(N, F)-codoped TiO₂ nanocrystals as visible light-activated photocatalyst

(N, F)-codoped anatase TiO₂ nanocrystals with active visible light response were prepared by using a simple sol-gel approach. X-ray photoelectron spectroscopy measurements suggested that the substitutional N and F species replaced the lattice oxygen atoms in TiO₂ nanocrystals. Such nanocrystals showed strong absorption from 400 to 550 nm, which was mainly induced by nitrogen doping. The phase transformation from anatase to rutile was hindered by fluorine doping at high calcination temperatures, which was verified by XRD patterns. The N₂ adsorption-desorption isotherms revealed the absence of mesopores in these nanocrystals. The (N, F)-codoped TiO₂ nanocrystals showed satisfying photocatalytic activity on the photo-degradation of methylene blue under visible light.