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

Polymeric bicontinuous microemulsions (BμE) 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 BμEs are efficient precursors to nanoporous materials having three-dimensionally continuous, ∼100 nm pores. Here, nanoporous polyethylene (PE) derived from a polymeric BμE 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 ∼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 ∼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.