Synthesis of Hybrid, Ordered Mesoporous Silica Membranes

We discuss the synthesis of hybrid membranes, consisting of ordered arrays of mesoporous silica grown inside the columnar channels of anodic alumina. The silica mesopores have a controlled diameter and are oriented perpendicularly to the external membrane surface. The silica-surfactant nanocomposites are grown by sol-gel chemistry of silica in confinement, and aspiration.

Incorporation of silica inside the channels of anodic alumina membranes has been extensively reported in the literature. However, for application as a membrane, it is desirable to produce a structure in which the mesoporous silica material completely fills the channels of the anodic alumina membrane to minimize loss of size-selective separation and transport of molecules. This is not easy to achieve on macroscopic scales. Additionally, it is essential to obtain the silica material inside the channels of anodic alumina, and not on its external surface. Synthesis conditions were varied to increase the inclusion of silica-surfactant nanocomposites inside the alumina channels, while avoiding the formation of silica deposits on the external membrane surface.

The synthesized hybrid membrane was characterized by scanning electron microscopy (SEM), small-angle X-ray scattering (SAXS), nitrogen adsorption and desorption, and size-exclusion permeation experiments. Our results illustrate the challenges of achieving a crack-free membrane with a high fill factor.

Functionalization of the inner walls of a mesoporous silica-alumina hybrid membrane, with specific functional groups, yields a membrane that, by emulating the mechanism of certain biological pores in cell membranes, could render it applicable to water desalination and (bio-)-molecular separations.