Direct evidence of the photocatalytic generation of reactive oxygen species (ROS) in a Bi 2 W 2 O 9 layered-structure.

In the present work, the Bi2 W2 O9 photocatalyst has been prepared by an easy and prompt co-precipitation route. From the structural characterization, we have stated that the formation of the Bi2 W2 O9 is accompanied by a small amount of the Bi2 WO6 oxide, which gradually decreases by increasing the calcination temperature. The conduction and valence band edges of the Bi2 W2 O9 semiconductor were experimentally estimated for the first time using the X-ray photoelectron (XPS) and diffuse reflectance (DRS) spectroscopies. The best photocatalytic performance was attained for the sample calcined at 700°C, which showed the highest production of hydroxyl radicals, superoxide ions as well as the highest photodegradation of the ciprofloxacin drug. In addition, by means of photoluminescence spectroscopy we propose that the effective separation of the photogenerated charge carriers in the sample calcined at 700°C produces a higher production of reactive oxygen species and thus a higher photoactivity under solar-like irradiation conditions.