Efficient Detection of Trace NO ₂ in Humid Environments Induced by Increasing Formation of Free Radicals on SV-MoS ₂ /Au

Semiconductor-based sensors continue to face challenges related to poor response and stability in humid conditions. Herein, Au nanoparticles (NPs) are successfully deposited on sulfur-vacancies-enriched MoS 2 (SV-MoS 2 /Au) to develop an enhanced humidity-resistant trace NO 2 sensor. The SV-MoS 2 /Au sensor exhibits a high response (115%) and rapid response/recovery rate (10 s/7 s) toward 50 ppb of NO 2 under visible light illumination. Additionally, it exhibits satisfactory reversibility, long-term stability, low detection limit (0.1 ppb), and good selectivity in a humid environment (relative humidity ≈60%) at room temperature. The sulfur-vacancies-enriched structure facilitates firm anchoring of abundant Au NPs on the surface of SV-MoS 2, leading to an effective utilization of water molecules to generate increasing free radicals ( · O 2 − and · OH) in the humid air. The in situ FTIR results and theoretical calculations demonstrate that the increasing formation of free radicals could effectively inhibit the formation of HNO 3 and HNO 2 during the reaction between NO 2 and H 2 O. Consequently, the sensors exhibit remarkable responsiveness to NO 2, providing important new perspectives for the future design of room-temperature semiconductor-based humidity-resistant gas sensors.