Enhanced Visible Light Active WO Thin Films Toward Air Purification: Effect of the Synthesis Conditions.

Taking our current environmental situation in the world into consideration, people should face growing problems of air and water pollution. Heterogeneous photocatalysis is a highly promising tool to improve both air and water quality through decomposition/mineralization of contaminants directly into harmless CO and HO under ambient conditions. In this contribution, we focused on the synthesis of self-assembly WO thin films via an electrochemical approach in the aqueous electrolyte containing fluoride ions toward air purification. The effect of preparation conditions such as applied potential (10-50 V), anodization time (15-120 min), concentration of HSO (0.5-1.5 M) and NaF (0.1-1.0 wt.%) on the morphology, photocurrent response, and photocatalytic activity addressed to removal of air pollutant in the presence of as-prepared WO samples were thoroughly examined and presented. The results revealed the growth of nanoplatelets and their gradual transformation into flower-like structures. The oxide layers and platelet thickness of the WO samples were found to be proportionally related with the synthesis conditions. The photocatalytic ability toward air purification was evaluated by degradation of toluene from air mixture using low-powered LEDs as an irradiation source (λ = 415 nm). The highest photoactivity was achieved in presence of the sample which possessed a well-ordered, regular shape and repeatable distribution of flower buds (100% of degradation). The results have confirmed that the oxide layer thickness of the anodic WO significantly affected the photocatalytic activity, which increased with the increasing thickness of WO (to 1.05 μm) and then had a downward trend. The photocurrent response evidenced that the well-organized sample had the highest ability in photocurrent generation under UV-Vis and Vis irradiation. Finally, a possible growth mechanism of WO NFs was also discussed.