(317a) Mesostructure and Pore Size Distribution of Mesoporous Silica / Anodic Alumina Hierarchical Membranes Tuned with Ethanol

Authors: 
Meoto, S., Rensselaer Polytechnic Institute
Coppens, M. O., University College London
Synthesis of a hybrid mesoporous silica / anodic alumina membrane is challenging, as many methods lead to overgrowth of silica on the external surface of the alumina membrane, incomplete alumina channel filling, non-uniform silica structures, or silica with a wide pore size distribution [1]. Silica nanorods with a controlled structure can be formed within anodic alumina channels, using the anodic alumina as a sacrificial template to facilitate the orientation of the silica pores. Mesopores of a controlled diameter can be created in the silica by a soft-templating method, using tri-block copolymer surfactant, introduced in the precursor solution. However, non-uniformity over macroscopic cross-sectional distances of the hierarchical silica/anodic alumina composite precludes use of these materials for reproducible membrane-based separations.

We show how ethanol content, in the silica precursor solution, has a significant effect on the type and order of the mesoporous silica phase. Varying the ethanol concentration controls the mesoporosity and the structure of the mesoporous silica over macroscopic distances, so that an improved mesoporous silica/anodic alumina hybrid membrane with controlled pore sizes is produced [2].

The hierarchically structured membranes were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), small-angle X-ray scattering (SAXS) and nitrogen adsorption/desorption measurements. These techniques provide evidence of the increasing degree of ordering and narrower pore size distribution obtained with decreasing ethanol concentration. Interpretation of the formed structures and the influence of ethanol are made possible by dynamic light scattering (DLS) experiments of the precursor solutions, which allow us to follow the evolution of the micelles that template the silica mesopores, for various ethanol concentrations.

The membranes are tested by using them to carry out protein separations, showing promise as a platform for membrane based applications. [1]. S. Meoto, M.-O. Coppens, J. Mater. Chem. A, 2014, 2, 5640 [2]. S. Meoto, N. Kent, M. M. Nigra, M.-O. Coppens, submitted

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