Integration strategies of ternary hierarchical nanocomposite designs with activated ultraviolet lights and surface acoustic waves for enhancing NO2 sensing at room-temperature

There is a great concern for nitrogen oxide (NO 2 ) due to its hazardous effects on environment and human health, therefore, many types of NO 2 sensors have been proposed. Among them, surface acoustic wave (SAW) NO 2 sensors show intrinsic advantages such as wireless monitoring, but their combined sensitivities, responses, and limits of detection operated at room temperature remain huge challenges. In this study, we proposed an integration strategy in which graphene oxide-molybdenum disulfide/tin dioxide (GO-MoS 2 /SnO 2 ) ternary composite film was rationally designed on a SAW resonator for detection of low concentrations of NO 2 at room temperature (25°C), and its response speed are enhanced with ultraviolet (UV) light irradiation. Characterization results revealed that MoS 2 and SnO 2 formed the MoS 2 /SnO 2 heterojunctions through interfacial chemical bonds of S-Sn-O, and the GO-MoS 2 /SnO 2 ternary composite showed a hierarchical structure with the heterojunctions exposed and covered by the flake-structure GO . It achieved a large specific surface area of 111.6 m 2 /g, abundant functional groups, and numerous surface defects, providing plentiful adsorption and reaction sites of NO 2 . The developed NO 2 sensor showed a low limit of detection of 1 ppm, a high sensitivity of ∼164.77 Hz/ppm, and fast response/recovery time of 16.4 s/19.1 s, as well as excellent repeatability, selectivity, and long-term stability. The key sensing mechanisms were identified as the large surface areas of the stacked composite leading to the increased adsorption and reaction sites, enhanced conductivity through the MoS 2 /SnO 2 heterojunctions, and numerous photogenerated charge carriers produced by UV activation.