Au-Decorated WS2/SnO2 Heterostructures for Enhanced Room-Temperature NO2 Sensing

Nitrogen dioxide (NO2) is a highly toxic oxidizing gas; therefore, the development of highly reliable room-temperature (RT) gas sensors with low power consumption is important for practical applications. Herein, WS2 nanosheet (NS)–SnO2 nanowire (NW) nanocomposites were synthesized and subsequently decorated with Au nanoparticles (NPs) using a UV irradiation method. The SnO2 content (1, 5, and 10 wt%) and UV irradiation time (1, 15, and 30 s) were systematically optimized to improve sensing performance. Among the prepared samples, the composite containing 5 wt% SnO2 (SW5) exhibited the highest response among the Au-free sensors, while the 15 s UV-treated sample (15Au-SW5) showed a significantly enhanced response of 11.7 toward NO2 at RT. The optimized sensor demonstrated reliable ppb-level detection, with an estimated experimental limit of detection of ~40 ppb and good selectivity, repeatability, and long-term stability. The improved performance is considered to be associated with the combined effects of WS2–SnO2 heterojunctions and Au-induced surface modulation, which may facilitate charge transfer and increase the density of reactive sites. This study highlights that the integration of 2D/1D heterostructures with controlled noble metal decoration is an effective approach for achieving high-performance RT gas sensors.