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.