Controlled synthesis of ultrathin MoS(2) nanoflowers for highly enhanced NO(2) sensing at room temperature

Fabrication of a high-performance room-temperature (RT) gas sensor is important for the future integration of sensors into smart, portable and Internet-of-Things (IoT)-based devices. Herein, we developed a NO(2) gas sensor based on ultrathin MoS(2) nanoflowers with high sensitivity at RT. The MoS(2) flower-like nanostructures were synthesised via a simple hydrothermal method with different growth times of 24, 36, 48, and 60 h. The synthesised MoS(2) nanoflowers were subsequently characterised by scanning electron microscopy, X-ray diffraction, Raman spectroscopy, energy-dispersive X-ray spectroscopy and transmission electron microscopy. The petal-like nanosheets in pure MoS(2) agglomerated to form a flower-like structure with Raman vibrational modes at 378 and 403 cm(−1) and crystallisation in the hexagonal phase. The specific surface areas of the MoS(2) grown at different times were measured by using the Brunauer–Emmett–Teller method. The largest specific surface area of 56.57 m(2) g(−1) was obtained for the MoS(2) nanoflowers grown for 48 h. This sample also possessed the smallest activation energy of 0.08 eV. The gas-sensing characteristics of sensors based on the synthesised MoS(2) nanostructures were investigated using oxidising and reducing gases, such as NO(2), SO(2), H(2), CH(4), CO and NH(3), at different concentrations and at working temperatures ranging from RT to 150 °C. The sensor based on the MoS(2) nanoflowers grown for 48 h showed a high gas response of 67.4% and high selectivity to 10 ppm NO(2) at RT. This finding can be ascribed to the synergistic effects of largest specific surface area, smallest crystallite size and lowest activation energy of the MoS(2)-48 h sample among the samples. The sensors also exhibited a relative humidity-independent sensing characteristic at RT and a low detection limit of 84 ppb, thereby allowing their practical application to portable IoT-based devices.