Construction of BiOI/Bi₂Fe₄O₉ heterojunction for visible-light-activated antibacterial: Photocatalytic sterilization of one plus one is greater than two

Semiconductor photocatalysts with narrow band gaps are usually handicapped in scenarios involving visible-light photocatalytic sterilization due to the rapid recombination of photogenerated electron-hole pairs, sluggish carrier transfer kinetics, and limited reaction active sites. To address these issues, heterojunction engineering was employed to construct heterojunction photocatalyst by coupling two visible-light-activated layered photocatalysts (i.e., an n-type layered BiOI semiconductor and a p-type layered Bi₂Fe₄O₉ semiconductor) for pathogen photoinactivation, aiming at achieving “one plus one is greater than two” photocatalytic antibacterial effect. The bacterial survival rates for single BiOI and Bi₂Fe₄O₉ irradiated under visible light for 60 min were 54.4 % and 55.8 %, respectively. In contrast, the flower-like BiOI/Bi₂Fe₄O₉ heterojunction with optimized component ratio possessed the lowest bacterial survival rate (2.2 %), indicating that the antibacterial activity of the coupled heterojunction photocatalyst is more than twice that of each single component photocatalyst. The instrumental results and density functional theory calculations reveal that the synergistic effect among (i) high sunlight absorption from two visible-light-activated photocatalysts, (ii) high specific surface area from the two layered materials and flower-like nanostructure, and (iii) the formation of the built-in electric field at the interface of BiOI/Bi₂Fe₄O₉ heterojunction contributes to boosting photocatalytic antibacterial performance. Finally, we elucidate the mechanism behind the improved charge separation and transfer kinetics, •O₂⁻ and •OH production, and photocatalytic sterilization activity. This work offers a novel material design concept of “one plus one is greater than two”, which may pave the way for the development of heterojunction photocatalysts for wastewater treatment and purification.