Phase transition of BiVO4 nanoparticles in molten salt and the enhancement of visible-light photocatalytic activity

BiVO₄ nanoparticles are prepared by molten salt method. Tetragonal BiVO₄ completely transforms to monoclinic phase after heating in molten LiNO₃ at 270 °C for 18 h. The average particle sizes of monoclinic BiVO₄ varied from 30 to 52 nm while the initial ratio of BiVO₄ to LiNO₃ changes from 1:6 to 1:24. The photocatalytic activity is evaluated by measuring decolorization of N,N,N′,N′-tetraethylated rhodamine dye solution under visible-light irradiation. Both of the de-ethylation and chromophore cleavage are responsible for the decolorization of RB. The sample with an average particle size of 52 nm and a moderate surface area of 10 m²/g exhibit the highest visible-light photocatalytic activity. The shift of Raman peak position indicates that the symmetry distortions in the local structure of the monoclinic BiVO₄. The variations of the local structure result in the modification of the electronic structure, which is responsible for the high visible-light photocatalytic activity.