Effect Of The Composition Of The Etching System MF-HCl (M = Li+, Na+, NH4+) on the gas-sensitive properties of Ti3C2Tх/Tioх nanocomposites

The influence of the nature of MF-HCl etching systems (M = Li+, Na+, NH4+) on the process of synthesis of Ti3C2Tx MXenes on the basis of Ti3AlC2 MAX-phase, microstructure, phase purity, interlayer distance, composition of functional surface groups, thermal behavior and yield of the obtained products has been studied. The room temperature sensing properties of Ti3C2Tx receptor layers deposited by microplotter printing were studied with respect to a wide range of gas analytes (H2, CO, NH3, NO2, NO2, O2, benzene, acetone, methane and ethanol). Increased sensitivity to ammonia was revealed for the MXenes obtained by exposure to hydrochloric acid solutions of sodium and ammonium fluorides and to carbon monoxide for the sample synthesized using the LiF-HCl system. High responses (~20–30% to 100 ppm NO2) were observed for all three receptor materials, but sensor recovery processes were significantly hampered. To improve the sensing characteristics, Ti3C2Tx sensing layers were subjected to relatively low-temperature heat treatment in an air atmosphere to form Ti3C2Tx/TiOx nanocomposites. It was found that a high and selective oxygen response at very low operating temperatures (125-175°C) was observed for the MXenes partially oxidized, which is particularly characteristic of the material produced using the HCl-NaF system.