Sensitivity-Enhanced, Room-Temperature Detection of NH₃ with Alkalized Ti₃C₂T_x MXene

A layered Ti₃C₂T_x MXene structure was prepared by etching MAX-phase Ti₃AlC₂ with hydro-fluoric acid (HF), followed by alkalization in sodium hydroxide (NaOH) solutions of varying concentrations and for varying durations. Compared to sensors utilizing unalkalized Ti₃C₂T_x, those employing alkalized Ti₃C₂T_x MXene exhibited enhanced sensitivity for NH₃ detection at room temperature and a relative humidity of 40%. Both the concentration of NaOH and duration of alkalization significantly influenced sensor performance. Among the tested conditions, Ti₃C₂T_x MXene alkalized with a 5 M NaOH solution for 12 h exhibited optimal performance, with high response values of 100.3% and a rapid response/recovery time of 73 s and 38 s, respectively. The improved sensitivity of NH₃ detection can be attributed to the heightened NH₃ adsorption capability of oxygen-rich terminals obtained through the alkalization treatment. This is consistent with the observed increase in the ratio of oxygen to fluorine atoms on the surface terminations of the alkalization-treated Ti₃C₂T_x. These findings suggest that the gas-sensing characteristics of Ti₃C₂T_x MXene can be finely tuned and optimized through a carefully tailored alkalization process, offering a viable approach to realizing high-performance Ti₃C₂T_x MXene gas sensors, particularly for NH₃ sensing applications.