Nanoscale heterojunctions of rGO-MoS2 composites for nitrogen dioxide sensing at room temperature

Chemiresistive sensors, employing binary and ternary hybrids of reduced graphene oxide (rGO), are developed to detect nitrogen dioxide (NO2) gas at parts per billion level (ppb) at room temperature. The sensors based on hierarchical structures of molybdenum disulphide (MoS2) sheets decorated rGO and further integration of it with silver nanoparticles (Ag NPs) exhibit improved sensing responses with lower detection limits than the unary counterpart (rGO). An increase of nearly 500% in sensing response is observed in the ternary hybrid device over rGO alone at a concentration of 1 ppm and a 1145% increase in response is observed at 104 ppm. The ternary hybrid device outperforms the binary and the unary counterparts in terms of sensitivity to NO2 over a wide concentration range from 1 ppm to 104 ppm. Additionally, the ternary hybrid device is highly selective to NO2 amongst other atmospheric pollutants like ammonia, sulphur dioxide and carbon monoxide. An experimental detection limit of 50 ppb is further achieved with this device which is lesser than the 53 ppb permissible limit declared by Environmental Protection Agency (EPA). A synergistic effect was achieved with the binary and the ternary hybrids with the electronic modulations at the nanoscale interfaces at the nanoheterojunctions playing a key role in selective and enhanced adsorption of NO2 at room temperature.