Recent developments on 2D-materials for gas sensing application.

The industrialization has severely impacted the ecosystem because of intensive use of chemicals and gases, causing the undesired outcomes such as hazardous gases, e.g. carbon monoxide (CO), nitrous oxide (NO), ammonia (NH), hydrogen (H), hydrogen sulfide (HS) and even volatile organic compounds. These hazardous gases are not only impacting the living beings but also the entire ecosystem. Thus, it becomes essential to monitor these gases for their efficient management. There are continuous efforts to realize such sensors, which rely on the functional materials properties. The widely used such sensors use metal oxide nanomaterials. However, these are not very sensitive and operate at higher temperatures. In contrast, two-dimensional (2D) materials such as Graphene, Borophene, MXenes, and transition metal dichalcogenides (TMDs) including doping, functionalization, and heterostructures offer unique physical, chemical, and optoelectronic properties. The chemical properties with high specific surface area of 2D materials make them suitable for gas sensing applications. The present review covers the recent developments on 2D-layered material, including MoS, WS, h-BN, and Graphene, as well as their heterostructures for gas sensing applications. The review article also emphasizes their synthesis and characterization techniques, especially for 2D materials. The electronic properties of these materials are highly sensitive to any chemical changes, resulting in significant changes in their resistance. It led to the development of the highly scalable chemiresistive-based gas sensor. The sensing parameters such as sensitivity, selectivity, gas concentration, limit of detection, temperature, humidity, response, reproducibility, stability, recovery, and response time are discussed in detail to understand the gas sensing characteristics of these 2D materials. This review also includes the past developments, current status, and future scope of these 2D materials as highly efficient gas sensors. Thus, this review article may lead the researchers to design and develop highly sensitive gas sensors based on 2D materials.