Green synthesis and characterization of anisotropic uniform single-crystal α-MoO3 nanostructures

Anisotropic uniform single-crystal nanostructures of alpha-MoO3 have been synthesized successfully via a novel green and facile approach, i.e., decomposition and condensation of peroxomolybdic acid under hydrothermal conditions. The structure and morphology of the products were characterized by means of X-ray diffraction, transmission electron microscopy, selected area electron diffraction, high-resolution transmission electron microscopy, scanning electron microscopy, thermogravimetric/differential thermal analysis, temperature programmed decomposition-mass spectrometry, and Fourier transform infrared spectroscopy. It has been found that the formation of alpha-MoO3 proceeds at hydrothermal temperatures higher than 83.5 degrees C and that of MoO2.67-(O-2)(0.33)(.)0.75H(2)O is at 81.5 degrees C with the 0.9 mol/L molybdenum solution. The as-synthesized uniform nanostructures grow preferentially along [001], and the dimensions are 200-330 nm in width, 60-90 nm in thickness, and up to 10 mu m in length during time spans from 20 to 45 h at 170 degrees C. The structure and morphology of alpha-MoO3 show a weak dependence on the molybdenum concentrations of 0.2-0.9 mol/L, while the growth in the b-axis direction can be enhanced distinctly and specifically by the addition of nitric acid to the initial peroxomolybdic acid solution. The critical point in temperature (81.5-83.5 degrees C) to form hydrate and oxide is discussed, and one possible mechanism is proposed.