Photoluminescent and photocatalytic ZnWO4 nanorods via controlled hydrothermal reaction

Abstract The synthesis of ZnWO4 nanocrystals via hydrothermal reaction was systematically studied in the wide ranges of solution pH (2-11), temperature (up to 180 °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 ∼7–20) as a representative, the effects of subsequent calcination (700 °C, in air and oxygen) on photoluminescent 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 (∼225–325 nm, peaked at ∼283 nm; λem = 482 nm) and emission (∼400–700 nm, maxima at ∼ 482 nm; λex = 283 nm) that arise from the 1A1g → 1T1u and 3T1u → 1A1g electronic transitions within the WO6 ligand, respectively. Calcination in air and oxygen improved the integrated emission intensity by ∼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 ∼93% of the MO molecules were degraded by the as-synthesized ZnWO4 nanorods with 80 min of UV radiation, while the values are only ∼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.