Bimodal porous silica monoliths obtained by phase separation in non-aqueous media

Abstract

Stable and crack-free bimodal macroporous silica monoliths were prepared for the first time in non-aqueous media and at room temperature by phase separation between a silica rich phase and a formic acid rich phase. Polyethylene oxide (PEO) was added to promote the phase separation between silica and formic acid leading to monoliths with 2 micron macropores. An additional basic treatment creates a supplementary mesoporosity of 7 nm. The addition of ionic liquid (BMIM-TFSI) in the synthesis increased the surface area of monoliths up to 760 m² g⁻¹ by inducing the formation of silica nanoparticles inside the monolith skeleton. Furthermore, the ionic liquid decreased the interaction between silica and PEO, which can then be removed by simple washing. The addition of methylsiloxane (MTMS) in the synthesis allows the ionic liquid at the surface of the macroporous monoliths to be maintained and represents the first example of supported ionic liquid associated with large through-flow pores. Such a system could therefore be used in chromatography for demanding and complex separation processes or in catalysis for the transformation of low-solubility reactants.