Platinum nanoparticle modulated titania electronic structure descriptors for selective photocatalytic CO₂ conversion

Modulation of the electronic structure of TiO₂ nanorod array (NR), which governs the selectivity for the photocatalytic CO₂ conversion, is demonstrated by the deposition of Pt nanoparticles (NPs) with various configurations. In-situ X-ray absorption near edge structure (XANES) measurements suggest that the active sites for the photocatalytic reaction are located on the surface of TiO₂ NRs, but not on the Pt NPs, because the photocharge transfer from TiO₂ NRs to Pt NPs is inefficient. The t_2g/e_g orbital ratio and d_z²/d_x²-y² orbital ratio of TiO₂ acquired from Ti L₃-edge spectra of the Pt NP/TiO₂ NR photocatalysts, which are strongly influenced by the feature of the deposited Pt NPs, are respectively well-correlated to the experimental selectivity of H₂ and CH₄ for photocatalytic CO₂ conversion as well as the density functional theory calculated adsorption energies of H atom and CO molecule on the TiO₂ surface. The Pt NPs thus play a crucial role as a promoter rather than as a cocatalyst. Besides the adsorption energies of H and CO on TiO₂, the t_2g/e_g and d_z²/d_x²-y² ratios of Ti 3d unoccupied state can be the electronic structure-based descriptors of TiO₂ heterostructures for photocatalytic CO₂ conversion to distinguish between H₂ evolution and CH₄ formation.