Effect of Ce-doping on the photocatalytic performance of TiO2 thin films

Ce-doped TiO2 thin films were prepared by sol-gel, spin coated on glass substrates, and annealed at 450 °C for 2 h. Solid solubility of Ce in anatase at the lowest doping level (≤0.25 mol% Ce) generated point defects that enhanced nucleation and recrystallization, resulting in relatively uniform grain sizes. In contrast, at ≥0.50 mol% Ce, overdoping, precipitation at grain boundaries, and liquid formation resulted in bimodal nanostructures with decreasing sizes of both the matrix grains and agglomerates owing to the progressive hindrance of Ti diffusion. The optimal photocatalytic performance at 0.25 mol% Ce was associated with a less densely packed array of fine matrix grains, while the performance at higher doping levels was dominated by liquid formation, greater packing densities, and blockage of active sites. The occurrence of Ce ↔ Ti intervalence charge transfer and associated oxygen vacancy formation are likely causes for the observed lowering of the band gap, reduction in the recombination rate, and enhancement of radiation absorption at longer wavelengths (red shift).