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.