Manipulating Excitonic Effects in Layered Bismuth Oxyhalides for Photocatalysis

Abstract

Two-dimensional semiconductors have attracted considerable attention in recent years because of their ability to utilize solar energy to mitigate environmental pollution through reactive oxygen species (ROSs) and synthesize solar fuels using superfluous CO2 as a raw material. However, low-dimensional materials usually display robust Coulomb interaction between electron and hole pairs because of their strong structure confinement ability, thus leading to the formation of electroneutral excitons. In light of this, excitonic effects overwhelmingly influence the photocatalytic properties of two-dimensional semiconductors, which should be comprehensively explored. Bismuth oxyhalides (BiOX, X = Cl, Br, I) of giant exciton binding energies are usually recognized as an excellent platform for excitonic effect investigation because their flexible geometric and electronic structures allow us to rationally manipulate the excitonic effects. This review first summarizes the recent progress in accelerating exciton dissociation for enhancing charge-carrier-dominated photocatalytic reactions and then demonstrates that harnessing the excitonic effects allows for the generation of singlet oxygen (1O2) for green chemical synthesis through a unique energy-transfer-dominated O2 activation route. We believe that a critical understanding of the excitonic effects in two-dimensional semiconductors can offer new perspectives and guidelines for the rational fabrication of advanced materials for photocatalytic applications.

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

“…with low spatial dimensionality have attracted considerable attention for photocatalytic O 2 activation. − Unfortunately, 2D layered photocatalysts usually possess strong internal Coulomb interactions that tend to bind the inherent photoexcited electron–hole pairs to form singlet excitons (S 1 , e – – h + ), which then drive the formation of lower-energy triplet excitons (T 1 ) through an intersystem crossing (ISC) (Scheme b). Excitons are pairs of electrons and holes that are entangled in energy while being separated in space . Triplet excitons can easily activate triplet O 2 ( 3 ∑ g – ) through excitonic energy transfer to generate the long-lived and reactive excited singlet 1 O 2 ( 1 Δ g ), which is a mild and nonradical ROS with particularly high selectivity for sulfoxidation of sulfides or desulfurization of heterocyclic sulfur-containing compounds. − However, 1 O 2 is not a competent ROS for organic pollutant control, especially refractory ones from which more harmful intermediates or products may emerge. − Therefore, for organic or inorganic pollutants that necessitate deep oxidation, it is of great environmental significance to weaken the excitonic effects of 2D photocatalysts and facilitate exciton dissociation toward the efficient radical or anionic ROS generation.…”

“…Excitons are pairs of electrons and holes that are entangled in energy while being separated in space. 20 Triplet excitons can easily activate triplet O 2 ( 3 ∑ g − ) through excitonic energy transfer to generate the long-lived and reactive excited singlet 1 O 2 ( 1 Δ g ), which is a mild and nonradical ROS with particularly high selectivity for sulfoxidation of sulfides or desulfurization of heterocyclic sulfurcontaining compounds. 21−24 However, 1 O 2 is not a competent ROS for organic pollutant control, especially refractory ones from which more harmful intermediates or products may emerge.…”

Metalated covalent organic frameworks: from synthetic strategies to diverse applications

“…The interaction of the triplet excitons with the substrate leads to abundant reaction chemistry, the most common of which is the energy exchange between triplet excitons and ground oxygen through the Dexter coupling mechanism, resulting in the formation of 1 O 2 , an excellent oxidant for green chemical synthesis. 638 In this section, we will introduce the application of photocatalysis in organic transformation reactions involving the two aforementioned mechanisms, excitonic and charge-carrier aspects.…”

Self-Accelerating Interfacial Catalytic Elimination of Gaseous Sulfur-Containing Volatile Organic Compounds as Microbubbles in a Facet-Engineered Three-Dimensional BiOCl Sponge Fenton-Like Process

“…BiOX (X = Cl, Br, I) is a part of V–VI–VII compound-bismuth oxide halide with high earth abundance and low toxicity, which has attracted considerable attention. Compared with BiOI and BiOBr, BiOCl is easier to form more Vo due to the lower bond energy and longer bond length of the Bi–O bond, thus greatly improving its catalytic activity for pollutant degradation. − Zhang et al found that two-dimensional BiOCl (2D-BiOCl) has abundant structural defects on different crystal planes, such as lattice distortion and atomic deletion, to construct a non-transition metal oxide 2D-BiOCl with low toxicity and regulable Vo concentration, thus realizing the transition from Fenton-inert to Fenton-active . The electron-gain/loss cycle of Vo has not been specified, but these findings shed light on the key role of Vo in the electronic modulation and electron transfer on catalyst surfaces.…”