Enhancing the visible light absorption via combinational doping of TiO2 with nitrogen (N) and chromium (Cr)

Chromium and nitrogen co-doped titanium dioxide photocatalysts were prepared by the solvothermal method. The samples were characterized by UV–vis diffuse reflectance spectroscopy, X-ray diffraction (XRD), transmission electron microscopy (TEM). The particle size of the codoped titania is narrowed to about 9 nm calculated from the XRD data. Doping of chromium and nitrogen ions effectively improves the visible absorption range with an optimal doping concentration of 2 at% and 10 at% (Ti:N or Ti:Cr) for nitrogen and chromium element, respectively. The main reason comes from the narrowed intrinsic band gap (∼1.8 eV) depended on the justly co-doping content. Meanwhile, the simple codoped models with different concentration of chromium were built and the corresponding electronic structures were calculated by the DFT method. Theoretical results show that the band gap is decreased with by increasing the doped concentration of chromium, which reveals well the changing trend of the experimental results of band gaps.