Surfactant-Assisted WS2 Nanostructures for Enhanced NO2 Sensing Performance

A 2-D WS2 is considered the next-generation sensor material due to its high surface-to-volume ratio and a large number of active sites. These characteristics of the WS2 sensor can be efficiently tuned by varying the surface morphologies of the deposited WS2. Therefore, in this work, we emphasize the role of surfactants (NaCl and CTAB) in the growth of various morphologies of WS2 nanostructures. Pristine-WS2, NaCl-WS2, and CTAB-WS2 exhibit nanorods, nanobelts, and flower-like morphologies synthesized via a facile hydrothermal method. The NaCl-assisted WS2 nanostructure exhibited a threefold increase in active surface area compared to pristine-WS2. Moreover, the NaCl-assisted WS2 sensor showed an elevenfold enhancement in sensing performance (23.2) compared to pristine-WS2 (2.3) and a fivefold improvement compared to CTAB-assisted WS2 (4.7) for the 100-ppm NO2 exposure. The optimum operating temperature for the developed NaCl-WS2 sensor is 75 °C, which is lower than 100 °C, making it suitable for use in portable sensor devices. At this optimal temperature, the NaCl-WS2 sensor exhibited an approximately eightfold increase in sensing performance (184.4) compared to the same sensor at room temperature (RT) for the 100-ppm NO2 exposure. Furthermore, the developed NaCl-WS2 sensor has demonstrated a significant response of 5.3 even at 250 ppb, with a limit of detection (LoD) and a limit of quantification (LoQ) in the range of 0.5 and 1.5 ppb, respectively. The higher sensing response, shorter response–recovery time, excellent selectivity, and ultrasensitive and selective nature toward the target gas NO2, even at sub-ppb levels, make the NaCl-WS2 sensor a promising candidate for domestic and industrial applications.