Sulfur K-edge XANES for methylene blue in photocatalytic reaction over WO3 nanomaterials

We investigated the photocatalysis of dendritic nanostructured WO3/W composite materials fabricated by He plasma irradiation to tungsten plates, followed by the surface oxidation. The samples promoted the decolorization reaction of methylene blue (MB) aqueous solution under near infrared (NIR) light irradiation. To verify the MB molecule is actually decomposed by the photocatalysis of the samples, reaction products were analyzed by S K-edge XANES measurements for the MB solution kept with the samples under the light irradiation or in the dark.By the light irradiation, the σ*(S–C) peak in the XANES spectra reduced and a new peak originated from SO42− species was clearly observed, suggesting that S–C bonds in a MB molecule are broken by the NIR light irradiation and finally the sulfur species exists in the solution in the state of SO42− ion. After the adsorption reaction in the dark, the XANES spectra of the sample surfaces showed a sharp π*(S–C) peaks, indicating that MB molecules are adsorbed on the sample surfaces and stacked each other by the π–π interaction. These results demonstrate that the photocatalytic decomposition of MB molecules really proceeds over WO3/W composite materials even under NIR light irradiation.