Fe₃O₄ Nanoparticle-Decorated WSe₂ Nanosheets for Selective Chemiresistive Detection of Gaseous Ammonia at Room Temperature

A 2D/0D heteronanostructure (HNS) employing WSe2 as 2D nanosheets and Fe3O4 as 0D nanoparticles has been facilely synthesized at room temperature using a simple wet chemical route. The process involved liquid-phase exfoliation of WSe2 nanosheets, followed by a coprecipitation method for the subsequent nucleation of nanoparticles on the former. The hence-formed hybrid along with its pristine counterparts has been investigated for ammonia-sensing properties. Herein, WSe2 behaves as a p-type semiconductor and Fe3O4 as an n-type semiconductor as per the trends observed in the modulation of electrical conductivity in the presence of ammonia. As expected, the HNS demonstrated ultrasensitive (R % = 510% to 3 ppm) and selective response toward ammonia at room temperature when compared to WSe2 (53.2% to 3 ppm) and Fe3O4 (128% to 3 ppm) alone. The 10-fold increase in sensitivity for ammonia sensing achieved by fabricating a heterostructure enabled the detection down to 50 ppb with a response magnitude of 2.4%. Moreover, our sensor exhibits an ultrafast recovery of 13 s toward 50 ppb NH3 at room temperature without any external stimulus. Importantly, the repeatability and long-term stability over a period of few months seem to be promising. Therefore, the sensor can reliably be deployed in a real environment for practical gas-sensing applications. The exemplary gas-sensing performance achieved here can be ascribed to the enlarged specific surface area (219 m2/g) and the electronic effect of type II p–n heterostructures. This work can pave the way for the utilization of HNS of other 2D/0D materials for the ultrasensitive and selective gas-sensing applications.