Single-crystalline BiVO4 microtubes with square cross-sections:: Microstructure, growth mechanism, and photocatalytic property

Single-crystalline bismuth vanadate (BiVO4) microtubes, with novel square cross-sections and flower-like morphology constructed by several tubes radiating from the center, were synthesized by a facile reflux method at 80 degrees C. No surfactants or templates were involved in the shaping process. The micrombes are of monoclinic structure with a [0 10] growth direction with a side length of ca. 800 nm and a wall thickness of a. 100 nm. A series of morphology evolutions of BiVO4 from nanoparticles, to microrods, and then to micrombes have been arrested. The growth mechanism for the BiVO4 microtubes is proposed to be a dissolution-recrystallization-induced concentration depletion mechanism, which is different from other micro/nanotubes formed by layered structure materials reported previously. The presence of NaHCO3 is crucial in forming the tubular structure by the equilibrium of the formation and dissociation of carbonic acid. Optical absorption experiments revealed the BiVO4 microtubes had strong absorption in the visible light region in addition to the UV light region, and the energy of the band gap was estimated to be 2.36 eV. The as-synthesized microtubes exhibited higher photocatalytic activity under visible light it-radiation (lambda > 400 nm) than that of the reference sample prepared by solid-state reaction, which may be ascribed to the special single-crystalline tubular structure and/or flower-like morphology.