Molybdenum Carbide Nanoflakes Synthesized Using a Facile Method for 2-Nitrotoluene Sensing at Room Temperature
Guruprasad Gorthala, Ruma Ghosh
Abstract
This work reports the synthesis of nanoflakes of molybdenum carbide (Mo <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$_{{2}}\text{C}$ </tex-math></inline-formula> ), 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 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$_{{2}}\text{C}$ </tex-math></inline-formula> @3 h, Mo <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$_{{2}}\text{C}$ </tex-math></inline-formula> @5 h, and Mo <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$_{{2}}\text{C}$ </tex-math></inline-formula> @8 h. As the sonication time increases, the thicknesses of the Mo <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$_{{2}}\text{C}$ </tex-math></inline-formula> samples were found to decrease from 700 nm for Mo <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$_{{2}}\text{C}$ </tex-math></inline-formula> @3 h to 80 nm for Mo <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$_{{2}}\text{C}$ </tex-math></inline-formula> @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 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$_{{2}}\text{C}$ </tex-math></inline-formula> , 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 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$_{{2}}\text{C}$ </tex-math></inline-formula> samples were tested for 2-nitrotoluene (2-NT) at room temperature. The response of Mo <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$_{{2}}\text{C}$ </tex-math></inline-formula> @5 h was found to be the highest (−2.14% to −27.33% for 10–100 ppm of 2-NT). The Mo <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$_{{2}}\text{C}$ </tex-math></inline-formula> @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.