Progress in engineering interlayer space modulated MXenes to architect next-generation airborne pollutant sensors

The globally expanding requirements of a growing population have led to extensive urbanization and industrialization, continually leading to air eminence degradation. It has raised the urgent demand to architect efficient airborne pollutant sensors. The state-of-the-art gas/vapour sensor is concerned with exploring advanced nanomaterials to attain commercial viabilities. Owing to the high specific surface area, optimum porosity, tunable physicochemical attributes, abundant surface functionalities and solution processability, 2D metal carbides/nitrides/carbonitrides (MXenes) are the most intriguing class of nanomaterials for devising high-performance airborne pollutant sensors. However, its commercial prospects are limited due to layer restacking, and oxidation in a humid and oxygen-rich environment. These issues have been catered to by modulating the interlayer spacing in MXenes through intercalation, delamination, surface engineering, heteroatom doping and hybridization. It also optimizes the physicochemical attributes of MXenes for targeted airborne analyte detection due to induced synergistic effects. This review comprehensively summarizes the current strategies to regulate the interlayer spacing in MXenes to design selective and high-performance gas/vapor chemiresistive-type sensors. Additionally, it highlights the challenges, possible solutions and cutting-edge prospects to architect intelligent and sustainable airborne pollutant sensors with the integration of modern-day technologies, including internet-of-things, 5 G communication, cloud computing and artificial intelligence.