Effect of the Heterovalent Doping of TiO2 with Sc3+ and Nb5+ on the Defect Distribution and Photocatalytic Activity

Two series of Sc3+- and Nb5+-doped TiO2 (rutile) samples were synthesized and characterized by SEM, ICPE spectroscopy, XPS, and BET methods. Photocatalytic activity of the doped TiO2 samples was tested in photocatalytic degradation of phenol. Dependences of the photocatalytic activities of the doped TiO2 samples demonstrate a volcano-like behavior, indicating the existence of the optimal dopant concentrations to achieve the highest activity of photocatalysts. Remarkably, the optimal dopant concentrations correspond to the extrema observed in work function dependences on the dopant concentrations, that indicates a significant energy redistribution of the defect states within the bandgap of TiO2. Such a redistribution of the defect states is also proven by the alterations of the optical and EPR spectra of the intrinsic Ti3+ defect states in TiO2. Based on the analysis of the experimental results, we conclude that both Sc3+ and Nb5+ doping of TiO2 results in redistribution of the defect states and the optimal dopant concentrations correspond to the defect structures, which are ineffective in charge carrier recombination, that ultimately leads to the higher photocatalytic activity of doped TiO2.

Automated summary

Two series of Sc3+- and Nb5+-doped TiO2 samples were synthesized and characterized, and their photocatalytic activity in phenol degradation was tested. The dependence of photocatalytic activities of the doped TiO2 samples demonstrated a volcano-like behavior, indicating the existence of optimal dopant concentrations for achieving the highest activity. The optimal dopant concentrations corresponded to the extrema observed in work function dependencies on dopant concentrations, suggesting a significant energy redistribution of the defect states within the bandgap of TiO2. The redistribution of defect states was also supported by the alterations in optical and EPR spectra of the intrinsic defect states in TiO2. The study concluded that Sc3+ and Nb5+ doping of TiO2 resulted in defect state redistribution and the optimal dopant concentrations corresponded to defect structures that are ineffective in charge carrier recombination, thereby leading to higher photocatalytic activity of doped TiO2.