Mesostructured vanadium phosphorus oxides assembled with exfoliated VOPO4 nanosheets

Hexagonal- and lamellar-mesostructured vanadium phosphorus oxides were synthesized by assembling exfoliated VOPO4 sheets using cationic surfactants (dodecyl-, tetradecyl-, hexadecyl-, and octadecyltrimethylammonium bromide, CnTAB). The products were characterized using X-ray diffraction, SEM, TEM, IR spectroscopy, elemental analysis, and TG/DTA. When a suspension of VOPO4 · 2H2O crystallites in 2-propanol was thermally treated, 2-propanol intercalated between layers of VOPO4 · 2H2O, followed by exfoliation of the layers. CnTAB was added to the alcoholic solution at 343 K. Treatment of the solution at 343 K for 10 min, followed by evaporation of 2-propanol, which resulted in the formation of hexagonal- and lamellar-phases at CnTAB/VOPO4 molar ratios of 0.5, and 1.0, respectively, with chemical formulae of [C16H33N(CH3)3Br]0.5(VOPO4) · 0.4H2O and [C16H33N(CH3)3Br]1.0(VOPO4), respectively. The unit cell constants of hexagonal- and lamellar-phases from C16TAB were a = 3.86 nm and c = 3.87 nm, respectively, and increased with carbon number of the primary chain of CnTAB. In the lamellar phases, the surfactant was incorporated as a double layer at an angle of approximately 27° and its wall consisted of two VOPO4 sheets.