Hierarchically Porous Silica Prepared from Ionic Liquid and Polymeric Bicontinuous Microemulsion Templates

Polymeric bicontinuous microemulsions (B mu E) are unique disordered morphologies found in well-designed ternary blends of two immiscible homopolymers and a diblock copolymer surfactant. By crystallization or vitrification of one component and selective extraction of another, polymeric B mu Es are efficient precursors to nanoporous materials having three-dimensionally continuous, similar to 100 nm pores. Here, nanoporous polyethylene (PE) derived from a polymeric B mu E is used as a rigid template, inside which a so-called silica ionogel is synthesized. The solvent used is a room temperature ionic liquid (RTIL), and is incorporated into the silica product, yielding a disordered, bicontinuous arrangement of discrete silica and RTIL networks with similar to 10 nm periodicity. Because of the confinement provided by the PE template, the ionogel and PE are also arranged in a disordered, bicontinuous manner with similar to 100 nm periodicity. Subsequent selective extraction of the PE template by a suitable solvent generates a three-dimensionally continuous network of macropores in the ionogel. Selective extraction of the RTIL further generates a three-dimensionally continuous network of mesopores within the macropore walls. The final silica product thus contains two bicontinuous pore structures: larger macropores interconnected by smaller mesopores differing in size by over an order of magnitude. This novel, hierarchically porous material simultaneously possesses high internal surface area and a large pore framework required by advanced applications in catalysis, sensors, and purification.