Insight into the relationship between redox ability and separation efficiency via the case of α-Bi2O3/Bi5NO3O7

Constructing heterostructured photocatalysts will generally improve the separation efficiency of photo-induced carriers; however, the change in the energy band position that affects their redox ability has received little attention. In this work, α-Bi2O3/Bi5NO3O7 heterojunctions are prepared via solution combustion synthesis and characterized by UV-vis DRS, Mott–Schottky and Kelvin probes, and the band structures of α-Bi2O3 and Bi5NO3O7 before and after the formation of the heterojunction are obtained. The results of the degradation of rhodamine B and tetracycline indicate that the main active species are holes and superoxide anion radicals, respectively. Although separation efficiency over heterojunctions is higher than that over individual Bi5NO3O7 and α-Bi2O3, lower degradation ability is observed. The reason is that the heterojunction formation causes an upward shift of the valence band of Bi5NO3O7 and a downward shift of the conduction band of α-Bi2O3, which reduces the oxidation ability of holes and the ability to activate molecular oxygen, respectively. The decrease in the redox ability outweighs the positive impact of enhanced separation efficiency.