Comparative investigation of surface-electrical properties of functionalized graphene and MXene thin films for CO₂ gas sensing

Nowadays, CO₂ detection has become significant in many applications such as monitoring of air quality and human health. CO₂ sensors are majorly based on solid-state materials, but they require high operating temperatures. Recently, two-dimensional materials have been explored to achieve room-temperature CO₂ detection. Among them, graphene and MXene gained attraction owing to their outstanding chemical and electronic properties. Sensing materials’ properties such as surface and electrical properties are very crucial to achieve highly sensitive gas sensors. In this work, we comprehensively investigate and compare the impact of surface-electrical properties of graphene and MXene on their CO₂ sensors’ performance. Initially, we synthesize and characterize the surface-electrical properties of functionalized graphene (FG) and Ti₃C₂T_x MXene. Later, chemiresistive CO₂ gas sensors are fabricated with these materials as sensing layers and their performance is examined. From material characterizations, we find that MXene surface is more hydrophilic, showing 1.5-fold higher interfacial energy, and has ~ 1.2-fold higher electrical conductivity than FG, whereas FG demonstrates lower surface roughness and outstanding stability over the period. The sensing behavior of both sensors is found to be repeatable, selective, and reproducible. The CO₂ sensor with the MXene layer reveals a lower response/recovery time (12/17 s) than that of FG (32/43 s). Also, MXene-based sensor exhibits a 25% response, revealing a 6% higher gas response than FG-based sensor. However, from the stability point of view, FG sensor outperforms the MXene sensors. We believe this study is extremely beneficial in realizing highly efficient gas sensors for air quality and health monitoring.