Miniaturized Flexible Sensors Empowered by MoS2/rGO 2-D Materials for Enhanced Ammonia Detection

In this work, we synthesized molybdenum disulfide (MoS2)-nanoflakes using a hydrothermal method and reduced graphene oxide (rGO) via a modified Hummer’s method, followed by preparing three distinct composites. Conductive inks were formulated with an appropriate binder, and NH3 sensors were fabricated using a simple, low-cost screen-printing technique on a flexible PET substrate. The influence of the active material, its density, and the number of overprints (OPs) on NH3 sensing properties was systematically investigated. The NH3 sensor with a 1:1 MoS2/rGO ratio and three OPs exhibited a linear response within the NH3 gas concentration range of 1–100 parts per million (ppm), with a regression coefficient 0.97. The sensor demonstrated superior performance, achieving a maximum response of 28.3% at 100 ppm NH3 gas concentration at room temperature. The fastest response and recovery times recorded were 56 and 106 s, respectively, at the same gas concentration. Additionally, the sensor exhibited remarkable repeatability and high selectivity toward NH3 compared to other gases. The observed response is attributed to the synergistic effect of MoS2 and rGO, which enhances charge transfer and surface interaction, with a proposed sensing mechanism that highlights the roles of both materials.