Vacancy-Engineered WS2/WSe2 In-Plane Heterojunctions for Selective Sensing of NOx (x = 1, 2): A DFT+U Investigation

Accurate detection and selective capture of NO_x (x = 1, 2) are critical for environmental monitoring and public health. This study employs density functional theory (DFT) to investigate the adsorption behavior of seven toxic gases (NO, N₂O, NO₂, NH₃, H₂S, SO₂ and CO) on WS₂/WSe₂ in-plane heterostructures with S or Se vacancies. Both vacancy- engineered monolayers demonstrate strong thermal stability. The introduction of vacancies significantly enhances adsorption strength and charge transfer, particularly for NO_x molecules. NO exhibits exceptionally high sensitivity (over 1800 %) and irreversible chemisorption, indicating strong potential for single-use capture applications. In contrast, NO₂ desorbs rapidly (<30 s at 698 K), enabling real-time high-temperature sensing. Weak interactions with the other gases further highlight the system's high selectivity toward NO_x. These findings offer theoretical insights for designing efficient NO_x sensors and capture materials based on TMD heterostructures.