Sub-10-nm Mixed Titanium/Tantalum Oxide Nanoporous Films with Visible-Light Photocatalytic Activity for Water Treatment

In the present work, anodic mixed titanium/tantalum oxide nanotubes are prepared for the first time with sub-10-nm surface pore size and tube inner diameter. The morphological changes induced by the introduction of Ta into the Ti metal matrix are investigated, leading to remarkable geometrical variations dependent on the Ta loading. The UV-light activation necessary to trigger electron transfer in TiO2 limits the range of applications, and the shift in light absorption toward the visible range represents a significant challenge. Here, the band gaps of the as-created nanotube thin-film arrays are calculated, and the results, showing the presence of a minimum in the band gap, correlated to the presence of titanium and tantalum suboxides and Ta loading. The potential of the thin films as advanced materials for photocatalytic water treatment is tested against that of pure TiO2, and an enhancement in the visible-light absorption and an almost 3-fold increase in the degradation kinetics under pure visible-light irradiation are demonstrated.