Improving charge separation, photocurrent and photocatalytic activities of Dy-doped TiO 2 by surface modification with s
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Improving charge separation, photocurrent and photocatalytic activities of Dy-doped TiO2 by surface modification with salicylic acid Chaima Ouled Amor1, Kais Elghniji1,2,* 1 2
, and Elimame Elaloui1
Materials, Environment and Energy Laboratory (UR14ES26), Sciences Faculty of Gafsa, University of Gafsa, 2112 Gafsa, Tunisia Materials, Environment and Energy Laboratory (06/UR/12-01), Science Faculty of Gafsa, University of Gafsa, 2112 Gafsa, Tunisia
Received: 2 May 2020
ABSTRACT
Accepted: 4 October 2020
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.
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1 Introduction TiO2 is the most widely used photocatalytic and photocurrent material because it acts as photoactive material for charge transfer processes. However, in the semiconductor-assisted photocatalysis TiO2 is not very efficient owing to its wide bandgap (* 3.2 eV) that allows it to absorb less than 5% of solar light. Therefore, a great effort has been devoted to extending the optical response of semiconductor TiO2
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https://doi.org/10.1007/s10854-020-04606-x
in the visible and solar region [1–3]. One of the promising systems is the photocatalytic activated by RE doping, which has shown huge potential in inhibiting recombination of hole/electron and expanding the light adsorption of TiO2. However, the effects of RE ions on the TiO2 crystal defect chemistry (oxygen vacancies and Ti3?) and hole/electron recombination mechanism are discrepant in the literature. For a sufficiently large RE (Pr, Gd, Er, Eu, Ce, Dy, Sm, Tb and La) concentration, the number of
J Mater Sci: Mater Electron
oxygen defects tends to increase, owing to the introduction of charge imbalance created by Ti4? and RE3? ions. Some authors reported the beneficial effect of RE3? in enhancing electron/hole separation resulting in high photocatalytic efficiency [4–8]. However, other authors suggested a harmful effect of RE3? due to the excess of oxygen vacancies generated in R
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