Mechanisms of Interfacial Charge Transfer and Photocatalytic NO Oxidation on BiOBr/SnO₂ p-n Heterojunctions

In this work, hydrothermally prepared p-n heterojunction BiOBr/SnO₂ photocatalysts were applied to eliminate NO in visible light. The as-synthesized BiOBr/SnO₂ photocatalysts exhibit superior photocatalytic activity and stability through the establishment of a p-n heterojunction, resulting in a significant improvement in charge separation and transfer properties. The morphological structure and optical property of the BiOBr/SnO₂ heterojunction were also investigated comprehensively. Extended light absorption into the visible range was achieved by SnO₂ coating on the surface of the BiOBr microsphere through the constructed heterojunction between BiOBr and SnO₂, thus achieving efficient NO removal. Moreover, the transfer channels and directions of charge at the BiOBr/SnO₂ interface were determined by a combination of theoretical calculations and experimental studies. Within this p-n heterojunction, the charge in SnO₂ migrates into BiOBr through the preformed electron transfer channels, thus generating an internal electric field (IEF) between SnO₂ and BiOBr. Under the influence of IEF, the photogenerated electrons of BiOBr migrate from the conduction band (CB) to the CB of SnO₂, thus promoting the separation of electrons (e^-)-holes (h⁺) pairs. The intermediates and final products were monitored by the in situ DRIFTS technology in the process of removal of NO in visible light; hence, the oxidation pathways of NO were reasonably proposed. Meanwhile, the construction of the heterojunction not only achieves more efficient NO photocatalytic oxidation but also inhibits the production of more toxic NO₂. This work provides mechanistic insights into the interfacial charge transfer for heterojunction photocatalysts and reaction mechanism for efficient air purification.