Surface Boronizing Can Weaken the Excitonic Effects of BiOBr Nanosheets for Efficient O₂ Activation and Selective NO Oxidation under Visible Light Irradiation

Abstract

The photocatalytic O 2 activation for pollutant removal highly depends on the controlled generation of desired reactive oxygen species (ROS). Herein, we demonstrate that the robust excitonic effect of BiOBr nanosheets, which is prototypical for singlet oxygen ( 1 O 2 ) production to partially oxidize NO into a more toxic intermediate NO 2 , can be weakened by surface boronizing via inducing a staggered band alignment from the surface to the bulk and simultaneously generating more surface oxygen vacancy (V O ). The staggered band alignment destabilizes excitons and facilitates their dissociation into charge carriers, while surface V O traps electrons and efficiently activates O 2 into a superoxide radical ( • O 2 − ) via a one-electron-transfer pathway. Different from 1 O 2 , • O 2 − enables the complete oxidation of NO into nitrate with high selectivity that is more desirable for safe indoor NO remediation under visible light irradiation. This study provides a facile excitonic effect manipulating method for layered two-dimensional photocatalysts and sheds light on the importance of managing ROS production for efficient pollutant removal.

Locally Asymmetric BiOBr for Efficient Exciton Dissociation and Selective O2 Activation toward Oxidative Coupling of Amines

“…Furfuryl alcohol (FFA) and nitrotetrazolium blue chloride (NBT) were then adopted as probe molecules to quantify the ·O 2 – and 1 O 2 yields, respectively (Figure S29). In agreement with EPR results, the accumulated 1 O 2 in BiOBr (0.38 μM) after 60 min of light irradiation was 9.5 times that of BiOBr-A (0.04 μM), while the ·O 2 – yield of BiOBr-A (2.27 μM), in turn, was 3.5 higher than that of BiOBr (0.51 μM). To this end, excitons in BiOBr could easily activate O 2 through energy transfer to generate 1 O 2 , while photoelectrons arisen from the robust exciton dissociation in BiOBr-A were supposed to dominate O 2 activation to ·O 2 – .…”

“…Meanwhile, the [Br] − slabs with highly localized valence electrons display reduced electronic screening that further makes e – –h + pairs strongly tangled in energy, eventually evolving into excitons (Scheme b). To this end, strong excitonic effects in layered BiOBr with highly ordered out-of-plane symmetry constitute shackles for charge carrier-driven photocatalysis, including O 2 activation ,− and CO 2 reduction . The introduction of defects, , dopants, ,, and disordered domains into exciton-based 2D layered photocatalysts has been previously demonstrated to enable destabilization of bound excitons via establishing discontinuously distributed energy landscapes, thus promoting exciton dissociation.…”

Tuning the Microstructures of ZnO To Enhance Photocatalytic NO Removal Performances

“…Thus, it is highly desirable to design and explore photocatalysts exhibiting high efficiency for NO conversion and inhibiting toxic byproduct yields to avoid secondary pollution. Witnessed efforts demonstrate that microstructure controlling, e.g., strengthening surface–interface interaction and promoting carrier separations on pure photocatalyst, is the most ideal and useful method to enhance reaction efficiency, which is still mostly desired and challenging. − …”

Boosting Exciton Dissociation and Charge Transfer in Triazole-Based Covalent Organic Frameworks by Increasing the Donor Unit from One to Two for the Efficient Photocatalytic Elimination of Emerging Contaminants

“…This indicated that COF-DBT with double donor units contained more free electrons in the COF skeleton than COF-DT with a single donor unit, which confirmed that COF-DBT had a stronger electron-donating capacity than COF-DT. 66 Clearly, strengthening D−A interactions via increasing the donor unit number from one to two could reduce the E b and improve the IRCT process in COFs, leading to the improvement of exciton dissociation and charge transfer. Therefore, via the significant improvement of the photogenerated charge separation efficiency, COF-DBT with double donor units could exhibit efficient photocatalytic pollutant elimination performance with light irradiation.…”