A multiphase BiVO₄ with the potential of being an environmental photocatalyst

Novel Y³⁺ and Mo⁶⁺ dual-doped, multiphased BiVO₄ nanoparticles (NPs) were synthesised using a modified hydrothermal method through a gradient doping method. Yttrium (III) was used as a phase-stabilising agent for the tetragonal phase, while Mo⁶⁺ was used to control the volume of the crystals. The NPs were characterised using SEM, TEM, PL, FTIR, XRD, and BET to determine crystal phase, morphology, and surface area. It was found that the introduction of the dopants and formation of the phase junction lead to diminished PL spectra indicative of reduced electron–hole recombination. The 10% (m–m) Y–Mo dual-doped multiphased BiVO₄ NPs have the highest electron–hole separation efficiency. However, 15% (m–m) Y–Mo had the least charge separation due to the formation of recombination centres at high degrees of metal doping. The multiphased systems also showed a red shift in the UV–Vis absorption spectrum. The Mott–Schottky plot obtained from electroimpedance spectroscopy confirmed the formation of a phase junction in the multiphased systems which resulted in an improvement of the photocurrent to twice that of the intrinsic BiVO₄ NPs for the 10% Y–Mo BiVO₄ NPs. The photocurrent for 10% Y–Mo was 0.025 A cm⁻², while that of the intrinsic BiVO₄ NPs was about 0.014 A cm⁻². This increase in photocurrent proves the improvement of charge separation. BET results showed that surface area increased with an increase in the degree of doping and that the 10% Y–Mo dual-doped BiVO₄ nanomaterials had a surface area of 9.009 m²/g. The 10% Y–Mo dual-doped BiVO₄ reached 99.1% Cr⁶⁺ removal in 60 min.