Photoactivity of nanostructured spheres of BiVO₄ synthesized by ultrasonic spray pyrolysis at low temperature

Brain-like nanostructures of BiVO₄ were synthesized by ultrasonic spray pyrolysis (USP) using citric acid as chelating agent at 350 °°C. Synthesis variables such as carrier gas flow, structural agent concentration and temperature were herein studied. The samples were characterized by XRD, SEM, TEM, UV–Vis DRS and N₂ physisorption. Particularly, HRTEM was used to calculate the crystallite size, d-spacing and assigned plane of all BiVO₄ samples. The photoactivity of the as-synthesized BiVO₄ was measured during the degradation of methyl orange under visible-light irradiation, while the hydroxyl radical production was rated in terms of its reactivity against terephthalic acid. The morphology of the samples revealed that the use of small flow of N₂ allows the formation of spherical hollow porous particles with brain-like structure with slightly smaller crystallite size. The photocatalytic activity of the BiVO₄ photocatalysts prepared by USP displayed a performance three times greater compared to the powders produced by co-precipitation. The PL spectra measured revealed that the charge separation process of the BiVO₄ powders synthesized by the USP technique was better compared to those obtained by co-precipitation. The energy diagram of the photocatalyst reveals that the usage of the USP technique does not require the formation of a heterojunction to efficiently promote the separation of photogenerated carriers, since it removes defects in the gap which generating states which that induce the recombination; and shorten down the transferring distance from the excitation zone to the active site on the surface of the BiVO₄ due to the production of nanostructures.