The detection of specific gas components under various working conditions while at the same time realizing other functions with the same devices has emerged through great efforts due to these devices’ superior energy-saving and high-efficiency properties. Although so-called multifunctional gas sensors have been fabricated with various novel materials, two-dimensional (2D) materials with unique physical and chemical properties used in multifunctional gas sensors have not yet been well studied. In this review, we summarize up-to-date multifunctional gas sensors based on different 2D materials, including graphene and its derivatives, transition metal dichalcogenides (TMDs), MXenes, etc. The progress of machine learning and artificial intelligence used in emerging powerful sensors is introduced. Their sensing abilities and mechanisms are discussed, and further smart devices equipped with IoT platforms and 5G communication are expected for future electronic use.

Since the discovery of innovative two-dimensional (2D) materials, significant efforts have been dedicated to exploring their intriguing properties and emerging applications. Among all candidates, transition metal dichalcogenides (TMDs) have proven to be exceptional for gas sensing, while defects engineering has been introduced to modify the pristine TMDs for better gas sensing performances. In this review, we systematically summarize types of defects, advanced characterization techniques, and state-of-the-art controllable synthetic methods. Various types of defects in TMDs can induce diverse changes in chemical and electron structures, which are closely correlated with gas sensing ability. Therefore, connections between defects and gas sensing mechanisms and performances have been addressed based on both defect categories and electron affinity of gases. This review will be a guide for researchers in defective materials and open up the field of precisely synthesis chemistry and deepen the understanding of the underlying effects of defects in other 2D materials.

Detection of specific gas components under various working conditions has emerged through great efforts, such as exploring novel materials and well-designed device structures trying to break the sensing limitations. However, the sensing mechanisms have not been thoroughly studied, i.e., the chemical structural properties of active sensing materials and their interaction with gas molecules. Magnetic resonance, commonly observed in nuclei and electrons when exposed to an external magnetic field, has the potential to offer abundant structural and interaction information without any damage. In this review, we first provide a concise introduction to the fundamental concept of magnetic resonance, followed by wide-ranging advancements in magnetic resonance-based techniques for investigating gas sensors, encompassing the determination of the structure of sensing materials and the elucidation of sensing mechanisms.