(617fb) Rare Earth Element Doped Titania (TiO2) for Heterogeneous Photocatalytic Applications

Titanium dioxide or titania (TiO₂) is a well-studied photocatalyst. The major drawback of titania is its bandgap. Having a very high band gap (~3.0 eV for rutile; ~3.2 for anatase), titania is only responsive towards UV light. There is interest in enhancing the light absorbing properties of titania by doping various metals through upconversion phenomenon. We hereby studied the effect of doping erbium (Er) and ytterbium (Yb) ions on the photocatalytic effects of titania. For our purpose, we used Rose Bengal as a model pollutant and phenol as a real pollutant. Efforts have been spent in understanding the phenomena of upconversion, adsorption, recombination kinetics etc. and its implications towards the photocatalytic degradation rates of pollutants. We prepared pure anatase samples along with those with erbium doping concentrations of 2% and ytterbium doping concentrations of 0%, 10%, 15% and 20% (all in elemental basis) in a hydrothermal process. These samples were characterized for crystal structure, surface properties, composition, particle size, band gap and band edge positions. Band gaps and band edges were measured using diffuse reflectance mode in UV-visible spectroscopy and by Electrochemical Impedance Spectroscopy (EIS) respectively. Computational calculations using density functional theory (DFT) have been conducted to probe the crystal structure of the doped material as well as their band structure. Vienna ab-initio Simulation Package (VASP) has been used for the purpose. The aqueous phase photocatalytic reduction rate constants were quantified for both the organic liquids under different light sources. The 2% Er doped TiO₂ sample performed ~ 3 times better than pure TiO₂ under simulated solar light. To further elucidate the effect of different light sources, LEDs with different wavelengths (405 nm, 530 nm, 660 nm and 940 nm) were used. We could obtain the photo reduction of phenol and Rose Bengal under 405 nm light. Plausible explanations are made for these photocatalytic reduction results based on suppressed charge carrier kinetics and a close correlation with the bandgaps and band edges (both from experiments and computations).