Manufacturing of Photoactive β -Bismuth Oxide by Flame Spray Oxidation

Photoactive tetragonal bismuth oxide powder with different semiconducting characteristics was synthesized from Bi-pellets by flame spray oxidation. The effect of feedstock particle size and standoff distance (SOD) on the physical properties of β-Bi2O3 keeping constant the fuel/oxygen ratio is here reported. The flame spray oxidized powder was collected either from evaporated or in-flight particles quenched in water. The combination of flame spray processing parameters led to different β-Bi2O3 phase contents, oxidation characteristics, size distribution (nanometric and micrometric sized), morphology, and optical properties of the sprayed powder. The highest micrometric β-Bi2O3 content quenched in water was obtained at a SOD of 30 cm using a particle size distribution of 12-60 μm of Bi-feedstock. The obtained powder from in-flight particles collected in water allowed us to analyze the oxidation characteristics of bismuth. Micrometric powder shows the synthesis of snowman-like Bi/β-Bi2O3 Janus particles. The nanometric sized Bi2O3 powder was continuously obtained by spray oxidation, where its collection efficiency depends on processing parameters and showed spherical morphology and a highly pure tetragonal phase with narrow visible light absorbance (Eg = 2.26 eV). These optical characteristics indicate that the obtained β-Bi2O3 powder is suitable for high-performance visible-light photocatalyst.