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

Abstract

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.