Exploring the properties of Ag5–TiO2 interfaces: stable surface polaron formation, UV-Vis optical response, and CO2 photoactivation

Using a combination of first-principles modelling, X-ray absorption spectroscopy, and diffuse reflectance spectroscopy measurements, we explore the properties of Ag5-modified TiO2 surfaces. A general electron polarization phenomenon associated with surface polarons on TiO2 has been revealed theoretically and confirmed experimentally. First, the Ag5 cluster donates an electron to TiO2, leading to the formation of polaronic Ti3+ 3d1 states on the rutile TiO2(110) surface. The analysis of polarization effects in the nearby electronic structure accompanying the polaron formation is confirmed with X-ray absorption spectroscopy measurements at the Ti K-edge of TiO2 nanoparticles. Next, the UV-Vis optical absorption spectrum of the polaronic state is also computationally modelled and an enlargement of the polaron wavefunction is predicted. Moreover, we find an overall improvement of the UV-Vis optical response of the material through diffuse reflectance spectroscopy measurements. Finally, we predict that charge-transfer processes at the Ag5–TiO2 interface triggered by solar photons might allow for a photoinduced activation of CO2 by sunlight.