Shape dependence of photosensitive properties of WO3 oxide for photocatalysis under solar light irradiation

Two morphologies of nanostructured WO3, nanoplatelets (NP) and pseudospheres (PS), were synthesized using a simple chemical route. The obtained powders were structurally characterized using thermal analyses and a combined XRD with Rietveld refinement. Their morphological and growth mechanisms were followed by SEM during the maturation phase. The results showed a square/rectangular shape and pseudospherical morphology, which exhibited a monoclinic phase after calcination at 400 degrees C and an orthorhombic phase after calcination at 500 degrees C. The temperature treatment induced an increase of grain size for the NP lateral size, while the PS size remains temperature independent. The photocatalytic activity was evaluated by the degradation of methylene blue under solar light irradiation. The degradation process was investigated by studying the photosensitive properties, optical absorption, photoluminescence and photoresistance. The photodegradation activity of methylene blue is composed of a rapid and strong adsorption step followed by a photoinduced catalytic process. The PS sample revealed a higher adsorption rate than NP powders at the low calcination temperature, while the photoinduced catalysis is better at the high calcination temperature, reaching 88% at 500 degrees C. The photosensitive properties showed a low luminescence intensity and a long charge carrier recombination time, thus indicating the photocatalytic efficiency of the elaborated samples.