MoS

Xylene, a representative volatile organic compound (VOC), poses significant risks to both human health and the environment, making its reliable detection essential. In this study, a quartz crystal microbalance (QCM) sensor was designed and evaluated for xylene determination using individual molybdenum disulfide (MoS2) and MXene films, as well as their bilayer configurations, operating at ambient temperature. The typical responses of all fabricated sensors were initially compared at 600 ppm xylene and 30% RH. Among the tested configurations, the MoS2/MXene bilayer demonstrated the most favorable sensing performance. The optimized bilayer was further evaluated across a broader concentration range (2.5–600 ppm) and varying relative humidity levels (30–99% RH) using frequency-shift measurements, achieving a detection limit of 1.23 ppm and a sensitivity of 2.46 Hz/ppm, along with enhanced selectivity. The improved response is attributed to the synergistic integration of MoS2—characterized by a high specific surface area and structural vacancies—with MXene, which provides high conductivity and a porous structure containing vacancy-induced active sites. Their coupling enables interfacial electron transfer from MXene to MoS2, likely through the formation of a Schottky-type heterojunction, which can subtly modulate surface interactions. This coupling also increases the density of vacancies and active adsorption sites, leading to enhanced sensor performance. Humidity-dependent measurements reveal a moderate reduction in sensing response with increasing relative humidity, consistent with the experimentally observed baseline drift and competitive adsorption effects. These results highlight the importance of humidity stabilization or compensation for reliable sensing under real conditions. Overall, the MoS2/MXene bilayer sensor offers a robust and selective platform for real-time xylene monitoring under ambient conditions, provided that humidity effects are properly managed.