Tail-Group Modulated Covalent Functionalization of Solvent-Dispersible MXenes for Selectivity-Tunable Gas Sensing at Room Temperature.

The advancement of highly selective and sensitive gas sensors is essential for various fields, and MXene has emerged as a strong candidate for chemiresistive gas sensing due to its high electrical conductivity, tunable surface chemistry, and ability to operate at room temperature. This study demonstrates a versatile strategy for covalently functionalizing Ti3C2Tx MXenes using diazonium salts with diverse tail groups, enabling tunable gas selectivity. By systematically modulating surface energy through the grafting of hydrophilic (sulfanilic acid diazonium) and hydrophobic (4-octylaniline diazonium and 4-(heptadecafluorooctyl)aniline diazonium) tail groups, MXene surfaces are tuned to interact strongly with specific target gases. Using this strategy, this work achieves distinct gas response patterns and cross-reactivity toward other gases is minimized, while density functional theory calculations revealed enhanced gas adsorption energies due to ligand-specific interactions. Functionalized MXenes via diazotization chemistry exhibits high selectivity toward either ammonia, acetone, or ethanol while exhibiting a large enhancement in gas sensitivity compared to pristine MXene. This ligand-tailored functionalization strategy enables precise tuning of gas selectivity by controlling the tail group structure and ligand grafting density, providing a versatile platform for developing advanced MXene-based multi-target gas sensors.