Enhancement of NOx photo-oxidation by Fe- and Cu-doped blue TiO₂

The present work is focused on the removal of NOx with reduced blue TiO₂ with Fe (blue Fe-TiO₂)- and Cu (blue Cu-TiO₂)-doped photocatalyst. TiO₂ was reduced via lithium in EDA (blue TiO₂). Fe and Cu ions were doped in the reduced TiO₂ (blue Fe-TiO₂ and blue Cu-TiO₂). The material resulted in a core-shell structure of amorphous and anatase phase. XPS suggests the existence of Ti³⁺ species and oxygen vacancies within the structure of TiO₂. Additionally, valence bond (VB)-XPS shows the generation of intermediate levels at the band edge of the doped photocatalyst. Photocurrent, electrochemical impedance spectroscopy and cyclic voltammetry confirmed the enhanced charge-separation process in doped reduced TiO₂. The photocatalysts were tested for the photo-oxidation of NOx. Blue Fe-TiO₂ reveals the efficiency of 70% for NO elimination and 44.74% for NO₂ formation. The improved efficiency of the doped photocatalyst is related to the re-engineered structure with Ti³⁺ species, oxygen vacancies, and charge traps. Electron spin resonance (ESR) measurement was carried out for blue Fe-TiO₂ to confirm the formation of reactive oxygen species (ROS). Furthermore, ion chromatography was used to investigate the mechanism of NOx oxidation. In conclusion, the doped blue TiO₂ has a strong tendency to photo-oxidize NOx gasses.