Graphene Loading with Polypyrrole Nanoparticles for Trace-Level Detection of Ammonia at Room Temperature

The outstanding versatility of graphene for surface functionalization has been exploited by its decoration with synthesized polypyrrole (PPy) nanoparticles (NPs). A green, facile, and easily scalable for mass production nanocomposite development was proposed, and the resulting PPy@Graphene was implemented in chemoresistive gas sensors able to detect trace levels of ammonia (NH₃) under room-temperature conditions. Gas exposure for 5 min revealed that the presence of nanoparticles decorating graphene entail greater sensitivity (13-fold) in comparison to the bare graphene performance. Noteworthy, excellent repeatability (0.7% of relative error) and a low limit of detection of 491 ppb were obtained, together with excellent long-term stability. Besides, an extensive material characterization was conducted, and vibration bands obtained via Raman spectroscopy confirmed the formation of PPy NPs, while X-ray spectroscopy (XPS) revealed the relative abundance of the different species, as polarons and bipolarons. Additionally, XPS analyses were conducted before and after NH₃ exposure to assess the PPy aging and the changes induced in their physicochemical and electronic properties. Specifically, the gas sensor was tested during a 5-month period, demonstrating significant stability over time, since just a slight decrease (11%) in the responses was registered. In summary, the present work reports for the first time the use of PPy NPs decorating graphene for gas-sensing purposes, revealing promising properties for the development of unattended gas-sensing networks for monitoring air quality.