Photoreduction of chromium (VI) using multi-phase bismuth vanadate (BiVO4) photocatalyst


Abstract : Sustainable development goals emphasise the importance of access to clean drinking water. However, due to industrialisation, a lot of pollutants find their way into water bodies. Heavy metals like chromium and arsenic are some of the most dangerous pollutants that are accumulating in water bodies due to anthropogenic processes. Recent research reported precipitation, coagulation, membrane technology, adsorption and flocculation as some of the possible techniques for the removal of these pollutants. However, all these techniques have serious draw back including that they produce sludge that may require further treatment or have high operational costs which make the impractical to use in real life. The purification of water through photocatalysis using nanoparticles (NPs) has emerged as one of the most promising approach to solving the issue of wastewater treatment. This work presents the use of novel multiphase BiVO4 NPs for the removal of hexavalent chromium from wastewater. Novel Y3+ and Mo6+ dual-doped, multiphase BiVO4 NPs were synthesized using a modified hydrothermal method through a gradient doping method. Yttrium (III) was used as a phase-stabilizing agent for the tetragonal phase while Mo6+ was used to control the volume of the crystals. The NPs were characterized using scan electron microscope (SEM), transmission electron microscope (TEM), photoluminescence (PL), Fourier transform Infrared spectroscopy (FTIR), X-Ray diffraction spectroscopy (XRD) and Braunnauer-Emmett-Teller theory (BET) to determine crystal phase, morphology and surface area. It was found that introduction of the dopants and formation of the phase junction lead to a diminished PL spectra indicative of reduced electron-hole recombination. The 10% (m-m) Y-Mo dual-doped multiphase BiVO4 NPs showed the highest electron-hole separation efficiency. However, 15% (m-m) Y-Mo had the least charge separation and due to the formation of recombination centers at high degrees of metal doping. The multiphase systems also showed a red shift in the UV-Vis absorption spectrum. The Mott-Schottky plot obtained from Electro Impedance Spectroscopy confirmed formation of a phase junction in the multiphase systems which resulted in an improvement of the photocurrent to twice that of the pristine BiVO4 NPs for the 10% Y-Mo BiVO4 NPs...M.Sc. (Chemistry

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