Highly Surface Active Phosphorus-Doped Onion-Like Carbon Nanostructures: Ultrasensitive, Fully Reversible, and Portable NH₃ Gas Sensors

Unique phosphorus-doped onion-like carbon nanostructures (P-OLCs) with superior surface properties have been synthesized through a temperature and pressure controlled thermal decomposition method. The substitutional doping of phosphorus in onion-like carbon nanostructures (OLCs) could facilitate the charge transfer during ammonia gas sensing. The presence of polar metaphosphates/phosphonate species in the active sites of highly crystalline P-OLCs due to interstitial doping of oxygen incorporated with substitutionally doped phosphorus atoms significantly enhanced the sensitivity with fast response and recovery characteristics (2.8 and 4.5 s) toward NH3 at room temperature. Further, ammonia gas adsorption kinetics in OLCs and P-OLCs have been meticulously investigated, which revealed the faster adsorption rate in P-OLCs (2.17 × 10–7 Ω–1s–1) compared to pristine OLCs (8.599 × 10–8 Ω–1s–1). This method can widely open up the feasibility to induce enhanced surface activity (phosphorus-containing groups allow the access of oxygen to the carbon lattice) by phosphorus doping in OLCs for gas sensing and other microelectronics device applications.