Photocatalytic CO2 reduction over postcalcinated atomically thin TiO2 nanosheets: Residual carbon removal and structure transformation

[Display omitted] •Organic residues can be removed after 350℃/O2/2 h or 350℃/Air/4 h postcalcination.•Postcalcination induced phase transformation from TiO2(B) to anatase and the formation of hetero-phase junction.•Atomically thin nanosheets transformed into interconnected nanoparticles after calcination.•Morphology and phase transformation enhanced the chemical binding and activation of CO2. Postcalcination has usually been used to remove organic residues from atomically thin two-dimensional (2D) semiconductor materials for CO2 photoreduction, while the effect of calcination on their structure and photocatalytic activity has remained unclear yet. In this work, the structure transformation of atomically thin 2D TiO2(B) nanosheets during calcination was analyzed, and the structure-function relationship was studied. The results show that after calcination at 350 °C in air for 10 h, hierarchical assembly of 2D TiO2(B) nanosheets was collapsed into a uniform structure and the TiO2(B) nanosheets were decomposed into interconnected high-crystallinity anatase nanoparticles. The morphology/phase transformation enhanced the chemical binding and activation of CO2, and promoted the transfer/separation of photogenerated charges, resulting in the improved CO2 photoreduction activity. This work aimed to show the importance of precise control over the postcalcination treatment for atomically thin 2D materials.