N-Doped lepidocrocite nanotubular arrays: hydrothermal formation from anodic TiO2 nanotubes and enhanced visible light photoresponse

New Cs-lepidocrocite nanotubular arrays were successfully prepared from anodically grown TiO2 nanotubes by hydrothermal conversion using CsOH in a water-ethanol mixed solvent. The obtained open nanotubular structure consists of plate-like nano-crystals, reflecting a preferred facet growth of the lepidocrocite with a 2-dimensional layered crystal structure. N-Doping of the Cs-lepidocrocite nanotubular layer was carried out by annealing in NH3 gas. The N-doped sample showed an incident photon to current conversion efficiency (IPCE) of 1.43% at 450 nm, which is 57% higher than conventional N-doped anatase TiO2 nanotubes.