Characterization and fabrication of nanoporous materials by template directed sol-gel methods

Abstract

This research project focussed on developing synthetic strategies to fabricate a variety of nanoporous materials ranging the full range of pore sizes from micro to macro using template assisted sol-gel routes. Both colloidal crystals and surfactant self assemblies were employed as templates.
Initial studies focussed on the fabrication of macroporous titano/alumino and tinsilicate materials by dip infiltrating colloidal crystal templates with sol-gel mixtures. The sols were prehydrolysed in order to ensure atomic scale homogeneity of the final material. These materials were subsequently characterised using SEM to observe the macrostructure whilst XRD, EDX, NMR and iR were used to characterise the thermal stability and chemical homogeneity. The work reports materials with metal:silicon atomic ratios for macroporous titanosilicates and aluminosilicates that are far in excess of those previously reported in the literature.
Following this research was focused on the production of hierarchically ordered meso/macro silica materials by dip coating a preformed colloidal crystal into a sol-gel solution which contained surfactants. This technique combines principles of colloidal crystal templating and liquid crystal templating and by varying the surfactant it was possible to obtain mesoporous pore walls with both ordered and wormhole pore morphologies. The materials were characterised with both SEM, TEM and Nitrogen sorption and exhibited surface areas in excess of 500 m2 g-1. It was further shown that the mesopore size could be tuned by choosing different surfactants and mesopore sizes ranging from 2-7 nm were produced.
Finally, the synthetic procedures developed to produce meso/macro silica were used to produce meso/macro titania and zirconia by extending the method to incorporate different metal alkoxides precursors. These materials were once again characterised by SEM, TEM and nitrogen sorption and it was shown meso/macro titania and zirconia could be easily fabricated using this simple approach. It was also shown that the ordering in these materials was more sensitive to the chosen surfactant with only larger tri-block copolymer surfactants yielding stable mesostructures.

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Identifiers

ORCID for George Attard: orcid.org/0000-0001-8304-0742

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