Influence of sodium doping on the material properties and photocatalytic activity of anatase titanium dioxide nanotubes prepared by anodization

The properties of semiconducting materials can be altered to meet our needs by tuning their bandgap with suitable methods. Here bandgap tailoring of anatase TiO2 nanotubes prepared by anodization technique is achieved by sodium doping at variant concentrations. The doped nanotubes with their reduced band gaps that match the visible range of solar spectrum exhibit greater photodegradation efficiency of methylene blue dye (97.3% in 180 min) than the undoped (56.8% in 180 min) with band gap in the UV region. Structural and morphological characterizations of the samples by X-ray diffraction, X-ray Photoelectron Spectroscopy, Raman Spectroscopy, Atomic Force Microscopy and Field Emission Scanning Electron Microscopy reveal that the doping-induced surface changes and increased Ti4+ to Ti3+ reduction play an active role in increasing the photocatalytic efficiency of the samples. Analysis of valence band photo emission spectra indicate shifting of fermi level away from conduction band edge with doping of Na1+ at Ti4+ site producing defect induced super radical formation for photocatalysis.