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

A salicylic-acid (SA)-modified samarium-doped TiO complex (Sm-TiO/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 surface through its phenolic/carboxylic functional groups. In the Sm-TiO/SA complex, a ligand-to-metal charge transfer (LMCT) is active, inducing a marked red-shift in the absorption spectrum of TiO, which extends to 550-600 nm. The synergetic effect between the LMCT process and the luminescent properties of the lanthanide ions (Sm) 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/SA complexes, the superoxide radical ion (O ) is the main active species responsible for the -de-ethylation pathway under sunlight irradiation. The cleavage of RhB by the hydroxyl radical (OH) appears, instead, to dominate with the Sm-TiO photocatalysts.