Meoto, L; (2016) Controlled Synthesis and Characterization of Hierarchically Structured Inorganic Materials for Membrane Applications. Doctoral thesis , UCL (University College London).

Abstract

There is great need for new ways to effectively purify and desalinate water. There are protein channels in cell walls that act as very efficient water desalination membranes by rapidly and selectively transporting water. The mechanism of these biological membranes could be implemented in the design of a synthetic membrane by creating a size and electrostatic barrier suitable for efficient water desalination. Ordered mesoporous silica is a particularly attractive material, with ordered arrays of uniform nanochannels of a controllable size that have a wide range of applications, including separations. The silica surface can easily be functionalized to create the required steric and electrostatic effects. The synthesis of mesoporous silica films typically leads to pores that are poorly accessible from the film surface, hindering membrane applications. This thesis explores the formation of mesoporous silica structures within vertically aligned channels of anodic alumina membranes, so that an externally accessible pore orientation is obtained. These mesoporous structures are grown via an aspiration method. The thesis examines the influence of experimental conditions on the confined growth of the silica structures. Surfactants P123 and F127 act as structure directing agents, yielding circular, columnar or lamellar structures, such as 2D hexagonal (P123) and 3D cubic (F127), within the alumina channels. Ordered mesoporous silica in the confined space is achieved by controlling ethanol content. Transitions between the mesophases and changes in textural properties are observed with variations in experimental parameters. These experiments reveal that obtaining a defect-free composite structure where the alumina channels are tightly filled with the mesoporous silica material is not as trivial as literature precedent would suggest. Challenges remain, which include filling the alumina channels uniformly and homogeneously, and detachment of silica from the alumina walls. Consequently, fabrication of a porous silicon membrane is explored as an alternative robust matrix for growing aligned ordered mesoporous silica.

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