Photoactivated borophene-WS2 heterostructure enables ppt-level NO2 detection with wireless alarm integration

Realizing reliable detection of ultralow-concentration nitrogen dioxide (NO 2 ) at room temperature remains a critical challenge for practical gas sensing. Here, we report a photoactivated sensor based on a van der Waals heterostructure of borophene and WS 2 , which uniquely integrates the high surface reactivity of borophene with efficient interfacial charge transfer across the heterojunction. Under 255 nm ultraviolet illumination, the sensor delivers an exceptional sensitivity of 19,047.5 % at 50 ppm NO 2 and maintains linear response down to 1 ppb, with an ultralow theoretical detection limit of 76.4 ppt. Compared with state-of-the-art two-dimensional (2D) material (rGO, MXene and MoS 2 ) based NO 2 sensors, these metrics represent one to two orders of magnitude improvement in both sensitivity and detection limit under ambient conditions. The device also exhibits high Rela_recover rate (>85 %), excellent selectivity, and long-term stability with only 6.7 % degradation over 30 days, outperforming many reported counterparts. First-principles calculations reveal that NO 2 preferentially adsorbs on the borophene surface, where strong interfacial coupling facilitates charge transfer and dynamically modulates adsorption–desorption kinetics under illumination. Furthermore, to enable real-world applicability, we integrate the sensor into a wireless alarm system, achieving continuous remote surveillance and timely hazard notification. This work establishes borophene-based heterostructures as a novel and highly promising platform for ultratrace gas detection and intelligent environmental monitoring.