Characterization and fabrication ofnanoporous materials by templatedirected sol-gel methods

摘要

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