Enhanced Gas Sensing Performance of Hydrothermal MoS2 Nanosheets by Post-Annealing in Hydrogen Ambient

Abstract

Abstract A two-dimensional (2D) MoS2 is considered as a next-generation gas sensor owing to its high surface-to-mass ratio and excellent selectivity. However, promoting the gas-sensing capability requires increasing the presence of active sites such as edges and S vacancies for gas adsorption. Herein, we report a process of post-annealing in a hydrogen atmosphere to improve NO2 gas-sensing performance of hydrothermally grown MoS2 nanosheets. The effects of the post-treatment on the morphology, chemical state, and resultant gas-sensing performance were investigated by varying the annealing temperature (100–800 °C). The annealing treatment eliminated residual organics formed during the hydrothermal process and increased both the S vacancies and crystallinity, without significant oxidation. A gas-sensing test using a resistive-type sensor indicated that the sensitivity for NO2 gas of 500 ppm at room temperature was enhanced from 258% to 451% (p-type response) as the annealing temperature increased to 700 °C, followed by a rapid decrease at 800 °C, owing to the n-type response. These findings demonstrate that post-annealing in a hydrogen ambient is effective at increasing the defective sites of 2D MoS2, and hence, the gas-sensing performance.