Monitoring ultralow nitrogen dioxide (NO₂) concentrations is crucial for air quality management and public health. However, the existing NO₂ gas sensors have several defects, like high cost and power consumption, and exhibit poor selectivity. This study addresses these challenges by presenting a novel hexadecafluorinated iron phthalocyanine-reduced graphene oxide (FePcF₁₆-rGO) covalent hybrid sensor for NO₂ detection. This innovative approach, which overcomes the limitations of fabrication cost, energy efficiency, and gas selectivity, is a significant step forward in gas sensor technology. The sensor demonstrates exceptional sensitivity toward ultralow NO₂ concentrations (15.14% response for 100 ppb) with a rapid 60 s UV light-induced recovery. Additionally, the sensor exhibits high selectivity for NO₂, achieving a limit of detection (LOD) of 8.59 ppb. This approach paves the way for developing cost-effective, energy-efficient, and miniature NO₂ monitoring devices for improved environmental monitoring and enhanced safety in workplaces where NO₂ exposure is a concern.

In the quest for more sensitive gas sensors, researchers have studied how heating the sensors, using UV light, and thermally annealing sensors improve performance. During thermal annealing, the heating process can improve the crystallinity of the material while also increasing the electrode and sensing material interactions to create more available active sites and thus improve sensor performance. Hexadecafluorinated iron (II) phthalocyanine (FePcF₁₆) nanowires have high sensitivity towards NH₃ selectively, and thermally annealing the NWs after the deposition can further improve the sensing response and recovery. For this reason, the effect of annealing FePcF₁₆ NWs at different temperatures was studied to optimize these systems. In this work, FePcF₁₆ NWs were synthesized using physical vapor deposition (PVD) to deposit on interdigitated electrodes. The NWs were characterized by SEM, EDS, PXRD, FTIR, and Raman spectroscopy to confirm their purity. The sensors were annealed at different temperatures, inserted into a gas sensing chamber, and exposed to 1 ppm NH₃ in air, and the electrical current was measured. The results show that the optimized FePcF₁₆ NWs have excellent sensing properties, with a 58% increase in response towards NH₃ after a stepwise annealing at 300 °C confirming these systems are good prospective candidates for sensing NH₃ at room temperature.