Influence of annealing atmosphere on photoelectrochemical response of TiO2 nanotubes anodized under controlled hydrodynamic conditions

• Annealing in argon and nitrogen atmospheres increase oxygen vacancies formation. • Nitrogen atoms appear in the matrix of the crystalline TiO 2 annealed in nitrogen. • Band gap of nanostructures decreases annealing in non-oxidizing atmospheres. • Nitrogen or argon atmospheres increases the photocatalytic activity of nanotubes. The influence of three annealing atmospheres (air, nitrogen and argon) and the use of controlled hydrodynamic conditions (from 0 to 5000 rpm) on morphological, structural, chemical and photoelectrochemical properties of TiO 2 nanotubes have been evaluated. For this purpose, different characterization techniques have been used: Field Emission Scanning Electron Microscopy, Raman Confocal Laser Spectroscopy, X-Ray Diffraction, X-Ray Photoelectron Spectroscopy, Incident Photon-to-electron Conversion Efficiency measurements, ultraviolet–visible absorption spectra, Mott-Schottky analysis and photoelectrochemical water splitting tests. According to the results, it can be concluded that both hydrodynamic conditions and annealing in non-oxidizing atmospheres improve the photoelectrochemical response of the TiO 2 nanotubes. This fact has been attributed to the oxygen vacancies formed after annealing in argon and nitrogen atmospheres and also to the presence of nitrogen into the TiO 2 lattice due to the thermal treatment in the nitrogen atmosphere.