Enhancing photocatalytic properties of doped bismuth vanadate nanoparticles

Abstract

The thesis work is focused on the enhancement of photocatalytic degradation of Methylene Blue (MB) by pH variation and Gd3+–Y3+ co-doping in Bismuth Vanadate (BiVO4) nanoparticles synthesized via hydrothermal technique. Pristine monoclinic BiVO4 synthesized at pH 9 exhibit better dye degradation efficiency compared to pH 3 and 7. Due to the incorporation of Gd3+ and Y3+ ions in Bi3+ site, a complete phase transition from monoclinic to tetragonal crystal structure along with a change in morphology from spherical to rod and rectangular shape have been revealed in the X–Ray Diffraction (XRD) patterns and Field Emission Scanning Electron Microscopy (FESEM) images of the undoped and co-doped BiVO4 samples. The tetragonal phase stabilization due to co-doping have been investigated by Raman and FT-IR spectroscopy. However, the monoclinic to tetragonal phase transition for doping/co-doping with Gd3+ and Y3+ ions also increases the bandgap from 2.4 to 2.8 eV in the undoped BiVO4 and doped/co-doped BiVO4 samples respectively which is observed by UV-Visible Spectroscopy. On the other hand, Photoluminescence Spectroscopy suggests that recombination rate of the photo-generated charge carriers decreases in the following order: undoped BiVO4 > Gd0.08Bi0.92VO4 > Gd0.04Y0.04Bi0.92VO4 > Gd0.06Y0.02Bi0.92VO4 > Gd0.07Y0.01Bi0.92VO4 sample. The highest photocatalytic dye degradation has been observed for Bi0.92Gd0.07Y0.01VO4 sample (95% after 120 min of irradiation) while undoped BiVO4 sample shows the lowest efficiency in dye degradation (34% after 180 min of irradiation). Such enhanced dye degradation efficiency for co-doping of Gd3+ and Y3+ ions in BiVO4 might be attributed to the synergistic effect of nanorod shape morphology, negative surface charge and decreased electron-hole recombination