Treatment-dependent surface chemistry and gas sensing behavior of the thinnest member of titanium carbide MXenes

MXenes, a rapidly developing family of two-dimensional materials possessing tunable electronic properties and abundant surface functional groups, are promising gas-sensing materials. Ti 2 CT x , with a thinner unit cell thickness compared to its compositional analogue Ti 3 C 2 T x and thus more profound surface-dependent properties, has been less explored over the past years. Herein, by etching the precursor Ti 2 AlC with a concentrated HF or LiF/HCl mixture, semiconducting Ti 2 CT x (HF) nanosheets and metallic Ti 2 CT x (LiF/HCl) nanosheets were obtained, respectively, arising from their treatment-dependent surface functionalization. In addition, the resulting metallic nanosheets were partially oxidized into TiO 2 /Ti 2 CT x (LiF/HCl) hybrid, which exhibited superior sensitivity toward NH 3 gas as compared with Ti 2 CT x (HF) and Ti 2 CT x (LiF/HCl). Detailed analysis suggests that a high concentration of surface oxygen containing species, such as -O x , -(OH) x and Ti-O-Ti, is generally beneficial for NH 3 sensing, and a relatively higher -O x concentration allows rapid gas desorption and sensor recovery. Treatment-dependent surface functionalization and gas sensing behavior of Ti 2 CT x -based materials.