MXene-based gas sensors

Recently, a new class of 2D materials called MXenes have attracted massive attention in a variety of applications. The abundant active sites, metallic conductivity, tunable surface chemistry and outstanding stability of MXenes make them desirable for gas sensing applications. In this context, an impactful amount of research has been performed on MXene based sensors and they can be considered one of the potential future materials for gas sensing. In a focused way, properties like high flexibility, convenient solution processability and easy functionalization of MXenes open the door to make their composites with other nanomaterials and provide a new avenue for advanced sensor research. Previously reported reviews on MXenes and their nanocomposites were not fully focused on the gas sensing application and covered a wide area of applications in energy storage, biomedicine, and photocatalysis. In this review, we focused on the latest research and advancement of pristine MXenes and their nanocomposites for the sensing of gases, volatile organic compounds (VOCs) and humidity. In this review, we first investigated the synthesis procedure of pure MXenes from the MAX phase by selective etching with the help of suitable etchants and delaminating agents. Subsequently, the synthesis procedure of MXene nanocomposites with other nanomaterials like metal oxides, polymers, 2D nanomaterials and other sensing materials has been reported. Later on, we briefly discuss the properties of MXenes involved in sensing performance and the modulation of properties after functionalization due to the synergistic effect of both materials. Finally, the detailed sensing performance and related sensing mechanism have been discussed for MXenes and their nanocomposite-based sensors for a variety of gases, VOCs and humidity.