Construction of flower-like BiOI/Bi2O2CO3 p-n heterojunction for photocatalytic degradation of Congo Red dye

Abstract

In this study, Bi₂O₂CO₃ photocatalysts were first synthesized under different hydrothermal temperatures (180 °C, 190 °C, and 200 °C). Congo Red (CR) dye was used as an anionic pollutant model for photocatalytic degradation experiments. The results showed that the photocatalytic performance was optimal at a hydrothermal temperature of 190 °C. Based on this temperature, the modification of Bi₂O₂CO₃ photocatalytic material was studied to solve the problems of easy recombination of photogenerated charge and insufficient quantum utilization. BiOI was coupled with Bi₂O₂CO₃, which has matched band structures, to construct a BiOI/Bi₂O₂CO₃ (BiOI/BOC) p-n heterojunction composite photocatalysts. Photocatalytic degradation experiments indicated that the BiOI/BOC composite with a molar ratio of 0.5 exhibited the highest photocatalytic activity. After 60 min of light irradiation, the degradation degree reached 78.7 %, and the first-order reaction rate constant was 0.0207 min⁻¹, which is 2.5 times that of pure BOC (0.0083 min^–1) and 3.1 times that of BiOI (0.0067 min^–1). The enhanced photocatalytic activity of the BiOI/Bi₂O₂CO₃ composites are attributed to the formation of p-n heterojunction at the contact interface between BiOI and Bi₂O₂CO₃. In the p-n heterojunction, the significant difference in Fermi energy levels between the two results in a strong built-in electric field. Driven by the built-in electric field, e⁻ in the CB of BiOI migrates to CB of Bi₂O₂CO₃, and h⁺ in the VB of Bi₂O₂CO₃ migrates to VB of BiOI, effectively promoting the separation of photogenerated carriers and thus enhancing photocatalytic activity. The photocatalytic degradation mechanism of the BiOI/BOC p-n heterojunction was proposed based on electrochemical tests and active species experiments.