Effects of doped vanadium ions on the photocatalytic behavior of TiO₂ for CO₂ reduction

In this study, we investigate the photocatalytic behavior of V-doped TiO₂ for CO₂ reduction in terms of the distribution, concentrations and chemical states of the doped V ions in the TiO₂ lattice. In addition, the interfacial charge transfer between the doped TiO₂ and CO₂ is examined to understand the thermodynamically reductive capability. The V-doped TiO₂ contained V₂O₅ crystallites at the surface after calcination above 300 °C. In contrast, V³⁺ and V⁴⁺ ions presented mainly at the inside lattice. High concentrations of V³⁺/V⁴⁺ ions trapped charge carriers to induce recombination, thus inhibiting photocatalytic oxidation. However, higher photocatalytic activity was found in a heavily doped TiO₂ for CO₂ reduction. Methane (CH₄) was the major product of the reduction when water was used as the reductant. The surface embedded V₂O₅ crystallites which facilitate charge transfer to CO₂ are the key for the high reductive activity.