Formation of a photocatalytic WO3 surface layer on electrodeposited Al-W alloy coatings by selective dissolution and heat treatment.

In this study, we explored the feasibility of WO3 surface layer formation on electrodeposited Al-W alloy coatings by selective dissolution and heat treatment, with the aim of providing corrosion-resistant Al-W alloy coatings with photocatalytic self-cleaning properties under visible light illumination. The selective dissolution of Al and oxidation of residual W was carried out by immersing Al-W alloy films in an aqueous solution of nitric acid. A nanostructured H2WO4·H2O surface layer was formed on the alloy film by this process. The H2WO4·H2O layer was dehydrated to WO3 by heat treatment, yielding a multilayered WO3/Al-W alloy film with an approximately 300 nm thick WO3 layer. The WO3/Al-W alloy film exhibited photocatalytic self-cleaning, as demonstrated by the photodegradation of stearic acid and methylene blue. We also confirmed that selective dissolution and heat treatment did not significantly diminish the corrosion resistance of the Al-W alloy films.