Efficient Detection of Trace NO₂ in Humid Environments Induced by Increasing Formation of Free Radicals on SV-MoS₂/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 MoS₂ (SV-MoS₂/Au) to develop an enhanced humidity-resistant trace NO₂ sensor. The SV-MoS₂/Au sensor exhibits a high response (115%) and rapid response/recovery rate (10 s/7 s) toward 50 ppb of NO₂ 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-MoS₂, leading to an effective utilization of water molecules to generate increasing free radicals (·O₂^- 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 HNO₃ and HNO₂ during the reaction between NO₂ and H₂O. Consequently, the sensors exhibit remarkable responsiveness to NO₂, providing important new perspectives for the future design of room-temperature semiconductor-based humidity-resistant gas sensors.