surfactants in the silica colloidal suspensions during the freezing process. The engineering of porosity and improvement on mechanical stability of the silica materials were achieved via a further soaking and sol-gel process. It was also possible to enhance the mechanical stability through the thermal treatment of the materials.