Review of Carbon Nanotube/Graphene Nanosheet Chemiresistive Gas Sensors

Chemiresistive gas sensors are essential for environmental monitoring, industrial process control, and healthcare diagnostics; however, their advancement has been limited by the constraints of conventional material platforms. Metal oxides exhibit robustness but require high operating temperatures, whereas polymers provide flexibility yet lack stability and reproducibility. Carbon nanomaterials, particularly carbon nanotubes (CNTs) and graphene, have transformed this field owing to their atomic thickness, large surface area, and tunable electronic characteristics that enhance molecular adsorption and charge transfer. These properties enable room-temperature, ultrasensitive, and mechanically adaptable sensing architectures. This review provides the first systematic, head-to-head comparison of CNT and graphene based chemiresistive gas sensors. We critically assess their sensing mechanisms, surface functionalization strategies, heterojunction designs, and hybrid composites that dictate sensitivity, selectivity, and response kinetics. The relative advantages and limitations of each platform are analyzed in the context of environmental effects, humidity interference, signal drift, and fabrication reproducibility. Emerging opportunities in flexible, miniaturized, and CNT/graphene hybrid systems are also discussed. By integrating insights from materials science, physics, and device engineering, this review establishes a unified framework linking nanoscale architecture with sensing behavior, offering a roadmap toward scalable, selective, and commercially viable carbon nanomaterial-based chemiresistive gas sensors.