Fabrication of flexible MoS2 sensors for high-performance detection of ethanol vapor at room temperature

Molybdenum disulfide (MoS2) possesses desirable electrical, mechanical, and physicochemical properties, making it an excellent candidate for developing flexible and high-performance resistive gas sensors that operate at room temperature. However, MoS2 exhibits limited response to carbon-containing gases, such as volatile organic compounds (VOCs), mainly due to its predominantly inert basal plane and the limited accessibility of active edge sites within its nanosheets. In this context, we propose a facile and effective strategy incorporating defect engineering and inkjet printing for fabricating flexible and high-performance gas sensors based on MoS2 for room-temperature detection of ethanol vapors. Firstly, a defect-rich 2H-MoS2 was synthesized via low-temperature annealing of hydrothermally synthesized ammonium-intercalated 1T-MoS2 nanosheets. It was observed that the introduction of defects induces hierarchical porosity with high-binding energy active sites, facilitating optimal interactions of the sensor's surface with ethanol molecules and yielding a response of 177 % to 70 ppm of ethanol, which is approximately four times greater than that of the defect-free sample. Furthermore, inkjet printing in device fabrication significantly enhanced the gas-sensing performance of the sensor, achieving a response significantly higher than its drop-cast counterpart. The printed sensor recorded an ethanol sensitivity of 4.579 ppm-1 and a limit of detection (LOD) of 153 ppb. The observed improvement could be linked to the enhanced effective area and micro-nanometer thick sensitive layer of the sensor, achieved via inkjet printing. Overall, this study underscores the synergistic effect of low-temperature induced defect creation and inkjet printing in enhancing the ethanol sensing performance of MoS2 nanosheets, highlighting a facile strategy for fabricating high-performance flexible MoS2 gas sensors.