Direct liquid crystal templating of mesoporous silica and platinum

Coleman, Nicholas Richard Boldero (1999) Direct liquid crystal templating of mesoporous silica and platinum. University of Southampton, Doctoral Thesis.

Abstract

Mesoporous silicas have been prepared with hexagonal (H₁) pore morphologies from TMOS/Brij 56/water/HCl mixtures. A detailed study of the synthesis of mesoporous silica from such mixtures revealed that ordered structures are formed at both high (~50 wt%) and low (~0.1 wt%) surfactant concentrations. The liquid crystal phase behaviour of Brij 56 in water showed that at low surfactant concentrations an H₁ structure formed from a phase separated solution. At the high concentrations of surfactant the H₁ phase was homogeneous throughout the sample and the hexagonal pore structure was a replica of the initial H₁ lyotropic phase with ~3.6 nm diameter pores and ~1.7 nm thick walls.

Direct liquid crystal templating of platinum has been studied by the reduction of a platinum salt in the aqueous domains of an H₁ phase to C₁₆EO₈. The most successful method of preparing H₁ platinum employed reduction with iron metal at room temperature. BET surface area analysis showed the mesoporous platinum to have a surface area of ~60 m²g^-1. This is almost twice the surface area for commercially available platinum black materials. The pore size of the H₁ materials was found to be ~2.9 nm with ~3.9 nm thick walls. A phase diagram study of the C₁₆EO₈/H₂PtCl₆/H₂O system made it possible to obtain cubic (V₁) and lamellar (L_α) mesoporous platinum. Finally, mesoporous silicas have been successfully loaded with H₂PtCl₆ and reduced to platinum metal as a method of preparing a supported platinum catalyst. The platinum was found to aggregate into particles rather than line the pores of the mesoporous structure after reduction.

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