Highly improved visible-light-driven photocatalytic removal of Cr(VI) over yttrium doped H-Titanate nanosheets and its synergy with organic pollutant oxidation

Rare earth metal (yttrium-Y) doped H-Titanate nanosheets (Y-HTNSs) were synthesized via a facile (one-pot) hydrothermal route. The samples exhibit a lamellar structure with the surface area ranging from 336 to 371 m²/g and smaller thickness. The process of the structural transformation of the P25 nanoparticles from three dimensions (3D) to two dimensions (2D) of the H-Titanate nanosheets was controlled by changing the weight percent of the yttrium source. The proportion of Ti³⁺ in the Y-HTNS samples gradually increased with the concentration of doped yttrium. The Y doping of H-Titanate nanosheets leads a shift in the absorption edge toward higher wavelengths, improving the utilization of the energy in the visible region of the solar spectrum. The photocatalytic performance of Y-HTNSs for the solution with RhB and Cr (VI) was enhanced initially with the concentration of Y up to 1.0 at.%, showed optimal performance at 1.0 at.% and then decreased for concentrations higher than 1.0 at.%. It was demonstrated that the appropriate amount of Y (≤1.0 at.%) effectively improves the separation efficiency of the photoelectron-hole pairs. However, for heavy doping (Y > 1.0 at.%), yttrium ions serve as electrons/hole pair recombination centers, resulting in a reduction in the efficiency of charge separation. In addition, the co-existence of RhB significantly promoted the photocatalytic degradation of Cr(VI), suggesting a synergy between the degradation of RhB and Cr(VI). Combining the surface photocurrent and electrochemical impedance spectral investigations, the mechanism of enhanced photocatalytic performance of Y-HTNS samples was proposed and explained.