Unique Interaction between Layered Black Phosphorus and Nitrogen Dioxide

Air pollution caused by acid gases (NO₂, SO₂) or greenhouse gases (CO₂) is an urgent environmental problem. Two-dimensional nanomaterials exhibit exciting application potential in air pollution control, among which layered black phosphorus (LBP) has superior performance and is environmentally friendly. However, the current interaction mechanism of LBP with hazardous gases is contradictory to experimental observations, largely impeding development of LBP-based air pollution control nanotechnologies. Here, interaction mechanisms between LBP and hazardous gases are unveiled based on density functional theory and experiments. Results show that NO₂ is different from other gases, as it can react with unsaturated defects of LBP, resulting in oxidation of LBP and reduction of NO₂. Computational results indicate that the redox is initiated by p orbital hybridization between one oxygen atom of NO₂ and the phosphorus atom carrying a dangling single electron in a defect's center. For NO, the interaction mechanism is chemisorption on unsaturated LBP defects, whereas for SO₂, NH₃, CO₂ or CO, the interaction is dominated by van der Waals forces (57-82% of the total interaction). Experiments confirmed that NO₂ can oxidize LBP, yet other gases such as CO₂ cannot. This study provides mechanistic understanding in advance for developing novel nanotechnologies for selectively monitoring or treating gas pollutants containing NO₂.