Construction of β-Bi2O3/Bi2O2CO3 heterojunction photocatalyst for deep understanding the importance of separation efficiency and valence band position

Constructing heterojunctions would result in the change of valence band position, which is an important factor determining the oxidative ability of photo-induced holes, has received scant attention. In this paper, β-Bi₂O₃/Bi₂O₂CO₃ composites with different ratios were obtained via ionic-liquid-assisted solvothermal and in-situ calcination processes. UV-vis DRS, Mott-Schottky test, and Kelvin probe measurement showed the change of band gaps of β-Bi₂O₃ and Bi₂O₂CO₃ before and after heterojunction formation. SPV, ESR, photocurrent, and scavenger experiments identified the separation efficiency of photo-generated electrons and holes, as well as the active species generated in the photocatalytic process. The photocatalytic mechanism was investigated by the degradation of Rhodamine B (RhB) upon visible-light and simulated sunlight, respectively. The results demonstrated that β-Bi₂O₃/Bi₂O₂CO₃ heterojunctions possessed enhanced separation efficiency and higher degradation ability than the individuals under visible-light irradiation due to effective electron transfer. However, lower performance under simulated sunlight was observed, although their separation efficiency remained high. The decisive reason for this was that the up-shift of valence band of Bi₂O₂CO₃ induced by hybridization and the transition of holes from VB of Bi₂O₂CO₃ to that of β-Bi₂O₃ with more negative potential decreased the oxidative ability of holes, which surpassed the positive influence of enhanced separation efficiency.