Synergistic photothermal catalysis over electrospun Ti-O-Cu dual-redox sites: toward high-efficiency toluene oxidation under solar illumination

Photothermal catalytic oxidation is widely regarded as a promising technology for VOC removal. In this study, a series of Cu-doped TiO₂ catalysts with varying Cu concentrations were synthesized via electrospinning. The thermal catalytic and photothermal catalytic performance followed the order: 5Cu/TiO₂ > 15Cu/TiO₂ ≥ 10Cu/TiO₂ > 1Cu/TiO₂. The promotional effect of light irradiation followed the order: 15Cu/TiO₂ > 10Cu/TiO₂ > 5Cu/TiO₂ > 1Cu/TiO₂. The improvement in catalytic activity could be attributed to the enhanced low-temperature reducibility and lattice oxygen mobility, which exhibit a strong linear relationship with Ti⁴⁺-O-Cu⁺ sites content. The enhancement of the promotional effect of light irradiation was associated with narrow bandgap, more negative conduction band position and good electron-hole separation, which displayed a clear linear relationship with Ti⁴⁺-O-Cu²⁺ sites content. The synergistic role between Ti⁴⁺-O-Cu⁺ and Ti⁴⁺-O-Cu²⁺ contributed to the overall photothermal catalytic oxidation. In situ DRIFTS results indicated that toluene was first oxidized to benzaldehyde and benzoic acid, and finally converted to CO₂ and H₂O. Benzaldehyde and benzoic acid acted as key reactive intermediates in the oxidation pathway, with the oxidation of benzoic acid serving as the rate-determining step. This study provided valuable insights into the mechanistic aspects of photothermal catalytic oxidation and offered innovative strategies for the rational design of high-performance photothermal catalysts.