Mesolamellar VPO phases obtained by incorporating long chain alkyl amine surfactants into the layered vanadium phosphate dihydrate phase

A series of mesolamellar VPO-amine phases have been obtained by intercalation of alkyl amines of differing alkyl chain lengths into the catalytically important VOPO4 · 2H2O phase. It is demonstrated that there is considerable variation in the conformation of the incorporated alkyl amines, which progressively assume a more disordered gauche conformation in their internal methylene groups with decreasing chain length. This finding contradicts the assumption made by previous workers that the alkyl amines incorporated into VPO-amine nanocomposites have fully stretched all trans conformations. From the present study, the observation that the basal spacing in long chain amine intercalated mesostructured VPO phases is smaller than that expected from the fully stretched amine molecule can be attributed to the shortening of the incorporated amine molecule due to the gauche conformation of the internal methylene groups. This is in contrast to the postulation of tilted configurations of fully stretched all trans amine molecules, made by earlier workers. It is also observed that the alkyl amine to vanadium ratio increases with increasing alkyl tail length of the incorporated amine, which is consistent with our observation of more ordering in the longer chain amines leading to better packing.