Phase and structural behavior and photocatalytic properties of new mixed bismuth-praseodymium vanadates

Abstract Mixed orthovanadates Bi1-xPrxVO4 (x = 0.04−0.9) have been synthesized by a solid-state reaction technique at 800 oС. The prepared powders were then studied using XRD, SEM, photoluminescence and photoluminescence excitation spectroscopy, diffuse reflectance spectroscopy and low-temperature nitrogen adsorption-desorption. The materials were tested as photocatalysts using the reaction of safranin T degradation in the aqueous solutions under visible irradiation. Significant changes of physical-chemical characteristics of the material with the Bi/Pr ratio were observed. Adding the praseodymium causes alteration of Bi1-xPrxVO4 structure from fergussonite-type monoclinic (x ≤ 0.04) to zircon-type tetragonal (x ≥ 0.40) structure with a immiscibility gap between them. This also results in a swift increase of the band gap value and luminescence emission intensity. Specific surface area changes irregularly with decreasing Bi/Pr ratio. The photocatalytic activity of the materials revealed that efficiency of degradation of safranin T depends on the crystal structure, values of the band gap and specific surface area. It is demonstrated that pure BiVO4 and Bi1-xPrxVO4 material containing 4% of praseodymium with monoclinic structure exhibit highest activity. It is suggested therefore that interfacial heterojunction formed in the material with monoclinic structure inhibits the photoinduced charge carrier recombination and facilities their separation thus resulting in the effective degradation of safranin T.