Absorption mechanism of dopamine/DOPAC modified TiO2 nanoparticles by time-dependent density functional theory calculations

RONCHI, COSTANZA; BOTTI, SILVANA; SORIA, FEDERICO; DI VALENTIN, CRISTIANA; FERRARO, LORENZO

Materials Today Energy

Elseiver

Año: 2020 vol. 19 p. 100571 - 100584

2468-6069

Donor-modified TiO2 nanoparticles are interesting hybrid systems shifting the absorption edge of this semiconductor from the ultra-violet to the visible or infrared light spectrum, which is a benefit for several applications ranging from photochemistry, photocatalysis, photovoltaics, or photodynamic therapy. Here, we investigate the absorption properties of two catechol-like molecules, i.e. dopamine and DOPAC ligands, when anchored to a spherical anatase TiO2 nanoparticle of realistic size (2.2 nm), by means of time-dependent density functional theory calculations. By the differential absorbance spectra with the bare nanoparticle, we show how it is possible to determine the injection mechanism. Since new low-energy absorption peaks are observed, we infer a direct charge transfer injection, which, unexpectedly, does not involve the lowest energy conduction band states. We also find that the more perpendicular the molecular benzene ring is to the surface, the more intense is the absorption, which suggests aiming at high molecular packing in the synthesis. Through a comparative investigation with a flat TiO2 surface model, we unravel both the curvature and coverage effects.