Mesoporous titanium phosphates were synthesised using three different approaches, involving reactions of titanium isopropoxide with long-chain alkyl phosphates, and subsequent aging at 80°C for several days. The resulting powders were characterised using XRD, TEM and N2 sorption.
The first approach involved the classical MCM methodology, where the modified titanium precursor was added to an alkylphosphate micellar solution. The resulting solids possess an organised, lamellar mesostructure. However, removal of the surfactant, either by heating or leaching in strong basic solution, leads to the collapse of the lamellar mesostructure.
In the second route, titanium alkoxide was pre-reacted with the long-chain alkyl phosphate, then hydrolysed with a large excess of water prior to ageing. Although the structure of the as-precipitated samples could be easily tailored by changing the processing parameters such as the alkyl phosphate chain length or phosphate/titanium ratio, surfactant removal by heating invariably led to the production of microporous samples.
The third approach involved the hydrolysis of the acetylacetone-modified titanium isopropoxide with excess water. The alkyl phosphate was then introduced into the resulting suspension. Subsequent ageing under acidic conditions destabilised the particles, leading to aggregation and subsequent gelation. In contrast to the previous approaches, the pyrolysed solid contained a significant proportion of mesopores, a high porosity (40%) and a surface area exceeding 300 m2.g-1.