Ultrathin Black Phosphorus Nanosheets for Efficient Singlet Oxygen Generation

Benefiting from its strong oxidizing properties, the singlet oxygen has garnered serious attentions in physical, chemical, as well as biological studies. However, the photosensitizers for the generation of singlet oxygen bear in low quantum yields, lack of long wavelength absorption band, poor biocompatibility, undegradable in living tissues, and so on. Here we first demonstrate the exfoliated black phosphorus nanosheets to be effective photosensitizers for the generation of singlet oxygen with a high quantum yield of about 0.91, rendering their attractive applications in catalysis and photodynamic therapy. Through in vitro and in vivo studies, the water dispersible black phosphorus nanosheets show notable cancer therapy ability. In addition, the photodegradable character of black phosphorus from element to biocompatible phosphorus oxides further highlights its therapeutic potential against cancer. This study will not only expand the breadth of study in black phosphorus but also offer an efficient catalyst and photodynamic therapy agent

Boosting Hot-Electron Generation: Exciton Dissociation at the Order–Disorder Interfaces in Polymeric Photocatalysts

Excitonic effects, arising from the Coulomb interactions between photogenerated electrons and holes, dominate the optical excitation properties of semiconductors, whereas their influences on photocatalytic processes have seldom been discussed. In view of the competitive generation of excitons and hot carriers, exciton dissociation is proposed as an alternative strategy for hot-carrier harvesting in photocatalysts. Herein, by taking heptazine-based melon as an example, we verified that enhanced hot-carrier generation could be obtained in semicrystalline polymeric photocatalysts, which is ascribed to the accelerated exciton dissociation at the abundant order−disorder interfaces. Moreover, driven by the accompanying electron injection toward ordered chains and hole blocking in disordered chains, semicrystalline heptazine-based melon showed an ∼7-fold promotion in electron concentration with respect to its pristine counterpart. Benefiting from these, the semicrystalline sample exhibited dramatic enhancements in electron-involved photocatalytic processes, such as superoxide radical production and selective alcohol oxidation. This work brightens excitonic aspects for the design of advanced photocatalysts

Giant Electron–Hole Interactions in Confined Layered Structures for Molecular Oxygen Activation

Numerous efforts have been devoted to understanding the excitation processes of photocatalysts, whereas the potential Coulomb interactions between photogenerated electrons and holes have been long ignored. Once these interactions are considered, excitonic effects will arise that undoubtedly influence the sunlight-driven catalytic processes. Herein, by taking bismuth oxyhalide as examples, we proposed that giant electron–hole interactions would be expected in confined layered structures, and excitons would be the dominating photoexcited species. Photocatalytic molecular oxygen activation tests were performed as a proof of concept, where singlet oxygen generation via energy transfer process was brightened. Further experiments verify that structural confinement is curial to the giant excitonic effects, where the involved catalytic process could be readily regulated via facet-engineering, thus enabling diverse reactive oxygen species generation. This study not only provides an excitonic prospective on photocatalytic processes, but also paves a new approach for pursuing systems with giant electron–hole interactions

Optically Switchable Photocatalysis in Ultrathin Black Phosphorus Nanosheets

Recently low-dimensional materials hold great potential in the field of photocatalysis, whereas the concomitantly promoted many-body effects have long been ignored. Such Coulomb interaction-mediated effects would lead to some intriguing, nontrivial band structures, thus promising versatile photocatalytic performances and optimized strategies. Here, we demonstrate that ultrathin black phosphorus (BP) nanosheets exhibit an exotic, excitation-energy-dependent, optical switching effect in photocatalytic reactive oxygen species (ROS) generation. It is, for the first time, observed that singlet oxygen (¹O₂) and hydroxyl radical (•OH) are the dominant ROS products under visible- and ultraviolet-light excitations, respectively. Such an effect can be understood as a result of subband structure, where energy-transfer and charge-transfer processes are feasible under excitations in the first and second subband systems, respectively. This work not only establishes an in-depth understanding on the influence of many-body effects on photocatalysis but also paves the way for optimizing catalytic performances via controllable photoexcitation

Highly Active Fe Sites in Ultrathin Pyrrhotite Fe₇S₈ Nanosheets Realizing Efficient Electrocatalytic Oxygen Evolution

Identification of active sites in an electrocatalyst is essential for understanding of the mechanism of electrocatalytic water splitting. To be one of the most active oxygen evolution reaction catalysts in alkaline media, Ni–Fe based compounds have attracted tremendous attention, while the role of Ni and Fe sites played has still come under debate. Herein, by taking the pyrrhotite Fe₇S₈ nanosheets with mixed-valence states and metallic conductivity for examples, we illustrate that Fe could be a highly active site for electrocatalytic oxygen evolution. It is shown that the delocalized electrons in the ultrathin Fe₇S₈ nanosheets could facilitate electron transfer processes of the system, where d orbitals of Fe^II and Fe^III would be overlapped with each other during the catalytic reactions, rendering the ultrathin Fe₇S₈ nanosheets to be the most efficient Fe-based electrocatalyst for water oxidation. As expected, the ultrathin Fe₇S₈ nanosheets exhibit promising electrocatalytic oxygen evolution activities, with a low overpotential of 0.27 V and a large current density of 300 mA cm^–2 at 0.5 V. This work provides solid evidence that Fe could be an efficient active site for electrocatalytic water splitting

Oxygen-Vacancy-Mediated Exciton Dissociation in BiOBr for Boosting Charge-Carrier-Involved Molecular Oxygen Activation

Excitonic effects mediated by Coulomb interactions between photogenerated electrons and holes play crucial roles in photoinduced processes of semiconductors. In terms of photocatalysis, however, efforts have seldom been devoted to the relevant aspects. For the catalysts with giant excitonic effects, the coexisting, competitive exciton generation serves as a key obstacle to the yield of free charge carriers, and hence, transformation of excitons into free carriers would be beneficial for optimizing the charge-carrier-involved photocatalytic processes. Herein, by taking bismuth oxybromide (BiOBr) as a prototypical model system, we demonstrate that excitons can be effectively dissociated into charge carriers with the incorporation of oxygen vacancy, leading to excellent performances in charge-carrier-involved photocatalytic reactions such as superoxide generation and selective organic syntheses under visible-light illumination. This work not only establishes an in-depth understanding of defective structures in photocatalysts but also paves the way for excitonic regulation via defect engineering