Van der Waals Gap-Confined Molecular Engineering of MoS2 for Selectivity-Enhanced and Humidity-Tolerant Gas Sensing.

Controlling interactions between sensor surfaces and target molecules is central to achieving high selectivity and stability in chemical sensing. However, in two-dimensional (2D) material-based sensors, unintended adsorption, particularly of water molecules, often disrupts these interactions, degrading selectivity and long-term stability. Here, we exploit molecular confinement within van der Waals (vdW) gaps of MoS2 to engineer sensor-analyte interactions. Ethanol (EtOH) confinement induces electron doping and hydrophobicity, whereas water confinement produces negligible doping and hydrophilicity. This combined modulation suppresses H2O adsorption while promoting selective NO2 adsorption, enabling the EtOH-confined sensor to detect NO2 from 200 ppb to 5 ppm, with a maximum response of 48% at 60% relative humidity and a detection limit of 36 ppb. Under highly humid conditions, it exhibits a sevenfold higher NO2 response and retains 95% of its initial response after 5 weeks, compared with 44% for H2O-confined films. First-principles calculations reveal that molecular confinement regulates sulfur-vacancy (Vs) configurations: EtOH favors isolated and lined Vs, which promote NO2 adsorption while suppressing H2O binding, whereas H2O stabilizes clustered Vs, which increase H2O affinity. This vdW-gap confinement provides a design strategy to tune surface chemistry, electronic structure, and defect configurations for selective, humidity-tolerant, and reliable 2D chemical sensors.