Unveiling the Size-Dependent Photothermal Synergy of TiO₂ in Catalytic CO₂ Reduction

The hydrogenation of CO₂ to produce valuable chemicals through photocatalytic or photothermal technologies represents a viable path toward carbon neutrality. However, typical nanosemiconductor materials, such as TiO₂, often exhibit limited activity, necessitating the optimization of their performance as a key research priority. Here, we demonstrate that the size of anatase TiO₂ significantly influences its performance in the selective photocatalytic and photothermal reduction of CO₂ to CO. The small-sized TiO₂ (S-TiO₂, 15 nm) exhibits a low CO yield of 32.7 μmol g^-1 h^-1 and shows almost no photothermal synergy. In contrast, the large-sized TiO₂ (L-TiO₂, 160 nm) demonstrates a high CO yield of 185.3 μmol g^-1 h^-1 and significant photothermal synergy, with the CO yield reaching 438.7 μmol g^-1 h^-1. We reveal that L-TiO₂ is well-crystallized and has a higher conduction band position compared to the S-TiO₂. This results in a higher charge separation efficiency and more effective photoexcited electrons for CO₂ reduction. Additionally, the external heating primarily enhances the charge separation in L-TiO₂, significantly improving the conversion of CO₂ to CO. This work provides insights into the relationship between the structure and activity of TiO₂ in photocatalytic and photothermal CO₂ reduction.