Effect of variation Mn/W molar ratios on phase composition, morphology and optical properties of MnWO4

Manganese tungstate (MnWO4) particles were successfully synthesized by a microwave hydrothermal method using MnCl2·4H2O and Na2WO4·2H2O as the starting materials. The products were characterized by X-ray diffraction, field-emission scanning electron microscopy, transmission electron microscopy and UV–vis absorption spectra. Results show that pure MnWO4 particles can be fabricated in the Mn/W molar ratio range from 1:2 to 2:1. The crystallinity of MnWO4 increases first and then decreases with increasing Mn/W molar ratio. MnWO4 morphology transforms from nanorods to aggregated spheres. UV–vis absorption spectra of these two morphologies exhibit a distinct redshift compared with bulk MnWO4. The band gaps of the nanorods and aggregated spheres-like MnWO4 particles are 2.75 eV and 2.65 eV, respectively.