Photoluminescent and photocatalytic ZnWO4 nanorods via controlled hydrothermal reaction

The synthesis of ZnWO4 nanocrystals via hydrothermal reaction was systematically studied in the wide ranges of solution pH (2-11), temperature (up to 180 degrees C) and reaction duration (up to 24 h), and the course and mechanism of phase/morphology evolution were revealed. With the well-developed ZnWO4 nanorod powder (aspect ratio similar to 7-20) as a representative, the effects of subsequent calcination (700 degrees C, in air and oxygen) on photo luminescent and photocatalytic performances were comparatively analyzed. Detailed characterization of the products was conducted by XRD, FE-SEM, HR-TEM, and FT-IR, Raman, fluorescence and UV-Vis spectroscopies. It was shown that the as-synthesized and calcined ZnWO4 crystallites all exhibited broad excitation (similar to 225-325 nm, peaked at similar to 283 nm; lambda(em) = 482 nm) and emission (similar to 400-700 nm, maxima at similar to 482 nm; lambda(ex) = 283 nm) that arise from the (1)A(1g) -> T-1(1u) and T-3(1u) -> (1)A(1g) electronic transitions within the WO6 ligand, respectively. Calcination in air and oxygen improved the integrated emission intensity by similar to 1.54 and 1.65 times, respectively. The calcination, however, significantly deteriorated the photocatalytic capability of ZnWO4 toward the degradation of methyl orange (MO) under UV irradiation. It was shown that similar to 93% of the MO molecules were degraded by the as-synthesized ZnWO4 nanorods with 80 min of UV radiation, while the values are only similar to 39.1 and 44.4% for the powders calcined in air and oxygen, respectively. The above results were interpreted by considering interaction of the excited electrons with oxygen vacancy defects, electron-hole interaction and UV absorbance of the ZnWO4 products.