Key to unlocking NO2 sensing performance of monolayer Ti3C2Tx: Regulating OH/F functional groups

A surface functional group modulation method was used to regulate the NO2 sensing performance of the Ti3C2Tx sensor. The monolayer Ti3C2Tx MXene was synthesized from Ti3AlC2 (MAX phase) by hydrofluoric acid (HF) etching. Ar/O2 hybrid plasma treatment was used to regulate the ratio of hydroxyl and fluorine functional groups (OH/ F) in the Ti3C2Tx surface structure. Room-temperature (RH) NO2 sensor based on modified Ti3C2Tx was fabricated by the dip coating method. The modified Ti3C2Tx sensor has a higher gas response (45.31 %) to 50 ppm NO2 compared with the untreated Ti3C2Tx sensor which shows more excellent sensitivity and linearity with the NO2 concentration of 5–50 ppm. It is due to that the presence of the hydroxyl potential on the Ti3C2Tx surface well amplifies the electronic surface activity of Ti3C2Tx. Concurrently, the modified electronic structure augments the adsorption propensity of Ti3C2Tx for O2 (2.26 |eV|) and NO2 (3.24 |eV|), thereby improving the NO2 sensing capability of the Ti3C2Tx sensor. These results demonstrate that Ti3C2Tx with a high ratio of OH/ F functional groups has great potential in developing high-performance room temperature NO2 sensors.