Tuning of physicochemical and photocatalytic properties of dual-phase TiO2: Rare earth mono-doping versus co-doping

Abstract

Modification of TiO 2 with rare-earth elements is an effective approach to improve photocatalytic efficiency and extend photoactivity into the visible region. Dual-phase anatase-brookite TiO 2 mono-doped with Sm, Gd, Tb, Tm, or Yb, and co-doped with SmGd, SmTb, SmTm, or SmYb, were prepared by a template-free one-step hydro-thermal method, and the effects of mono-versus co-doping on the morphological, structural, textural, optical, and photocatalytic properties of the materials were systematically compared. X-ray diffraction, Raman, Fourier-transform infrared, and high-resolution transmission electron microscopy confirmed that the dual-phase anatase-brookite structure is preserved after doping. The formation of mesoporous materials with developed porosity was proven by nitrogen physisorption. It was established that mono-doping favours the formation of powders with increased surface area, while co-doping supports the formation of larger pores. Ultraviolet – visible diffuse reflectance spectroscopy and photoluminescence spectroscopy demonstrated enhanced visible-light absorption and suppressed charge recombination for the doped powders, with stronger effect for co-doped materials due to the synergistic contribution of coupled dopants ’ energy levels. The photocatalytic performance was evaluated in the degradation of a commercial diclofenac drug under UV and visible-light illumination. In the tests, the most active catalyst was TiO 2 co-doped with Sm and Gd, which reached the drug removal rates of 20.4 % and 79.9 % under visible ( > 450 nm) and ultraviolet light, respectively. These results provide new insight into the structure – property – activity relationships of mono-and co-doped REE anatase-brookite TiO 2 composition and will aid the optimal design and fabrication of photocatalysts for pharmaceutical waste decomposition in aquatic environments.