Influence of synthesis procedure on the morphology of bismuth oxide particles

A modified sol-gel procedure, based on the esterification reaction, was used to prepare the Bi₂O₃ precursor, which was then heated to 400 or 500 °C. β-Bi₂O₃ obtained at 400 °C showed well-shaped plate-like particles. The mixture β-Bi₂O₃/α-Bi₂O₃, obtained by prolonged heating at 400 °C, yielded pseudospherical particles having about 100 nm in size and much larger particles, as found by FE SEM. α-Bi₂O₃ obtained at 500 °C consisted of particles of varying shapes and sizes. Vitrification of α-Bi₂O₃ was also observed. XRD showed a small fraction of unidentified phase(s) in these samples. Different microstructures were obtained when the precipitation from aqueous Bi(NO₃)₃ solution with tetramethylammonium hydroxide at pH ∼ 14 was used. The precipitation at pH ∼ 3.5 yielded cloverleaf-like particles of good uniformity, which were assigned to BiOOH (isomorphous with (La_0.26Bi_0.24)Bi_0.5OOH. It was found that these particles were made up of much smaller primary BiOOH particles.