Salicylic Acid-Modified Sm-TiO 2 for Photoluminescence and Photocatalysis under Real Sunlight: Synergistic Effects between Ligand-to-Metal Charge Transfer (LMCT) and Sm 3+ Dopant.

A salicylic-acid (SA)-modified samarium-doped TiO 2 complex (Sm-TiO 2 /SA) was synthesized via a sol-gel method followed by impregnation. A Raman Fourier transform IR and X-ray photoelectron spectroscopic study showed that SA (as an electron donor) forms a surface complex on the Sm-TiO 2 surface through its phenolic/carboxylic functional groups. In the Sm-TiO 2 /SA complex, a ligand-to-metal charge transfer (LMCT) is active, inducing a marked red-shift in the absorption spectrum of TiO 2 , which extends to 550-600 nm. The synergetic effect between the LMCT process and the luminescent properties of the lanthanide ions (Sm 3+ ) is discussed and supported by the photoluminescence spectra. Further photocatalytic experiments (under sunlight) and the study of the effect of different scavengers show the presence of competitive reactions between de-ethylation and cleavage of Rhodamine B (RhB) during its degradation. With the Sm-TiO 2 /SA complexes, the superoxide radical ion (O 2 •- ) is the main active species responsible for the N -de-ethylation pathway under sunlight irradiation. The cleavage of RhB by the hydroxyl radical ( • OH) appears, instead, to dominate with the Sm-TiO 2 photocatalysts.