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 (NO2) due to its hazardous effects on environment and human health, therefore, many types of NO2 sensors have been proposed. Among them, surface acoustic wave (SAW) NO2 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-MoS2/SnO2) ternary composite film was rationally designed on a SAW resonator for detection of low concentrations of NO2 at room temperature (25 degrees C), and its response speed are enhanced with ultraviolet (UV) light irradiation. Characterization results revealed that MoS2 and SnO2 formed the MoS2/SnO2 heterojunctions through interfacial chemical bonds of S-Sn-O, and the GO-MoS2/SnO2 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 NO2. The developed NO2 sensor showed a low limit of detection of 1 ppm, a high sensitivity of similar to 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 MoS2/SnO2 heterojunctions, and numerous photogenerated charge carriers produced by UV activation.