Ink-jet Bi2O3 films and powders for CO2 capture and self-cleaning applications

Highlights: • Thin films of β-Bi₂O₃ were fabricated by ink-jet printing method. • β-Bi₂O₃ performance for CO₂ capture was twice that of α-Bi₂O₃. • Low thickness and high surface area of the films promoted enhance CO₂ capture. • Bi₂O₃/Bi₂O₂CO₃ heterostructure films were produced. • The Bi₂O₃/Bi₂O₂CO₃ films show self-cleaning capability up to 45% of methylene blue. -- Abstract: Thin films and powders of bismuth oxide were synthesized by a combined sol-gel and ink-jet printing method. The films were deposited over glass substrates, which were submitted to a heat treatment to promote the formation of the tetragonal polymorph of bismuth oxide (β-Bi₂O₃), while the powders crystallized in the monoclinic phase (α-Bi₂O₃). The capacity of the materials to capture CO₂ was assessed at room temperature and it was followed by X-ray powder diffraction, scanning electronic microscopy, and gas chromatography. The β-Bi₂O₃ film with 3 layers exhibited the highest CO₂ capture (1.5 mg_CO2), while α-Bi₂O₃-powders captured 4.2 mg_CO2. Nevertheless, if the results are normalized per mass of material, the efficiency obtained with the film was twice higher (82 mg_CO2 g_Bi2O3⁻¹) than by powders (42 mg_CO2 g_Bi2O3⁻¹). When exposed to CO₂, both Bi₂O₃ samples (powders and thin films) were converted to Bi₂O₂CO₃; however, some residual Bi₂O₃ was detected in the samples. The resulting Bi₂O₃/Bi₂O₂CO₃ mixture was applied as a photocatalyst to remove methylene blue in order to evaluate the sample's self-cleaning performance. The results indicated that a combination of these two materials promoted a synergistic effect related to a more efficient charge transfer due to their favorable band positions. This effect was able to promote up to 45% of removal of the pollutant on the Bi₂O₃/Bi₂O₂CO₃ surface.