Enhancement of the photocatalytic response of Cu-doped TiO₂ nanotubes induced by the addition of strontium

The influence of adding strontium to Cu-doped TiO₂ nanotubes on the photocatalytic performance of the resulting materials was herein studied considering changes in structural, textural, optical and morphological properties. Addition of strontium was performed in a 0.2–1.0 wt% range while an optimized fixed Cu loading of 0.5 wt% was used. TiO₂ nanotubes were obtained using alkaline hydrothermal treatment of P25 followed by a calcination treatment at 400 °C. The resulting TiNT material was then impregnated with copper using an incipient wetness impregnation followed by a new calcination at 400 °C (0.5Cu-TiNT). Strontium was then added under similar impregnation-calcination conditions. The effect of adding various amounts onto 0.5Cu-TiNT was therefore deeply characterized using X-ray diffraction, N₂ adsorption–desorption measurements, scanning electron microscopy coupled with energy-dispersive X-ray analysis, Raman, UV–vis diffuse reflectance, X-ray photoelectron, and photoluminescence spectroscopies as well as determining dielectric properties. Results clearly emphasize that up to a Sr loading of 0.8 wt%, the addition of Sr results in in situ formation of Sr-O-Ti entities on the surface of 0.5Cu-TiNT. Above this threshold loading, excess Sr loading leads to the formation of segregated SrO species. Finally, a direct correlation was observed here between the optimized formation of surface Sr-O-Ti entities and an enhanced photocatalytic response due to improved stabilization of photogenerated charges on 0.5Cu-TiNT resulting from the ferroelectric interference of neighboring SrTiO₃ entities.