Two-dimensional nanomaterials in gas detection: Experimental investigations and first-principles perspectives

The presence of ammonia (NH 3 ), nitric oxide (NO), hydrogen (H 2 ), nitrogen dioxide (NO 2 ), sulfur dioxide (SO 2 ), hydrogen sulfide (H 2 S), carbon monoxide (CO), volatile organic compounds (VOCs), and other hazardous gases impairs workplace safety, public health, and environmental sustainability. The timely detection of these gases is necessary for a safe and sustainable environment. Despite the widespread use of conventional sensing platforms such as electrochemical sensors and metal oxide semiconductors, they suffer from poor selectivity, low sensitivity, and slow response/recovery due to their instability in complex environments. The advancements in two-dimensional (2D) materials, such as graphene, transition metal dichalcogenides (TMDs), and MXenes, have opened new possibilities for high-performance gas sensing, stemming from their rich surface chemistries, atomically thin structures, and adjustable band gaps, offering quick charge transfer, improved adsorption, and allowing room-temperature operation. Recent developments in the synthesis routes and device architectures of 2D materials for gas detection are summarized in this review. Additionally, their sensing mechanisms, such as charge transfer, gas adsorption, and Schottky barrier modulation, are highlighted. Density functional theory (DFT) modeling guides experimental interpretation and reveals the atomistic mechanisms underlying adsorption energetics, electronic modulation, and the effects of defects or doping. Smart, selective, and energy-efficient gas sensors are being developed more quickly thanks to the combination of DFT modeling and experimental research. Collectively, these developments position 2D nanomaterials as a revolutionary candidate for next-generation sensing technologies for industrial safety, healthcare diagnostics, and environmental monitoring.