Alkali-etched Ti3C2Tx MXene for High-performance Room-Temperature Gas Detection via Surface Chemistry Modulation

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Abstract
Owing to their high specific surface area, excellent electrical conductivity, and tunable surface functional groups, MXenes show great promise for room-temperature gas sensing. A key limitation, however, arises from the prevalent -F terminations in MXenes prepared by (in-situ) HF etching, which bind gas molecules weakly and result in low sensitivity. To address this, we tailored the surface chemistry using NaOH-assisted hydrothermal etching to synthesize single- or few-layer Ti3C2Tx. This method drastically reduces the -F fraction from 62.11% to 22.68% while elevating the -OH fraction from 12.84% to 63.01%. Consequently, the response to 100 ppm NH3 at 27℃ increases by approximately 30-fold, from 2.09% to 62.55%. Furthermore, we provide the experimental substantiation of proton-conduction and redox mechanisms in MXene-based sensors for NH3 and n-butyl alcohol, with DFT calculations elucidating the pivotal role of the -OH-rich surface in these sensitization mechanisms. This work establishes a clear and definitive correlation between the intrinsic surface functional groups and the gas-sensing performance of MXenes.

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