Enhanced Visible Light Active WO₃ 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 CO₂ and H₂O under ambient conditions. In this contribution, we focused on the synthesis of self-assembly WO₃ 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 H₂SO₄ (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 WO₃ 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 WO₃ 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_max = 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 WO₃ significantly affected the photocatalytic activity, which increased with the increasing thickness of WO₃ (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 WO₃ NFs was also discussed.