Molybdenum Carbide Nanoflakes Synthesized Using a Facile Method for 2-Nitrotoluene Sensing at Room Temperature

This work reports the synthesis of nanoflakes of molybdenum carbide (Mo
$_{{2}}\text{C}$
), a transition metal carbide using a simple liquid exfoliation technique. Three different samples were synthesized by varying the sonication time from 3 to 8 h–Mo
$_{{2}}\text{C}$
@3 h, Mo
$_{{2}}\text{C}$
@5 h, and Mo
$_{{2}}\text{C}$
@8 h. As the sonication time increases, the thicknesses of the Mo
$_{{2}}\text{C}$
samples were found to decrease from 700 nm for Mo
$_{{2}}\text{C}$
@3 h to 80 nm for Mo
$_{{2}}\text{C}$
@8 h when studied using atomic force microscopy. A similar trend in the lateral dimensions was also observed in electron microscopy. In contrast to the bulk Mo
$_{{2}}\text{C}$
, a conductor, finite bandgap (1.8–1.9 eV) was observed in the exfoliated samples when characterized using ultraviolet–visible (UV–Vis) spectroscopy. All the Mo
$_{{2}}\text{C}$
samples were tested for 2-nitrotoluene (2-NT) at room temperature. The response of Mo
$_{{2}}\text{C}$
@5 h was found to be the highest (−2.14% to −27.33% for 10–100 ppm of 2-NT). The Mo
$_{{2}}\text{C}$
@5 h sample was also tested for NO2, NH3, and CO and was observed to exhibit −1.5% to −10.77%, 1.01% to 8.34%, and 4.89% to 8.17% response, respectively to 25–100 ppm of the gases. A novel method of discriminating between the gases using weighted response times of a single Mo2C@5 h sensor was developed. The reasons behind the observed sensing performances are described.