Selective photocatalytic reduction CO2 to CH4 on ultrathin TiO2 nanosheet via coordination activation

Ultrathin TiO2 nanosheet with abundant Ti3+ is constructed as a photocatalyst for CO2 conversion in the absence of any sacrificial reagents. The exposed Ti3+ as a Lewis base site may activate CO2 to form bridging Ti···CO2−···Ti, resulting highly CH4 yield via the synergistic effect of coordination-activation and photocatalysis. [Display omitted] •Ultrathin TiO2 nanosheets (NST) with abundant Ti3+ sites are constructed as a photocatalyst for conversion CO2.•The catalyst (NST) exhibits a high yield (147.2 μmol g−1 h−1) and selectivity (96.8 %) for CH4.•CO2 would be selectively activated on the surface of NST via forming the bridging Ti···CO2−···Ti coordination species.•The synergistic effect about coordination-activation and photocatalysis can greatly enhance CH4 yield efficiency. Ultrathin TiO2 nanosheet (NST) with abundant Ti3+ sites is developed as a photocatalyst which exhibits a high yield (147.2 μmol g−1 h−1) and selectivity (96.8%) for CO2 to CH4. The results of in situ FTIR, in situ EPR and density functional theory (DFT) calculation suggest that CO2 would be selectively activated on NST surface via forming the bridging Ti···CO2−···Ti coordination species which not only lowers the activation energy barrier, but also determines the selectivity of CH4. Additionally, NST with the better separation and transfer ability for photogenerated electrons-holes can fleetly supply the electrons to CO2 molecules for high efficiently producing CH4 via the Ti-C coordination bond. Finally, a possible mechanism of the synergistic effect about coordination-activation and photocatalysis is discussed at a molecule level. This work would offer a perspective for designing an effective photocatalyst and tailoring the selectivity of products by coordination activation.