Inverse effects of lanthanide co-doping on the photocatalytic hydrogen production and dye degradation activities of Cu doped sol-gel TiO2

•Ti3+ sites formed by Cu doping increases the photocatalytic reduction activity of TiO2.•Lanthanide co-doping decreases the photocatalytic reduction activity of Cu doped TiO2.•Lanthanide co-doping increases the photocatalytic oxidation activity of Cu doped TiO2.•Lanthanide doping modifies pore structure and improves dye adsorption on TiO2 surface. Copper doped and lanthanide-copper co-doped titania powders were prepared by sol–gel technique and the effects of co-doping on the photocatalytic reduction and oxidation activities of titania were investigated in this work. Characterization studies indicated that a reduced structure was formed due to the presence of Ti3+ species in copper doped titania powder and a more stable structure was formed when lanthanides were used as co-dopants. Copper doped powder had a significantly higher activity in photocatalytic hydrogen production (1037 μmol/g/h) than the co-doped powders (∼400 μmol/g/h). The oxidation activities of co-doped powders however were determined to be about 2 times higher than that of the copper doped powder. The decrease in the reduction activity was attributed to the decrease in the number of Ti3+ sites, whereas the increase in oxidation activity was probably a result of the increase in the surface area and dye adsorption due to lanthanide co-doping.