Mesostructured vanadium phosphorus oxides assembled with exfoliated VOPO4 nanosheets

Hexagonal- and lamellar-meso structured vanadium phosphorus oxides were synthesized by assembling exfoliated VOPO4 sheets using cationic surfactants (dodecyl-, tetradecyl-, hexadecyl-, and octadecyltrimethylammonium bromide, CTAB). The products were characterized using X-ray diffraction, SEM, TEM, IR spectroscopy, elemental analysis, and TG/DTA. When a suspension of VOPO4 center dot 2H(2)O crystallites in 2-propanol was thermally treated, 2-propanol intercalated between layers of VOPO4 center dot 2H(2)O, followed by exfoliation of the layers. C(n)TAB 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 C(n)TAB/VOPO4 molar ratios of 0.5, and 1.0, respectively, with chemical formulae of [C16H33N(CH3)(3)Br](0.5)(VOPO4)-0.4H(2)O and [C16H33N(CH3)(3)Br](1.0)(VOPO4), respectively. The unit cell constants of hexagonal- and lamellar-phases from C(16)TAB were a = 3.86 nm and c = 3.87 nm, respectively, and increased with carbon number of the primary chain of C,TAB. In the lamellar phases, the surfactant was incorporated as a double layer at an angle of approximately 27 degrees and its wall consisted of two VOPO4 sheets. (c) 2005 Elsevier Inc. All rights reserved.