Interface charge density matching as driving force for new mesostructured oxovanadium phosphates with hexagonal structure, [CTA]_xVOPO₄·zH₂O

Hexagonal mesostructured mixed-valence oxovanadium phosphates [CTA]_xVOPO₄·zH₂O, in short ICMUV-2, have been synthesized through a S⁺I^- cooperative mechanism using cationic surfactant (cetyltrimethylammonium, CTAB) rodlike micelles as a template. On the lines of the hypothesis that the driving force leading to the formation of mesostructured solids is the charge density matching at the interface between the supramolecular-organic and supramolecular-inorganic moieties, the self-assembling process between CTA⁺ micelles and VOPO₄^q- planar anions can be thought of as consequence of the adequate adjustment of the metal mean oxidation state. X-ray powder diffraction and TEM techniques show that the solids consist of hexagonal arrays of mesopores filled with surfactant, whereas spectroscopic results allow us to propose an oxovanadium phosphate bond topology similar to that observed in the Na_xVOPO₄·nH₂O layered derivatives. The thermal behavior of the mesostructured materials has also been investigated, given that both the easy elimination of CTA⁺ species and their V:P = 1:1 molar ratio make ICMUV-2 solids adequate pyrolytic precursors of the (VO)₂P₂O₇ catalyst.