Lanthanide co-doped TiO2: The effect of metal type and amount on surface properties and photocatalytic activity

•RE doping enhanced the photocatalytic activity under visible irradiation.•Acetic acid oxidation over RE-TiO2 under Vis light leads to formation of CO2.•All rare earth metals are present in the form of oxides (RE2O3) at the TiO2 surface.•RE-TiO2 could be excited under visible light in the range from 420 to 450nm. Preparation of new rare earth metal-containing TiO2 nanocomposites (Nd3+/Er3+, Nd3+/Eu3+, Eu3+/Ho3+-TiO2) using sol–gel route and their photoactivity under visible and ultraviolet light is reported. The obtained photocatalysts were subsequently characterized by Brunauer–Emmett–Teller (BET) method, UV–vis diffuse-reflectance spectroscopy (DRS), luminescence spectroscopy, X-ray photoelectron spectroscopy (XPS) and X-ray powder diffraction analysis (XRD). Photodegradation efficiency of phenol and acetic acid was estimated for visible light (λ>420nm) and UV irradiation. It was found that introduced rare earth (RE) metals are presented in the form of metal oxides (RE2O3) at TiO2 surface. Our study demonstrated that Eu3+/Ho3+co-doped titania exhibited higher photocatalytic activity than P25 in phenol degradation under visible light, whereas Nd3+/Eu3+ co-doped TiO2 showed one of the highest activities in both phenol and acetic acid degradation reaction either under UV and visible light among all the rare earth doped samples. Action spectra analysis of the selected samples clearly showed that RE-doped TiO2 could be excited under visible light in the range from 420 to 450nm.