A sol–gel method is used to synthesize Ce–S codoped TiO2–SiO2 composite nanocrystalline films on the glass substrates in this paper. The influence of the metal/nonmetal ions codoping on both the physicochemical characteristics and photocatalytic performance of the composite film was studied. It was found that ions codoping induces a better charge separation and a smaller band gap energy, which are responsible for the improvement in the photo-degradation with respect to the acid naphthol red aqueous solution under visible light illumination. Moreover, the morphology, crystalline structures and compositions of the films were analyzed, and the doping mechanism was also investigated.

Ag+ and La3+ surface codoped TiO2 films were successfully prepared by the improved sol–gel and doping processes. The as-prepared specimens were characterized using differential thermal analysis-thermogravimetry (DTA–TG), X-ray diffraction (XRD), high-resolution field emission scanning electron microscopy (FE-SEM), X-ray energy dispersive spectroscopy (EDS), Brunauer–Emmett–Teller (BET) surface area, Photoluminescence spectrum (PL) and UV–vis diffuse reflectance spectroscopy. The photocatalytic activities of the films were evaluated by degradation of an organic dye in aqueous solution. The results of XRD, FE-SEM and BET analyses indicated that the TiO2 films were composed of nano-particles or aggregates with a size of less than 10 nm. With the codoping of Ag+ and La3+, TiO2 films with high photocatalytic activity and clearly responsive to the visible light were obtained. The improvement mechanism by ions doping was also discussed.Graphical AbstractThe PL intensity of Ag+ and La3+ surface codoped TiO2 was the lowest among all samples, indicating the recombination of electron and hole was effectively prohibited compared with pure TiO2, Ag+ and La3+ bulk codoped TiO2.Highlights► Ag+ and La3+ codoping can reduce the crystal size of TiO2. ► Ag+ and La3+ surface codoped TiO2 films have an obvious optical response red-shift. ► Ag+ and La3+ surface codoped TiO2 films can exhibit excellent photocatalytic activity under both UV and visible light irradiations.