Improving charge separation, photocurrent and photocatalytic activities of Dy-doped TiO2 by surface modification with salicylic acid

Salicylic acid-modified Dy-TiO 2 (Dy-TiO 2 /SA), novel visible light-sensitive material was synthesized via a sol–gel followed by impregnation method. Salicylic acid (SA) molecules are mixed with the TiO 2 and Dy-TiO 2 samples in hexane which promotes their direct adsorption. SA-modified TiO 2 particles (TiO 2 /SA and Dy-TiO 2 /SA) were finally obtained after drying at 120 °C. FTIR spectroscopy shows the formation of a fairly stable complex between Ti 4+ surface ions and salicylic acid. In Dy-TiO 2 /SA complex, a ligand-to-metal charge transfer (LMCT) is active giving light absorption in the visible region (500–600 nm) indicating a bandgap of ~ 2.24 eV, lower than unmodified TiO 2 samples. Electron paramagnetic resonance (EPR) and photoluminescence analyses demonstrate that LMCT process stabilizes the defect states within TiO 2 bandgap, suppressing the electron–hole recombination process. The charge separation of SA-modified TiO 2 complexes was evaluated through the photocurrent and the photocatalytic performances of Dy-TiO 2 /SA under visible light irradiation.