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

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 Ti₃C₂T_x 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.