Dual-responsive F–N–W-codoped TiO2 nanoparticles with strong visible light response and low-temperature thermo-oxidation activity

F–N–W-codoped TiO2 nanoparticles were successfully prepared by a sol–gel-mixing method without hydrothermal or calcining treatment. Effects of the F, N and W ion dosage concentration on crystallinity, morphology, grain size and chemical status of TiO2 were investigated. The results showed that the appearance of F–N–W-codoped TiO2 powders was uniformly spheroidal nanoparticles, whose average particle size was about 7 nm. The F–N–W-codoped TiO2 nanoparticles owned high catalytic activity under visible light irradiation and low-temperature thermo-oxidation activity in the dark. The highest degradation rate of Rhodamine B dye was obtained by TiO2 powders modified with 0.5 at.% W (N/W = 6/7) and 4.0 at.% F. Even in the dark, the degradation rate increased with the increasing of temperature. It was as high as 92% when the mixing liquid was kept at 60 °C for 2 h. The high catalytic activity of the F–N–W-codoped TiO2 might result from larger specific surface area and high surface acidity because of surface F ions, the band gap narrowing caused by WxTi1−xO2 or O–Ti–N, as well as lower recombination rate of charge carriers because of valence variation of W ions (W6+ → W5+) in the forbidden band.