Beyond conventional characterization: Defect engineering role for sensitivity and selectivity of room-temperature UV-assisted graphene-based NO₂ sensors

The term graphene-based gas sensors may be too broad, as there are many physicochemical differences within the graphene-based materials (GBM) used for chemiresistive gas sensors. These differences condition the sensitivity, selectivity, recovery, and ultimately the sensing performance of these devices towards air pollutants. Continuous ultraviolet irradiation aids in the desorption of gas molecules and enhances sensor performance. Under these conditions, the devices from this work can reliably monitor NO₂ and CO at room temperature, below the human-recommended exposure limits, presenting NO₂ LoD down to ∼20 ppb. By selecting GBMs with different levels of defectivity, which influence gas adsorption dynamics, and through comprehensive characterization, including D, D', D″, 2D, and G Raman bands, graphene-based gas sensors can be tailored to meet specific sensing requirements. This study examines five different non-oxidized GBM to develop tools and gain a deeper understanding of the relationships between GBM properties and their sensing performance. This research introduces a new standard for defect assessment, moving beyond graphene's D and G Raman band intensity ratio, to facilitate the successful integration of graphene-based gas sensors into everyday applications, such as environmental monitoring and industrial safety, and potentially impacting other 2D materials, thereby reducing health risks associated with air pollution.