Dye decolorization under visible light irradiation using bismuth subcarbonate

The photocatalytic decolorization of organic dyes is considered one of the most efficient and promising methods. Bismuth Subcarbonate (Bi₂O₂CO₃) exhibits photocatalytic activity, although its wide bandgap limits its ability to absorb visible light. Therefore, it is important to extend the light-responsive range. In this work, Bi₂O₂CO₃ photocatalysts were prepared by adding bromide (Br) sources and subjecting them to nitric acid treatment under various conditions. The photocatalytic activity of the prepared Bi₂O₂CO₃ was evaluated by decolorization experiments using Rhodamine B (RhB) as a representative dye.

To provide pretreatment Bi₂O₂CO₃, Br sources were dissolved in nitric acid solutions of different concentrations. Then, Bi₂O₂CO₃ was added to the resulting solution, and the mixture was stirred for 2 hours. Finally, the products were washed with water and ethanol and vacuum-dried at 60°C for 12 hours.

The photocatalytic activity was assessed by the decolorization of RhB. In particular, 20 mg of the synthesized photocatalyst was dispersed within the RhB solution (10 ppm, 35 mL) and stirred in the dark for 60 min to achieve adsorption/desorption equilibrium. The solution was then irradiated with a 500 W Xe lamp (λ ≥ 420 nm). At regular intervals, the aliquots of the solution were collected and centrifuged. The decolorization rate of RhB was analyzed using a UV–visible spectrophotometer by measuring the absorbance at 554 nm.

Pure Bi₂O₂CO₃, as well as catalysts treated only with acid or only with a Br source, exhibited almost no photocatalytic activity under visible-light irradiation. Acid-treated Bi₂O₂CO₃ with cetrimonium bromide (CTAB) as the Br source enhanced RhB decolorization performance. The results showed that the combined effects of these modifications are essential.