CO2 Preactivation in Photoinduced Reduction via Surface Functionalization of TiO2 Nanoparticles

Salicylate and salicylic acid derivatives act as electron donors via charge-transfer complexes when adsorbed on semiconducting surfaces. When photoexcited, charge is injected into the conduction band directly from their highest occupied molecular orbital (HOMO) without needing mediation by the lowest unoccupied molecular orbital (LUMO). In this study, we successfully induce the chemical participation of carbon dioxide in a charge transfer state using 3-aminosalicylic acid (3ASA). We determine the geometry of CO2 using a combination of ultraviolet-visible spectroscopy (UV-vis), surface enhanced Raman scattering (SERS), C-13 NMR, and electron paramagnetic resonance (EPR). We find CO2 binds on Ti sites in a carbonate form and discern via EPR a surface Ti-centered radical in the vicinity of CO2, suggesting successful charge transfer from the sensitizer to the neighboring site of CO2. This study opens the possibility of analyzing the structural and electronic properties of the anchoring sites for CO2 on semiconducting surfaces and proposes a set of tools and experiments to do so.