Green Synthesis and Characterization of Anisotropic Uniform Single-Crystal α-MoO₃Nanostructures

Abstract

Anisotropic uniform single-crystal nanostructures of α-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 α-MoO3 proceeds at hydrothermal temperatures higher than 83.5 °C and that of MoO2.67(O2)0.33·0.75H2O is at 81.5 °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 μm in length during time spans from 20 to 45 h at 170 °C. The structure and morphology of α-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 °C) to form hydrate and oxide is discussed, and one possible mechanism is proposed.