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

Abstract

In this work, hydrothermally prepared p−n heterojunction BiOBr/SnO 2 photocatalysts were applied to eliminate NO in visible light. The as-synthesized BiOBr/SnO 2 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/ SnO 2 heterojunction were also investigated comprehensively. Extended light absorption into the visible range was achieved by SnO 2 coating on the surface of the BiOBr microsphere through the constructed heterojunction between BiOBr and SnO 2 , thus achieving efficient NO removal. Moreover, the transfer channels and directions of charge at the BiOBr/SnO 2 interface were determined by a combination of theoretical calculations and experimental studies. Within this p− n heterojunction, the charge in SnO 2 migrates into BiOBr through the preformed electron transfer channels, thus generating an internal electric field (IEF) between SnO 2 and BiOBr. Under the influence of IEF, the photogenerated electrons of BiOBr migrate from the conduction band (CB) to the CB of SnO 2 , 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 NO 2 . This work provides mechanistic insights into the interfacial charge transfer for heterojunction photocatalysts and reaction mechanism for efficient air purification.

Tin dioxide nanomaterial-based photocatalysts for nitrogen oxide oxidation: a review

“…Many attempts have been made to enhance the photocatalytic activity and take better advantage of SnO 2 for the NO x abatement, including the combination with other metal oxides [ 70 ], organic semiconductors [ 71 ], or metallic nanomaterials [ 72 ] to form a heterojunction/composite photocatalyst, and self-doping [ 73 ] or elemental doping [ 39 , 74 ]. Hybrid or doped photocatalysts ideally exhibit an improved photocatalytic efficacy due to the reduced recombination rate of photogenerated charge carriers and the lower activation energy.…”

“…The photocatalytic degradation of NO x over SnO 2 as a host photocatalyst is reported to be considerably enhanced after the combination with organic semiconductors such as graphitic carbon nitride (g-C 3 N 4 ) [ 71 ]. When acting as an auxiliary photocatalyst, SnO 2 promotes the photocatalytic activity of the primary material [ 38 , 70 , 75 – 76 ].…”

“…Electrons in SnO 2 transfer into BiOBr over pre-formed charge migration channels and an internal electric field at the BiOBr/SnO 2 interface, which directs photoinduced electrons from the CB of BiOBr to that of SnO 2 , thus prolonging the lifetime of photogenerated electron–hole pairs ( Figure 8 ). The NO-to-NO 2 conversion and intermediates and products were confirmed via in situ diffuse reflectance infrared Fourier transform spectroscopy during NO oxidation [ 70 ].…”

“… Proposed mechanisms for photocatalytic NO oxidation via interfacial charge migration over BiOBr/SnO 2 p–n heterojunctions. Figure 8 was reprinted with permission from [ 70 ], Copyright 2020 American Chemical Society. This content is not subject to CC BY 4.0.…”

Tailoring of Visible Light Driven Photocatalytic Activities of Flower‐Like BiOBr Microparticles Towards Wastewater Purification Application

“…[37,38] In terms of the spatial structure of BiOBr, it exhibits [Bi 2 O 2 ] 2+ slabs interleaved by double Br − slabs through Van de Waals interaction. Notability, such a kind of structure can generate built-in electric field, which is beneficial for separating the photogenerated hole-electron pairs, between the [Bi 2 O 2 ] 2+ and 2[Br − ] slabs, [39,40] leading to the preeminent photocatalytic behaviors of BiOBr. However, most of the synthesized BiOBr compounds still suffer from unsatisfied photocatalytic performance due to some unknown reasons.…”