Visible light responsive N-F-codoped TiO2 photocatalysts for the degradation of 4-chlorophenol.

N-F-codoped TiO2 (NFTO) photocatalysts were synthesized by a simple sol-gel process with tetrabutyl titanate (Ti(OBu)4) as the precursor of TiO2 and ammonium fluoride (NH4F) as the source of N and F. The synthesized photocatalysts were investigated by Xray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), ultraviolet-visible diffuse reflectance spectroscopy (UV-Vis DRS) and photodegradation reaction tests of 4-chlorophenol under visible light irradiation to understand the relationship between the structure of NFTO catalyst and corresponding photocatalytic activity. The crystal phase and particle size of catalysts were found to be largely affected by the calcination temperature. In addition, N-F-codoping could inhibit phase transition of TiO2 from anatase to rutile. The presence of N and F atoms in the lattice of TiO2 is responsible for the visible light catalytic activity. In UV-Vis DRS tests, the spectrum of NFTO exhibited red shift compared with Degussa P25 and the band gap was reduced to around 2.92 eV. Under optimal calcination temperature and dopant concentration conditions, the NFTO photocatalyst exhibited the highest activity in the photodegradation reaction tests of 4-chlorophenol under visible light irradiation with a degradation rate of 75.84%. Besides, the 5-recycle test showed that NFTO photocatalyst could be reused and its activity kept stable under visible light irradiation.