Enhanced Gas Sensing Performance of Surface-Activated MoS ₂ Nanosheets Made by Hydrothermal Method with Excess Sulfur Precursor

Defect engineering of two-dimensional (2D) nanostructures is of significant importance for achieving enhanced surface properties in optoelectronic, sensors, and catalytic applications. In this work, the authors study the gas-sensing properties of 2D molybdenum sulfide (MoS ₂ ) nanosheets fabricated using a hydrothermal synthetic route with various nominal S/Mo precursor ratios, in order to generate nano-domains on the surface. The effect of the excess S precursor on the morphology and the resulting gas sensing performance are investigated by varying the S/Mo precursor ratio in the range of 2–12. Nano-domains are generated on the MoS ₂ basal plane for all samples, and their evolution became significant as the S/Mo precursor ratio increases. The presence of the nano-domains provides additional active edge sites, enhancing the surface-to-mass ratio and the resulting gas-sensing properties. Resistive type gas sensing tests using such 2D MoS ₂ show that, when the S/Mo precursor ratio is increased from 2 to 12, the sensitivity to 500 ppm NO ₂ gas at room temperature increased from 27 to 213%.