Anodic Alumina-Mesoporous Silica Hybrid Membranes: A Systematic Study Of Alumina Filling

1. Introduction Mesoporous materials with ordered arrays of uniform nanochannels of a controllable size have wide-ranging applications, one of which is membrane separation. In order to be used as a membrane for size-exclusive separation of molecules, it is necessary to synthesize a defect-free structure with continuous nanoporosity. Mesoporous silica and porous anodic alumina have been extensively used to prepare new hierarchically ordered structures [1]. Mesoporous silica, SBA-15, is a particularly attractive material, because of its advantageous properties including an ordered pore structure, a narrow pore distribution of controllable size between 2.5 to 30 nm, high thermal stability and a well-known silane chemistry for surface functionalization [2]. An anodic alumina membrane is a suitable substrate because it has pores of a well-defined orientation, which are aligned perpendicular to the surface. As a result, a uniform alumina-mesoporous silica membrane with perpendicularly oriented nanochannels can be used as a nanofluidic device for molecular separation. However, the filling of the columnar pores of anodic alumina is not as easily attainable as literature suggests. A major issue in fabricating an alumina-silica hybrid membrane is realizing high inclusion of silica-surfactant nanocomposites inside the channels of the alumina membrane. We demonstrate this using two often used techniques, the sol-gel method [3] and aspiration [4], to fabricate alumina-silica hybrid membranes.