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

Abstract

Salicylic acid-modified Dy-TiO2 (Dy-TiO2/SA), novel visible light-sensitive material was synthesized via a sol–gel followed by impregnation method. Salicylic acid (SA) molecules are mixed with the TiO2 and Dy-TiO2 samples in hexane which promotes their direct adsorption. SA-modified TiO2 particles (TiO2/SA and Dy-TiO2/SA) were finally obtained after drying at 120 °C. FTIR spectroscopy shows the formation of a fairly stable complex between Ti4+ surface ions and salicylic acid. In Dy-TiO2/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 TiO2 samples. Electron paramagnetic resonance (EPR) and photoluminescence analyses demonstrate that LMCT process stabilizes the defect states within TiO2 bandgap, suppressing the electron–hole recombination process. The charge separation of SA-modified TiO2 complexes was evaluated through the photocurrent and the photocatalytic performances of Dy-TiO2/SA under visible light irradiation.