Abstract:

Hierarchically porous SiO₂ monoliths were prepared via sol-gel process accompanied by the phase separation and template method. The microstructure and pore structures of the monoliths were characterized, and the formation mechanism of hierarchically porous structures was investigated. The results show that the addition of poly(ethyleneoxide)-block-poly (propyleneoxide)-block-poly (ethyleneoxide) (P123) induces the phase separation to adjust the formation of the macroporous structure, and the spherical P123 micelles are also formed and distributed into the skeletons as templates. The addition of the micelle-swelling agent 1,3,5-trimethylbenzene (TMB) expands and stabilizes the P123 micelles, so that uniform spherical mesopores are successfully introduced into the macroporous framework. Meanwhile, the gel nanoparticles on the skeletons aggregate to form micropores. As a result, the hierarchically porous structures are constructed by well-defined interconnected macropores-spherical mesopores-micropores, and the corresponding porous monoliths are prepared. When the mole ratio of tetramethoxysilane (TMOS) : P123 : TMB is 1 : 0.015 : 0.353, the optimum hierarchical structure is obtained with macropore size of 0.5-1.5 μm, mesopore size of 3-4 nm on the skeleton, apparent porosity of 66.1% and Brunauer-Emmett-Teller (BET) specific surface area as high as 616 m²·g^-1.

Key words: Sol-gel, Silica, Hierarchically porous structure, Porous monoliths, Template, Micelle-swelling agent