Synthesis of β-Bi2O3 nanoparticles via the oxidation of Bi nanoparticles: Size, shape and polymorph control, anisotropic thermal expansion, and visible-light photocatalytic activity

Bismuth trioxide (Bi2O3) is known for its simple composition but rich polymorphism that allows a number of phase-dependent physicochemical properties and technical applications. We here report our controllable synthesis of highly discrete beta-Bi2O3 (tetragonal) nanoparticles (NPs) via the thermal oxidation of nearlymonodisperse Bi NPs. The size and shape (spherical and tear- or rod-like) of beta-Bi2O3 NPs are tunable by the size of parent Bi NPs whereas beta and alpha (monoclinic) polymorphs can be selectively achieved by tailoring the oxidation temperature. The phase stability of beta polymorph from room temperature to 450 degrees C enables us to perform an in situ high-temperature XRD study on the temperature dependence of its lattice parameters, which reveals a marked thermal expansion anisotropy in beta-Bi2O3 with a linear thermal expansion coefficient of +35.1 x 10-6 degrees C- 1 in the c axis, fifteen times higher than that in the a axis. Meanwhile, the narrow band gap (2.27 eV for beta vs. 2.77 eV for alpha) and strong visible-light absorption endow beta-Bi2O3 NPs with a good photocatalytic activity for the visible-light Rhodamine B dye degradation. We expect that our work could be a valuable reference for the studies on the size, shape and polymorph control, thermal property, and photocatalytic application of Bi2O3.

Automated summary

Bismuth trioxide (Bi2O3) is known for its polymorphism and versatile applications. In this study, highly discrete beta-Bi2O3 nanoparticles (NPs) were successfully synthesized by thermal oxidation of nearly monodisperse Bi nanoparticles. The size and shape of beta-Bi2O3 NPs could be controlled by the size of parent Bi NPs, and the beta and alpha polymorphs could be selectively achieved by adjusting the oxidation temperature. The beta-Bi2O3 NPs exhibited remarkable thermal expansion anisotropy and good photocatalytic activity for visible-light degradation of dyes.