Influence of the Composition of the MF–HCl (M = Li+, Na+, $${\text{NH}}_{4}^{ + }$$ ) Etching System on the Gas-Sensing Properties of Ti3C2Tx/TiOx Nanocomposites

Abstract

A study was made of the effect of the nature of the MF–HCl (M = Li⁺, Na⁺, \({\text{NH}}_{4}^{ + }\)) etching systems on the synthesis of Ti₃C₂T_x MXenes based on the Ti₃AlC₂ MAX phase, microstructure, phase purity, interlayer distance, composition of functional surface groups, thermal behavior, and work function of the resulting products. The gas-sensing properties of Ti₃C₂T_x receptor layers deposited by microplotter printing were tested to a wide range of gaseous analytes (H₂, CO, NH₃, NO₂, O₂, benzene, acetone, methane, and ethanol) at room temperature. An increased sensitivity to ammonia was detected for MXenes produced by exposure to hydrochloric acid solutions of sodium and ammonium fluorides, and an elevated sensitivity to carbon monoxide was determined for a sample synthesized using the LiF–HCl system. High responses (~20–30% per 100 ppm NO₂) were measured for all three receptor materials; however, sensor recovery processes were much more difficult. To improve the sensory characteristics, the sensitive Ti₃C₂T_x layers were subjected to relatively low temperature heat-treatment in an air atmosphere to form Ti₃C₂T_x/TiO_x nanocomposites. It was detected that partially oxidized MXenes exhibit a high selective response to oxygen at very low operating temperatures (125–175°C), which is especially typical of the material produced using the HCl–NaF system.