Metastable h-MoO3 and stable α-MoO3 microstructures: controllable synthesis, growth mechanism and their enhanced photocatalytic activity

Metastable h-MoO3 hexagonal prisms have been fabricated through a simple green ultrasonic-assisted chemical route. After calcination at 440 degrees C for 2 h, the thermodynamically stable -MoO3 nanoplate-based rods have been achieved through a process of in situ phase transformation. The as-synthesised products have been characterised by powder X-ray diffraction, field emission scanning electron microscopy, Fourier transform infrared spectrum, UV-vis diffuse reflection spectroscopy and photoluminescence spectroscopy. The phase transformation from metastable h-MoO3 to stable -MoO3 is observed at 419 degrees C according to the differential scanning calorimetry results. The possible growth mechanism of MoO3 crystals has been proposed based on the experimental results. The prepared two kinds of MoO3 samples both display higher photocatalytic performance for degrading rhodamine B compared to that of commercial MoO3. In the present system, -MoO3 nanoplate-based rods exhibit slightly higher degradation activity than h-MoO3 hexagonal prisms, which is possibly due to its smaller band gap energy, smaller scale of nanoplate, better adsorption capacity and lower recombination of photogenerated electrons and holes.