Preferentially oriented Ag-TiO2 nanotube array film: An efficient visible-light-driven photocatalyst.

Ag-TiO2 nanotube array films with the preferential orientation of crystals were fabricated on ITO glass by magnetron sputtering and anodization. Comprehensive characterization was performed to ascertain the composition and microstructure characteristics of thin films. The photocatalytic activities were evaluated through the reduction of hexavalent chromium (Cr2O72- (Cr (VI)) as a model compound under visible light irradiation. XRD and XPS studies reveal the development of preferred orientation along [001] in anatase TiO2 nanotubes by adjusting the Ag content during magnetron sputtering. Such unusual behavior is attributed to the minimization of anatase (001) surface energy assisted by Ag. The Ag-TiO2 nanotube arrays having preferred crystal orientation exhibit superior separation/transfer of photo-induced charges. Furthermore, the Ag-TiO2 nanotube arrays show improved absorption of visible light due to the SPR effect induced by Ag and the formation of heterojunction between the TNAs and Ag2O. TNA-3Ag exhibits the highest photocatalytic activities by removing 99.1 % Cr (VI) in 90 min under visible light illumination.