Ti₃C₂T _x MXene with an organ-like structure was synthesized from Ti₃AlC₂ (MAX phase) through the typical hydrofluoric (HF) acid etching method. Ti₃C₂T _x MXene was further alkaline-treated with a sodium hydroxide solution to obtain alkalized Ti₃C₂T _x. Room-temperature planar-type gas- and humidity-sensing devices were also fabricated by utilizing Ti₃C₂T _x MXene and alkalized Ti₃C₂T _x sensing material based on the dip coating method, respectively. The intercalation of the alkali metal ion (Na⁺) and the increase of the surface terminal oxygen-fluorine ratio ([O]/[F]) in Ti₃C₂T _x can effectively improve humidity- and gas-sensing properties at room temperature. The developed alkalized Ti₃C₂T _x sensor exhibited excellent humidity-sensing characteristics (approximately 60 times response signal change) in the relative humidity (RH) with a range of 11-95% and considerable NH₃ sensing performance (28.87% response value to 100 ppm of NH₃) at room temperature. The improvement of NH₃ and humidity-sensing properties indicated that alkalized Ti₃C₂T _x has great potential in chemical sensors, especially in NH₃ and humidity sensors.

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